Primitive Archer
Main Discussion Area => Bows => Topic started by: lostarrow on October 13, 2012, 01:40:32 am
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I know some guys will probably jump all over this one but here it goes............ When you "heat treat a piece of wood ,what you are doing is removing the moisture from the cells. The more you do it , the less moisture. Wood is made mostly of water while growing ,and when we cut it ,it starts losing that water immediately. When they talk about a piece of wood reaching equilibrium they are talking about it losing or gaining moisture ,relative to the ambient humidity present in the air.(RH- relative humidity) When a piece of hardwood is brought down to say 10-12% MC(moisture content) the cells have shrunk significantly already. They will never again be able to contain as much water as when fresh cut.Even if submerged in water.If that piece is brought out of the kiln in mid summer when the RH is 80-90% it will absorb some moisture and maybe creep up to 18% or so depending on species.After the winter when the air is drier and the board has come down to 6-8% in some areas ,in the spring and summer of the following year,it will not get back up to the 18% it did the following year.And so it goes through time until the wood has lost more and more ability to hold the moisture that once made it flexible.Old and brittle. Some woods fight this better than others . When we heat treat we are artificially collapsing the cells(shrinking them ) making the wood more compact but in turn ,less able to absorb moisture. The wood turning brown from heat is the sugars in it caramelizing,just like onions in a fryingpan or sugar heated with a torch on Creme Brulé. MMMMMMMMMMM yummy! the more sugar ,the browner it gets. When the wood reaches a point where it no longer contains enoughwater to keep the temperature below the woods flash point, it cumbusts.You don't need a spark or flame to make fire, you just need enough heat. If you leave the heat gun on the same area too long you shrink the cells to the point where they can no longer bind to each other .Too much of a good thing.If you can heat a piece quick enough,you can harden the outside without collapsing the cells all the way through to the back.If its really thin and the wood doesn't contain much sugar, you may wind up drying the whole piece through before you see any toasting happen. the cells on the back have then collapsed and are no longer able to regain enough moisture to become elastic again.You now have a dry brittle piece of wood. Try this for an experiment,it might give you a better idea ,visually of what is going on. Take a piece of wood 3/4"x3/4"x24" long. Straight grain(ish) Square and straight.Heat one side only , in the very center, for about 6" or so .Heat it until it becomes light brown on that side only.Maple would work good for this.The two ends on the side that is heated will draw into reflex because the cells have shrunk.The piece of wood will now be narrower in the middle as well . The side closest to the heat will be narrower than the side farthestThe piece may also twist ,depending on the grain.The cells closest to the outside of the tree will be larger and therefor shrink more. On a larger sample you can shrink one side until it cracks the opposite . This is what happens to your staves when they dry and split. The larger cells shrink more than smaller ones near the center of the tree or around knots.Back to the experiment......... Measure the size at the middle and both ends. Now throw the piece into some water for a few days. Extreme ,I know , but leave it for the amount of time that you would leave a bow after heat treating. Take it out when you are satisfied that it can gain no more moisture . Dry it off with a towel and stand or hang it somewhere to dry so that it dries even all around. When it no longer appears wet on the outside, measure your spots again. The ends should be larger than 3/4" the toasted side is probably the same and the side opposite might be marginally larger but still smaller than the3/4" you started out with. The cells will never be the same ,even on the side you didn't think you heated. You've changed the specific gravity of the wood in essence, as the same amount of cells are still there, they just occupy a smaller space and are more compact.They are now more resistant to compression ,but also less resistant to tension.Some guys use oil when they are doing heat correction ,as the oil has a higher evap. temp and keeps the cells from collapsing while bringing the wood to a temp.high enough to bend.Just make sure it's compatible with your finish.Contemporary accounts of native bowyers of the 19th century said they applied grease or oil from animals to the back of the bow to keep it flexible while they were making it and throughout it's working life .Once again ,if you wanted to sinew back it ,this would not be advisable. Hope this helps. Sorry if it was long winded,but there is allot of info for one small aspect of wood.
Cheers, Dave.
This was taken from another post ,I just didn't want to type it all out again.Thought this info might help demistify heat treating
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It makes sense, thanks for posting!
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Not really. No amount of drying duplicates heat treating. It changes cell structure in ways other than just shrinking. I'm not really sure why people are quite so obsessed with explaining how it works rather than just accepting that it does work.
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So what is the verdict here? It almost sounds like heat treating would compromise a bow's longevity. It's always worked for me, but my bows have not been around all that long. Does a well treated bow last just as long since it supposedly can't gain good moisture?
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Marc St Louis wrote a chapter in TBBIV on just this subject. Marc did years of studying and lots of experimentation before he wrote the chapter in TBIV. Read that and you will understand the process and the results much better.
One thing that Marc does is substitute the moisture in the wood cells with a mixture of pitch and turpentine, while it is still hot to seal and protect the cells that have been scorched in the heat treatment.
Heat treating does probably shorten the life of the bow in the long run but it also increases the compression strength of less strong woods(mostly whitewoods) which can increase the life of a bow. There are trade offs in every aspect of wood bow building. It is up to you to decide which trade off is best suited for you as a wood bow builder.
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Well put fellas.To conclude my end of thinking here.Wooden bow building to me is a process of problem solving a lot of times.You can't fix nothing without tools.Heat treating is a very valuable tool in the bag a bow maker has to get the best out of a piece of wood.Without it you would'nt see a lot of the beautiful bows shown on this forum.I think Marc St. Louis has investigated the process and the durability of it to the extent noone else has done.He stated many times how tension strong wood is best suited for heat treating.So it can keep in step with the bellys increased compression strength it gets from heat treating.If a bow fails for me because I heat treated it too many times I blame myself.
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Great article lostarrow, thank you very much for posting.
Did you collected these datas or you copied it from somewhere? If it is yours, are those the things that you tried personally or from some other documents collected?
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Hey guys, I,m not so sure why some are getting defensive on the subject.This is presented as information to aid you should you decide to heat treat.No where in this post do I contradict the findings of Marc St.Louis ,but on the contrary support his findings with a little background info on wood cells . Knowing how something works will save you much time and aggravation. I Just reread the chapter that Marc wrote in TBB ,based on Pat's reply to see If I had somehow missed something, and as I recalled he simply stated the results of his experiments. No B.S. , no wild theories , just the facts. That's what earns Marc the respect he has achieved over the years. Thanks Marc ,for taking legend and making it fact! If it wasn't for Marc we wouldn't have this tool in our bag of tricks. It may have been lost for eons until someone stumbled onto it again.
Bead man ,the point you made just once again supports the info here and as presented by Marc.
Jimmy, heat treating shouldn't shorten the life of the bow if done correctly. It will end it immediately if done wrong. That's why I posted this, to hopefully save someone the heartache of breaking what could have been a good bow.
Pat M , I try to present things in a way that is easy to understand, so I will not be going into the complex world of lignins,cellulose,antibiotics, minerals and the effects of heat thereon. Yes ,heat affects all of these ,but as they are in unknown quantities for any given species in various regions and growing conditions ,we shall overlook them . The more important point I was trying to make is that once those cells have shrunk ,they hold less water. Water is the main ingredient in flexibility(for our purposes).Desirable to some extent on the back, but can be detrimental on the belly.(increased set and sluggish cast).
Druid, I present only the info that I have gained from over twenty five years of cabinet and furnituremaking. Some from college ,much more from hands on experience.Over the years ,I have learned from many skilled artisans and learned more from people that decided to throw centuries of knowledge to the wind to increase production, only to have it all bite them in the butt when things started to fall appart. I have studied traditional ways of craftsmanship in many fields and found that much info can be transferred from one trade to another. Timber Frame construction to Furniture,Boat building to timberframing, Stained glass to Cabinetmaking, and so on.Some info comes from High school science class,(teacher didn't like that I asked so many questions,but I needed to know why,or the info didn't stick)and some I can't recall where I learned it , because I use it every day.Like trying to remember how you learned to walk or talk.Bow building is just my latest obsession.The above is what I believe happened to that piece of "tree of heaven" . too much heat for a tension weak wood.Low sugar content meant much more heat to "toast " it . by the time that happened,it was over cooked, and cause a tension failure.
Please , if anyone finds anything I post to be in error, feel free to quote the statement and present your argument for the contrary. I'm only human and am not offended by being proven wrong. Humbled perhaps, but not offended. When we stop learning , we die.
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I for one enjoyed reading your post. I, like you and many others enjoy the pursuit of knowledge for it's own sake. It's how I roll. I see the same quality in my 7 year old boy. I need to know the whys and hows of a particular problem in order to fully understand it. I at least need to be able to question the whys and hows. Not taking sides here so much as acknowledging that, at least for me, your post was informative and interesting. Not sure about your facts (not that I question them, I just don't know their validity yet) but a worthwhile read. Thanks.
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There was quite a bit of controversy on this subject when I first started to post my findings and moisture loss was at the top of the list as an explanation. One person in particular, I believe his name is Lennie, did some testing at the time using fairly precise instruments to measure the moisture loss from heat-treating, he measured the wood before heat-treating and after. He found that the actual moisture loss was less than 2%, not a very large amount. It was concluded at the time that moisture loss was NOT an explanation for the increased compression resistance from heat-treating.
All of these old posts were on the old PA message board and I wish we could have access to it. There is a huge volume of interesting posts and information sitting out there somewhere
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On the same subject of moisture loss and heat treating.... I heat treated a couple of bows that I built last spring. They turned out to be good shooting bows, one that weighed in the low forty lb. draw weight, the other right on fifty. I toasted the belly on both of them. I revisited these bows after they had been hanging on a hook in the air conditioned interior of my house for about six months.... Both of them had gained about ten lbs of draw weight! I reasoned that the wood was dried outside in my shop. Not heated or air conditioned - higher humidity shop never allowed the wood to reach optimum moisture content. These bows did reach their proper moisture content inside the house and gained draw weight - well AFTER the heating they received during construction..... That made me realize a couple of things.... 1. I need to dry my wood inside before I attempt to make a bow out of it - that and check to make sure it is completely dry; and 2. normal heat treating doesn't remove that much moisture from a bow. There is a blundering budding bowyer's take on it....
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Thanks for the comments Marc. I am not surprised with what your friend found for moisture readings.As you wrote in your findings you were using well cured hardwoods for specimens which probably had a reading around 9% or so If it were in the late fall or winter where you are . What I am saying is that when you shrink the Physical size of the vesel , you can't get the same amount of water in as you could before. The vesel in question isn't full of water when you heat treat it .It merely contains some water. From 9% down to 7% would make a good bit of difference in a piece of elm or hickory, probably just right. If you continued down to say 6% or 5% that would likely cause trouble. If your heat treating continues too long you may be drying too far into the back working portion of the bow, causing a very dense belly and a less elastic back. Which from your own research once again it looks like you found from the samples that didn't make it. Tension failures on the back and cracks instead of crysals on the belly, on the samples that were Carbonized(charred ) instead of Caramelized( lightly toasted ). I like the idea you had with the turpentine /varnish being applied while hot . I would expect this finish to penetrate deeper into the wood to add more long term protection. As a side note ,I was in your neck of the woods last weekend.(Pembrooke)Beautiful trip , lots of HHB.Some day when I get up that way I may even get a chance to look you up.
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So I just read through the post again because I was confused about the comments about heat treating not drying out wood very much.I 'm not sure we are on the same page as far as how little a difference a couple of % points of moisture will make in a piece of wood.Here is an example. A Hardwood floor for example,if laid in the summer with a moisture content of 12% has a nice tight fit .That winter the temp drops down to -20deg Celsius with a relative humidity of around 15%.With no artificial means of moisture(humidifier) ,the content in the wood now drops to a drastic 8%.The floor boards now have a gap of 1/8" -3/16" between each one.The next summer sees relative humidity as high as 90%, but the boards will be only scarcely larger than they were in the winter.They will never again return to their size they were when laid. The transverse would be fitting a flush drawer in a cabinet. The cabinet made in the winter must take into account the up coming summer swell of wood.if you leave 1/16" all of the way around , it will likely be jammed tight in the summer .If you had years to wait ,it would settle in and stabilize to an acceptable rate of swelling and contracting ,diminishing over the years to where it just can't absorb hardly any moisture at all. This all varies greatly with species and even within the species based on growing conditions and orientation of grain etc. In short , 6% MC in a bow will likely explode,while 8-9% would be ideal,12-13% would likely be sluggish. Again ,just examples. That's why people would prefer a board that is air dried for 7 years over one that is kiln dried 6 months ago. It has gone through several cycles of high and low moisture and is more stable, more predictable.
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Well spoken again!
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lostarrow, The shrinkage and decreased moisture uptake of the heat treated wood still doesn't explain things. A heat treated bow can at least be brought back to an intolerably high mc for a regular bow and still perform better. You may not be able to turn a raisin back into a grape but a moist heat treated bow performs better than a bone dry regular bow.
I'm not sure if anyone has dried a stave for 7 years in forced reflex and compared it to a bow heat treated into reflex though.
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As I said, the weight loss was LESS than 2% and this was right after heat-treating. After letting the wood sit for a few days it regained most of the lost weight. I do agree that the shrinking of the belly would mean that there would be less space for moisture to return but this is one of the benefit of heat-treating. Simply air dried wood will not achieve the same results even if you dried it for 20 years. The heat-treating process plasticizes the belly wood and allows it to be re-shaped, I'm sure that this plasticized wood does not allow moisture back in. One of the things about high density tropical wood species that makes them so heavy and resistant to water is their lack of air space in their cells, space that can be occupied by water. By heat-treating the belly of a white-wood you basically shrink it down and increase its density which increases its compression strength.
I sent a fairly short heat-treated Elm recurve many years ago to a guy in Arkansas. He brought the bow to one of the first Mojams and was showing it to some people down there. He told me that the guys were amazed to see the bow keep it's reflex when unstrung after being held at full draw, the weather was quite humid at the time.
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I should leave this thread with the last word said by the innovator of this thread but I'm selfish.Sorry I'll work on it.Everybody's up early today.Guess we are all church goers......LOL.OOOps that's a touchy subject....sorry.Personally I'm just up for no reason other than I can't sleep no more.....LOL.
This bow making to me is having a knowledge of the properties of different types of woods.To back up what hrodes said I always take a future bow inside roughed out from a stave.Weigh it till it quits losing weight at a controlled humidity.That can take weeks sometimes to get that last moisture point.Then finish it out.I don't own a moisture meter.I've been told by different bow makers oh that's a lot of fuss to do.Then their bow after being made follows the string bad or does'nt cast very well and blame the wood.To me it's worth the time.
After heat treating I have weighed bows made too.2% loss mass weight is about right.Most times it does'nt gain very much back.Whitewood gains draw weight.Hedge does'nt so much for me because it is already plenty dense.
Good post lost arrow.
I'll quit now no sense in beating a dead horse to death.
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lostarrow, thank you one more time for these datas. Great to see so much expirienced faces here in this topic.
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I am constantly mystified by the tendency to promote anecdotal experiences without checking whether scientific studies on a given subject have already been done. The document linked below presents clear evidence about the results of heat treating wood. It is a lengthy document, but very useful as the subject relates to bow making.
http://www.ncsu.edu/bioresnnources/BioRes_03/BioRes_03_2_Kocaefe_PB_ThermalTreat_Aspen.pdf (http://www.ncsu.edu/bioresnnources/BioRes_03/BioRes_03_2_Kocaefe_PB_ThermalTreat_Aspen.pdf)
Jim Davis
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Hi Jim , thanks for the link to the article . It appears to be a paper written in 2008 if I'm correct. Looks like someone was trying to convince a lumber company to try heat as an alternative to chemical treatment for lumber.This is all old info in the industry and is taught in most of the better Cabinetmaking and Furnituremaking schools as the basics. As I mentioned in an earlier reply I am trying to present the info in a way that is easy to understand and practical for our purposes on this site .I'm trying to give the reasons behind the successful anecdotes to help people understand why a "proven method" may have let them down.Basically ,what the document said in dozens of pages, with volumes of information was summed up in a few paragraphs above in laymans terms with a visual experiment to further the understanding. I'm not trying to take the magic out of bowmaking ,just trying to make us all better magicians.If you wanted to do a thorough search you could find a hundred more articles saying the same thing. I too am leery on anecdotal evidence but based on my own education and firsthand knowledge on the subject of wood and how to shape and manipulate it , I found Marc's presentation of his findings to be very well founded.He may not have used the" standards of scientific testing" but he never suggested that he did. He gave his findings based on what he tried and the results he could measure based on the equipment he had to measure them.If not presented in the "real life scenario" that Marc did in TBB , few people if any would be doing it today. Thanks again for the link. (I had to type in a search on the site to get it . "Thermal manipulation Aspen" I believe is what I used )
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I think it was already explained in layman's terms by Marc. What you have done is misrepresented the process in layman's terms.
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Just a little extra info for those interrested in the "why" behind the "how" PatM. If you feel the info is incorrect , please feel free to present a rebuttal. I believe this is a discussion forum for the advancement of "Bowyery"and in the spirit of such ,discussion is a good thing.NOWHERE were there any statements, attacking or contradicting the findings of Marc.On the contrary I posted the info in the belief that a slightly more in depth look at the subject would further promote the benefits of this technique! A question presented by another member ,in another post prompted me to write it to give a possible conclusion to the failure of his bow. In doing so, I realised this info may have been of interrest to others. Please take the time to read all of the posts here again and let me know where I've offended you, so I can assure you it was unintentional. At the risk of reiteration , I found Marc's conclusions to be well founded and completely supported by the scientific knowledge we have gained over the last century regarding cell structure of wood and how it responds to heat.
Please , if anyone finds anything I post to be in error, feel free to quote the statement and present your argument for the contrary. I'm only human and am not offended by being proven wrong. Humbled perhaps, but not offended. When we stop learning , we die.
In response to your previous postlostarrow, The shrinkage and decreased moisture uptake of the heat treated wood still doesn't explain things. A heat treated bow can at least be brought back to an intolerably high mc for a regular bow and still perform better. You may not be able to turn a raisin back into a grape but a moist heat treated bow performs better than a bone dry regular bow.
I'm not sure if anyone has dried a stave for 7 years in forced reflex and compared it to a bow heat treated into reflex though.
The shrinkage of the heat treated cells cause the hollow portion of the cell that holds the water to decrease in size, while the solid portion of the cell walls(lignin,cellulose ,minerals etc. ) contain the same amount of material(very slight amount may be lost ,but not enough to be concerned with for our purposes),thereby creating a more dense structure. As we know , a higher density is a desirable for the belly of a bow as long as the back can tolerate the extra strain. The higher density and the Crystallization of the "sugars " (several chemicals exist in wood and form hundreds of compounds that research has only scratched the surface on ,so for us it is the sugar that helps the tree grow.)slow the transmission of moisture into the heat treated area. The back , having not been "toasted " will allow the transmission more readily.Extra moisture in this area is more desirable as it keeps the wood more flexible. In this way we are changing the ratio for the characteristics of any given wood. A wood already good in tension but not so much in compression, comparatively, will now act like a wood with a higher compression to tension ratio. A moist, heat treated bow CAN outperform a bone dry regular bow all dependant on the ratio.To understand moisture content and how it is measured ,scientifically compared to in the field might greatly help understand as well. Scientifically , you cook a sample of wood until it stops losing weight and calculate the difference based on what it weighed at the beginning . In the field it is measured by placing electrodes into the wood and comparing the electrical conductivity to the known conductivity of water. (close enough for the purposes of most people dealing with wood) The non-probe method uses the same principal only with magnetic fields as opposed direct electrical connection. The big problem with these is that they would have to take into account the variable mineral and chemical compounds within the would to be accurate. The $400 ones attempt to take this into account but there are a huge amount of variables to look at depending on where a species grows. A Cedar tree growing in a swamp filled with iron is going to have a different composition than one growing in a fertilized garden.Iron conducts electricity differently than "Miracle Grow" . (HAHA)They are an indicator only and should not be relied on %100. As you said yourself heat changes wood like no amount of drying.That was never a question. As wood shrinks ,it will never again be able to hold the same amount of water it did before.It can still absorb water ,just not as much and at a different rate.As for the seven year drying ,that would refer to the extra stabilization a piece of wood has after going through the moisture loss/gain cycle seven times compared to one. Having said that, if improperly stored ,(excessively dry) ,that piece could be worthless for bows because it could have lost enough moisture to break the bond between the cells. I've dealt with one and two hundred year old hardwood that was like a piece of sponge toffee(furniture restoration days).
I try to read these posts over after I've written them to see if they make sense ,but it made perfect sense to me the first time I wrote it at 1am. I may be taking some things for common knowledge and not getting the point across as intended but keep questioning, that's the only way to advance. Thanks.
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About the 2% weight loss right after heat treatment:
Say that you lower the MC (moisture quota would be a better name) from 10% to 0 % on the belly and maybe a couple of mm inside. How big a portion of the bows total volume is that? Maybe a 1/5. Then 1/5 x 10% = 2% water or weight loss.
Then it regains some water so the MC is maybe 6% on the belly. 10-6 =4 x 1/5 = 0,8 % total weight loss.
Just an example how to value the weight loss. (Sorry if I am no good at explaining)
I really appreciate your work and patience lostarrow, keep going!
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IT'S PERTY MUCH MY THINGING ALSO.
PERSONALLY I DON'T heat threat my personal bows. But for 2 reasons I do once in a while.
(1) When your building someone a bow to MOST people when the think bows the see a straight limbed glass bow.
(2) For the last 15 years. I have reflex and untwist as soon as I cut my staves. Then its do natural NO HEAT NO CELL DAMAGE.
Then you can build the bow as staight as you want in most casts. If I do use any heat it's in the handle area to help line up the tips.
UNFORTENTLY I CUT 100'S OF STAVES WHEN I STARTED 21 YEARS AGO. AND DID'N T KNOW ABOUT REFLEXING THE NATURAL WAY. Some of these I have to heat for some people. If they really don't understand self bows, like I said the exspect a staight limbe bow.
What I see on here ALOT is the wrong use of the kind of heat used on the wrong wood. THEY'LL SAY I'VE ALWAYS DID IT LIKE THAT. IT WORKS FOR ME AND IT MIGHT WORK. FOR A WHILE BUT YOUR NOT GETTING ALL YOUR BOW AS TO OFFER.
Heating kinda like getting set or string follow. Once the damage none or you change wood cells it's none and you can't go back. And you can't build the bow to it full protental.
I do beleive if it not done right (IT CAN'T BE IN THE REAL SINCE) or if it's none at all in most woods. The bows not what it could be and the bows life with excessive shots would'nt last as long as it should. FOR THE ADVERAGE PERSON WHO ONLY SHOOT A FEW ARROWS EVERY COUPLE DAY OR LONGER IT USWLLY WON'T MATTER.
Were not talking bending the tips or the handle. Heats won't hurt your bow heating a none working part. I DO THIS, I'LL BEND A HANDLE AREA TO LINE UP THE TIPS IT I NEED TO. BUT LIKE I SAID ON PERSONAL BOWS I NEVER HEAT A WORKING PART.
I'd say OSAGE TAKES HEATING FAR BETTER THAT ANY WOOD i KNOW OF. The risins and oils help to stop the wood for srinking the wood cell like said.
They heat up and you don't have to heat the wood near as much as others. Meaning you do'nt get the koisture loss as you do from heating other woods.
Your right people do get real defencive. When heats wood comes up. I think its just because your telling them differnt ,went they've been doing it their way all along. Changes not bad. I've built over 100 bows but don't think my ways the only way. It suits the ways I do it.
IF I READ A POST THAT I CAN USE TO MY BENIFIT I CHAGNE RIGHT AWAY AND TRY IT ON THE NEXT BOW. BUT FOR A LOT OF PEOPLE YOUR HURTING THERE WAYS OF THINKING AND THE WAY THEY LEARNED.
EXSECIALLY ON THE NO BAINER THINGS.
VERY GOOD AND WELL WRITEN POST.
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I'm not sure why you guys are getting upset that a poorly written, sweeping generalization post might be critiqued a bit.
It is quite easy to see how the post can be misinterpreted as making a reference to heat treating just being "super permanent drying".
I wasn't aware that so many people were struggling with the process so if you think that first post is a lesson in how to heat treat properly, then that's fine.
The last post goes into a bit of the detail as to what goes on in heat treated wood and we ignorant buffoons can understand the slightly more complex lingo of the non layman's terms. ;)
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Wood is wood no matter if it's heat-treated or not. Tempering wood does not affect its elasticity and that is the determining factor on how long a bow will last. If you heat-treat a bow, properly, and reflex the heck out of it then it will not last as long as the same bow with less introduced reflex. This is because the heat re-shapes the wood cells (plasticizes) so that it can be re-formed into a different shape. The elasticity of the wood is not affected but the new belly shape has to undergo higher compression forces for the same draw length. If the back has enough tension strength/elasticity to survive then at one point the belly will start to fail. If you want a shorter lived, high performance hunting bow that will only be shot in hunting situations then a highly reflexed, heat-treated bow will give you years of use. On the other hand if you are going to use this same bow for steady target practice in addition to hunting with it in the fall then it's life span will be considerably reduced. If it's a target bow you want then simply heat-treating the wood with no additional reflex will give you a slightly better performing bow than one that has not been heat-treated and this bow will last as long as the bow that has not been heat-treated. Once again, the elasticity of the wood being heat-treated does not change, unless you take your heat-treating too far. Remember, Brown is good, Black is bad.
As to bows I have made. I have some out there that were heat-treated 10 years ago. They were highly reflexed bows used extensively for hunting/target and they are starting to show their age. Whether or not these same bows would have survived longer without the heat-treating is unknown as I can't go back in time and take it back :-).
P.S. There was a tech paper available from the USDA Forest Service on using heat and chemicals to re-shape wood. I read the paper many years ago and it was an interesting read. Unfortunately I went to the site and couldn't find it anymore.
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I think the facts of that article and folks experience with heat treating wood can be summarized by saying that there is a temperature at which wood starts to become stronger in compression. Through a fairly small range of higher temperatures, the strength in compression continues to increase. At a higher temperature, the wood begins to decrease in compression strength, and possibly in tension strength.
The best temperature for strength gain can be gauged by the color change in the surface of the wood. A color similar to lightly toasted white bread indicates a temperature that strengthens the wood. Colors darker than that indicate temperatures that are weakening the wood.
This is in line with what Marc said above and in his chapter on heat treating in the TBB.
Refining these principles requires good measuring equipment or judgement based on experience.
J
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Thanks again for your input Marc. I believe we are stating the same point of view.If you think something doesn't jive with your findings (I agree with everything I have seen)please quote the statement in question so we can further our Knowledge in productive manner without having to repeat ourselves .Once again thank you for the straight forward findings you have presented. I think we may have exhausted this one for now.
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My simple mind hurts you guys..........
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Mine too! Still I sure would like to know what happens to the wood when we heat treat it. We all seem to agree that some moisture is removed. That might bring on some structural change. But heating treating does not appear to be same as simple drying and there might be even some chemical or molecular level changes. The simplest way to test this is to seal the back and sides of a bow real well and dry its belly as long as it takes to the level of just heat treated belly.
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I feel a strong desire to post on this subject , yet the wisdom of years has taught me there is so little that I can actually prove, and so much that I have forgotten or remember only as I want it to be !
I refrain from stating things as fact ,as long as I catch myself first,yet there is so much to think on that happens inside of our bows !
Demystifying all of that, most likely will not happen.
We could be left with out any reverence for this awesome thing we jokingly call our addiction !!
Info sharing is a strange bird in and of itself with all the preconceived notions we carry into our outlook on things!
Lostarrow seems to be saying basically the same as I was told way back when .
Heat definitely changes wood as we can see what is being done today to treat wood by heat instead of chemically to slow down the decaying process ! And then there is its use for musical instruments and such!
Marq has a tryed and proven way to do a bow and yet we want to know how to do variables !
So much to do and so little time ,life is short !
Have fun folks and enjoy an awesome pastime !!
Guy
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I know that its been a while since someone posted here last. I just got into bamboo but I am using laminated strips. I am getting good results but I have questioned the heat treating process. I have not done that yet but I have experimented.
I tried a heat gun but it took a really long time so I tried a torch. There is a really fine line between brown and black in a 1 mm laminate.
The important thing I discovered in my experiments is that the browned bamboo was definitely stiffer than the untreated ones, hands down. You can easily see this when applying pressure to arch the specimen. It even made me worry that the heated one might not bend enough for my recurve mold shape. I did eventually test that and it will flex far enough. I am not sure how that translates into bow characteristics but I know that my stiffer bow woods have more spring that the softer woods. When I make my next bow from bamboo laminate, I will be able to compare draw strength with non-heat treated bamboo I have used until now.
The next issue is compassion strength after heat. The studies I read say that it goes up but I have no way to objectively compare that. Maybe someone has an idea.
The other important item is fracture strength. I partially heat treated a number of laminate pieces and flexed them into a circle until they fractured. Every piece, no matter how I made the circle tighten, fractured at the untreated portion first rather than at the heat-treated part. This may not be a fully scientific process but at least the treated laminate does not fracture easier than than the untreated one.
I anyone has any more information on the subjects of MoE and compassion strength in dried bamboo, I would love to hear from you.
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The wood most commonly used to make bass, and guitar necks is rock maple. The new trend now is to toast the necks at the factories. They end up a sort of amber color, and are supposed to make the necks more stable under changing climate conditions. Their is a steel truss rod that runs through the neck to makes adjustments for warp age to a certain point. . I bought an 1983 Kramer bass that was stored in a basement for decades, and the neck looked warped beyond repair, but because of heat treating bows, and seeing the magic it can do with hardwoods I took a shot at building a jig , heat treating the neck, and clamping it back to straight. It worked fine. String action is excellent, and the neck has stayed stable, and the instrument plays beautifully. I will leave the science to you guys, but my bow building has made leaps, and bounds, because of the use of the heat treating process especially with white woods when it comes to bow building.
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Rich. I have done a fair bit of my own research and testing on the heat treatment of bamboo specifically. It does benefit from proper heat treatment. It all depends on what type of bow you are building with bamboo and where on the bow the heat treated laminate is placed. A good scorched belly belly lam works well. James Parker has made many many of these. I’ve recently made some experimental boo bows that are bamboo backed and belly laminated with heat treated lams. It’s crucial to not exceed 180 degrees in my testing. It’s moe drops off at higher temps. I found this correlates with some research papers I found on heat treatment of bamboo laminations for building purposes. I heat treat my lams by using radiant heat element to lightly toast the belly for about 30 mins. I also toast the back lightly to assist with removal of some moisture. You’ll see the moisture escape the ends of the lams while doing so. I then place the lams into a reflex if doing a simple single layer boo bow with power fibers as the back into a convection oven for a few hours at 170-180 degrees. I have done extensive fail testing at higher temps with lambs and they pulled splinters or broke altogether. I use mosso pole bamboo. Test pieces were all between 1 3/4”-2” wide by 25” long. Strength increased greatly in the samples and the weight dropped also. It’s recovery to it’s relaxed state was also better. Set was greatly reduced. I observed the belly of the bamboo to also be harder as it was harder to dig my fingernail into. I’ve build simple 5 piece bamboo self bows with this heat treatment method with great results. I was impressed with results of such a simple bow design. Hope this gives you some idea for bamboo. I could give some more details on the process if needed.
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So, superdav,
You don't think that you should heat to a brown color?
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Correct. Especially the power fiber side of bamboo. You may get away with it more toasted in the belly but even there I’ve had failures. The odd one will survive but it’s no noticeable gain that I’ve noticed going darker toasted Color. It’s the lignins and pectins in bamboo that caramelize or harden with in the cells of the wood that give it more compression ability. Tension is already pretty good on dry bamboo and so heat treatment used on the outside surface is risky in my opinion and experience from my builds. The main benefit may be the loss of mass or moisture content. I always measure my before and after weights when heat treating bamboo and do notice a difference in overall mass. There is some acclimated moisture that returns but never to the same degree it was at all. I seal mine soon after heat treatment too to prevent too much mc creeping back.
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Thanks for that info. I was asking because you get more attractive looking wood with more toasting, but not at the expensive of wood integrity.
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I don't really have much to add to this beyond just personal observations that sometimes contradict themselves. For example, many dense tropical woods I have worked with don't seem to benefit from heat treatment with a couple of exceptions. One of them is massaranduba, but in its case, it is also known to have issues with water retention. Osage responds very well to heat treating and it does resemble the tropical woods more than it does most northern hemisphere woods. I am convinced that moisture removal and improvement in the ability of the wood to stay dry is a major factor, especially in white woods. But I also believe there is some plasticity gained by heat treatment. I never wait for a bow to rehydrate after heat treatment. As soon as it cools I tiller it. I have never had any issues with them losing draw weight after they acclimate. I tend to leave them about 3# heavy if I finish them right after heat treatment. Hoping when they rehydrate the weight will go with it. I never does change, and I always have to go back and take off the 3#.