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Just finished my drying cabinet, which is a modified CD tower that I got on sale for 14 bucks at Ames with my sale price and over 55 discount  on Tuesday. Inside dimension is about 58 long by 10 wide and 8 deep and I have set it up to handle 3 rods. Door is a piece of Plexiglas on a piano hinge and held shut with a cabinet magnet and a Velcro dot.

I have started with a 40 watt light bulb and one rod in the cabinet as a test. beginning to think the 40 water is not enough. Anyone out there with a similar setup who might want to give advice on bulb size.   The honey dew list is growing as I'm playing.  (Jim Tefft)

Give that 40 watt bulb a few hours to heat things up, and you might be surprised.  My drying cabinet is 12" PVC, 8' tall.  I have a little 18" fluorescent tube in there, and it keep the whole thing about 15 degrees warmer than the rest of the room.  But it does take quite a little while to heat up.  Be patient.  You can always put a 60, 75, or even 100 watt bulb in tomorrow.  (Harry Boyd)

I have a little "Y" fitting in my socket so I can put 2 bulbs in. I personally find 2- 60 watt bulbs give me the best results, but my cabinet is a bit larger.  (Shawn Pineo)

40 watts is plenty.  I have found that too cool is better than too hot! (Taylor Hogan)

Over the weekend I built a drying cabinet with a Glass front which is powered by a 60 Watt bulb. I've just varnished Rod No. 1 using my new drain tube, which worked great and hung the rod in the cabinet.

On the tin of marine varnish is says, 6 hours between coats and 24 Hrs to fully dry, but I was wondering how long other people normally leave a rod to dry in their drying cabinets?

Also, being a little bit safety conscious I didn't want to leave it on all night, 6 hours would be up at midnight, I thought I may switch the box of after this.

I was interested in other people drying regimes, hence this post?  (Nick Brett)

A while ago I built a drying cabinet and first tried a 100 watt bulb. Except near the bulb the cabinet didn't warm much at all, a few degrees.  My cabinet was all wood so that was the extent of its insulation.  Yours with a glass door will run cooler yet.  If your cabinet were 12x12x72 inches and all 1/2 wood with a 60 watt bulb, you could expect the temperature inside to rise by 4 degrees, assuming the heat were distributed uniformly.  It won't be near the bulb.  Anyway, this was all  by way of saying your cabinet won't get too hot.  Probably not hot enough to do much good.

So, I've abandoned by drying cabinet in favor of my oven convection oven which is well controlled with a PID controller to a few degrees.  When I want a fast cure, I air dry overnight, then put the sections in the oven (150F) on cedar blocks and cure for 12 to 24 hrs depending on whim.  They come out well cured.  I use the fingernail pressed into the varnish test to see how hard it is.  With 24 hrs they're definitely hard enough to sand or steel wool.

The can might say fully dry in 24 hrs, but if it's "real" varnish it won't be hard enough to sand unless you've "speed cured" as above.

BTW,  all of what I've done is with Minwax Poly Spar Varnish.  It air dries more quickly that others but still needs speed cure before sanding.  Other varnishes will vary.  (Al Baldauski)

Drying times are dependent on formulation, temperature and time. I use Polyurethanes exclusively and the coatings are touch dry within 24 hours (cured at room temp). That said I give a rod at least a week between coats before handling and three months before fishing after the final coat.  (Paul Blakley)

And humidity, when it comes to air dried finishes.  (Mark Wendt)

At present I use a 12x12x60 box I built on a 1 1/2" x 1 1/2" frame covered with door skin. Insulated with 1 1/2" foam panels with foil on one side. The top is 1/2" ply with 4- 1" vent holes. Bottom is hinged 1/2" ply with 4- 1" holes with paint strainer filters and has a closet light fixture mounted. Depending on the time of year/outside temp, one light bulb will maintain 70+ degF My shop/garage has a peaked roof so I hung the box from the peak so it's up and out of the way. The box will hold 6 section at a time by pulling each section up into the box and tying off on a cleat near the bottom outside of the box. Close the bottom and turn on the light.  (Don Schneider)

You're going to get a plethora of opinions on this one!

When using a drying cabinet if there is no air movement your drying time actually can increase rather than decrease.  The instructions for reapplication can be stretched from 6 hours to 12 hours.  The idea is that there is a window in which you can reapply without having to sand in between coats.  If your intention is to sand between coats then you should probably wait 24 to 48 hours.  Then test with your finger nail.  If you can make a dent in the finish then you need to wait longer.  If you try sanding too early the varnish will gum up your sandpaper rather than create a fine dust.  All of this is dependent upon the humidity, varnish and additives. No hard and fast rules.

I have done it both ways and prefer to do 2 successive dips 12 hours apart and then wait 24 to 48 hours and see if I need to fix anything.  If not, I might put a third coat on the butt section.  (Ralph Tuttle)

My plan was to sand between coats, I think.  I'll also have a couple of small runs in the varnish to attend to, so sanding should fix these.

I'll follow your advice and wait 48 hours and test before sanding.  (Nick Brett)

I use the same type of drying , except I use 4 X 100 watt bulbs and heat treat the blanks after they are glued using 1 bulb over night the while they are still wrapped. The next day while they are still wrapped I turn on all the bulbs and get the cabinet up to 220 for three hours. You can just start to smell the bamboo. This method both heat treats the bamboo and also sets the glue, works for me.  (Bob Norwood)

I find these responses very curious. My drying cabinet is a 5' long box made out of 1x12 with a Plexiglas door on the front, it hangs on an exterior wall in the spare bedroom I use for wrapping, varnishing and fly tying and I keep the heat register closed unless I'm in there working or have some reason to warm it up. I just have a 60 watt bulb in a closet fixture mounted to the bottom of the box, on the assumption that heat rises. When I get done with what I need lite for in there, I just put a coffee can over the bulb so it radiates the heat maybe a little more evenly, but mostly so my wife doesn't say "Hey, you left the light on in there."  When I go in there to check things the next morning, the box seems evenly warm and significantly warmer than the rest of the room, I would guess 80-90 degrees when the room itself is maybe 55 (we keep the rest of the house at 60). I used to keep a thermometer in there and that's what it usually read, I have since moved the thermometer to a more useful location. Another one of those things that work a little differently for everyone who does it.  (John Channer)

First,  How dare you use a 60w light bulb and add to global warming.   (I've often wondered what I was going to do when incandescent bulbs are no longer available.)

Second, I've used the system for years and have had no problems.   First: make sure you have air vents at the bottom and top of the cabinet.   2nd: put an oven thermometer in the cabinet and monitor it.   I think you'll find that the temp never gets above 200 degrees F.

Which is way below the point you'd have to worry about it.   (Terry Kirkpatrick)

There sure are a lot of different answers on this one.

I built a drying cabinet out of 1X10's.  The cabinet is 6 feet tall.  I lined the bottom half with aluminum foil.  The door is wood also and hinged.  The seal around the door has self adhesive weather stripping and is pulled tight when the door is latched shut.  In the bottom of the box is a standard light fixture with a 100 watt bulb.  Covering the bulb is an old can with holes punched in the sides.  The light is wired to a baseboard thermostat which is mounted about four feet up.  I put my thermometer in just above the thermostat and have the light set to turn off when the temp reaches about 80.  This box is in my unheated shed.  I have left freshly varnished blanks in the cabinet overnight when the outside temps were well below freezing and the temps in the shed were near freezing.  Some mornings the light was off, others it was on, but the temp inside the box was always around 80 either rising or falling. The thermostat usually cuts the light off around 83 and turns it back on around 77.  Works good for me.

Oh yeah, I have four 1" holes drilled in the top for vents that are covered with paint strainers to keep dust out.  (Greg Reeves)

Thank you everyone for your replies, I'll leave it for 48 hours, just a few more to go an then leave it in the cabinet for a week before I do anything else. Ambient temp is pretty low here at the moment in London.  (Nick Brett)

I have been through several incarnations, at least my cabinet has. I presently use a plywood box with foil bubble insulation. Three 100 W incandescent bulbs for warmth, and a fluorescent up the side for light. Plexiglas windows, and small inset windows so I can reach in without losing the heat. It actually gets too hot (110 F) so I usually go with one or two bulbs on at a time. With that setup, it takes 24 hours for spar varnish to dry completely to the point of being able to  touch the surface without a finger print.

This setup arose from a cold basement that is now much warmer after reconstruction. Will be interesting to see what happens with the next dipping session in a month.  (Jeff Schaeffer)

For years now I have used a converted CD tower with a 60 watt clear lite bulb to dry my rods and to provide a warm environment for the glue in my sections. With the advent of the low wattage bulbs I find it increasingly hard to find the clear lite bulbs. What conversion would you all suggest as a replacement lite source.  (Jim Tefft)

You can still find flood lights in the 100w range that work very well.  I see racks of them at HD and Lowes.  (Louis DeVos)

I'm not sure of your question.  If you're concerned  about clear versus frosted, watts is watts.  A 60 watt frosted bulb will do the same job.  (Al Baldauski)

And I think a watt is a watt, so if you want 60 of them, you could use 4 or 5 fluorescent bulbs that ADD to that amount (NOT what they say they're equivalent to in light output). Frank can correct me if I'm wrong on this one.  (Art Port)

That is so - 15 x 4 = 60 .  As Al suggested, a watt is a watt is a watt is a  -  OK enough.  (Art Port)

A watt is a watt is a watt, as a measure of power.  What we're looking for on the other hand is the heat generated per watt, and incandescent bulbs beat fluorescent  bulbs hands down in that regard.  (Mark Wendt)

You have to be careful because although a watt is a watt, this will not apply to you. When companies who make light bulbs classify a light bulb in watts they mean the amount of power they use to produce the light required. Old light bulbs were inefficient they produced lots of heat which was just wasted power when all they needed was light. The new bulbs use the majority of their input power to make light not heat and hence they will be of no use to you. Florescent tubes are cold lights and will also be of no use. You may be better getting infrared bulbs which make heat not light which is what you want really (so you can save money too). I’m not sure what fitting you use (screw or bayonet) but I think you will be able to get them easily. You could try somewhere like here, or I would think a local hardware store should have them. I hope this helps.  (Michael Kennedy)

If the light can't get out of the box, won't it will be turned back into heat eventually? It would heat the box, which would heat the air within it. These kinds of puzzles keep me awake at night.  (Frank Stetzer, Hexrod, Taper Archive, Rodmakers Archive)

I got a device  through Cabelas  called a  "Goldenrod" which  is a heat-generating electric stick about 18" long. No controls, it's made to keep gun safes dry, but will add  a lot of heat without having a single hot spot or bright light when you look in.

In an insulted cabinet it keeps things pretty warm even in a Maine winter.  (Henry Mitchell)

Thanks for the help. I think I'll try the Goldenrod from Cabela's which is a gun cabinet heater and dehumidifier. Will stay in touch and let you all know how it works.  (Jim Tefft)

When I recommended this gizmo I forgot that my dipping/drying cabinet is insulated. This morning there was a twenty degree difference between the shop and the cabinet. If your cabinet is uninsulated it probably will be inadequate. It generates less heat than a 60-watt bulb, which had things way too hot in the summer,  which is why I thought of the "goldenrod."  (Henry Mitchell)

The light generated  by an incandescent bulb is a byproduct of the heat.  Incandescent bulbs are essentially heat machines.  The hot, filament glows, providing illumination.  In florescent tubes, a gas is made to glow, providing illumination with much less heat being created.  In either case, the heat created is the result of the process used to create the light, not the result of or carried by the light.  (Roland Cote)

I'm hoping in the spirit of new thinking to decrease my carbon footprint.... ;-)  Of course it is hard to show old horses new tricks... :-D    Think I'll go lite the smoker.  (Jim Tefft)

I think you have a bit of a typo there..  The heat generated by an incandescent bulb is the byproduct of converting the power delivered to the filament, causing it to glow brightly, which creates the heat.  (Mark Wendt)

If the goal is to speed up the drying process, try UV bulbs.  Most varnish will cure at a MUCH accelerated rate when exposed to UV light.  I have a friend who makes custom pool cues and he uses UV light to cure his finishes.  Not, the light he uses is part of a $2500 box of UV lights, and they aren't average quality bulbs, they're the best you can buy, but he told me that he used to use nothing more than a box with 4 UV bulbs in it.  These are the kind you can get at WalMart.  Common Black lights.

Here's what he told me.  He uses a finish that dries in UV light in 30 minutes... BUT, he's a bit of a varnish guru and tells me that if I'll expose my Tung Oil Based varnished rods to UV light, that it would probably quadruple the cure time.

Personally, I don't care.  I have enough to do while varnish is drying on one rod to keep me busy with another, so waiting 24 hours isn't a big thing to me, but it may be to someone.  The advantage of Black lights?  Low heat, will work in normal fluorescent fixtures and actually do something to kick the varnish.  (Bob Nunley)

The only problem with UV curing is that some varnish makes cure too quick under it and they fracture as the film dries too quickly. I suppose it depends on the varnish and the thickness of the layer. The label on the varnish should say if it is UV stable and I think most are so that would be a super quick way to cure the finish.  (Michael Kennedy)

I use incandescent bulbs for heat, a UV light for curing, and a 4' long fluorescent just for lighting. I've been happy with the heat from the incandescent bulbs (one 100 watt in summer and two in the winter) but I always have either new rods or repairs/restorations sections in the cabinet so my lights stay on all the time (literally 24/7/52). The 100 watt bulbs seem to  last a month or so before burning out and I really would like something that could stay on all the time without burning out so fast. I wonder how many CFL bulbs I would need to get the same heat as my two 100 watt incandescent.  (Jeff Fultz)

I used an eve trough heater in my drying cabinet.  You know, these are those thing you put on the roof to melt the ice.  You plug them in in the fall & if you're lucky you remember to unplug them in the spring.  I run mine from an on/off controller, but you can run them from a dimmer.  Just match the wattage of the heater to the dimmer.

I have had the cabinet on for weeks on end with no problems.  It'll go from ambient to 140 degrees.

Take a look at Todd's Tip Site for pictures.  (Ron Larsen)

My fingers, as normal, were workin faster than my brain when I typed the blip about UV lights and curing varnish.  In the original post I sad that UV light could quadruple your cure time.  What I should have said, or meant to say was "UV light could quadruple the rate of cure" or "UV Light can cut your cure time to 25% of normal".   (Bob Nunley)

Indeed, incandescent bulbs generate more heat for a given amount of light than compact fluorescentS (CFLs).  However, we have 2 60W. globe CFLs in the bathroom, and after they have been on a while they are uncomfortably warm to the touch.  Not enough to burn you, at least not right away, but still they give off quite a bit of heat.  I'm thinking a couple of them would do the job, especially in an insulated box.  (Neil Savage)

I believe you are confusing heat and light. The purpose of the bulbs is to provide heat in a heat cabinet so an incandescence is simply the emission of light by a hot object. I believe that you desire to have heat and the light is just a by product?  (George Wood)

I don't have my cabinet lined with anything. It's just a basic plywood box. I have one UVA fluorescent bulb at the top. Varnish seems to cure quick and evenly. I use a Philips TL-XXW/03 which peaks at 420nm. I believe you need a high peaking bulb to help the polymerization of varnish. I know an incandescent style black light bulb won't do much of anything because of the low UVA output.  (Jeff Fultz)

Someone on the list mentioned using the Goldenrod fixture from Cabelas for their Drying Cabinet.  I was wondering if anyone has used one for heating their Dip Tube.  I am looking for a good source to heat up my varnish during the winter.  (Tom Peters)

I've got a Goldenrod fixture in the gun safe.  Its been running continuously for maybe 10 years.  It really doesn't produce much heat...I measured the surface with a dial thermometer and it was about 90F.  I really doubt if it would raise the temp of a dip tube more than a few degrees, especially if it was in a cool environment like a basement.  (Frank Stetzer, Hexrod, Taper Archive, Rodmakers Archive)

I use an old hearing pad set on low wrapped around my dip tube. At least during the winter when we let the house get down to 55° at night.  Crank it all the way up to 62° during the day. I'm cheap!  (Larry Swearingen)

Someone here on the List mentioned using the wiring and controller from an electric blanket.  I picked up an old blanket at the flea market for $2.  (David Bolin)

Mother-in-law was throwing away an old style hair dryer with heat unit connected to a bonnet type thing they put on their head connected by a hose.  Threw the bonnet away and use the dryer to heat the dip tube.  The dip tube is a 5 foot piece of clear plastic PVC in a cabinet with about 12 inches exposed at the top.  Connected the hair dryer hose at the bottom of the cabinet.  It has three setting so I have pretty good temp control.  Dropped a Marine thermometer Gage sensor down into the cavity to keep track of the temp.  Also have a 300 watt work light mounted on the wall at the top of the cabinet to heat the exposed end of the tube.  Turn things on a few minutes before dipping and it works good.  The shop has electric and propane heat so it never gets too cool in there. Also use the hair dryer to keep the metal warm on the Abbot Press.   (Richard Perry)

I use a hair dryer for the varnish heat source. My dip tube is incased in a 6” diameter PVC tube with a round disk fitted inside the top and bottom and a hole the size of the varnish tube. The dip tube has a coupling on the top and a cap with drain cock on the bottom so the dip tube is captured in the 6” tube and can’t slide up or down. The varnish tube projects out of each end of the larger PVC tube. I mounted a PVC coupling that accepts a two speed hair dryer near the top of the larger PVC tube. Pop riveted a piece of sheet metal on the inside of the larger tube to deflect the hot air so it doesn’t blow directly on the varnish tube. On the bottom sides of the larger tube I drilled 1/2” holes around the circumference to let the warm air out. Been using it for a few years and no complaints.  (Don Schneider)

I received my Goldenrod via UPS from Cabela's and immediately installed it in my drying cabinet for a test run. It is the 18 inch 18 watt model rated for 200 cubic ft and my cabinet isn't much over 5 cubic feet. The beginning temperature was 66 degrees F and after an hour it had raise to 73 degrees F and stabilized. I used a 100 watt frosted bulb and it reached 80 degrees F in less than a half hour.

It is probably going to meet my requirements for a stabile cozy environment for drying my rods since I'm not looking for a  high heat environment of any sort.  (Jim Tefft)

If I remember my conversions correctly 1 Watt equals 3.413 BTU's. Thus, the 18 Watt Goldenrod equals 61.434 BTU's. A 100 Watt bulb equals 341.3  BTU's. Therefore the difference in temperature.  (Dick Fuhrman)

I've had a pair of Goldenrods in my drying cabinet as the primary heat source for the past two years.  Together they keep the Plexiglas cabinet temperature from 20 to 25 degrees F over the ambient room temperature.  They have been running 24/7 since I put them in.  (Chris Carlin)

I do not remember who posted using a coffee filter in the downdraft for his cabinet, but thanks a million. The comment caused my 2 remaining neurons to make a connection. The coffee filter gets rid of the dust particles that seem to collect in my drain tube between coats. Works like a charm.  (Jon Holland)

I posted probably a year ago about using one of those metal re-usable coffee filters. It worked very well for me. It was disturbing the amount of junk that was at the bottom of my gallon can of varnish. It was Ace Hardware Marine Spar. Good stuff,  I like it a lot. However, it looked like there were rat turds at the bottom. I drained a can of Helmsman Spar Urethane and that can was clean and clear. I still have the can if anybody doesn't believe me.  (Scott Bearden)

I dried my first eight rods by hanging them in the spare room, tip toeing out and asking my wife not to open the door. As she was running out of patience with me I decided to bite the bullet and have just finished building a drying cabinet. It is MDF, twelve by twelve by sixty five inches, lined with foil covered bubble wrap. It is powered by a single 100 watt incandescent bulb with four filtered one inch holes at the bottom and five at the top. I have run it for several hours and it is holding at seventy two degrees f at the bottom and seventy six f at the top in my very cold garage.

Is the temperature high enough and does the disparity in the temperatures top and bottom matter?  (Simon Reilly)

Sounds as though you have done a really nice job.  Four degrees difference from top to bottom will not matter.  And those temperatures are plenty warm.  (Harry Boyd)

I'd say you did good. That seem to me in the perfect temperature range.  (Don Schneider)

I use a 200w in my cabinet and maintain high nineties. (Timothy Troester)

Something like mine Simon but mine is between stud spaces in a utility room. And mine doesn't have any holes. I think the bulb will circulate heat as it's intended to do and it will circulate the dust with it. (Don Ginter)

I just hang them in my varnish room and dry.  I keep it around 75, so I think you're fine.  (Bob Nunley)

Thanks to all who answered. I thought it was probably close enough but I wanted to bounce the numbers here before going ahead. I will be dipping my  attempt at a Payne 98 this afternoon. So far all has gone well and I would hate to screw it up now.  Once again you have shortened the learning curve for me.

At this rate I may even become adequate some day, maybe. (Simon Reilly)

100 w in the winter may get temps too high once summer rolls around.  For my last set-up in a garage that varied 60 degrees from summer to winter I used 60, 100 and 150 watt bulbs depending on conditions.  I also use a digital BBQ thermometer with a transponder/receiver an alarm on it so if the temp ever gets above 105 it goes off at the receiver which I keep with me at all times including on the nightstand when I'm sleeping.  Nice insurance to avoid too high temps and warn me way before I get to the point of a fire.

FWIW I like a temperature more like 90 degrees for glue and varnish.  The varnish really seems to set up nice and hard at that temp and is faster than 75.  (John Rupp)

A dimmer switch makes a good manual control of the higher wattage bulbs.  (Larry Tucker)

I wired in a baseboard thermostat mid way up the box and can regulate the temps that way.  I have it set to turn off the light at about 80 degrees.  When the temp drops down to about 75 it kicks back on.  I have never had a problem with the temps going up and down during the cycles.   It usually takes about 10 minutes to fall that 5 degrees before the light kicks back on and about the same time to heat back up until it turns off.  (Greg Reeves)

If you scour your local surplus or hardware stores you can find very cheap bimetal snap thermostats.  I set mine to 90 for my dip/drying cabinet and then you can walk away.  They have about a 3 degree range and are very simple.  Mine cost $5 at the local Axman store.  (Ralph Tuttle)

Yup, that’s the way to go.

Even cooler, you can go hog wild and install a Honeywell forced air furnace limit switch that has a cap tube and bulb sensor to go in the heated area, with the controller mounted on the outside of the cabinet.

Looks really high tech and initially impresses people when they walk into your garage, and than they realize you are just nuts…

By ‘em on eBay for a couple of bucks used. (Tom Vagell)

I like the thermostat, why ?   A simple way to handle and control the temperature despite the environment.  If it is cold outside or hot outside?  You do not have to worry about thermal mass/inertia (the time it  takes  to stabilize … but I would let the chamber to heat up for an extended before you place the rods in).

In the garage, your Relative Humidity will likely significantly change through the seasons, what that will do to the varnish, I have no idea.  In fact, in summer, it is possible the light never turns on a thermostat set at 75F.  (Dave Wilson)

I’ve dried varnish at up to 200F with no ill effects but I did it in my PID controlled convection oven after the varnish was dry to the touch.

In a light bulb oven, the thing to you have to do is shield the rod sections from line-of-sight of the bulb/bulbs.  If you don’t the ends of the sections will get much hotter than the air temp due to radiant heating.  (Al Baldauski)

The clip-on lights they sell at Lowe's are perfect for shielding off the sections as Al suggested  - comes with a bowl shaped aluminum shield built in. I think they are less than $10 and you can just mount a small bracket inside your cabinet to which you can clip the light to.

The other thing that works great are the small single track lighting fixtures, I found one a thrift store for $1. Use your imagination.  (John Rupp)

I should have remembered to say that the cabinet holes are filtered and that the light is shielded to protect the sections. I got that from the tips page.

I think that I have a thermostat somewhere in the garage. I might get it wired in for the summer. Tho' more likely I'll just go fishing and leave the building until winter. :-D (Simon Reilly)

I finally joined the drying cabinet gang after 12 rods.  ID is about 8 x 10 and I drilled 2 one inch holes in the top and bottom for draft. Used water heater insulation blanket around the cabinet.  I find that I get about 105-108 degrees with 2 forty watt bulbs.  I'm wondering if this is too much heat for drying Helmsman spar?  Also the unvarnished blank that I am drying in the cabinet sat in the basement in 60 plus % humidity most of the last 6 weeks.  How long  would you leave it in the cabinet before dipping?  (Dave Kemp)

These are my opinions and my opinions alone.  This should not be construed as gospel but the observations of one rodmaker.

So much for the disclaimer.

I use helmsman spar and after 6 to 12 hours of air drying time I bake my rods in my oven at 200 F overnight to cure my varnish.  I don’t think it is necessary to dry your blanks before dipping.  I never do.  It takes so much longer for the rod to reabsorb that moisture after you varnish and it will, no maybe’s about it.  Of course drying the varnish in a cabinet or an oven also dries the rod out even with varnish on it.  It may take up to six months to get that moisture back into the bamboo. 

Just as an example, I made a bamboo spey rod last march with molded-in-place graphite ferrules that fit the taper of the mating section.  When I finished the job, I marked the rod with a “witness mark” so I could see if the ferrule seated in the same place every time.  I just had the rod on the front lawn this morning and found that the male end of the butt section had absorbed enough moisture that it slipped into the graphite female 3/4  of an inch short of  where it  used to.   That’s about 0.002 inches increase in diameter.  And that’s for about a 15% change in Relative Humidity.  (Al Baldauski)

This opinion is probably worth about what you are paying for it, but I really believe that you are better not to apply any heat at all for quite some time after applying your varnish. 

This applies especially to the urethane spars, but also to a lesser extent to the traditional varnishes.

These things have a great capability to "right" themselves while they cure and dry, and while I have a drying cabinet, with the mandatory 2 incandescent bulbs in it, I usually do not turn them on for 4 or 5 days after I hang the sections.  Where I live ( Tasmania, Australia )  the ambient temperature sits some where between 7 or 8 degrees and the high twenties in my cabinet.  Sorry, we use the Centigrade scale for temperature.

After 4 0r 5 days or a week, I will turn on the heat ( one 40, one 75 watt ) for a couple of days.

I dip varnish before wrapping on the guides, and cut my problems by about 90% by waiting at least a month after  that before trying to wrap fine silk onto the varnish.

As so often seems to me  to be the case in this bamboo business, the essential ingredient is Tincture of Time.

Incidentally, our previous glorious leader in Australia legislated out of existence incandescent bulbs, and we can now only buy those mongrelized fluorescent things, so Heaven knows what I will do for a heat source when my supply runs out.

Actually, the light they produce is so poor that I will possibly not be able to see any varnish imperfections in the first place, so it will be OK after all!  (Peter McKean)

How do I simply and effectively heat my heat/drying box so that the entire box is one consistent temperature? I have a 10 x 12 x 84 with a generic every-day light fixture mounted in the bottom of the box.  I drilled a 1" dia. hole in the bottom and top thinking that I would get convection and heat the entire box. Well, no such luck.  I've considered installing a computer fan in the top to try to pull the hot air up thus hopefully achieving a consistent temperature.  (Derrick Diffenderfer)

I built a box similar in size to yours with 2" semisolid insulation silver side facing the inside of the box. Four 1" holes in top and bottom. The bottom holes are covered with paint filter disk to keep out dust. top holes unfiltered. Bottom of the box is hinged with the light fixture mounted on it. Hung the box from rafters in shop. Holds 6 sections at a time.

Played with the wattage of the bulb until the box would maintain 70+ degrees near the top of the box. (Don Schneider)

I'm not sure this is much help, but the problem you described has plagued bakers for centuries!  No 2 parts of an oven have the same temperature.  Various factors, both internal and external, conspire to make the heat uneven.  Think of the heated column of air (which you can't see) as a trout stream (which you can see).  As you view the water in the stream, you will see multiple currents and eddies.  If you were to measure the water temperature in each of those areas, you'd find significant differences.  The same is true of any oven.  The heated air moves in swirls and eddies inside the oven.  That's why bakers rotate pans part way through the baking process.  It's also why commercial ovens move the shelves, to make sure the product is exposed to the average oven temperature, and to promote even baking of the whole batch.

Not sure what you can do with your drying box.  Ventilation holes and circulation fans will certainly help, and better insulation will reduce heat loss, but none of these will eliminate the problem.  (Paul Gruver)

Take a look at my drying cabinet on Todd's Tip Site.  In the third picture you'll see a 40' eve trough heater running up and down the box.

The heater is one of those things you use to de-ice your gutters and downspouts: you plug it in in the fall and, if you remember, you unplug it in the spring.  I control the heater with an on/off temperature controller, but you can use a dimmer for an incandescent light.  Just make sure the dimmer is rated high enough for the heater. 

Heat rises, so I installed a fan at the bottom of the box to create a downdraft.  You can see the fan inlet at the lower left of the box, partially blocked.  I drilled three holes in the top of the box and covered them with filter paper.

The temperature is consistent top to bottom.  (Ron Larsen)

I use the same heater wire wrapped around my dipping tube to heat the varnish. You have to cut the thermostatic controller off the original to wire it into the rheostat. I over wrap that with silver insulating tape.

Works great and is cheap.  (Gordon Koppin)