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Hollow Building

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I'm going to dredge up an old topic, but am wondering if anybody has any insights into how much to add to the dimensions of the hollowed section to compensate for the weight reduction in the hollow rod section.

After doing a search of the archives, I would have to agree with some comments that state that the balance of the rod is off when you hollow and don't add anything to the overall dimensions.  I have read Milliard's book and the section on hollow building, but unless I missed anything, I still can't come up with an amount or a calculation.  The graph he gives is unclear and just can't see how much to add.

Tom Smithwick writes in an old post to add 2% or 3% to the overall hollowed dimensions.  Does anybody have anything else to add or is this the accepted amount.

I have tried to hollow build a  Thramer 8' 4 wt rod and love the rod, but the balance is out.  I planed off the pith and reduced the dimensions by a third.  Seemed like a good place to start off.  Rod is light in the hand, but its almost like I have to add some mass to the reel seat area to balance the rod out.  Seems to be defeating the purpose. Have not found it practical as of yet to load up a 9 wt reel with 4 wt line.   (Mark Babiy)

Suggest you read Bob Milward’s book.  Treats this subject quite well.  

If you look at his charts of equal bending resistance it is just a job of increasing the area at a given point.  On a quad figure the area, increase by the factor then translate the increase in area by taking the sq. root.  Found factors for determining the area of hex's in one of my old machining handbooks.  (Jerry Young)

I was not talking about balance with the 2-3%, but rather compensating for a loss of casting power when the center of the rod is removed. I don't know if there is a real rule of thumb on this, and I suspect it is influenced by the type and amount of hollowing you do. Did you hollow any portion of the tip?  (Tom Smithwick)

Did not hollow the tip, only the butt and I went straight through the ferrule section also.  Was worried, but have fished the rod for about 2 years with no adverse affects.  Rod is great, but seems almost too light in the butt and off balance.    (Mark Babiy)

For what it's worth, I'm working on finishing up a Leonard Tournament 8' 3 piece 3 wt like the one Miles brought to SRG.  I did no hollowing on tips (as usual), took the walls to .065 in the mid and .070 in the butt with dams every 3.5" and solid under ferrules +2".  I increased the taper on a slope from 1% to 4.5% from the top of the mid down to the butt swell.  It seems to have worked out very well (per test-casting).  I increased the butt more since a greater % is taken out to get to .070.

When I've hollowed on faster tapers, I've made no adjustment and just gotten a smoother rod.  (Jerry Madigan)

Here is an idea I came up with after talking to a few listmembers who use a hand held belt sander for doing hollowing and who use a belt sander for node work (taking pith away and displacing nodes with a notched vise).

I tape the strips together as if I was going to glue up, and I open them with the scalpel I use.  The trigger clamps hold the taped together strips parallel to each other.  The rubber feet of the clamp have a good grip and do not damage the apex like metal hold downs would. You could easily mark the spline exactly where you want to hollow. If you use a carrier like cedar (I never have) you would know exactly when to stop sanding because you would be almost through the cedar.

It is not as good for glue up as fluting ALA Winston, but it sure is an easy way to do a one off steelhead rod.  (Bob Maulucci)

Bob stated the following after talking to him:  I made a back plate out of aluminum. Strips go through the middle and are held flat against the plate with my hands.  There is a "curb" on each side of the backing plate that is raised up .070". When the belt hits the metal I know I am done. All  the scallops are more even now.

Thanks for the idea and the link to the pic.  I have used a similar setup in the past to sand the interior of the node in the past.  Works great, but it sure is easy to get carried away.   (Mark Babiy)

How in the heck do you control how much the best sander takes off, or maintain any consistency from one hollowed section to the next?  I've used the belt sander on the inner part of the nodes, but can see that operation getting away from me in a BIG hurry.  (Harry Boyd)

Go really slow. Use your dial calipers. My mistake on the first few was to not use something to stiffen the way the strips are held. Now I am experimenting with some flat stock help in the clamps behind the enamel. Keeps the strips from twisting. No offense meant, but from what I have heard about the Powell process, it wasn't really all that accurate. Even if you just did this belt sander method by eyeballing the strips, it may work just as well. I am not even sure that extreme accuracy would matter. After all, is the glue being distributed evenly in the strips? This is obviously not as good as the Hand Mill fluting set up or some others, but it sure works. I cannot find a spline that has a kick, or a real big difference in dimensions when glued up.  (Bob Maulucci)

For those of you that are hollow building, how thick have you left the wall?  Do you decrease the wall in the tip section?  Where do you leave dams (end of the grip, ferrules stations, last 10" of the tip?).

If you look at this purely from the perspective of Garrison stress type model, the walls can get pretty thin without sacrificing much strength at all (less than 5%).  Depending upon the taper, rod length, line weight, etc., one can theoretically cut the wall in the tip section to about 0.040, and the butt to about 0.060, and still retain almost all of the original strength.  Using the same model, one can then determine a new diameter to regain the loss in material strength.... typically only need to add back 0.005 or less from my limited study so far.

This is all great in theory, I am just wondering what some of you have found that really "works" when fishing a hollow built rod.  From what I have learned so far there is a benefit of weight savings in the butt for longer rods, and it can significantly speed up the action in the tip.  (Kyle Druey)

I've built a few hollow rods.  I generally leave the walls from .060" - .080" on butts, and a little smaller on tips and mids.  I leave things solid for a couple inches at the ferrules, just to be safe.  And I leave things solid for 1.5" at each node, just for peace of mind.

My last project with hollow-building was a direct comparison with the Payne 101 that I've built so often.  I used Bob Milward's charts to help me know how much to increase each station to give the same strength as building it solid.  Hollow building to .070" in the butt, and to .050" in the tip gave me a weight savings of .6 oz overall.  That's about 30% -- a significant weight savings in my mind.   I've cast  the hollow and solid versions side-by-side, and they are very much alike.  So I guess I'd say that the project was a success.

In my mind, what limits the wall thickness isn't as much strength as practicality in building.  If you get much thinner than .060", there really isn't much gluing surface left.

Tom Smithwick was a big help to me as I got started in hollow building.  Please let me know how I can help you.  (Harry Boyd)

Were you hollowing the sections flat or fluting?  Seems like if hollow fluting is used it might be possible to get down to a 0.040 wall thickness and still have enough surface area for gluing.  The hollowing jig I've built is based on using a Dremel, and they make ball end cutters that have diameters of 1/8, 1/16, and 1/32.  Seems like the small diameter cutter could be used on thin walled tips to provide more of "dished" cut for gluing.

Did you use the full corrected diameter from the chart or half the correction?  One thing Milward suggests is to increase the diameter by only half of what is calculated for the correction.  He says there is no engineering basis for this, but it is based on his estimate that 50% of the energy transmitted in the rod via a cast is used to move the self-weight of the rod.  He seems to think that the only correcting for 50% works well.

I'm surprised you did not notice a difference in the two Payne 101s you built.  (Kyle Druey)

We had a discussion of hollow building at Corbett Lake this past April.  The general consensus was  about what Harry stated below - most folks leave a wall thickness .070-.080, some go thinner for tips, and up to .090 for the butts of steelhead and salmon rods.  Powell had a problem with rods shattering at much below .070 (though that might have been related to a number of factors such as less glue strength using the scalloping, rather than fluting method; choice of glues; the way the rods were cast (most were tournament rods really pushed to the max).

The general recommendation to convert a solid to hollow rod was to add 5% to the diameter in the hollowed area as a starting point.

Always  leave  the  area  under the  ferrules solid  (and at least 1.5" - 2" on either side).

As to weight savings, to my mind it isn't so much as how much lighter the rod is (though it is noticeable) but more how the rod "balance", or feel in the hand, changes for the better (the rod feels like it has less swing weight, therefore feels crisper and lighter in hand).

Just some food for thought.  (Chris Obuchowski)

It should be mentioned that most EC Powells, if they do fail. they fail with lengthwise splits.  Some of the old beast distance casting rods have lengthwise splits through the center of a flat -- not along a glue line.   One way  I determine  if a  rod is a hollow-built or solid rod, with Buddy Powell rods that are rarely if ever marked for example, is to sight down a flat.  If I see what looks like a minor crease in the center of a flat, I know the rod is hollow-built.

I have never had an EC rod fail and I have a lot of them and even abuse them steelheading.  (Chris Lucker)

I currently have been doing my hollow building with my Grizzly minimill. Bob Venneri built me a wonderful little jig that clamps to my table and holds down 60 or 90 degree strips. I can easily set the cutter depth/wall thickness (I usually use shims) and I use the table's cross slide to cut the strips either fluting down the center of the strip with a ball end 1/8" milling cutter or with a flat cutter and doing a Powell style hollowing with dams. The problem is that the process is painstakingly slow, and when I move the strip down in the clamps, it can often throw the center off when fluting.

My question is...what are some other effective ways that listers have been able to do hollow strips under power. I would prefer to do a fluting style set up and make one pull through the whole strip. I figure that will help ensure the cutters stay on center. Yes, I am missing my Hand Mill and the fluting jig! Could I just use some round milling cutters and flute  right on my bamboo mill? (Obviously, I would need some spacers to center the cutters on the strip.)  (Bob Maulucci)

For the Powell method my vertical scalloper can cut 6 strips at a time and do all the hollowing in a short time. As for fluting I suggest you look at Milward’s book. His design for fluting is simple and inexpensive.  (Adam Vigil)

The jig I made for fluted hollowing will cuts a strip in about 5 minutes.  This may not be fast enough for you but the idea is based around a Dremel drill press.  I made a hollowing jig that uses design ideas from the Milward book grooved strip guide) and the roughing beveler sold by Golden Witch (spring loaded hold downs).  This jig fits in conjunction with the Dremel drill press.  The wall thickness is set with the drill press using shims and the strips are fed through and pushed by hand.  Dremel has a large selection of diameters for ball end cutters.   (Kyle Druey)

I have reworked my jig so that I can pull the strips through by hand. Now, what I am wondering,  is the minimill  running at too low a speed? Would I be better off trying this jig in a router or Dremel based set up? The top speed on the minimill is something like 2700 RPMs. The minimill seems to have some chatter when feed by hand. Of course, it is fine when I am taking 15 minutes a strip!!!  (Bob Maulucci)

I have for sometime now been trying to create in my mind a jig for hollow building rods. How can you have a continues pull through when the hollowing is made in two inch sections down the length of the strip.  Also how are you holding the strip from moving off center while milling?  (Mark Dyba)

If you want to make an easy fluting tool, use a router with a biscuit slot cutter.  They have three wings with a carbide blade with square corners.  They are called slotting cutters.  They come in 1/8 to 1/4.  I have used the 1/8 and 5/32.  Take a diamond stone and round the corners as desired and Bingo, you have a good cutter for fluting.

All you need is a guide for pushing the strip through.  The easiest way to make the  thing adjustable  is to use a MicroFence -- look it up on Google -- it is a micrometer adjustable fancy router guide.  Make a simple bed with a couple of holddowns and adjust the depth of cut so you do not cut deeper than say 0.080" or whatever.

If you want to try an EC Powell scalloping method, you were REALLY doing it the slow way by using a mill.  Simply clamp all six strips side by side as though you were applying glue.  Take a common hand held belt sander and touch the END of the sander to the points where you want to scallop.  It is easier to see when to stop sanding when you have Port Orford Cedar laminated to the inside of the cane because you simply sand only through the cedar.  You will probably need to make sander-stopper rails alongside the bamboo to stop the sander when it reaches a depth of 0.072" or so.  Make the stops out of steel so you can see sparks or feel the contact, or probably hear the contact.

Hope that helps.  I have tried both and do the EC Powell method.  (Chris Lucker)

Seems like the hollow building thing raises it's head every now and then I took a shot @ Vince Marinaro's. rod taper based on his book drawing last winter. Found out the taper I made from how I understood the drawing was a lot more heavy than VM's.

The questions are:

1] Can the weight of a finished blank without varnish, guides, cork etc. be calculated from tapers.

2] Can the weight of a hollowed out finished blank be calculated?

3] Can the weight of a hollowed out finished blank be calculated if some of the pith is retained.

I would assume that a series of 60 degrees strips would have to be measured and weighted accurately. Some with pith - some without. Different power fiber  depths would also require weighing.

Anybody out there in radio land want to take a shot @ it? I will make the strips + weight if someone would do the math.

What I envision is a neat and tidy program where the taper was put in and the weight puked out.

Another program where the guides & ferrules were "bridged" by pith and the rest hollowed. This program would get a lot more complicated as the bridging would have to be entered in terms of inch of rod travel.  (Don Anderson)

1] Can the weight of a finished blank without varnish, guides, cork etc. be calculated from tapers.

I think you might be able to make an reasonable estimate but as the rod got bigger the possible error would be greater

2] Can the weight of a hollowed  out finished  blank be calculated?

I think one would be increasing the margin for error again.

3] Can the weight of a hollowed out finished blank be calculated if some of the pith is retained.

I think the difference from culm to culm is only one of the variables in the equation you suggest.

I would assume that a series of 60 degrees strips would have to be measured and weighted accurately. Some with pith - some without. Different power fiber depths would also require weighing.

Again, I think you could define a range for a variable but there could not be a constant, hence the comparison of strips.

Anybody out there in radio land want to take a shot @ it? I will make the strips + weight if someone would do the math.  What I envision is a neat and tidy program where the taper was put in and the weight puked out.

Come on, Don! You're being short sighted. Be a visionary. I'm shooting for a machine that I can toss my shavings in one end and have it poop out a varnished rod on the other. Now that would be something to see!  :^)  (Timothy Troester)

Probably not worth the effort to add too many details.  Many of the Hexrod programs can compute the weight of the blank using an average bamboo density.  You just compute the weight of the solid blank (with or without the extra 3% diameter). Then compute the weight of the tiny rod consisting of hollowed part.  Use the original diameters less twice the wall thickness.  Subtract the weights of the two; and, viola.  Guesstimate how much to add back in for the bridging if you want.  (Jim Utzerath)

Let's say I build two theoretically identical rods, one solid built, and one hollow built, to the same taper.  Would there be any differences in the two rods characteristics, other than the obvious one of one rod being lighter than the other?  (Mark Wendt)

The hollow built rod would have slightly different flexing characteristics, depending on wall thickness, etc.  Milward's book has a good discussion to use as a starting point.  (Harry Boyd)

Care to expound?  I don't have the Milward book as of yet, so I look forward to your inspiration.  (Mark Wendt)

There are a tremendous number of variables to consider... how thick are the walls? Is wall thickness the same in all areas?  Is it fluted or scalloped?  Is it solid at grip and ferrules, or hollowed?  How far up the tip is it hollowed?

Generally speaking, I'd say that the hollow built rod is 3% - 10% less stiff, based on Milward and a simple wild guess from a little personal experience.  Adding 3% to a taper is usually about .010" at the butt.  That's not much material, and it makes the rods pretty close to even in action.  If hollow building decreases the weight by 25-30%, adding three percent more "wood" doesn't hurt your weight savings very much.

I've just finished two 8' 7 weight blanks, very loosely based on the Dickerson 8015.  One is hollow in butt only.  The other hollow in the tips, too.  Wall thickness for butts ranges from .078" to .060".  In the tips, wall thickness is from .060" to .045".  Just wiggling them, the one with the solid tips seems much stiffer.  Unfortunately, the one hollowed in butt only is for a customer, so we won't be able to cast them side by side at SRG.  I'll have the one which is all hollow with me, if someone doesn't buy it first <g>.

Now, if you make a hollow built taper and it seems a little soft, you can fix it.  Add some intermediate wraps.  It is absolutely amazing how much they stiffen up a rod. (Thanks Tony Y, and Reed and others) Adding three wraps between each guide makes the rod go from medium to medium fast.  Adding five wraps moves you from medium to almost fast. That's as far as I have gone.  Why do intermediates quicken the taper? My guess is that by adding thread you simply increase the diameter.  (Harry Boyd)

Interesting information.  I wonder how much weight putting 3% more in the diameter of your taper would really add.  After all, you are adding back weight in the densest part of the strip, in the power fiber area.  Whereas, when you hollow out the inside, you are hacking away at the least dense part of the strip.

I like the idea of the intermediate wraps though.  Nice easy way to influence the action of the rod.  How many wraps do you need for each individual intermediate for it to actually have some effect?  (Mark Wendt)

Keeping all other factors unchanged between the two rods, except that the wall thickness of one rod is reduced, will slow down the action of the hollow built rod.  You have to add wood to the Hollow Built rod if you want it to have the same action as the solid built rod.  (Kyle Druey)

I understand that John Long and Bill Waara had long and detailed discussions concerning what happens to a rod when hollowed. When John gets his book finished someone might ask him about it. Personally, I think adding to the diameter of the rod defeats the purpose of hollowing. When I have hollowed I have found that the rebound is quicker I assume from the less weight of the rod itself. When I have added diameter to a rod that I have hollowed I ended up with a completely different, stiffer, taper not so when I did not add to the final dimension. Go figure! There's an odd ball in the bunch.   (Timothy Troester)

The true test then would be to get the two rods together and let a group cast them and not tell them which was which and then see if they can tell the difference.  (Dave Norling)

You don't really have to add all that much extra wood to the hollow built rod when trying to achieve the same stiffness profile of the solid rod parent taper.  For example, a recent 8' hb quad I made had the following corrections:

30" 0.000 (no hollowing due to wall thickness)
60"  0.002 (about 0.9%)
80" 0.006 (about 2.1%)

The corrections for the in between stations are not proportional to those listed above, and are not generic, but are taper specific.  The amount of extra weight added is minimal but improved performance enhancements are provided, in my opinion, in most any rod length.  Less input energy from the caster is absorbed by the rod to rotate and accelerate the wood, which provides more energy to the cast... IE., more efficient than the solid built rod.  (Kyle Druey)

Am I assuming correctly with your dimensions that the increase is linear from 0.000" at the tip to .006" at the butt?  If not, using your example, how do you determine where to add the weight to the rod?  (Mark Wendt)

It's not linear but rather it is based on equivalent moment of inertia.  The MOI of the hollowed cross-section is made to be equivalent to the MOI of the solid cross-section.   (Kyle Druey)

Sounds similar to what I'm doing:

1. Through anecdotal observations,  it appears that 3.5% to 4% is about right for a butt of about .310 with a .070 wall thickness.

2.  Anchor my calculations at 3.5% or 4% for .310 and then make adjustments in proportion to the bamboo removed for various cross-sections and wall thicknesses.

I leave dams, so that has some impact.

Just slightly more scientific than a WAG.  (Jerry Madigan)

I have done exactly what you are proposing. Built 2 rods from the same culm. Alternated the strips so that each rod had strips in them as close as I could match them. Same guides & pattern. Same node pattern. Left 0.080" side wall. Was about the maximum of power fiber. Left bridges on each side of the guides and at ferrule.  Finished the same.

Took them out on the lawn and the solid rod out cast the hollowed one by about 15' feet.  So the trade off seems weight Vs. performance.  (Don Anderson)

Then the next step would be to make three rods, one solid, one hollow built with the same taper as the solid, and one hollow built, increasing the taper by 3%, like Harry mentioned. Problem is, you'd need mighty wide culm to get three rods out of it.  (Mark Wendt)

I came to the conclusion that offsetting the taper to get the same performance was not worth the effort. The rod would gain in weight. Seemed like a "why bother" for trout lengths. For longer rods, a real saving could be made in weight.  (Don Anderson)

Exactly, the hollow-building was done as a finagle to give maximum power fiber within the rod weight restrictions of tournament casting... these were long rods. I don't see the advantage for short rods or normal casting ranges for trout. After all, the mass of the rod can actually be of benefit in loading for short casts.  (Reed Curry)

I'm just wondering.  I'm building a 8 1/2" 9 wt salmon rod, and on Harry's suggestion, hollow building it.  I too am wondering if it's worth the effort to off set the taper.  The 3% that Harry mentioned doesn't seem like that much.  (Mark Wendt)

In my opinion and experience, hollow-building a rod of less than 6 wt. and 8'6" is pointless in terms of a weight savings. Obviously, the higher the line weight, or the longer the rod, or both, the more benefit is seen from hollow-building.  (Martin-Darrell)

This one's going to be an 8 1/2' 9 wt salmon rod, that's why I'm considering the hollow building.  (Mark Wendt)

The weight saved by hollow-building an 8 1/2' rod won't be very much. You're still casting a 9-wt. line and that's where you'll feel the weight.  (Ron Grantham)

Probably true, but look at the knowledge and experience I'll gain.  (Mark Wendt)

For me, weight savings is not close to the main reason for hollow building.  For fast tapers, I typically don't adjust and end up with a smoother feeling action.  Other tapers, I adjust up to 3.5%, varying by how much cane is removed.  The rod ends up slightly lighter, more lively.  In both cases, I think that tracking is improved.

Since most of the cane comes out of the butt, hollowing gets you closer to what might the ultimate rod: a graphite butt with a bamboo tip.  (Jerry Madigan)

Ray Gould was doing something along those lines.  He'd hollowed out the butt section completely, and used a tapered carbon fiber tube glued up inside of the bamboo.  He discussed it a bit in his book.  (Mark Wendt)

Following what I feel to be very good advice by some of you that this may be the best method of building hollow sections I wonder how one should go about this.

Being in the UK I don't have ready access to some of the books you all seem to have, but please don't let that stop you recommending one!

My best guess so far is to flute the straight triangular section obtained from my Medved type beveller using a rather special router bit, then plane up the final taper.  But I did say it was a guess!  (Robin Haywood)

Make a jig that allows you to hold the strip enamel side down with V-notched (spring loaded) hold downs. Clamp the jig to your milling machine table. Use a ball end 1/8 milling cutter and set the depth and pull the strip through. Keep the hold down blocks close together, barely big enough to fit the cutter between.

If you do not have a milling machine, make a platform to hold a router or Dremel tool inverted. Use a set screw to determine the depth of cut.

Or use a biscuit cutter on your router and make something to hold the strips as you push them through,  (Bob Maulucci)

Ah! Thank you.

I had in mind cutting something like a 60 degree inverse flute, but a ball end cutter is easier to obtain!  (Robin Haywood)

Bob Milward's book (Bamboo: Fact, Fiction and Flyrods) has plans for a fluting jig using a router, as well as other mills and binders and a wealth of information about bamboo.  It's one of the most thought-provoking books on bamboo available.

As far as I know it's only available from

Bob Milward Bamboo Flyrods
1851 Rufus Drive
North Vancouver, BC  V7J 3L8
(604) 985-0860

(Robert Kope)

I'd like to ask a question on hollow building.  What approach is used when gluing up to minimize the amount of glue that gets squeezed into the cavity?  On my solid rods I have always been generous with the glue and as a result plenty of excess is squeezed out, if I did the same on a hollow rod I think the hollowing effort will be wasted.  However the glues I have used - Epoxy or Aerodux - both resent being applied too thinly, any thoughts?  (Gary Marshall)

Slather the glue on as usual, but when you are done clean out the hollows.  I like to to Q-tips as they are cheap and plentiful and readily absorb the glue.  I typically use 2 or 3 Q-tips per section to clean up the excess glue before binding.  (Kyle Druey)

Do any of you take the weight of the pith you take off to make a hollow built butt, thinking perhaps in an 8' #6. I was doing some test and I do not obtain reasonable weight off going near the power fibers in a spiral hollow design vs. action or strongest problems to perhaps I would find. I can obtain important lost off weight with my bamboo ferrule design but the pit I take off from the hollow prototype  don't weight nothing.

Any of you have a good reason to encourage me to continue with my test rod?  (Marcelo Calviello)

How much pith are you removing?  To attain substantial weight savings one must take off most of the inner portion of the bamboo.  I've built several hollow rods with wall thickness of .070".  On an 8 foot 6 weight rod, I would expect a weight savings of about 25-30%.  (Harry Boyd)

Perhaps an equally important point is  the diameter of the section that you are hollowing.  If you are leaving .070 wall thickness on a Gillum 86 for example, the average diameter of the hole in the is about .184".  On the other hand, if you hollow build a Paul Young Perfectionist, the average diameter of the hole is only .115".  The difference in weight will be much greater on a big rod than on a smaller one.  (Bill Lamberson)

I went ahead and built the hollow rod.  When I tested the Hollow build I don't noticed a great less of power but a great balance improve that result in the feeling of a lighter rod. (Marcelo Calviello)

I just finished building a fixture for the drill press to hollow flute bamboo strips. I don't have a clue as to what size router bit/end mill I should use for this. The rod taper is based on a Garrison 212E that has been modified to a 7 weight with RodDNA. The plan is to mildly hollow the butt and the first third of the tip.  (Jerry Drake)

I have 3/32 and 1/8 ball end mills. That is a good starting point.  (Bob Maulucci)

I did not read if anyone posted this already, but when I fluted a rod, I used a biscuit slotting router bit with two wings.  It had carbide blades and I rounded the carbide by eye using a diamond stone.  I used a MicroFence to make the bed and make the depth adjustable.  You can find the MicroFence using a Google search.  (Chris Lucker)

Under the tutelage of another member of this list, I use a chisel to help out in hollow building my rods.  I just finished up a couple of hollow built blanks and realized I know next to nothing about working with a chisel.  I'm fairly competent with a block plane, but chisels are a vast unknown.  The good news is that I know some of you are quite competent woodworkers and have some knowledge and experience.

Here's my questions:  Is it possible to buy good chisels without taking out a small mortgage?  At what angle do you sharpen a chisel?  Do you use a micro bevel?  Do you spend as much time on the back of the blade as the bevel?  And so on.  (Harry Boyd)

I have sometimes found really good chisels at flea market type antique shows.  Buck Bros. made chisels in the late 1800's that beat anything I can afford in modern tools.  Look for the words "Cast Steel" on them.  I only buy antique tools if they are in good shape though.  "Buyer Beware" as usual.  I don't spend a LOT of time on the backs and I DO use a micro bevel.  A plane is essentially a tool for holding a chisel at a predetermined angle.  (Neil Savage)

Piggybacking on Neil's line - a chisel is a plane blade with a handle.  Treat them exactly the same as you would a plane blade.  I've gotten a few chisels over the years, and like Stanley or Hock blades, some are good, some not so good.  Woodcraft has an updated line of Swiss chisels that are pretty nice, and they average around $30 a piece.  They also carry the Sorby line of chisels, for a bit more money, most of the sizes we would use are around $50 a piece.  (Mark Wendt)

I have 4 Buck Bros. chisels I purchased new in the early 70's. I can't imagine a better chisel. They are as good today as the day I got them. Says right on them "Life Time Warranty". Sharpen them the same as a plane iron with a micro bevel, scary sharp. As far as I know they still make them in Millbury, MA. I use them to plane nodeless splices, much faster than a plane. Count your fingers before and after use. :>)  (Don Schneider)

The newer Buck Bros. chisels have gotten really cheesy.  They don't look to have the same quality or feel that the old ones have.  They're probably being out-sourced now...  I saw a set of the in the local Home Despot the other day.  (Mark Wendt)

As in sharpening a plane blade, once the back is ground flat and polished mirror smooth you won't need to do it again, unless you sharpen past the polished area.

Buying used chisels - old plane blades too for that matter, pay attention to the length. The hardened part that takes and holds a good edge is only about a couple inches long. Some old chisels and plane blades have that hardened part sharpened away over the years of their use and the only thing left is the softer unhardened steel. Date of manufacture seems to play a big role in the quality of the steel in old chisels. Before the late 1930's or early 1940's they were made of an excellent steel - or perhaps they were hardened better, but after that they don't hold an edge nearly as well. Again as everyone else has been saying, this is with the low to midrange quality. You can still spend megabucks and get excellent chisels today. If you are doing this as a living perhaps you should consider it. Do some research in old chisels and look on eBay. I got a few great planes from eBay, but  in  retrospect  maybe I  should have  just popped  for the Lie-Nielsen planes from the start.  (Darryl Hayashida)

Just want to brag a bit. I built a new Steelhead rod this spring and just returned from a week of fishing in Michigan. The new rod is everything I expected plus. The rod started life as a Garrison 212 E taper that I used RodDNA to bump up to a 7 weight. Then I hollow fluted the strips for both the butt and tops. The butt was fluted with  a 3/32  inch ball  nose end  mill to  a wall  thickness of 0.085'. The tips were fluted with a 1/16 inch ball nose end mill to a thickness of 0.075'. The fluting stopped 1 1/2 inches from the ferrule station. The finished rod weight is a bit over 5 ounces. If I were to change anything it would be to make the rod 8 1/2 foot long to help in rolling split shot on a floating fly line. This rod is a replacement for serial number one which is going into retirement.  (Jerry Drake)

Way cool!  I did a hollow built version of Jim Wilcox's 8 1/2' Wolverine Creek taper that I fished up in Meechigan last year.  I fluted mine also, and it worked beautifully!  Hope you have as much fun with yours as I do with mine.  Salmon or Steelhead on cane is a trip!  (Mark Wendt)

Did you alter the taper in any other way to accommodate the loss of material? Do you think that removing the central power fibers alters the action or makes the rod more appropriate for a lighter line than it would be if not hollowed? I'd like to make a Dickerson 8615 if I could make it lighter.  (Henry Mitchell)

To answer your questions. It all depends. On how you hollow and how much you hollow and how large a rod you are hollowing. Often making the rod about 3% larger in the butt and less as you go to the tip of the butt will get you close but that also depends on how you hollow. I use a MHM but I have used a red devil scraper before I bought the MHM. Using the MHM there is very little removal of power fibers. Tom Morgan using the MHM that you hollow the butt to .070 mids to .060 and tips to .050. I hollowed a Garrison 229 with a red devil to .070 with dams too far apart and I caught lots of bass up to 24 inches and catfish to 25 inches before it broke in the handle. Repaired that and later it broke again above the handle but I had the dams too far apart. This is not an exact process just go for it.  (David Ray)

But how would this compare to hollow-fluting?  I believe that Jerry hollow-fluted this rod instead of hollowing with dams.  I wouldn't think you'd lose nearly as much in the taper fluting as you would using the dams.  (Todd Talsma)

I have done it both ways and much prefer hollow fluting I would agree with you. I normally hollow flute to .070 on the butt, .060 on the mids and .050 on the tips.  (David Ray)

On the Wolverine Creek taper rod that I fluted, I didn't change the taper at all.  An interesting test.  At last years CRG, Jim Wilcox and another fella brought out their Wolverine Creek rods, that weren't hollow built.  We did a sorta test, since we all had different kinds of line on the rods, and the hollow built rod was definitely lighter...  I have a Wulff TT 9 wt line on mine, I think Jim had a WF 9 on his, and the other guy had a WF 9 on his also.  The hollow built rod felt a little nicer with shorter line out, but the solid rods came alive with longer lines in the air.  I guess to be more scientific, we should have swapped lines to see how they felt, but we were just having too much fun with three almost identical rods side by side, throwing line...(Mark Wendt)

Todd is correct. The rod is hollow fluted, no dams. I can run a wire from the butt to the ferrule station. Hollow all the way.  (Jerry Drake)

I think that is the best way. Then there is the question as to how wide is the flute etc etc etc. I would not worry about it. I have three widths on the MHM. Tom Morgan also suggests that you plug the end with a dowel.  (David Ray)

I did not alter the taper to accommodate the loss of material due to the fluting process. The fly line I used was a SA Steelhead taper in a 7 wt. This line has a very long back taper to aid in mending. The head length on this line is about 65 foot long before you get into the running line. Not having a 7 wt.  of the same taper to compare with the hollow one, I can't say what the difference is for sure. The hollow rod does seem to be a little quicker in response than you might expect. I am going to try it with a RIO Nymph taper in an 8 wt. I suspect it will handle that line just fine. I will post the  results.  (Jerry Drake)

The next question is how do you keep unnecessary glue from getting into the hollow, as any glue there would add back some of the saved weight.  (Henry Mitchell)

When I glued mine up, I took a Q-Tip and just ran it down the fluted channel to sop up the excess epoxy.  (Mark Wendt)

How did it perform with a fish on the end?  (Nick Kingston)

The rod performed great with Steelhead on the end of the line. 11 landed and at least that many  more lost. Some logs in tight places you just can't keep them out of. You usually know that going in but fish there anyhow. There are two places I fish that I have not landed a fish in three years. Hooked plenty. Maybe next year I will get lucky and hook a dumb one.  (Jerry Drake)

I'm planning on taking a Garrison 212E and extending it 2" and hollow fluting it in the butt section, starting about 2" above the grip and stopping 2" before the ferrule station. Anybody with experience in hollow building, have any ideas on how this will effect the action? Crisper, slower, no difference? I'm planning on making this as a tailwater rod for streamers and some distance but, would like to lighten it up a little with minimum change in the action. I haven't built anything in a hollow built configuration before, so if you have any suggested changes to how I'm doing it, would love to hear that as well (also, suggested wall thickness for this application would help).  (Bill Walters)

I just completed a Steelhead rod in March on that very taper. I used the 212E and boosted it to a 7 weight. The butt is hollow fluted with a 3/32 inch ball nosed end mill from 1 1/2 inches from the ferrule station to the butt. Before installing the butt cap you can see the fluted hollow. The tip is fluted with an 1/16 inch ball nose end mill from 1 1/2 inch from the ferrule station to a point that the end mill no longer cut any material at the tip end.  The wall thickness of the butt is 0.085 inches and the wall thickness of the tip is 0.075 inches. Gluing the rod is a trick to keep the glue out of the center of the rod. I used Nyatex Epoxy spread with a stiff brush. Put it on, wait 10 minutes then brush off all you can. Wipe the channels clean and bind. The fit of your strips must be near perfect to use such a small amount of glue. So far, so good. The PM Steelhead couldn't damage the rod.

How does the rod perform? GREAT!

A week of Steelhead fishing on the Pere Marquette River ended with a dozen Steelhead brought to hand and probably that many more lost to the wood piles. At  no time were there any doubts that the rod was not up to the task. The rod is lighter and I think a bit crisper in action. People who cast this rod always have the same reaction. They are amazed that the light yet powerful feel of the rod.  (Jerry Drake)

I also use the hollow-fluting technique and have found that a pencil eraser works well to clean the glue out of the flutes.  First, hold the eraser to a sander and give it a sort of conical (bullet) shape, then just run it down the length of the grooves.  Wait for several minutes, as Jerry suggests, to let the excess glue flow downward, off the strips.  That way, the glue is less likely to squeegee back into the grooves when you roll the strips together for binding.  (Bill Harms)

If you recalculate the outside diameter to allow for hollow building properly it will make no difference at all to the action. Milward is probably the best source on this, but you will still have to take a view on the actual percentage area of the total that you are removing, since the fluting does not remove an exactly circular cross sectional area, but the mathematics are really very basic. Because you are removing mass from the butt, but not from the tip(s) the balance will be altered because the center of mass will inevitably move towards the tip. Strictly, you should remove a constant percentage of the outside diameter all the way to the tip, but I am well aware that this is easier said than done!  (Robin Haywood)

I was just wondering whether anyone had tried just shaving off the inner apex all through the rod, by a conservative amount, say 50% of the section thickness, gluing it up and testing it?   I suppose one could always plug the ferrule stations afterwards by about a couple of inches, but I wonder if it is necessary?

If it works, if...., then it makes a quick and easy way of hollowing the whole thing, although a bit of measuring will be necessary.  The reason I fancy it is that, apart from simplicity, it gives a nice predictable hollowing effect which should not alter the action or affect the balance.  As far as i can calculate an increase in overall diameter, or section height of only 1.5% should retain the original stiffness, or line rating, if you prefer.   Don't worry about shooting this down, it was just a notion that came to me in  my bath.  The 25% weight reduction seems an appealing benefit on longer rods.  (Robin Haywood)

I have shaved off 60 to 70 percent off two three piece rods except for the tip sections. They work. I have never had a problem. I never built the taper solid so I have nothing to compare them to. They have have heavy stresses put to them. I always shave the inner apex some. I guess a lot of people do that though. (Timothy Troester)

I always plane a little off the apex. The six strips nestle better since they don't have to fight for room in the middle. This makes for smaller or no glue lines. Of course, some will say that, when the strips are planed perfectly, they always nestle well. Am I the only one with imperfect strips?? So sometimes I plane off a little more; not really measuring, and not doing more than 50%. Works fine. There must be some weight savings, but not too much I think. The shavings I have after planing the apex sure don't weigh much... Is the feeling different? I never made the same rod hollow and full, so I can't say.  (Geert Poorteman)

I did just that a few years ago with a rod.  I just started planning off the apex prior to glue up and kept going.  It did not seem like I removed a lot.  I just made it hollow.  It definitely worked to lighten up the rod.  The rod however, just did not feel right.  What I should have done is added a small percentage to each dimension to beef it up a little before I did this hollowing.  The rod just did not feel right.  It was lighter, but I did not seem to have the feeing that I wanted when I cast the rod.  I think that since I removed pith, I decreased mass and in turn also decrease/changed the action of the rod.  Describing the action is difficult on the best of days.  Maybe the balance point was off.

That being said, I like the rod, but I found that I added a heavier reel to it and it helped a little.  I also do not have anything to compare it to.

If I were to do it again, I would add a certain percentage to the dimensions of the rod.  Say 3% to 5% along the entire rod and then would hollow it.  I think that this way I could preserve the feel or character of the rod while making the rod feel lighter in the hand.  (Mark Babiy)

The figure I gave of plus 1.5% is correct for a 50% reduction in wall thickness all through the blank, if you went further, say to removing 60% you need to add 3.5%.

These figures will very slightly underread, no harm in adding another .5%!

There is rather more to this, for instance, removing 60% will increase the tendency to ovality in the butt section under load.  This will be more obvious in any butt section which does not have a concave taper form.  Heretical to the last I firmly believe that all butt sections should be of concave taper because all cantilever beams either are, or should be, designed like that!

Don't get me going on this one!  (Robin Haywood)

Is a hollow rod that great?  Do they plane the one side of 60 degree strip flat? Why are they so expensive?  (Durick Schonfeldt)

You could search this list's archives - I think I sent you that address?

On the other hand for more specific questions this place is the best.

As for your questions

Is a hollow rod that great ?

I haven't made one yet but can well believe that for longer heavier line-weight rods (9 ft plus 5 wt plus), where self weight becomes an issue, hollowing must be better, provided the rod is still well balanced. I am sure others will chime in here.

Do they plane the one side of 60 degree strip flat?

I think some have. eg Wayne Maca apparently does (in a manner of speaking because I don't think it is as simple as that), but then he uses highly toxic epoxy glues, vacuum chambers and other esoteric processes. Most common are various forms of scalloping the strips or fluting them. Basically you need enough remaining wall thickness for strength and enough surface area for gluing.

Why are they so expensive?

Because they are handcrafted and take so much longer to build?  (Stephen Dugmore)

Thank you to all who helped me with the design for a hollow fluting mill. It's almost done and I promise to post some pics, but I do have on more question: I based it on 3 flute slot cutting router bits, 1/16 to 1/8 width in 1/32 increments, and my question is do any of you know someone who can grind a radius on these bits? I'm looking to keep the width of each cutter, but I just am going for that half round scallop similar to Winston. Any help, once again and I again promise to share the goods when I am done.  (Eamon Lee)

Perhaps you could consider using ball end mills instead.  (Ralph Tuttle)

I found a guy that makes custom bits. I'm sending him drawings and he 's going to get back to me with a quote. Let you know. Thanks to all who replied. You've been very helpful.  (Eamon Lee)

Anyone know of any online tutorials on hollow building? Naturally, I want to do it the cheapest, easiest and most effective way.  (John Channer)

I've done a few hollow rods, using extremely crude tools and processes. The most important step is to plan out exactly where you will hollow,  and where  you  won't.  I  leave  "dams"  every 2-1/2", and leave solid the area in front of the grip, the stripping guide, and all ferrule stations. Also, it's important to correct your taper for hollowing - i.e. add a few 000's" to compensate for the hollowing. I've found the table in Bob Milward's book to be very useful for this.

First, I made a hollowing jig by gluing and screwing two .090" brass strips to a piece of wood, leaving enough room between the brass for all six strips. The rod sections are assembled and taped together, then split as in applying glue. Then, put the taped, open sections into the jig and hollow out using a sanding block with 100 grit paper. This process is not very accurate, and won't take the strips down to final wall thickness, but it gives you a start and lets you know where the hollow sections are. After the initial hollowing is done, I take the strips apart and use a Dremel Tool with a small sanding drum to take the hollowed sections down to the desired wall thickness. I used .070" on my last rod.

For glue, I had numerous recommendations from the Rodmaker List to use Epon rather than my usual Probond PU. The advantage of Epon is that it won't leave hardened "foam" inside the hollowed out sections. I did a couple of tests where I glued hollowed sections together and then cut them apart, and found that if you wipe off the glue as best you can from the hollow flats, Probond doesn't leave enough residue to be concerned about. So I'm still using Probond.

Is hollowing worth it? Yes, especially for fast, stiff action tapers over 8 feet. That little bit of weight you take away makes the rod feel lighter and more responsive. Hollowing probably isn't worth it for smaller rods, since you don't remove enough material to make a big difference. Also, the consensus among spey rod makers at Corbett Lake last year was that hollowing weakened the rod too much for this type of fishing - so I wouldn't hollow out a rod I was going to use for salmon or steelhead fishing.

Other folks have developed much more efficient, sophisticated systems for hollowing. I'll probably pursue these in the future, but my crude system seems to work well and doesn't take that much extra time.  (Tom Bowden)

Sounds like shims on either side and something or other to carve with is the ticket. I have most every type of sander known to man and a selection of chisels to match, and I already use Epon, so it sounds like all I have to do is come up with the shims. Come to think of it, I have a package of various thicknesses of brass shim stock,  so I might be equipped in that department, too. I'll have to find my copy of Milward’s book and see what has to say about it,  I forgot about his book as I don't refer to it much.  (John Channer)

I have searched the archives, the tips page, and the rodbuilding forums and I can't find an equation for determining how to calculate the taper dimensions for hollow building.   I have a rod I want to build and I would like to try and hollow build it as well as build it solid to compare the two.  I have read that some people don't add to the dimensions, some add 3.5%, some add 1% in the smaller portions and increase to 4.5% the closer they get to the butt, and some add x% based on Y wall thickness, and others suggest getting "Milward's book" and read up on it because there is a great section on hollow building.  I plan on doing the type of hollowing where you leave a dam every so many inches, I believe it is called scalloping.  Here are my questions:

1.  What is the name of "Milward's book" and where do I get a copy?

2.  Is there an equation to determine the added dimension and what is it?

3.  How long are the dams?

4.  How long are the scallops?

5.  Do I hollow under the nodes, handle, and guides?  (Greg Reeves)

Check Power Fibers Vol. 17, 18 & 26  (Ron Larsen)

Milwards book appears to have gone unobtainable, which is a shame, in spite of

its quirks. At least he tried to codify rod design, rather than ignoring it, advocating

plagiarism or treating it as some form of arcane black art, which it most certainly is not. Modifying rods is pure cantilever beam physics, and of a very basic sort indeed, since our fly rod cross sections are, and should be, whatever Mr Montagne thinks, radially symmetrical.

Let us grasp for basic principles first by assuming that the whole rod is to be hollowed, like a composite one. This is even easier for a hex section because we can take each strip as an equilateral triangle, and, by bisecting its vertical axis produce a structure capable of  being divided into four identical triangles. So, it can readily be seen that if we reduce the wall thickness by 50% we have removed 25% of the mass of the section. You can try this on a bit of paper, its not sissy to not think like a mathematician, my wife and son do, I most certainly do not!

So far then, we have reduced the weight of our blank by 25% by simply planing the strips to half their thickness. I am advised that this is perfectly feasible and nothing breaks, but until I can get more workshop time I tend to leave the ends a bit, er, solid. If you want it mathematically then the weight of a symmetrical cross section is proportional to the square of its radius. So, to try another example, if we reduce the original section thickness by 60% (a wall thickness of 40%) of the original. Then the weight reduces by 60% of 60%, which is 36%. And you better be good with a plane and glue brush, I think!

And now for stiffness!

The stiffness of a tubular structure is proportional to the fourth power of the  outer diameter, minus the fourth power of the inner diameter. In other words the original bit minus the bit you removed with a plane! Since the original bit is, for the moment, the same, then the effect of removing the inner bit, (which we will revert to the original 50% of overall thickness) is that stiffness is reduced by 50% of 50% of 50% of 50%, which is 6.25%. You might not notice this, but in case you think you might then what needs to happen is that stiffness is increased by 100/93.75x100/1: IE by 6.66%. I'm sure all this precision is pointless, but we do have some very Garrisonesque characters reading this. One just hopes their rods have moved on a bit. Since stiffness is proportional to the fourth power of the diameter then we need to increase that by an amount which increases the stiffness by 6.6%, not helped by the fact that the cross section is hollow! So we have to erect hypotheses and test them. Which means guess a bit and see if the guesses work. To save boredom, for the two of you still reading this, we will see what an increase in overall dimensions of 1.5% makes. So that's 101.5x101.5% x101.55x101.5%= 6.13% increase in stiffness. Good enough.

The formulae, if you want them, are simply these.......

Deflection is proportional to wl3/d4

Where deflection is the dip of the tip, w is the load applied to it, l is length and d is diameter. If you want to push hollow building further then you may encounter a situation where the wall thickness results in ovality, by which I mean that the cross section becomes something that the misguided Mr. Montagne may approve of, by which I mean radially asymmetrical. When this occurs, and it occurs in the butt then the the law of diminishing returns sets in and the stiffness of the whole is not proportional to d4 but the major axis multiplied by the cube of the minor axis. As the former gets bigger the latter gets smaller, but three times over, if you see what I mean. I have always maintained, and am not likely to stop, that any butt section, whether solid or hollow, should be of concave taper form (as graphed), in the case of hollow sections at least, you can now see why. It is possible you will want to add dams and things, if so you can always increase the dimensions by 1% and see what happens. It is important to hollow the tip as far as possible, and if you want to know why then I refer you to the theory of levers!

I first hit this 48 years ago when I was 14, and I don't think it is really as simple as all that until you've thought it through, feel free to email me publicly or privately for any clarification you might want, no question too simple, although some may be too complex! Fear not! My eldest is an overqualified civil engineer, cantilever beams are playthings to him, we'll ask him!  (Robin Haywood)

In deriving my formulae, I inadvertently used the rod's Section Modulus instead on the Moment of Inertia.

The corrected formula is:

%OD  adder  =fourth  root(((((Original OD - Wall Thickness*2) / Original

OD)4)+1))*100

This now will agree with Robin's numbers.

A 50% reduction in wall thickness will require a 1.53% increase in OD  (Al Baldauski)

And I accept the .035% correction to my original guestimation with apologies and humility!  (Robin Haywood)

Am I right to assume that the increases in stiffness allow for the reductions in weight carried?  (Harry Boyd)

Actually, what it doesn’t allow for is the fact that the cross section is hollow! Its the correction for a solid cross section. But don't tell anyone, it’s another of my errors that might be unnoticed!  (Robin Haywood)

If you hollow 50% you remove 25% weight.  If you take that into account when casting a rod, it has the equivalent effect of shortening your line out by about 8 feet.

This is based on a comparison of a Dickerson 8013 with 50 feet of line out as the reference point.  It deflects, when cast, 38 inches from  a straight line.  If you hollow it 50% with the same line out, it deflects 35 inches, the same as the solid rod with only 42 feet out.

It doesn’t seem stiffer, it is, dynamically.

My program doesn’t include the ability to correct for the dynamic differences, YET.  (Al Baldauski)

Shouldn't it lengthen the line out? The reduction in blank mass for a given stiffness should increase the line loading by the same amount, more or less. I get a horrible feeling I've missed something here.  (Robin Haywood)

The reduction in blank mass would have the same effect in dynamic deflection as reducing the line out, IE the rod would deflect less.  Conversely, to get the same deflection, hollow Vs solid, you’d have to increase the line out.  You’d be making up for lower blank mass with more line mass.  (Al Baldauski)

I've got you now, many thanks.  (Robin Haywood)

You got me thinking and I can make some approximations with my program to guesstimate the effect of less “swing weight.”  At first blush it seems that if you wanted a hollow rod to “feel” like its solid sister, dynamically, you’d actually have to remove about  1.5% from the OD instead.  It seems the reduced weight results in more of a deflection change than does the change in stiffness. (Al Baldauski)

And thanks to all for confirming my suspicions that if I want to try and keep the original stiffness I will have to bump up my planning measurements by roughly .001 give or take depending on the section.  I think I will have to get better at my planning to keep that tolerance anyway.  Thanks for the equations and explanations.   (Greg Reeves)

As long as you don't reduce the section thickness by more than 50% and try and hollow the whole blank then you will not be noticeably wrong.  (Robin Haywood)

I read all that and it was great because it all makes sense but I wonder if there's an easier way to get to a starting point? Not the same thing I know because they're normality in compression and when they're not things go bang but when hollow building a mast the general thing is to go with a quarter of the solid dimensions for the walls using tapered blocking at rigging points. I'm not suggesting a quarter for strips but what what as a realistic stating point?

Also, you mention it looses stiffness then suggest it gains. I see this in a static way but I know from having started once with a solid mast them made one hollow on the same boat (it's too painful to tell of the glue I used and why) a hollow mast is stiffer than solid on a fractional rig at least and I think but could be wrong that this is because in real use inertia is reduced in the hollow mast.

I had a trained engineer tell me that a hollow mast is significantly stronger than solid in actual use simply because of the effects of the mass being driven back and forth in a typical storm or whatever is what breaks masts apart from knockovers and accidental jybes and broken stays that account for most of the the rest.

There are all sorts of reason to use a hollow mast not least just having less mass above the deck which brings this back to rods but I found that when I "pumped the rig" to point better to windward the mast bends about as much solid or hollow but during sailing the hollow mast seemed to impart more power and that can only be due to increased stiffness of the rig overall.

I repeat a mast is always in compression so it's not the same as a rod but I wonder about the hollowness and stiffness aspect.  (Tony Young)

I think that you would do well to check this book very closly as to statements made.

I would refer you to pages 97-99 where Mr. Milward proceeds to show how using his methods and analyzing the photographs which he has taken of a "Garrison type rod" except that after changing the taper from 6" stations to 5" stations it turns out that the rod is nothing like a Garrison. In fact the rod is very much like his type B rod on page 91, which he again refers to it as a Garrison type when it is not even close to one. Both the one he calls B type and the one used in the calculations on page 98-99 are actually a soft tip rod with a flex area built into it at the tip then from 20" to 50" it is very much a Straight line taper where at 50" there is a Large flex area all the way into the butt, just like the type B rod.

When tapers are plotted on 6" stations it just makes it much more difficult to check the data, why was this done on page 98 when the tapers on page 91 are given with 5" station?

Back to the rod given on page 98, I would characterize it as a 4/5 wt with a large flex area just after the handle, which would make the rod slow and full flexing, making it difficult, for me at least, to keep 60' of line in the air to take pictures.

For those of you who are not familiar with a large flex area in the butt, the rod gives a double hump stress curve with one stress peak at 60-65 inches and one in the tip (250,000) at 10" with 50 feet of 5 weight line. So I would have to question Mr. Milwards description of both these rods as "Garrison Like" and also question the stress curve he drew on page 99, which is something like a Garrison rod would be, except it is wrong for the rod taper he gave on page 91 and 98.

I would be happy to send anyone interested a Graphing of both tapers and also a Garrison rod if you require.  (Bob Norwood)

Other rods which are similar to this one are:

It's a complicated question.  Basically, you want to increase the outside diameter an amount to make up for the stiffness you lost in the middle.  If you remove a constant percentage of material, then a simple percentage increase of the OD can be used.  If you keep the wall thickness constant then the amount you remove becomes less as you approach the tip.  Therefore the increase in OD must reduce towards the tip.

Examples:

How do you arrive at 4%?  (Robin Haywood)

There are an interesting Excel spreadsheet made by Gabriele Gori to solve this problems using the concept of Equal Momentum of Inertia.

You can download all here, then at "come determinare..... a parità di momento d'inerzia" and finaly "Scarica in inglese" (download in English).

You will download a .zip containing an explanation file and the Excel file. The files are scanned for viruses!  (Marco Giardina)

Thanks for the program.  I ran the numbers for my taper through the Excel sheet and come out almost exactly with the dimensions I calculated multiplying by 1%.  All but a couple of them and they were only off by .001.  It said that I should save a full ounce so I'll be interested to see if that is true or not.  I plan to weigh the strips before and after the hollowing process to see what the overall weight savings are in the material itself.  I also plan on making the solid built rod along with it to cast along side it to see what the differences are.    (Greg Reeves)

It's a complicated question.

Al and Robin, While we are talking about this, let me ask a question. It seems to me there are two benefits from hollowing. The obvious one is the lighter in the hand feeling, which is considerable, especially in longer rods. The less obvious one is that once loaded, the rod would seem to have to spring back at a faster rate, just because there is less weight for it to sling. So if you got the rod to deflect the same as a heavier solid rod, it would propel the line faster, and in effect, feel faster and stiffer to the caster?  (Tom Smithwick)

Rate of recovery from flexing is a characteristic of the material, not its cross section, but is related to the mass and its distance from the center of flexing. I don't have greater detail to hand, someone else may wish to assist us here. There is no doubt that the difference, very obvious, between carbon and glass is the speed of recovery of carbon being much greater than for glass. On a first approximation it must, as you say, make a difference, but when we factor in the inertia of the line this difference is obviously to some extent mitigated.

Anybody out there with some figures?  (Robin Haywood)

Not to put too fine a point on it, but Rate of Recovery is a characteristic of the material AND its cross section.  One material, e.g. graphite, is stronger and lighter than say bamboo, so it needs a smaller Moment of Inertia therefore smaller cross sectional  area to achieve the same stiffness.  Consequently it requires a smaller mass.  The spring, IE the bent rod, has less mass to return to rest so it does it faster.

So, if a bamboo rod is made lighter by hollowing, it too will have a smaller mass and it will recover quicker than the solid rod.  But not as fast as the graphite rod!  (Al Baldauski)

Does that mean that, for a given material and cross sectional area, a hexagonal cross section will have a different rate of recovery than, say a square one?

I don't know, I'm not sure I've ever known, but "old men forget...."  (Robin Haywood)

If a hex and a square rod have the same cross sectional area,  then  the  hex  rod  must  have  a flat-to-flat dimension 7.4% larger.  Since the cross sections are the same, then the weight per inch of length for any section will be the same so the “swing weights” are the same.  Therefore the recovery will be a function of which one is stiffer.  The MOI of the sections determines the stiffness, and in this case, the square rod is 4.2% stiffer.

BTW: I’m only two years behind you in age so you might be suspicious of everything I say.  (Al Baldauski)

You have shamed me out of idleness.

But...............

The relative stiffness I have are .812 against .792, giving 2.65%.  But are we quite sure that this makes any difference to rate of recovery from flexing?  (Robin Haywood)

I’ve double checked my numbers using formulae straight out of an engineering handbook and stand by them.  Perhaps, being as old as you are, you may be suffering the inaccuracies inherent in a slide rule, I use a modern calculator. J

Does it make a difference? Yes it does.  Is it noticeable?  I don’t know.  (Al Baldauski)

No, I got them out of a book!

Stiffness is the result of a static stress strain test, the rate of recovery from any given position is a separate characteristic of the material.

Internal damping, for instance, can be just one of several factors which control the parameter.  (Robin Haywood)

Me thinks we’ve got beyond the realm of practicality when we start considering internal friction of materials.  They are what they are in bamboo and do affect the overall performance but we have to talk about what we can control.  We can control weight to stiffness ratio by choosing different cross sections, we can control total weight by choosing to hollow build or not.  I would GUESS the overall weight, the stiffness of the particular taper, the wind resistance, and the tip damping caused by the line “attached” to it are all greater factors than internal resistance.  (Al Baldauski)

Yes, absolutely! I was merely endeavoring to discover what the link with stiffness and rate of recovery from flexing might be. I've got as far as knowing that material weight must make a difference, because if you weight one end of a steel rule it twangs about more slowly than if you don't! As this was the original question then we can, (as everyone but me suggested), assume that hollow building will produce a sharper, brisker feel to the rod. Without affection its overall stiffness of course. Therefore it cannot affect the line rating, as i see it.  (Robin Haywood)

I haven't made any hollow built rods myself but I've got a little information for you. I have been in contact with Per Brandin on this subject several years ago. Per is a tournament caster and a very good one at that. I've seen where he's scored 100 in the dry fly event so we're not talking about someone who's just got off the boat. Per also is a bamboo rodmaker, very well known, and his rods sell for big bucks and there's a waiting list to get one of  them. Anyway, Per makes hollow built rods and he told me if I wanted to get into tournament casting (9’ rod) that I'd be best off to hollow the butt section of the rod I choose to make. He also suggested I hollow about half of the tip section as well. What he said was the weight savings with hollowing was minimal and you wouldn't think this small amount of reduction in weight would matter. In reality he found the difference in feel was very significant compared to a non-hollowed rod. He explained it in terms of swing weight in golf clubs. A small difference really was noticeable. I never built the tournament rod nor have I cast any but I surely know the difference in different swing weights with my golf clubs. (Jim Bureau)

As we’ve discussed in this thread, a 50% hollowing will result in a 25% weight reduction.  That’s significant!  I’ve only built one hollow rod and I was astounded at the difference in feel just holding it, no casting.  It was an 8’4” rod for the Challenge last year.  It was a brute of a rod yet it was lighter and felt much more comfortable than my Para 15.  (Al Baldauski)

Wonderful stuff but.... The object in question here is scalloped. Lets assume 1.5" hollows, with .25" dams. Does the hoop strength of the dams or the solid mass (not hollow) enter into your equations? Does it change anything? Or does it become too complex to worry about? Seems like I would have to increase the OD of the scalloped areas and decrease the OD of the dam area to arrive at a fixed overall Delta.  (Jerry Foster)

In your scenario the dams (damns) represent only about 15% of the total. The difference in stiffness when not considering dams is relatively small so the error induced by the dams is negligible. The dams are too far apart to significantly impact the hoop strength centered between them, where the failure is likely to occur.  My opinion not backed with empirical data.  (Al Baldauski)

We can leave hoop strength out of this possibly, unless you are worrying about butt ovality, that is a complex issue best resolved with a test rig that allows you to measure it and thus test any changes you might make to eliminate it. Personally, and its a raw opinion, I think that it might be very hard to create a cane section that was durable but suffered from the problem of ovality, but if someone has done the research to prove this opinion to be fallacious then we can all learn from it.

If you are merely concerned with stiffness then I think you have to try to estimate how much material you have actually removed and thus back work the formula to  give a stiffness reduction.

From distant memory, even using 6'' hollows and half inch dams the lightness was noticeable but the reduction in stiffness was not, I just put it down to material difference and production tolerances!

But I put anything, up to about 10% either way down to that! I find it to be so much less soul-searing than the likely truth, which is chronically crap workmanship of course.

I may be guilty of mot understanding your post fully, especially the bit where you appear to want to produce a sort of sine wave taper over 1.5'' nodes and quarter inch sub-nodes.

No, thought you  didn't!  (Robin Haywood)

The rod I built last year for the CRG competition had a 40% wall thickness except for the last 15 inches of the tip which was solid.  The dams were 1/4 inch spaced 5 inches.  This proved to be too thin and/or the spacing too great.  The rod failed pretty much uniformly along the hollowed section.  In an area where it didn't fail, I bent it to a radius that would be considered about maximum during casting and fastened it with string to hold the radius. Then I measured across three sets of flats in one location which was nominally 0.160 across.  I found a deviation of about 0.001 in dimension relative to the unbent rod.  That gives you an idea of how little the rod goes "oval".  The failure mode was difficult to determine.  Some areas showed bamboo failure, some showed glue joint failure.  (Al Baldauski)

Absolutely invaluable practical experience of the sort we need.

The ovality problem only seems to be critical in very thin walled composite tubes and in the butt sections. I have an idea that this was because the ratio of wall thickness to overall diameter was not kept constant and therefore the butts were relatively much thinner walled. It took a couple of decades for composite blank designers to stop thinking like mechanics and start thinking like engineers!

You experience certainly suggests that those who believe in fluting are on to a winner.

I just wish I could understand how to build the rig for it. I remember it all looked very logical but for the life of me can't recall how to make it!  (Robin Haywood)

I started another topic on hollowing on coming up with the new dimensions for the taper. Now I would like to know if it is o.k. to hollow the area under the handle and under the nodes?  (Greg Reeves)

I'm sure it is, but I don't know by how much. Weight under the handle is much less important than weight at the tip, as it has little if any leverage on the hand, purely inertia loading on the wrist.  (Robin Haywood)

Keep the rod solid under the ferrule, and for about 2" before. Theoretically, the rod should be solid under the cork, and in front of the cork for a few inches, to resist hoop deformation, but in practice I hollow my rods through the handles (.070--.075" depending on rod weight) and in the 8 years of doing so have never had a problem.  (Chris Obuchowski)

PS: I flute ALA Winston on a MHM and add 3-4% to compensate for it. The tips I have hollowed  progressively from .070 at the ferrule, down to .045-.050 toward the tip.

What is the easiest way for a low-tech builder like myself, with just a planing form, block planes and a dial caliper, to try hollow building?  Fun as they are to build, I don't have room for any more big contraptions.  (Frank Stetzer, Hexrod, Taper Archive, Rodmakers Archive)

It would be tedious as hell but you could use a sanding drum on a Dremel cutting and checking all the way for six strips! YeGads.  I know, you didn't say you had a Dremel, but I assumed almost everyone does, they're so damned handy and compact!  (Al Baldauski)

I've done a few rods with this method and it really works surprisingly well and is very easy.  Not the most precise method out there as far as repeatability goes, but it does work.  All you need is a hand drill and an 80 grit 1 1/2" drum sander. See this post.  (Chris Carlin)

Tape the planed strips to your bench top side by side on double face tape. put a shim strip on either side of the strips. The shim should be the same size as the wall thickness you want. I have used steel shims,  and stacked Formica, but hardwood would work, too. For a simple hollow job, you could just plane the apexes down to the shim. To leave solid dams, mark their position on the shims, then get a sharp carpenter's chisel and carve away the apexes  between the marks. I use a 3/8" chisel and carve the strips one at a time. Even things up with a card scraper when you finish carving each section.   (Tom Smithwick)

I recently finished my first hollow rod based on a Powell B9 taper.   The rod is a 6/7 wt and has exceeded my expectations. The hollowing technique is fluted, not scalloped like a Powell.  I am considering replacing the pith with P.O. Cedar on my next rod (per Powell design) and wonder if this will make a difference. I also wonder if anyone has compared scalloped vs. fluted scalloping hollowing techniques (or maybe a combination).  My goal is not to make the lightest rod possible but to understand the trade offs of swing weight vs. action.  (Ray Taylor)

If when you hollow build and remove, say 50% of the inside, believe it or not you only reduce the stiffness by 6% but you've reduced the weight by about 25%.  This reduction in stiffness is not noticed because the reduction in swing weight makes the rod feel stiffer.  The change in rod deflection due to the reduction in weight is the equivalent of casting 48 feet of line instead of 50 feet of line.  Who among us can feel that difference?

All that being said, double building with cedar adds back swing weight with little to no difference in stiffness.  My opinion based on calculations.  (Al Baldauski)

Has anyone tried hollow building with balsa wood filler, similar to Powell's cedar laminated rods.  I would be interested in other materials as well (plastic, high density foam, etc.).  A search of the WWW shows balsa with a weight of 11 pounds per CFT and northern white cedar with a weight of 22 pounds per CFT.  The balsa may present some challenges.  Interested in anyone's thoughts.  (Tom Todd)

The high density foam really strikes an interesting note... hmmmm. Seems it would be quite easy to accomplish, especially with fluted hollowing. I do like the idea of some sort of foam that can fill the  void and  add virtually NO weight.  (Mike St. Clair)

Would not the filler soak up the glue and take on more density and weight?  (Keith Paskin)

I was thinking after the rod was cured and dried. And only if one used the fluting method, like on the MHM. IT would not have any wet glue to soak up. Density... yes (some), weight... nominal (JMHO)

Might be worth a try at some point, just to see how it does effect it.  (Mike St. Clair)

For those interested in what a foam-cored hexagonal rod looks like, check out the Hexagraph rods.  Graphite substitutes for bamboo power fibers, but the rods are constructed, just as a bamboo hex rod, from 60º strips glued together to form the hexagonal shape.  A cane rod builder (Walter Powell) was involved in the design of the rods.  The foam is, I believe, closed cell and does not absorb glue.

Not that I am advocating buying a Hexagraph, but the construction is appropriate to the question raised.  (Tim Anderson)

Richard Tyree has an article in The Planing Form on using foam.   It was probably published 12 or so years ago and I think is in one of "The Best of" books.  (Bill Lamberson)

This is not meant as a dig but why would you want to? Many modern makers have already shown you can make a superior rod without the fillers. Why replace one dead material with another?

Again not meant as a dig, i'm genuinely curious what someone would hope to accomplish by doing that.I'm in the process of starting to hollow build myself. Are you simply trying what he did or do you have some other theories you're working on?  (Jim Lowe)

My thought is this:

There is a trade off in how much you can hollow before the rod begins to fail.  If you completely fill the hollowed void, there is less tendency for the cross section to collapse so you could hollow out a greater percentage. Counteracting the hollowing is adding back material of a finite weight and rigidity.  Again a trade off.

My opinion is: there is too much aggravation with not enough payback to fill or "double built" a hollow rod.  (Al Baldauski)

I may be a traditionalist, in fact I am sure if it, but I cannot conceive why one would build a hollow built rod then line it  with something else -- balsa, Port Orford cedar, foam, etc.  The good Lord has already given us a filler with the natural pith.  To go to the trouble of hollowing and refilling seems to me to be an exercise in ... I was going to say stupidity, but that would offend people, so use your own word hollow building does have one advantage and that is to remove some weight:  However, removal of the pith leads to a flattened tube in flexion.  We all know that that is no better than those ugly black soda straws.  Only Wayne Maca has come close to solving that problem.  I have seen him bend a rod in a complete circle without failure.

I have always had a strong conviction that bamboo rods should not be hollow built, hollow built with carbon fiber reinforcement, hollow built with wood center, double built and triple built are all bad rod construction.  We have nearly the perfect material to build cane rods and to muck around by altering this structure is little more and an exercise in ego enhancement.  For those who disagree, I grant you the right to differ.  (Ralph Moon)

Not all "hollow" builds are completely hollow. The MHM allows for the "star" cutter that leave the apex intact while removing the material on either side, thus giving a "rib" throughout the length of the rod.

There are purists in every facet of life... including bamboo building, and they have their place, too.

I'm thinking that giving something different a try won't cause the earth to wobble too much. We'll see.  (Mike St. Clair)

I can understand that but it seems that collapse really isn't a problem with modern rods.

I would agree it seems like a lot to go through with little return. Besides my understanding is that the benefit from hollowing is really in the improved casting characteristics. One would likely have to think hard to find a filler material that would actually improve casting and that begs the question, why not make rods with that material.

I know Hexagraph used some sort of filler and it may have been my inability to cast it properly but I could only describe the two I have cast as "dead stick".  (Jim Lowe)

I've had relatively little hollow building experience but can say that collapse is an issue depending on how much you hollow.  I used the scalloping method with dams at 5" and wall thickness of 40%.  This rod failed.  Then I built a rod with dams at 2.5" and a wall thickness of 50%. This rod survived.  So somewhere in between is the "hairy edge".  With a stiff enough filler material you might be able to use a wall of 30% to 40% and still survive but I'm guessing that any filler that is stiff enough will offset the weight savings.

Any filler will have the effect of damping the rod vibration, hence the "dead stick" feel.  Different but not necessarily a bad thing.  (Al Baldauski)

If you're not having failures, you're not learning anything. Keep experimenting.  (Ron Grantham)

I guess that was my point. Like anything else, collapse doesn't seem to be a problem once you figure it out.

I think I remember somewhere that Powell had trouble with his glues and maybe that prevented him from going all the way.  (Jim Lowe)

I've not yet worked out what advantage it might have over thin air.  (Robin Haywood)

Ah, but Robin... there's a vast amount of difference between the air where you live and the air around L.A.

Never trust air you can't see.  (Mike St. Clair)

You can't see it here sometimes, but the rest of the time its very visible indeed as sea-mist.  (Robin Haywood)

All good things to think about, and I am thick skinned so no offense taken from anyone.  I have been building for about ten years and am a bit of a traditionalist myself.  I have almost always built shorter rods and now would like to build some specific longer and HEAVIER rods for my use.  My thoughts are:

1.  Hollow rods are lighter and maybe livelier.

2.  A filler would displace the void and supply additional rigidity and not necessarily absorb glue.

3.  With the filler you may be able to reduce the bamboo thickness slightly more than if you had a void.

4.  My 61 year old body appreciates any reduction in weight.

5.  So far......no one has talked me out of it.

Any additional thoughts are appreciated.   (Tom Todd)

See Ray Gould's book. He has tapers in there using graphite cores. I don't recall him giving data on how he matches the size of the filler to the hollowed cane, but I was impressed by the idea.  (Art Port)

We use high-density urethane foam in my day job.  it comes in 15 and 18 pounds-per-cubic-foot densities, among others.  You'd have to laminate strips of it onto your bamboo, as is done with double builts, before planing.  Personally, I'm not convinced it'd hold up under the constant flexing of casting, as it is designed to be part of a rigid system.  I suspect it would disintegrate over time.

I suppose anyone using gorilla glue with hollow-building techniques is getting pretty much the same effect - a foamy hard set PU core. At least that way you'd avoid the troubles of laminating.  I wonder if the glue, as it expands, would push the hollowed sections apart?  You might have to experiment with how much glue is the right amount, to fill the cavity but not to push the strips apart.  Any Gorilla gluers out there to shed light on the subject?  (Lee Koch)

I've tried the PU glue (Gorilla) on hollow-fluted sections to see what would happen. My test showed that the foam has no strength and adds nothing to prevent the rod from collapsing under stress.  (Ron Grantham)

Thanks for the info Ron.  I suspect that a rod with a High Density urethane core would exhibit the same behavior, and for pretty much the same reasons: HD urethane has no directional strength, IE no "grain."  (Lee Koch)

I’m only on my third rod, but I still don’t see why anyone would try to get by with something other than the tried and true glues like URAC and Resorcinol.  (Reed Guice)

I'm not conversant with American terms and brands. But Resorcinol has a most unfortunate color and, worse, gap fills badly. If URAC is what I think it is, which is some sort of Urea Formaldehyde then the problem is longevity. It may be bacterial attack or just age deterioration but after a time the bond seems to crystallize and fail. I've been using an epoxy which sets up stronger with heat, although I think they probably all do.  (Robin Haywood)

To my knowledge, the long term breakdown of UF that you refer to is limited to the non catalyzed resins IE what used to be Cascamite not to either of the Aerolites or Urac.  If anyone knows better I would be interested to hear?

Resorcinol only gap fills badly when it contains no filler but gap filling is of no interest in rod making except in the avoidance of starved joints or if visible joints are wanted.  Ironically a well planed rod glued with an unfilled Resorcinol (Polyphen for instance rather than Aerodux) actually shows virtually no glue lines.

The UF glues have one major advantage over Epoxy, they are water clean up, the only disadvantage is that you have to be quicker and that is not a disadvantage if you make rods professionally.  UF also gives the stiffest blanks.

I have nothing against epoxy, I have made numerous rods with it.  (Gary Marshall)

I did once have a bit of a thing about clean up, but I find it takes no longer with a big mill file on Epoxy than larking about under running water with water solvent adhesives.

I'm sure your planing is 100% impeccable 100/% of the time just as certainly as I'm 100% sure mine is neither of those things!

Aerollites used in DH Mosquito construction certainly weren’t that durable, but things may have moved on since 1942!  (Robin Haywood)

Using Resorcinol to fill gaps would seem to indicate a problem with your planing and maintaining 60 degree angles, rather than a problem with the glue.  (Nick Kingston)

My planing is entirely adequate for the job it has to do, but on my experimental rods, which is most of them, it will show purple glue lines which I don't care for. Also, the color seems to darken with age. Even on rods where the planing is exemplary it shows.  (Robin Haywood)

Resorcinol does show - that’s undeniable and was never denied - and even if your planing is exemplary, yes, it will still show.

But I repeat - in response to your previous comment "and, worse, gap fills badly.":

Using Resorcinol to fill gaps would seem to indicate a problem with your planing and maintaining 60 degree angles, rather than a problem with the glue.

To elucidate further:

Resorcinol is not designed to be a gap filling glue - and if you are using it for that purpose:

a) You have chosen the wrong glue; and

b) You have a problem with your planing - even I know that. (Nick Kingston)

I just said it doesn't gap fill, everyone reading can decide whether that matters to them. Or not. I tend towards nodeless but if you don't then gaps around the nodes can happen. I don't mind the gaps, I mind holes which allow ingress of water and/+or horrible purple splotches.

I don't mind if you stick your rods together with hide glue mixed with par boiled parrot poops, I was merely explaining the characteristics of some adhesives.  (Robin Haywood)

I used Gorilla glue on my "I-beam" or magic star hollowed rod and it seemed to work fine. I thought the excess glue would just fill in the hollowing and not add much weight. I didn't need the glue to add any strength the basic hollowing design does that.  (Ken Paterson)

If you scalloped/sanded right to the end of the section, what would stop the Gorilla from expanding out the bottom of the  section (unless you have something against poopy rod sections, of course)?  (Understanding that most hollow-built construction will leave a length of solid construction at the ends, or along the length, or both).  (Steve Yasgur)

I use only PU glue, and make hollow as well as solid rods. This is my experience: No foaming of the glue inside hollow rods happens. I do NOT add water, or vapor, I simply apply the glue with a toothbrush, brushing thoroughly to minimize the layer of glue,  just as I do when building solid rod. That’s it....... Have sawn test rods to see what actually happens, foam vise, and the answer is........: nothing.  (Carsten Jorgensen)

Even if it did foam the foam is light and has little structural strength.

In spite of all appearances PU glue also doesn’t gap fill all that well.  (Robin Haywood)

I have been doing some reading on hollow building. There doesn't seem to be a lot of information out there on the topic.

The only info I have found so far is from conversations with Mark, Clark's web site, the Rodbuildingforum, Power Fibers or very early issues of The Planing Form, in particular, an article by Richard Tyree.

I am interested in building a lightweight hollow rod for saltwater use, and was wondering if anyone out there has built an entirely hollow rod with long lasting results. I am also interested in any other techniques such as scalloping or fluting, pros and cons, any special adhesives/techniques recommended, or just anything related to building hollow rods.

I've learned quite a bit from this board over the years. Someday I hope to be able to help others out the way you all have helped me.  (Kurt Wolko)

At this stage, keep it simple.

Forget scalloping, the advantages are small and the investment in time making up jigs is great. Golden rule number one: The hollowing must be a constant percentage of the total section thickness and it must go right to the tip.

Why? is the degree level syllabus, and you're still doing "O" levels!

But there's no reason to be anally retentive about this, near enough, in my experience, is good enough! In fact, I hollow all my sections, even under the ferrule and handle, by a visible amount that leaves a gap obvious. How much should you hollow by? 50% of section height is reliable and produces a 25% reduction in weight. Its really incredibly easy, take a couple of cuts with your hogging plane, measure the wall thickness and fine tune with your finishing plane. Don't worry if you overdo it a bit, or even underdo it, it all balances out and its natural material, after all. You may need additional advice if you are using a heat curing epoxy, but provided you don't overdo thigs you probably won't. If you are combining this with cane ferrules you may wish to consult me privately, before the nice people get cross with us!  (Robin Haywood)

Is it asking too much of the glue we use to build a hollow rod in a nodeless fashion?  (Louis DeVos)

Not at all, we've used Epoxy and TB3, the nodes don't make a difference, but hollow might.  (Robin Haywood)

I have built many nodeless rods, approaching 200, and the only ones with which I have had structural issues have been the few that I have hollow fluted (Winston style hollowing).  I glue splices with Titebond II and strips with resorcinol.  The problems have consistently occurred in the butt section a few inches above the cork.  Perhaps I have hollowed them too much.  Splices have popped and the strips have split, not at the glue seams, but in the longitudinal center, the thinnest part after hollowing.  It hasn't been possible to tell which comes first splice popping or strip failure.  On a couple rods built in that fashion I have put a series of intermediate wraps at 4" intervals from the cork to the stripper and that seems to have solved the problem.  (They are also handy for measuring fish (12", 16", 20", etc. (I even got to use the 24" on a rainbow earlier this spring.))  My hypothesis is that the tubular butt is collapsing and basically folding causing the strips to fail.  The intermediates give it "hoop strength" and help prevent the collapsing.  I have also hollow built some rods using the magic star technique in which "spokes" prevent the rod from collapsing.  The weight reduction is less with magic star hollowing, but I have had no failures.  (Bill Lamberson)

I have wanted to add hollow building to my rodmaking techniques for awhile. It seemed a risky proposition considering the amount of work that's gone into making a rod before the hollowing cuts are made. So I was after something with good control and accuracy. Unfortunately in contrast to other aspects of rodmaking, there doesn't seem to be much information out there on the details of how to do it. Such as I did find referred to links that were dead. So I finally had to resort to invention. The result I think is worth sharing, so I did up a page on my web site on what I came up with.  (Mike McGuire)

Rodmaking ingenuity at it's finest. Thanks for sharing that with us Mike!

Of course, if you would have put a little more thought into it you could have hooked it up to CNC controls.  LOL  (Will Price)

Thanks for taking the time to make that link to your site, taking those pictures and detailing/sharing them along with good explanation. (Some of us really need that...) I found it answered some of my wonderment as to how I'd go about fashioning a jig to do the hollowing.

Good stuff!  (Jeremy Gubbins)

I've just finished a hollow scalloped 7' 3 piece #4. It's drying as I type. It has got me thinking about hollowing and the various things I have read about it. Thinking over what little I know, it occurs to me that although there is plenty to read about hollowing in general, there isn't much about so called "extreme" hollowing. So in the opinion of the house, what is "normal" hollowing, if I can use that term, and what is "extreme?”

Or how skinny can I go before it gets daft? (Simon Reilly)

You could rattle Jerry Drakes chain if he is still on here...he could probably provide a fairly comprehensive definition of what constitutes extreme hollowing.  I know he's played around with that topic quite heavily. (Lee Slikkers)

I usually plane the top half of the triangle off, giving a 25% weight reduction, except for under the ferrule, the extreme tip, and usually a bit less under the handle.With a curved cutter in a suitable rig you could take a little more off, so that the flat top is concave, but i doubt its worth the effort in weight reduction terms. It is very important to hollow right out to as near the tip as possible, weight at the tip has more leverage than weight at the butt, on an eight-foot rod a gramme at the tip would be worth seven at the butt end, for instance.I find UHU endfest 300, which is an epoxy two pack which heat hardens to be ideal, there is a much reduced glueline and a bit of gap filling ability saves a lot of pain. (Robin Haywood)

You can get as skinny as you have nerve enough to go. Most rod makers limit on wall thickness for a tip when hollowing is thicker than what I use for the butt sections on my rods. I just finished a little 6', 2 weight that weighed 1.44 oz. You can see light through the tip. (Jerry Drake)

Gabriele Gori, who is the Chairman of the Italian Bamboo Rodmakers Association, did an interesting study on hollowing. I think you can find the article on the Bamboo Journal. He has calculated a conversion factor to transform the taper for solid built rods to hollow so that you maintain the same Moment of inertia. In practice if you hollow a solid taper without converting it you change the moment of inertia. Anyway in my experience the walls in the tip section (at least in a scallopped rod) should not go below 1.5 mm, although I recently tested a scalloped rod where the walls had been thinned down to 1 mm. I don't know what garantees you have with such thin walls but the rod I tested seemed to hold well enough! I was casting a silk 5 weight forward line and I double hauled it to about 25 - 30 yards.  (Moreno Borriero)

The decrease in stiffness when hollowed is slight. The example I mentioned which involves halving the section height would only require an increase in diameter of 1.5%, well within normal tolerances for the material.If you want to work it out for other hollowing rates the stiffness=fourth power of the outside diameter minus the fourth power of the inside diameter. This really is as simple as it looks, for instance if you go mad and reduce the section height to 40% of original you need to increase the diameter by3.5%.And the very best of luck, because at that rate of hollowing you will; need to radically trdesign the butt tapers to cope with ovality (when a different set of calculations apply) and the thing will probably blow up on its first cast! Cane has its limits. (Robin Haywood)

40% for a section 0.100 are you saying you are leaving 40% which would make walls 0.020 or are you saying that you are removing 40% which would make walls of 0.030? In either case, that is a pretty thick wall.  (Jerry Drake)

I would'nt dare remove 60%, but that is the example I used, for most of you are not only more courageous, but also much better craftsmen! (Robin Haywood)

In the Bamboo Journal issue n. 7 (www.rodmakers.eu) on page 55 there is an article about the types of hollowing ... even "extreme", with interesting comparisons and scientific verification of the moments of inertia of the various sections (Alberto Poratelli)

I would appreciate it if anyone could suggest a book with a thorough discussion of hollow rod building.  (Doug Hojem)

Bob Milwards' book has some good info.  (Harry Boyd)

I use Poratelli/Gori "Sharktooth" method. Details can be found here. It is essentially a type of scallop and dam method with very small (less than 1/2") scallops and dams. The main advantage of this method is that it does not require any special tools. A 1/2" round or half round file is all that is required. I use a Dremel with a 1/2" sanding drum to do the scalloping and space the scallops 2 per inch.  Although it does reduce the weight of the rod, I use this method primarily to move the balancing point of the rod back toward the grip. It also seems to improve the dampening of the rod.  (JW Healy)

Doesn't exist yet. There are some composite fly rod design books that can provide insight, else you need to find a mentor, piece it together from Internet and list serve info, or learn by trial and error.  (Chris Moore)

To convert a solid rod to a hollow rod, adjust the outside diameter to make up for loss of stiffness caused by hollowing. Keep the deflection of the new hollow rod the same as the deflection of the solid rod.

The answer lies in the formula for beam deflection. (Jerry Drake)

I've decided to hollow build my next rod, an 8013 for my son. I haven't tried hollow building and I'm wondering if the easiest way might be to use scalloping. Any one have any suggestions on the least complicated way to take a little weight out of the rod? (Bill Walters)

Take a look at my article on a scalloping jig setup. (Mike McGuire)

I use Alberto Poratelli's "Shark Tooth" method. It is essentially a scallop and dam approach but the scallops are less than 1/2" in width. Poratelli's write up can be found in IBRA Journal #5 p. 56. It can be found here. The principal advantage to this method for me is that no special equipment is needed. It can be done with a 1/2" round or half round file. I use a Dremel with a 1/2" sanding drum and 60 grit bands and cut 2 scallops per inch.  (JW Healy)

Every now and then there are discussions about hollow building on the list. You perhaps have noticed on Clarks site a topic "Is this possible" - a challenge to make 7' #3-4 rod weighting less than 2 oz. 

I tried to meet the challenge using a hollow-building tech of Rolf Baginski by inserting composite material based on wadding and PU glue to bridges inside the totally hollow rod. 

I resulted in 56.8 gram (2 oz). I like the quite simple technique requiring no other than hand tools. No long-term experiences, yet. 

The how-to-do site with pics is here.  (Tapani Salmi)

Do you have more info about the internals? Is it the fiber that adds strength? I'm asking because I was discussing briefly with Tim Anderson at the HF last June about using a really foamy PU on a hollow rod to make a quick internal structure--don't need to cut or shape anything and will always get a perfect fit--that would act like the internal structure of bone. His thinking was that the foam would be too soft to add any significant stiffness, might break down over time with movement, and wouldn't have enough strength to increase hoop strength to prevent collapse. (Chris Moore)

Since the time I talked with you, Rolf introduced at a European rod makers' gathering his method of making dams in a hollow rod to mimic Powell type hollowing.  Each dam is made with a little ball of moistened cotton soaked with a foaming PU glue such as Gorilla Glue.  The combination of cotton fiber and glue makes a rigid dam, but does not fill the rest of the hollowing.  Another of Rolf’s clever ideas.  Many are probably familier with the Baginski beveler which he invented.  He is a very innovative rod maker.

I suspect fibers other than cotton could also be used. (Tim Anderson)

Any "soft" fiber is suitable for the composite, I have tried with cotton, wadding, lamb wool, yarns, silk fibers, even bamboo shavings (from the floor!). "Hard" fibers like graphite or glassfibre do not work with PU (I have tried them too) they should be mixed with epoxy, but it does not swell like PU (Tapani Salmi)

This is just an idea for me now, based on buying four second hand hollow built rods in the last 18 months. Actually, I have had a couple of Powell hollow rods earlier. So, I have not set up my MHM yet for hollowing although I have the fluting device. As mentioned at Cressy Cane, I have issues with the operation of the MHM, possibly including backlash in the cut control. Maybe other issues. But that’s a project for November as Steve Wyatt wants to give me a hand. He was a trained machinist whereas I am in all things a generalist and surprise myself by looking deeper at times.

So, nothing to report yet on personal experiments. Just on the action of the work of the few who are active in the hollow field. And how refreshing the best are... (Sean McSharry)

Since this is a completely different subject from the original thread, I have changed the title.  I would just like to say that the fluting tool for the MHM works wonderfully.  I use it to hollow all of my rods, hollowing out to the tiptop.  For the final 10” or so of a tip, I do remove the apex before hollowing because of the tendency of the strip to rotate from under the cutter.

If you are having trouble with backlash, my guess is that you have the original MHM plane. The newer version (all aluminum body) has essentially no backlash.  I have the newer version, but have read that, with the original, you should adjust the cut downwards and then avoid banging the plane down at the start of the cut.  Banging the plane down may result in the cutters moving down (and cutting too much) and adjusting downward makes it so the cutters can’t move up during cutting (and cutting too little). (Tim Anderson)

I would like some input on hollowing a bamboo fly rod. I have done some reading up on the subject and do not have a clear answer myself. I have heard some rod-makers who say to hollow the butt and not the tip. Then they say if you do it that way, then it is to light in the butt. What really is the story on hollowing a bamboo fly rod.  I am building a Shelbyville 88 which is a 6-7 weight rod. It seems that if hollowing a bamboo rod were such a good thing there would be more talk about it and more of it being done.

Any thoughts or ideas on hollowing? (Lew Boyko (8/3/2016))

You can find much discussion here.

As with so many things, there is no single answer. 

Disclaimer:  I hollow my rods stem to stern, butt through the tip. (Tim Anderson)

I hollow using Poratelli's "Sharktooth" method (details at www.aprods.it). It is essentially a scallop and dam method but the scallops are only less than 1/2" wide. They are made using a 1/2" round file or a Dremel with a 1/2" sanding drum. Poratelli claims that there is no need to develop an internal taper as the hollowed rod deflects exactly the same as a solid one. I don't hollow for weight reduction but rather for improved balance and better vibration dampening. I start as close to the tiptop as is reasonable given the flat to apex dimension (about 20" from the tiptop on a typical 5 wt 2pc) and continue to 11" from the end of the butt section, leaving 1 1/2" plus the length of the barrel and tabs below the female and above the male ferrule stations solid. That distance is just my SWAG. It works quite well and has the additional advantage of not needing any special tools. (JW Healy)

It works quite well and has the additional advantage of not needing any special tools.

No special tools, what is wrong with you JW? (Scott Grady)

Thanks, I am going to glue up a Shelbyville 88.  I want to see how it handles and casts a 7wt line.  Then next winter I will build the same rod, but will hollow it to see the difference.

My problem with my jig is cutting the hollow out.  I have a set up per Mike McQuire web site.  But getting the jig to hold the strip and cut the hollow are giving me some problems. I must spend more time and work on that end of it. (Lew Boyko)

Mostly $$$ (there are a few other things wrong with me too but they're off topic).  (JW Healy)

I want to set up a hollowing jig based on Tim Abbotts design using a slot mortise unit from Inca. These are no longer available, but I got one of the last ones. The strips would be laid side by side on a moving table, and the table is then pushed into a 1/2” roughing end mill in a horizontally mounted router which, in effect, drills into the side of the strips one after the other. I am thinking the most convenient and adaptable way to hold the strips down would be with rubber pads backed by plywood, and pushed down on the strips with a toggle clamp or similar. I want the rubber, or substitute, to be strong enough not to get cut or grooved by the strips, but soft enough to conform to the strip shape at least a little and hold them down without crushing them. The pattern cut would be the Poratelli shark tooth method of scalloped hollowing. My problem is that I am not familiar with the specs relating to durometer hardness and other qualities for rubber. It is easy to buy the stuff in small sheets from guys like Enco and McMaster Carr, I just don’t know what to buy. Anybody out there familiar with the stuff? (Tom Smithwick (10/26/2016))

I can almost see using a kitchen type of sponge for what you are needing. If you get one that has the scouring pad side, it would have the flexibility of the sponge without allowing the strips to create groves. Velcro it to the plywood and you can easily replace the sponge as needed. (John Smith)

I subscribe to the theory of easy to replace and then replace as often as needed. When building jigs, I sometimes add a sacrificial part that makes it easy to just saw cut or drill through. As long as it’s easy to change, no fretting over tearing it up. (Matt Woods)

You might seek input from a local gasket supply house.  I found one not too far from me that helped with belts for binders, neoprene for steamers, etc.  Usually those guys like a kind of wild goose chase. (Harry Boyd)

I use a hollowing jig similar to what you describe. The original design had a moving table, but I found it difficult to maintain accuracy with that arrangement, so I fixed the table in one position and instead slide the strips along the table by hand. The strips are held side-by-side on a sticky masking tape backing. The backing tape has to be trimmed flush on each side of the bundle of strips, to avoid inadvertently raising the tape backing if it strikes the backing flange or mount of the table/mill. This can easily give a very thin strip, as one happened to me early on.
     
The bit has a radiused or rounded end, to allow gradual entry into the bank of strips. This system gives good results for me. The hollowed section of the strips occasionally have some small fuzz or tufts on the superior or pith side at each end of the cut. These are easily removed by scrubbing them off with a small brass-bristled brush.
  
The rubber I use to push down on the top of the strips while advancing them through each hollowed section is a small rectangular pad, cut from pool or pond liner. It is not too hard and not too thick; as Goldilock's baby bear would say," it's just right!". I use this protective pad just in case the strips grab and are propelled along rather quickly; that has not happened yet, but intact fingers are good!
 
Good luck with your project. Remember that is important to preserve the "time spent ratio" of three parts setting up the shop, to one part actually making rods! (George Deagle)

I am getting ready to glue up my first properly hollowed rod. Anything I should look out for, guard against or suggestions?  I will be using Epon thanks to Cliff Parmer. (Marv Loopstra (11/114/2016))

Just a couple of things I found.

Don't wipe off too much glue before you roll the strips together. It is easy to starve the strips of enough glue.

Bind from the tip to the butt to prevent pushing excess glue into the tip.

Take your time! (Scott Grady)

I hollow all of my rods completely and use epoxy (not Epon), applying as thin a coat as possible to all “internal” surfaces.  No wiping off.  With my Winston-style fluting, I can see the length of the inside of a blank.  There is essentially no squeeze-out into the hollowing.  I have not had any problems with glue failure. (Tim Anderson)

I have glued a lot of scallop and dam hollowed rods with Epon. It's not really any different from gluing a solid rod. I have had no problems binding from the butt end. I do wipe the hollows with cotton swabs, but I am not sure it is necessary.  I have dissected a scrapped rod that was hollowed and glued with Epon by heating it a few minutes in a 300-degree oven and the flexing it. It came right apart, and I could see no noticeable amount of glue in the hollows. (Mike McGuire)