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From some of the experiments on heat treating, could one conclude there is a difference or no difference in the rate of moisture absorption between heat treated and non-heat treated bamboo? If there is no difference, I'm wondering why we go to the trouble of heat treating other than color and straightening when the strips are bound or treated in a fixture. Also; I don't see why we need the high temp, 325° - 375°, to drive out moisture/straighten when 200° for a longer period of time would achieve the same goal. Thoughts anyone? (Don Schneider) Many years ago there was a discussion on this list about whether heat treating was needed, or maybe it was one of those things done just because it has always been done. So I made a rod without any heat treating at all - or maybe I should say I made a blank because I never finished to the point where I put guides and a handle on it. When bent the blank would hold the bend for about half an hour and slowly return to straight. I taped on guides and test cast it. The term "felt like a wet noodle" took on a whole new meaning. Driving out moisture is not the only change bamboo goes through when heat treating. (Darryl Hayashida) John Long says if you flame, you don't need to heat treat any more than that. I made two Young Perfectionists from the same culm, one flamed and heat treated the other just flamed. I don't claim to be an expert either in rodmaking or fly casting, but my son-in-law is an excellent caster/fisherman and HE can't tell any difference in them. How they will stand up over time is still a question, of course. (Neil Savage) I did a series of test years ago that were published in the Planing Form. Cane used came from the same culm - strips side by each. Each tapered and treated @ various times/temps. Conclusion - heat treating is a myth. Untreated cane performed better than some treated cane. Still, I heat treat. No sense flying in the face of convention. My testing was replicated by Tom Folk who came to the same conclusion. If anyone has done similar testing that is not subjective, I'd certainly like to hear from them. (Don Anderson) Sorry, but my testing was actually making a non heat treated rod - real world application, not test strips, and I'm going to continue heat treating. (Darryl Hayashida) A thought came to mind. I think we all agree that the physical properties of bamboo change during heat treating. Supposedly for the better for our uses. The thought is; does the hardness/durability of bamboo change during the process? The spectrum is form none to burned but where is the optimum? Has anyone ever checked the hardness and correlated an optimum from the results? Or are we saying, that's the way the Masters did it and that makes it right? Any thoughts? (Don Anderson) John Long's Grand experiment had one rod that was the same Waara taper as all the others but not heat treated. When I and many others cast it we could not tell the difference between it and the original taper heat treated. Perhaps John could chime in on the "set" aspect, since the rod had been around for two more years and may have been fished enough to take a set. Also, wouldn't glue joint "creep" potentially be a bigger issue in sets and wet noodles than heat treating the cane? Also, wouldn't glue joint "creep" potentially be a bigger issue in sets and wet noodles than heat treating the cane? (Doug Easton) My Grand Experiment rod did not have any heat treating. Checked it about 5 minutes ago and it still does not have a set. It was also a spiral. (Scott Grady) Interesting... A non heat treated spiral rod. Seems to retain it's stiffness and doesn't take a set. Something to look into. (Darryl Hayashida) I think there is something to this. Lambuth never heat treated, and no one complains about his rods, BUT, he was apparently very accomplished at selecting cane. I believe you could get away with more in a spiral rod than a straight one, but I doubt you could compensate for really poor cane. Let me turn the question on it's head. Has anyone seen a rod that was heat treated to a significant color change that DID take a set easily? I never have. (Tom Smithwick) If by not heat treated you mean the bamboo was flamed with no further heat treatment after, I can see this happening. I used to do that myself - flame just the outside of a culm, split and plane from there. In fact, most of the rods I have made have never seen the inside of an oven. I don't currently own an oven even now. That's why I said I consider flaming a heat treatment, and I mean flaming the way most other people do it, not the way I mega flame the inside of my culms. I eliminated glue creep as a reason my non heat treated rod stayed bent because it did straighten out by itself in about a half hour. If it was glue creep it would have stayed bent - at least a little, and I would have seen some sort of displacement between the strips. (Darryl Hayashida)
Anyone here have any experience using zip ties to hold strips to the MD Fixtures during heat treating? Any problems? I usually bind the strips by hand but I thought the zip ties would be much quicker and easier. I put one in my kitchen oven for 15 min @ 350 and it did not seem to have any ill effects. Might have been slightly more pliable, but not much. The best part was it did not melt. Tomorrow I am going to visit a friend who has a rod oven, and give it a try. Just thought I would see if someone else has tried it already. (Matt Fuller) If it doesn’t melt, I wouldn’t see much of a problem but it would seem to get pretty expensive and time consuming to have to zip tie every inch or so to ensure that the strips are bound to the forms. (Greg Reeves) I was not going to use that many......maybe 6 - 8 per section. I get them on sale at Harbor Freight and they are not very expensive. (Matt Fuller) If you use only 6 or 8 I would look out for 6 to 8 dips in each strip. Then, if you try it and it works, wahla! Since no one has done it before, the only way to know for certain is to give it a go. Let us all know. (Timothy Troester) Call me a renegade but I am going to go for it. Hell, this might even lead to a Zip Tie sponsorship. The possibilities are limitless (okay maybe a bit limited). I had a couple 2 inch cut offs from the MD fixtures (the fixtures were too long for the oven I use) which I was going to use with some scrap pieces to see if the plastic left any marks on the cane. I think in one of my cleaning modes, I said, "I am never going to use these" and tossed them. Very unlike me. I am a pack rat by nature, a clean pack rat, but regardless, a pack rat. (Matt Fuller) Unlike metal, stretched plastics/rubber (with few exceptions) contract when they are heated. Has to do with entropy. The stretched state is the more ordered state (thermodynamically), so heating it goes to disorder (higher entropy). Which happens to be the unstretched state (shorter). If you don't believe me take a piece of rubber hose or a big rubber band and hang a weight to it and mark where it is when cold and then mark where it is when heated with a heat gun. You may be surprised to find that the hot band is shorter. This explains why you get nylon marks when you bind with it. The stretched nylon shortens. Cotton is better for this application. (Dave Burley) The ones I have are nylon. I am going to give it a try anyway. If it does leave marks, hopefully they will not be too deep and will be taken care of when I remove the enamel. (Matt Fuller) Actually there is a nice use for this effect if you glue with Epon and then heat set. If after the initial glue up is set, you find gaps, glue lines, close wrap the length of the gaps with D-size nylon rod wrapping thread. It will shrink during the heat setting process and usually close the gap. When I have done this, I have not found any marks from the thread. (Mike McGuire) I use polyester thread and it shrinks and will leave marks on the soaked strips. To avoid leaving marks on the enamel side I put my strips in the fixtures with the "Pith" side out. The marks are left on what I will be planing off. You might try that. (Tony Spezio) If it gets more pliable it can stretch. I would see if it loosens up. Nylon will leave a mark on blanks so I would look to see if the tis leave a tattoo of sorts. They make a tool that cinches up zip ties tight. Not expensive. (Timothy Troester) It might be tough to keep the pressure consistent. Why not just bind by hand. Seems like it would be much faster. In the fixtures (sold by Harry) you only need to bind one way. There was someone years ago who used O rings to bind. His main advantage was they were reusable. (Scott Grady) Try wrapping with your cord coming out of a well anchored brake arrangement like one uses for wrapping guides. That takes most of the sting out of hand wrapping. In fact that's how I bind my rods after gluing. It's simple, quick and as fast any mechanical binding setup. I find about three hitches seems to tie off well enough and not hard to do in my setup. (Mike McGuire) Granger and MSC sell a heat shrink tape 1/2" wide. I have had some success binding strips to the fixtures with the tape before heat treating. As the tape heats up it gets tighter and the shrinking problem seems to be less severe. (Harry Boyd) It will depend upon the material used and associated stabilizers that may expire. I am no expert, but had to experience-manage some challenges that are similar. Buzzword to look for Nylon 6.6 or Nylon Heat Stablized. Some Nylons, such as Nylon 11 will be a problem at your temperatures. I do not really design with Nylon, so I do not know what cheap tie-wraps will use for material. Remember, if testing, the thermal conductivity of plastics is such that it will burn you well if it begins to melt. (Dave Wilson) I heat treated the strips today using the nylon zip ties. 325-350 degrees for about 17 minutes. No problems. No black marks. They stayed tight and I don't think they shrunk much, if at all. Not sure at what temp I would start to see problems but I am happy with the results. (Matt Fuller) I'm wondering if anyone has ever tried to use heat shrink tubing for binding glued rod sections? Might be a stupid question, but I bought some at Harbor Freight and was going to give it a try to see what happens. I am always experimenting. BTW I purchased a Sully's rod wrapper a while ago and used it on my most recent rod. This this works great. I am very happy with it and would recommend it to any new rod maker who doesn't like sore shoulders and cricks in their necks The best part of this thing is that you can walk away from your wrapping job in the middle of it and not have to rewrap. I did modify it a bit to accommodate the smaller Pearsalls spools. I also changed the green felt to soft garment grade leather using either the smooth side or the suede side, both seem to work well. I found with my other wrapper that this was necessary as the rod can pick up the fuzz from the felt and then the next thing is I had whole bunch of felt stuck and wrapped around my rod section. I had some scrap leather laying around from an earlier project and used it. Not sure where to where to buy small pieces of this type of leather, my son gave me this a long time ago and as I never throw anything away, it came in handy. (Phil Crangi)
As a follow up, the article by Adam Vigil is in the January 2002, page 26 Power Fibers. I also wanted to comment on an email that Al Baldauski sent this summer on the time it takes for a bundle of bamboo strips to reach set point temperature for heat treatment. I used Al's analysis that is based on an oven set point temperature of 350 degrees F. Al bundle 6 strips of bamboo without and with MD fixtures. His test basis was to preheat the oven to 350 degrees F and then put the bundled bamboo in the oven while recording the temperature of a strip in the bundle using a thermocouple. This is a Dynamic problem and using Al's data I estimated that the time to reach oven temp for the bundle without the fixture is about 7 or 8 minutes, while the bundle with the MD fixture is about 14 or 15 minutes. This suggests that one must adjust their cooking time to account for this Dynamic heating of the bamboo bundle - with or without fixtures. So if one thinks about "time at temperature", one should add the additional heat up time to the desired heat treating time. In my case using MD fixtures and a 325 degF oven set point temperature, I have increased my time from 20 to 35 minutes to account for the bundle heat up. I am sure Al can provide the data again if there are any questions and answer any questions about his test procedure. (Frank Paul) I have not carried out tests as careful as Al's, but have observed what is true in my heat-gun oven. I have two digital thermometers inserted in the oven with variable possible locations and probe depths. Although others have questioned the possibility of having a uniform temperature in a heat-gun oven, mine can maintain temperatures, along its length, varying by only a few degrees Fahrenheit. I make 3-4 piece rods and heat treat all of the bundled strips at once in the oven. I first heat the oven to a constant temperature along it entire length before inserting the bamboo bundles. With the bundles in the oven, one of the thermometer probes has its sensing tip (the part which measures the temperature) in the center of the air flow below the bundles. I hold the temperature shown by that thermometer at the temperature of the oven before the bamboo is inserted. The second thermometer is higher and has its sensing tip in the middle of the bundles of strips. It takes much longer than 15 minutes for that thermometer to show the same temperature as the lower thermometer. In humid weather, when the cane strips contain more water, it takes longer than during dry weather when the cane is dryer. If the sensing tip of the upper thermometer is pulled out of the center of the strip bundles and into the air flowing around the bundles, it shows that the temperature of the air streaming past the bundles is the same as the temperature shown by the lower thermometer. What's my point? It takes time for bamboo to come up to the temperature of the oven. The amount of time depends on factors such as the oven type, how many strip bundles are in the oven, and on how spread out they are. If you want to know the final temperature your cane has achieved, consider making your own measurements on your own oven. I just bought MD fixtures from Harry and am curious to see the effects of their heat conduction. (Tim Anderson) This is the biggest problem with the heatgun type oven. It has no large heat sink such as bricks or steel mass which will maintain the temperature of the oven when the bundles are put in. Thus, the times must be adjusted to make up for the time it's fallen down to about 300F. It's the reason why Milward built and uses an oven that maintains temperature. (Don Ginter) I've got a piece of steel from the hardware store (2 inches wide & the length of the oven) down the pipe where the cane rests. Takes a lot longer to heat it up but holds the temp better. I'm sure I got the idea from someone on this list years ago. I use my heat gun oven in a horizontal fashion. (Frank Stetzer, Hexrod, Taper Archive, Rodmakers Archive) Well that's certainly a step up in my opinion. My heat gun oven already takes over a half hour to reach 380F so I wouldn't attempt to put a large piece of steel in it because that would certainly increase the time. However, once the oven is up to temperature, I would think yours is a superior setup. The temp drop of mine is drastic when I put two bundles in. I do put the bundles in at close to the same diameter though and that's maybe a bit more bamboo mass than what some people have to contend with. (Don Ginter) Not all heat gun ovens are the same. Some hold temperatures fairly well. (Harry Boyd) My heat gun oven has a large amount of Sacrete cast into the bottom. I don’t know if it holds that much heat but that's why I put it there. (Doug Easton) You are right Harry, my heat gun oven is insulated heavily and will generally only drop 10 or 15 degrees if I open and close the door quickly. (John Rupp) How much does the oven drop when you put in a couple of bundles of strips? And does it contain a heat sink of steel or bricks? (Don Ginter) Insulation can have a big impact on an oven's thermal conductivity without having much impact on thermal capacity, depending on the thermal mass of the insulation. Fiberglass insulation would reduce heat loss by reducing the oven's thermal conductivity but have a small effect on thermal mass. Insulating with fire bricks would add thermal mass as well as improve the heat loss problem. Of course a firebrick insulated heat gun oven would be a chore to store and move around compared to a fiberglass insulated version. I greatly improved the thermal capacity of my fiberglass heat gun oven by filling up the part not occupied by the inner 3" pipe with lengths of 1/2" and 3/4" iron pipe that I normally used for my pipe clamps. On a pound for pound basis iron is pretty good for adding thermal capacity, better than copper and a lot better than lead. (Joe Hudock) Harry, Noted, but if they don't contain a large heat sink, as is common to heat gun ovens, then they can't compete with ovens that do have the mass. While I think my heat gun oven is only adequate for now I wouldn't try using your MD fixtures in it as that would only compound my problem of trying to adjust for temperature fall when the bundles go in. I gotta love the principle of the fixtures and will probably use them some day but for now, trying to adhere to something close to the proven science of heat treating is better than a crapshoot where temps vary over 100F+- or times vary over 20 minutes+-. I hesitate to comment on the subject of ‘good enough' because what is 'good enough' for me would most certainly not be good enough for the old masters. (Don Ginter) Try operating any heat gun oven horizontally. It's amazing how much that helps even out temperatures. Add a 60" long x 4.5" wide piece of expanded metal as a shelf for the bamboo sections. That provides a heat sink to keep the temperatures from dropping too seriously. Ask your local sheet metal guy to break it over to 135* on each corner. He'll probably do it for nothing. Careful!!! Those edges are very sharp. Make the boxes (ducts) with similar dimensions and insulation of a typical mica strip oven and your heat sink capabilities are at least as good as with the mica strip and rat wire shelf. Use some dual wall furnace exhaust pipe for the inner tube and prevent lotsa bad stuff from happening.
I've made 26 of 'em so far this year and have parts for half a dozen more in the shop. I'm reluctant to claim temperature variances of one degree Fahrenheit from one end to the other for every oven I make, but will gladly speak of variances of no more than 1% from end to end. Internal temperatures drop about 10% when adding six bundles of strips on heat treating fixtures. Solution? Pre-heat to 10% above your target temperature (thanks Tony Spezio). Many thanks to Martin Darrell, Mark Wendt, David Bolin, Larry Blan, Frank Paul, Wayne Cattanach, (and many others on this List I'm sure) and especially Jud Moore for help in figuring out what works and doesn't in an oven. I've tried ceramic bricks, pounds of steel and/or aluminum, separate chambers and all kinds of other stuff to keep temperatures from dropping. I don't do that anymore. Wanna guess why? (Harry Boyd) He ain't heavy, he's my heat-treating oven? ;-) The main reason for separate chambers in a heat treating oven, especially convection ovens, is to keep the radiant heat from the elements from reaching the cane, allowing only the convective heat. Radiant heat is much harder to control for consistency than convective heat. (Mark Wendt) Another option to consider is increasing the air flow to even out the heat. My heat gun oven has many of the features Harry mentioned with the addition of dual heat guns. I can heat up fairly quickly but with the additional blow it evens out the temps after it gets up to temperature very nicely. A good heat-gun oven does not really need a large heat sink. I tried to make clear in my original note that the air blowing upward below the bundled strips is at the desired temperature and the air blowing around and past the bundled strips is at the desired temperature. In other words, the bundles are surrounded by moving air at the desired temperature. As Al Baldauski has pointed out, the cane itself takes time to rise to the temperature in the oven. A radiant source of heat, such as a heat sink could represent, might increase the rate at which the cane heats up. My point remains that it takes time for the bamboo to rise to the desired temperature and the amount of time can vary from oven to oven. It is useful to check what that rate is in the oven you use. By the way, if you read Harry's description (on his website) of how to use one of his heat-gun ovens, he has worked out an interesting method to take care of the thermal inertia of the cane. (Tim Anderson) I hear ya on heat gun ovens and in fact the hot air flow may be very desirable compared to not. I have three Thermos in my oven and I note the temps at each location. I also upend the two bundles at about half time. This timing and temp. is recorded for each rod I do and so it's getting fine-tuned somewhat now. Just to let you and others know that it's not a crapshoot for me as I'm aware of many variables such as ambient, bundle size, bamboo % humidity, etc., etc. But to put my tip sections up against a test alongside other tip sections from other makers, I don't know? I strive for the recommended temps and times but still my oven won't reach the desired 392F. (Don Ginter) Perhaps if you lowered your set temp to something like 360 or 375 and lengthened your time period, you'd have a larger margin of error to play with? Is there some reason you're trying to reach such high temps? Just curious. (Mark Wendt) I have no 'set temp' for my oven. I use a heat gun and although it's a very powerful heat gun it is difficult to even attain 380F. I think this is a common problem with most 120V heat guns. But that's assuming that you accept the suggestion that it's a problem? My goal is to cook bamboo at as close to 392F as I can because I am accepting of the advice of Schott and Milward. Therefore, the margin of error of which you speak, is for me the error between 380F and 392F. That's the best way I know of to explain my preferences. If you would like to discuss what I am doing and why any further, then please let me know and I'm willing to explain off list as I don't think that would be infringing on any copyrights. Trust me though, it's not a shot in the dark. (Don Ginter) Not that it was a problem, I was just curious about how you were heat treating, what kind of regimen you were using, and why 392 degrees was the magic number. (Mark Wendt) The reason I don't go higher than 392 on my heat gun oven is that that's where my thermometers from Walmart top out. Isn't 392 the same as 200 on the Napoleonic scale? To get my oven high enough on cold days I throw the old bedspreads that I also use for painting drop cloths over the fiberglass insulation on the oven. I pick up another 20 to 30 degrees on the American scale that way. (Joe Hudock) Is that your set temperature that you actually heat treat at, or is it a temperature you use to take into account the cold shock when you insert your cane? (Mark Wendt) After playing around heating strips in the MD fixtures, I decided to return to my usual regimen of just binding & heating them, mostly because of the uncertainty introduced by the fixtures. Now, I do not soak strips nor plane wet strips and I was having good results with my pre-fixture setup: 350 -375 degrees in a heat-gun oven. Now, I remember a similar discussion took place here a few months ago, and I asked a question about what the "old masters " did for heat treating. I've discovered that Paul Young's shop did no heat treating beyond flaming in the "ring of fire". Dickerson & Payne had other ideas. What about Granger & Heddon? I'm willing to bet that their methods were simple & effective. Sometimes close enough is close enough. (Paul Julius) Just curious, what uncertainty is introduced by the fixtures in your heat treating regimen? (Mark Wendt) I could not be certain of how long to heat the cane/fixture assembly. I knew for a fact that if I used my usual heating times, the cane never got warm in the center, and the sweeps did not disappear. How much longer did I need to heat the cane/fixture assembly? If I heat the cane/fixture assembly until the fixture (the center of this setup) is hot, am I exposing the power fibers on the outside to the setup to too much heat? Hence, the uncertainty. I reverted to binding the strips together & baking at my usual time and temperature, and getting good results: nicely tempered cane & straight strips. (Paul Julius) Since every oven is different, each requires its own heat treating regimen. What works for me in my convection oven, of course will not do a very good job in a mica strip or maybe even a heat gun oven. That requires experimentation on everybody that uses some kind of oven for their heat treating. The way to get past any kind of uncertainty is to run a series of scrap test strips, at different temps and/or different times, and determine the exact requirements necessary for your oven to be able to determine your correct regimen. Did you run any experimental strips using different times, and then check the results? It took a while, and a bunch of experimenting between myself and M-D to settle on a good heat treating regimen when he got a hold of the first few fixtures and sent me some. His oven was pretty similar to mine, and we both worked out a very similar heat treating regimen. Mine was slightly different than his, but only because no two ovens are exactly alike, even though they look virtually identical. Takes a little time, and a few scrap strips to find out what it takes, but once you've got that figured out, the benefits of using the fixtures far outweigh not using them. (Mark Wendt) The way to get past any kind of uncertainty is to run a series of scrap test strips, at different temps and/or different times, and determine the exact requirements necessary for your oven to be able to determine your correct regimen. Did you run any experimental strips using different times, and then check the results? I'm curious -- what results does one check for: color, dryness, brittleness, stiffness, weight, set, shrinkage, or what? Does one check immediately after taking the strips out of the oven or later: a day, a week, a year, or what? (Ron Grantham) Simple answer - yes. The more complicated answer is, are you getting the results "you" want? What do you hope to achieve with your heat treat regimen? Typically, most guys look for the chemical change, a slight coloration change on honey/straw colored strips and increased stiffness. Of course, I'd wait till at least the strips cooled down... ;-) (Mark Wendt) About 10 years ago I did some stiffness tests on a sample of 24 bamboo strips. The results were published in The Planing Form #66. My results were that some test strips were a bit stiffer, some were less stiff. On average my test strips were slightly less stiff. They were all baked together at 350F for 15 minutes, then allow to cool. The tests were conducted over several days. (Ron Grantham) Excellent set of numbers. Thanks That was my opinion at the time from using treated and untreated rods, and from comments made by others, but I have no absolute proof. (Ron Grantham) Neat stuff! I'd not seen that one before. Thanks for sending that. Looks like more than half (16) were stiffer, by varying amounts. All were lighter though, by at least 4%. Were the strips all from the same culm or different ones? Wonder how the results would have turned out with higher temperatures or longer times. (Mark Wendt) The test strips were all from the same location between the same nodes on the same culm, chosen at random. Higher temps may have shown different results, but I've found that longer times at 350 F would have darkened the strips -- I like blondes. (Ron Grantham) The initial test I had done on bamboo stiffness vs heat treating I found was flawed because I made the test strips and measured them. Then,after heat treating they were smaller because of loss of moisture. This altered the outcome of my MOE calculations. As the strips sat around they absorbed moisture and increased in dimension giving me different results from fresh out of the oven. Eventually, I heat treated samples and allowed them to equilibrate to a "standard" 60%RH environment before making measurements (both dimensional and MOE) and got more consistent results. That's when I decided there were insignificant differences amongst the typical heating regimen we typically use. (Al Baldauski) A good experiment would be to weight each piece and measure the stiffness over days/weeks to see if the stiffness went up or down as the strips picked up water from the air. A prebake weigh in would also be interesting to see if it comes back to the same value after the bake. (Dave Burley) Some years ago I did a test with a couple of rodmaker friends to find out how much bamboo shrinks with heat treating and how much it expands over different amounts of time. The results can be seen here. Basically, it took a week for the bamboo rod sections to recover about 60% of the loss due to heat treating. In other words, the bamboo shrinks when heat treating but doesn't recover the full amount in size. See my previous email for stiffness testing. (Ron Grantham) If you get the chemical change in the strips from the elevated temps, the prebake weight will probably always be more than the post-bake weight. That's cellular moisture that cannot be re-absorbed. (Mark Wendt) And one is moved to ask whether the time necessary to reach ambient oven temperature varies directly, or otherwise, with different ambient temperatures. In other words, does it take 14 or 15 minutes for splines in an MD fixture to reach, say, 392 degrees F. (just to pull a number out of the air)? Al, whaddya think? My thermocouple is in the shop this week . . . (Steve Yasgur) It definitely does. That's one of the reasons I run the self-tune function on my PID controller with every change of season. It takes longer to heat a colder chamber, and shorter to cool down a hot chamber when the ambient temps are low. So, I "re-train" my controller for different ambient temps. Most ovens that are decently insulated are pretty efficient at holding temperatures. That can work for you or against you depending on how you've structured your heat treating regimen. (Mark Wendt) The starting temp of the bamboo will affect the time to desired temperature but very little. In the beginning stages of heating the rise is very quick and then tapers off as the bamboo approaches the set temp. My experiment showed the temperature rise in the first minute to be greater than 30F. So if your ambient temperature were low by 10F the added time would be less 20 seconds. I would have guessed that the strips in the MD would heat up faster as they would have more surface area in contact with a heated surface. Yeah, that's how I arrived at my data. I drilled a small hole into the end of a strip in a bundle, either bound without an MD fixture or with the fixture. I can't remember, did you use M-D fixtures when running the tests? If not, were you able to take into account conductivity of the aluminum in transferring the heat from the fixtures to the cane? The beauty of the fixtures is they're able to "hold" a strip in a position to help with the straightening of the strip, yet leave quite a bit of surface area open to the heat, as well as transferring the heat where it does touch the strip. For those who aren't familiar with the M-D fixtures, picture a six pointed snowflake, with a small "bud" on either side of each of the points that run the length of the fixture. This allows for air and heat to pass by a large amount of the surface area of the strip, and the "buds" hold the strip rigidly in place, and transfer the heat from the fixture to the strip. (Mark Wendt) I ran the test with six strips bundled without the MD fixture and then again with the MD fixture. A thermocouple was inserted into a tiny hole drilled into the end of one strip to measure temperature rise. What I found was that it took 54 minutes to reach 347F with the convection oven set at 350F using the MD fixtures. It took only 30 minutes to reach 347F when the strips were bundled with NO fixture. While the aluminum is a good conductor, it is also a large thermal mass compared to the bamboo. It is insulated from the heat source by the existence of the bamboo nestled into the fixture and the air gaps are so small as to be a significant impedance to flow. The end result is longer heat up time. (Al Baldauski) Thanks. I couldn't remember if you'd used the fixtures or not. The fixtures being such a large thermal mass is why I stick them in a cold oven and bring both them and the oven up to the set temp. (Mark Wendt) Now that's interesting! And exactly what I would not have guessed. (Dave Burley) Another thing to remember about the fixtures is that even though they may make it take longer to achieve the set temp, the temperature is distributed evenly down the length of the fixture because aluminum is a very good conductor. (Mark Wendt) I'm going to add a bit of heat to this discussion. You said, "The significant time increase is at the other end of the heating cycle as you approach desired temperature. For instance, in approaching a set point of 350F the time it takes to get from 338F to 348F is 14 MINUTES (only 10 degrees). It might take another 14 minutes to go that last two degrees! I didn’t time it. Sometimes close enough is close enough." Now, if you wait long enough your oven will eventually reach your desired temp of 350F. If you then open the oven and insert the room-temperature strips and possibly an M-D aluminum fixture the oven temp will immediately decrease by perhaps 10 or more degrees. If it takes 14 to 28 minutes to recover, then what is the effective temperature of the oven during the actual heat-treating process? I agree with you that sometimes close enough is close enough. (Ron Grantham) Well that's a good question. Everyone's oven is different and therefore its recovery time so it can only be determined experimentally with some careful measurement. My guess is that most ovens will recover much more quickly that it takes to get to setpoint in the first place. The heatup time is mostly due to heating all the metal components. When you open the oven for a brief moment to load your bundle, the metal components act to preserve the temperature and your recovery is mostly due to heating up cooled air AND your room temp bundle. The numbers I quoted were the heat up time constants for the bamboo bundle with and without the MD fixtures that I took from Al's data. Full temperature is reached in about 4 time constants or 98% change from the cold bundle to the full set point temperature. The type of oven will influence the heat up time also, as the time constant is proportional to the mass of the bundle and inversely proportional to the heat transfer coefficient in the oven. An oven with air flow (forced convection) will have a higher heat transfer coefficient than my oven which does not. I am not sure of Al's oven design configuration but it influences the time constant I extracted from his data. I hope I did not confuse anyone. (Frank Paul) My oven is a convection type with ~700 cfm flow rate. (Al Baldauski) Your experiments are corroborated by experiments done by a violin maker who contacted the list some years back. He explained to us that sound conduction velocity is a sensitive and accurate measure of modulus of elasticity and is used in instrument making and in structural engineering. He volunteered to measure the sound conduction velocities of strips he cut from a single culm, which he mailed to a number of volunteers for heat treatment.. The volunteers heated treated them at several different temperatures and times in their ovens. The samples were returned to him to test and he couldn’t find any significant differences in conductivity between strips treated with any of the different time/temperature regimes we tried. I wish I could remember the details. The data might be in the archives. (Doug Easton) What started out as a simple comment on your post has grown to the epistle below as a way of my putting thoughts in context, as I realized I needed to summarize recent comments and ask questions. Doug said: I think the reason he didn't find any difference was that he was measuring moisture content as part of this sound conductivity and these had all equilibrated with atmosphere. The speed of sound (what I believe you mean by "sound conduction velocity") in wood is an important part of musical instrument design and relates to a lot of wood properties, especially density, which relates to lots of other properties like stiffness, etc. His work proves that measurement of equilibrated, heat treated wood does not change the density (and by implication) the stiffness. I suspect some here will disagree with the idea that heat treating does not change stiffness. Is there data to prove this either way? Electrical conductivity instruments have become pretty common over the last few years (or am I just becoming aware of them?). HF sells one pretty cheaply and it works. Wood moisture is a critical measurement when gluing up thin woods (like musical instruments) as too much moisture, which dries out after gluing and. Oops firewood. I don't think moisture content is the issue or a measure of proper heat treating, as like all wood, bamboo changes over time to reflect the environmental moisture (humidity). A result of the above work suggests that a bamboo rod stiffness (or feel) is sensitive to humidity. Is there a data set which confirms this? Glue joints (as in musical instruments) can split from changes in moisture content from when the rod was assembled. Thus, many rodmakers allow their heat treated splints to equilibrate with the atmosphere before assembly. Gluing dry splints could cause splitting of the joint as the dry splints expand by absorbing moisture. A second issue which is not often addressed here is what is going on in heat treating besides drying out? I would appreciate any additional comments here. As I understand it, Bamboo is made up of cellulose fibers and a cellulose "varnish", hemicellulose (a low molecular weight cellulose, sort of) some lignin resin and odd other bits of organics. We all know that these same basic contents in wood, heated to a certain temperature at which the lignin softens allows us to bend wood and upon cooling in this position, it will retain the majority of the bend. Ditto Bamboo. So when heat treating, temperatures go above the boiling point of water and the bamboo does dry out with warm air heating. However, in the good old days, steam bending was the standard method, so apparently these resins soften enough at this temperature (say 250F) to allow bending. This was also a common straightening method in early rod making, as I recall. Another straightening method, once bottled gases became available, was flaming. This also heated the bamboo, but largely on the surface and provided some color (due to the caramelization of the starches/cellulose). The disadvantage of this heating method is that it could also affect the integrity of the cellulose fiber which largely reside near the outside of the bamboo strip. Daniel H solved this by flaming the pith, while simultaneously heating the strip allowing straightening. Hot air ovens come along and we bind the six rough strips and heat treat to remove any sweeps and finish planing, gluing, etc by a second heat treatment to cure the glue. Tony Spezio uses polyester thread to bind the strips, so that at the higher temperatures, as the polyester tightens (those who want to know why, think entropy, or contact me for more info) providing clamping. Pretty ingenious Tony. There are other issues discussed here and it relates to the thermal mass of the oven and content. I have never seen (but it must exist) the thermal conductivity of bamboo and how long it takes a strip to come to a constant internal temperature. This wil depend on a number of factors, including whether or not the MD fixtures are utilized. Summarizing this process helps me understand more thoroughly what everyone has been saying. It also provides me a way to ask questions in context. Please correct and comment on these comments. Providing data will be appreciated. (Dave Burley) Logically it follows that those who bake with their strips loose in the oven like I do should subtract cook time, all sides of the strips are exposed to hot air and thus cook faster and possibly more evenly. Think of flank steak vs. a 2" rib eye. (John Rupp) That's one of the reasons I put the strips/fixtures into my oven with the oven cold. I bring the strips/fixtures up to temp with the oven, then hold the set temp for 30 minutes. That way I'm assured of reaching and holding my set temp. This also avoids the cold shock to the oven's temp that happens when you insert cold strips and fixtures into the heat treating chamber. Nota Bene - this is using a convection oven. If you tried this with a non-convection oven, you run the risk of burning up your strips. (Mark Wendt) For those of you interested in the data from my experiment, here it is again. Interesting but a previously said not surprising given the insulating effects of the cane strips. In your setup did you have cane all the way to the edges of the aluminum fixtures? I wonder what the results would be for a bundle with say 6 inches of MD fixture extending beyond the ends of the cane? Given the excellent heat conductance of the aluminum would the exposed material tend to transfer heat rapidly to the inside of the bundle of strips? I think I like Marks approach of putting everything into the cold oven and letting it rise to near the desired temperature before starting to time the treatment. Another factor is the orientation of the strips. I seem to remember that Tony Spezio exposes the pith side instead of the enamel in order to get them to dry out faster-this would also tend to allow the cane to reach full temp faster since the evaporation of free water has a buffering effect on temperature rise. (Larry Puckett) As I recall, the strips were flush with the end of the fixture. I would speculate that a 6-inch overhang would help somewhat but maybe only the first 12 inches of cane. But then that would cause the ends to get to set point quicker than the middle of a section. Still another variable. (Al Baldauski) Since aluminum conducts heat pretty well, maybe that variable would be quite minimal? (Mark Wendt) While aluminum is a good conductor, it's ability is inhibited by the small surface area exposed to the airflow thru which the heat gets into it. I'm, by no means, arguing against using them. They can only help achieve better uniformity. (Al Baldauski) True, but unless you cut the fixtures shorter than delivered, there's usually quite a bit of it sticking out one end or the other for normal length rod strips. I'm talking about the original 6' length fixtures. There will obviously be less sticking out on the 5' fixtures. (Mark Wendt) You are correct, I do expose the pith side for drying and also for heat treating. There are two reasons I started exposing the pit side. One reason is, I am using Polyester thread when binding my roughed out soaked strips for drying. With heat, the thread shrinks and leaves marks on the edges of the soaked strips that extend above the MD fixtures. I would rather the marks are in the pith side. As I have mentioned in other posts, I check the opening left at the oven cap with a small mirror for moisture. When no more moisture appears on the mirror, the strips are dry. I use 125F for drying and the oven is somewhat Pre Heated. The sections are then removed from the oven and the thermostat is reset for 475F. I have added a small pilot light to my oven control box, (I have one of Bret's ovens) that tells me when the heat strip is on or off. The pilot light will be on when there is power going to the strip and off when there is no power going to the strip. With the thermostat reset for 450.F, I let the oven stabilize at this temp for a minimum 3/4 of an hour before inserting the three MD fixtures with six strips each. Then I reset the thermostat to 375. The pilot light is off at this time. When the pilot light comes back on at 375F, I start my timing. I generally use 12 minutes for medium Honey colored rods and 15 minutes for darker Honey colored rods. Is my oven accurate, I don't know, am I really getting the 450F and then the 375F? I don't know. I have a set of thermocouples but have still to get them installed. I do know I like what I get and my rods have not taken a set. I will say this, using the fixtures for drying and heat treating saves a lot of time for me by not having to straighten the sweeps in the strips. They seem to straighten themselves when drying in the fixtures. I modified my Garrison binder so that I can run the fixture through with the six strips. (see Power Fibers # 5, Oct 01). With the cotton thread I was using to bind the strips, I had to rebind them for heat treating because the thread would be loose after drying. With the Poly thread, the strips stay bound tight in the fixtures. I also use the fixtures to heat set the Epon glue I use. Am I making a rod that will last 50 years, I don't know and I will not be here to find out, I am already past 80 years. I am doing what I like and what works for me. (Tony Spezio) I have a hard time with heat treating even though I do heat treat my strips. I am a luthier (string instrument maker) by trade and we air dried all our wood. we found the moisture content was something that had nothing to do with how good the instrument turned out to be. We worked in conjunction with the catgut acoustical society (at Harvard U) and helped in the development of a way to measure stuffiness in the plates, top and back, in violins, mandolins, guitars, viola's, cello's and basses. When wood dries only time will aid in some of the chemical changes that take place, such as short chain molecules changing into long changed as they combined with other chemicals that make up what wood is. You can make Jell-O in an oven or in an icebox, though they will both be Jell-O, but will be two different beasts. Whether these things pertain bamboo drying I don't know but I air dry all culms about 5 years and I fell that the rod feels better.? The first rod I made was from a pre WWII culm and heat treated just before we made our rods (1965) and it was the nicest feeling rod I had ever cast till I cast some of the rods Hoagie had at Merritt a few years ago. Good musical instruments are made from good wood and good rods are made from good culms. The differences between air dried wood and kiln dried was significant. (Pat Coffey) I am an amateur luthier and I don't think anyone suggests that air drying vs kiln drying makes the instrument better. Without a doubt slow oxidation of the resins in wood with aging will bring about changes in the wood's flexibility, but waiting a century to build a bamboo rod is beyond most builders' horizons and I doubt a better rod will be built anyway. I believe it is just that dried wood used in assembling the instrument (or rod) makes the long term outcome more predictable. Wood doesn't split, joints don’t separate and in that sense the instrument (rod) is better. Assembling "wet" wood and then exposing the instrument to low humidity will most likely cause the joints or wood to fail at some point. I suspect the purpose of heat treating bamboo (which dates from an era where electricity was not available and hide glue the norm) was simply a method to start out with a somewhat known quantity. Various methods of heating gained their mystique and color of the rod somehow was thought to be related to performance. It is a lot of unproven mystique as far as what has been recorded and I have been able to read. I do think starting with a culm with a known moisture content range (achieved by heat treating or possibly air drying) is important - to avoid (possibly microscopic) joint separation. Thus humidity sensitivity, and possibly the tendency to take a set in the finished rod. (Dave Burley) A while back when the discussion started I sent Bob Milward an email letting him know that we were discussing the contents of his books and I didn't feel at liberty to quote long passages from them and so I asked him if he would want to take part. Today I got an email back from Bob, asking if I would post an attachment he sent on heat treating on the listserv. Bob doesn't take part on the listserv so here is the attachment he asked me to post. (Don Ginter) -------------------------------------------------------------- Some people cannot tell the difference between fact and anecdote. In the first edition of my book the composition of bamboo, pages 5-10 and damage caused by heat darkening, page 13, are stated categorically by professors of Botany and Wood sciences (fact). The simple multi-sample test on pages 14-16 confirmed this (fact). On page 18 I wrote, "Any darkening of the bamboo color represents loss of both tensile and flexural strength, due to degradation of cellulose fiber." (fact). The conclusion that flaming is bad for rods is inescapable. Written on page 123 I recount (obviously anecdotal) my experience in 1988 when I flamed a culm under the supervision of a well-known retired commercial bamboo rodmaker, using his equipment. There was no discernible improvement over my rudimentary oven cooking. Discerning readers noted that I made no recommendation for heat treatment in the first edition. Flame treatment had been discredited. A definitive optimum oven treatment remained "The last great problem of rodmaking." In the 9 years between the first and second edition Dr. Wolfram Schott published the results of decades of heat treatment testing on university quality equipment. I subsequently completed a 9-month long experiment which flexed heat-treated rod sections 118 000 times simulating use, ageing, set and strength loss. As a result, optimum practical heat treatment is known, and the damage due to heat coloring is demonstrated beyond question. The second edition contains approximately double the hard information on rod building and is not just a re-hash of the earlier work. So far, worldwide, only 207 people and their friends have this hard information and anyone expressing an opinion on heat treating bamboo who has not read the second edition is ignorant of the facts. If you want anecdote, I have been repairing bamboo rods for 22 years and the total is over 250 rods by 36 named makers dating from 1890 onwards. Many of them are major structural problems which others will not touch. With hindsight I realized that the vast majority of splits, breaks, bad sets and flaking power fibers occur in dark heat colored rods. I wish I had kept a documented record. My anecdotal ramblings could go on for hours. I hope this helps. Regards, Bob Only now I have read the note of Mr. Milward regarding the conversation between the list members on Heat Treating. I think that is unusual the Mr. Milward approach regarding this discussion. He says, "...only 207 people and their friends have this hard information and *anyone expressing an opinion on heat treating bamboo who has not read the second edition is ignorant of the facts." *In other words, "Shut up! if you have not read my second edition book!" I think that Mr. Milward neglect that other persons can have made different resources, have different opinions, different approach to the problem only because *ignorant of the facts *do the lack of reading is book (II ed.) (?) But I do not think that Mr. Milward book is the only true source of the Truth. Mr. Milward talks about "facts". One facts is "...stated categorically by professors of Botany and Wood sciences (fact)", but he forget to add the references of the works and publications. So this "facts" risks to become "opinions". A second fact is the work of doctor Wolfram Schott, also published in Power Fibers. Very interesting work. But Dr. Schott is a respected mineralogist by profession in a German University, and his approach to the problem is related to the Thin Section Microscopy, typical approach used in the studies of minerals and rocks in Geology. This type of approach is mainly used for a visual interpretation (or images interpretation) of the rocks thin sections, and the dr. Schott paper do not cite structural tests regarding the materials under the different conditions. So, this work not change the elements of discussion. Third fact. By the way, I am one of the 207 owners of the Second Edition Book and I have also the First Edition. (Marco Giardina)
Do we have any testing that involves putting a thermocouple or two on the enamel skin of the strips, while trying different heating regimes and then break test the strips to find out where the skin temp and time combination comes to failure (brittle cane) and where a certain combination produces no result? Split the difference and it should produce a combination to shoot for. I'm guessing that the answer to your question Harry is that there are variables in everyone's set up that either have not been accounted for or are not obvious. What makes the most sense to me is finding out what the optimum skin temp and dwell time needs to be. (Bill Walters) Seems to be enough of an issue just to get people to use a thermocouple and measure actual strip temperature to know what temperature cycle the bamboo has actually gone through. Instead it seems to be wishful thinking and bragging about how uniform in temperature their ovens are. (Mike McGuire)
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