Primitive Archer
Main Discussion Area => Bows => Topic started by: lonbow on January 29, 2021, 01:14:05 pm
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Hello together!
I have a question about heat treating/ fire hardening bow woods. Is there only a notable effect if the wood changes its colour, or is it also possible to archive a long mild heat treat with lower temperatures without any colour change?
Thanks you!
lonbow
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If it doesn't change color at all I would think all your doing is hyper drying it.
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Heat treating dries and hardens wood. Whether you need to heat to color or not I'd guess it may matter a bit but how much. You can't go exclusively by the amount of color because different woods caramelize at different rates, some woods darken quickly where others color very little over a long period of time.
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No you want to be darkening it significantly to get any real advantage.
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Thank you for your answers! So I think that my bow was too far away from the glow. How far away would you put the stave over the glow? I´ve watched the fire hardening video on shannon outdoors, but there wasn´t any recommendation.
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Thank you for your answers! So I think that my bow was too far away from the glow. How far away would you put the stave over the glow? I´ve watched the fire hardening video on shannon outdoors, but there wasn´t any recommendation.
I keep my heat gun on high and 4” above the limb.
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personally i dont have a heat gun. i make a fire and use the coals. the only problem is that wood warps when dries because for some reason wood being cooked shrinks. so find a way to make sure the wood don't move
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personally i dont have a heat gun. i make a fire and use the coals. the only problem is that wood warps when dries because for some reason wood being cooked shrinks. so find a way to make sure the wood don't move
It shrinks from water loss. Like when you order a 8oz steak that's it's raw weight after it's cooked it's much lighter
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Heat treating dries and hardens wood. Whether you need to heat to color or not I'd guess it may matter a bit but how much. You can't go exclusively by the amount of color because different woods caramelize at different rates, some woods darken quickly where others color very little over a long period of time.
Well put Pat !
Arvin
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personally i dont have a heat gun. i make a fire and use the coals. the only problem is that wood warps when dries because for some reason wood being cooked shrinks. so find a way to make sure the wood don't move
Old ways are ways but new heat is easier controlled. Your and my choices. 😀😀😀
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You can get colour change without heat-treating if you put your bow too close to the heat source. Then again if you're too far from the heat source then you won't get the desired results. The temperature needed at the surface of the wood should be about 350~400 degrees F
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personally i dont have a heat gun. i make a fire and use the coals. the only problem is that wood warps when dries because for some reason wood being cooked shrinks. so find a way to make sure the wood don't move
It shrinks from water loss. Like when you order a 8oz steak that's it's raw weight after it's cooked it's much lighter
It's more than just water loss.
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You can get colour change without heat-treating if you put your bow too close to the heat source. Then again if you're too far from the heat source then you won't get the desired results. The temperature needed at the surface of the wood should be about 350~400 degrees F
Thanks for that information Marc I’ve been guessing but probably pretty close to those temps.
Arvin
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You can get colour change without heat-treating if you put your bow too close to the heat source. Then again if you're too far from the heat source then you won't get the desired results. The temperature needed at the surface of the wood should be about 350~400 degrees F
Marc,
I guess you are saying it's possible to quickly scorch the surface without getting any penetration of the desired effect? How do you assure effective treatment depth.
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Lonbow my experience is if treating over coals its best to start high and check color every few minutes and lower as needed. Really depends on how hot your coal bed is, outside temperature and wind are also variables that can effect the process. Hickory can take a lot of heat, osage can be ruined quickly. Even if you char the belly on hickory I have scrapped it down to good wood and still made a good bow out of it.
I have burnt up a few osage staves and cauls as it is very different from hickory but plan on trying again. These are the only woods I habe tried so far.
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Over a fire I use a leather glove, and heat treat one limb then the other as I go. I string the bow backwards. You can get heat to penetrate from the belly through the back with with very little color change to the belly. The back will feel very hot to the touch. Then I switch to the other limb,and go back ,and forth like that till I get a good heat treat.
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High temperatures weaken wood and particularly affect modulus of rupture. See kiln dried wood vs air dried.
It is impossible to change the color of wood fibers by heating them, without imparting damage.
The American Indian bowyer Ishi considered it bad and amateurish to discolor arrows when straightening them with heat.
I have never seen evidence of heat treating on any archaelogical bows or arrows from traditional cultures, English longbows, American Indian bows, central Asian bows, etc.
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You need to look harder.
Ishi also apparently couldn't reliably tie a knot to keep his bow strung. That doesn't mean it's not a good idea to learn a new technique.
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High temperatures weaken wood and particularly affect modulus of rupture. See kiln dried wood vs air dried.
It is impossible to change the color of wood fibers by heating them, without imparting damage.
The American Indian bowyer Ishi considered it bad and amateurish to discolor arrows when straightening them with heat.
I have never seen evidence of heat treating on any archaelogical bows or arrows from traditional cultures, English longbows, American Indian bows, central Asian bows, etc.
:fp
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High temperatures weaken wood and particularly affect modulus of rupture. See kiln dried wood vs air dried.
It is impossible to change the color of wood fibers by heating them, without imparting damage.
The American Indian bowyer Ishi considered it bad and amateurish to discolor arrows when straightening them with heat.
I have never seen evidence of heat treating on any archaelogical bows or arrows from traditional cultures, English longbows, American Indian bows, central Asian bows, etc.
You can build them that way for sure but it’s not the better shooting bow. Just facts. That being said enjoy your builds. Arvin
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You need to look harder.
Ishi also apparently couldn't reliably tie a knot to keep his bow strung. That doesn't mean it's not a good idea to learn a new technique.
Ok, but just because Ishi wasn't good at one thing, doesn't mean he was devoid of any knowledge at all.
It's a well documented fact that heat damages wood. Quoting Myer Kutz, Handbook of Environmental Degradation of Materials (2018):
Hemicelluloses are generally most susceptible to heat damage, followed by cellulose and, finally, lignin. Damage can begin to occur as temperatures reach 100⁰c, but the effects are very gradual at these temperatures (Zabel and Morrel, 1992).
The question is, how gradual is the damage imparted by heat treating as applied by people on this forum? If it results in as little as 5% loss of MOR, that is kind of a big deal for a bending object like a bow or an arrow.
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That's why people experiment to get the maximum gains with the minimum risks.
Just like the guys making tempered bamboo flyrods.
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I agree Pat, but without documented tests and investigations, it's still hocus pocus.
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Did you look for tests or do any yourself? What works is real.
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well heres the thing. anything bad that happens during a good heat treat ISNT A BIG DEAL and heres my proof. go to any thread where someone is showing off a heat treated bow. guess what.... that piece of wood is still a bow. And there are some AWESOME heat treated wood bows!
thats the bottom line. heat treating is not going to cause failure if done right, and if done right it can make a bow better. and you can say whatever you want about how it doesnt and how it damages a bow but, facts dont care about what you say. if you say that a heat treated bow will be bad, it doesnt matter because what you say does not determine how good a bow is. what matters is how you make the bow.
maybe wood does get damaged, maybe were heating it to just before it gets damaged to make it harder, maybe we think we know why but we actually dont, maybe we just dont know how it works. but no matter how it works or what happens, heat treating works if done right and in the right scenarios.
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Young man I respect Your enthusiasm and ability to read articles in depth. I’ve been building bows as long as you have been drawing a breath of air. That does not make me a person of superior knowledge. I have not built thousands of bows but. Have hundreds. This knowledge you are challenging has been proven to be successful and has been shared by hundreds on this and other forums . It just works and that’s why it’s done. The old archers and bowyers of years gone by did what you and all of the rest us are trying to do. Build a better bow. Again happy bow making. Arvin
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We all know that heat should not be applied the the back of a bow. This doesn't mean it's not good for the belly. There is more to it than simply good or bad.
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I did an experiment with heat treating on two Elm longbows.
I used the best comparison you can get, a large sapling split in half (twins) and seasoned them the same. They were roughed out at the same time, to the same dimensions and were very close to the same mass all along the process.
They were also very straight, so the tillering was very similar.
So one got heat treated at about 20in and again at full draw all sanded up.
The other got no heat treat at all.
Result, both shoot well and have the same draw weight.
The heat treated one took a fraction less set and 'feels' more springy and also outshoots the other by about 4-5m on average.
I didn't heat treat to the extent of changing the colour too much because I don't like that look and I oil the bow during the process to prevent it.
My conclusion is that it does make a better bow performance wise but it may reduce the life span, but I won't know that until one of them fails.
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There were actually documented tests done by an engineer in CA on heat-treating a few years ago, can't remember his name right now. These tests were performed at a university where he taught/teaches by some of his students who performed these tests under controlled conditions. He sent me the results of the tests, which I can't seem to find right now either, and there were indeed positive results to heat-treating bow wood. The person in question is a well known figure in the bow building world, blast his name is on the tip of my tongue.
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There were actually documented tests done by an engineer in CA on heat-treating a few years ago, can't remember his name right now. These tests were performed at a university where he taught/teaches by some of his students who performed these tests under controlled conditions. He sent me the results of the tests, which I can't seem to find right now either, and there were indeed positive results to heat-treating bow wood. The person in question is a well known figure in the bow building world, blast his name is on the tip of my tongue.
Can't tell you the number of times I've heard something similar to this, only to later find out that there was no such study.
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The experience of Bamboo flyrod builders seems to mirror our experience. Of course we know bamboo is grass and not wood.
I wonder if Marc is thinking of Dick Baugh?
Here's the bamboo tests:
http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf
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Pretty sure it was Badger that did the testing, he had pictures in his post as well on how he did it.
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Heat can weaken wood's tensile strength, mainly by damaging cellulose. But heat can also strengthen its compressive strength, mainly by affecting lignin.
Using silicon heating strips on the bow's belly only, I try not to damage its back, while strengthening its belly. I go all the way up to the temperature that plasticizes lignin just near the belly. The belly of the bow would be browned, but its back would never be.
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The experience of Bamboo flyrod builders seems to mirror our experience. Of course we know bamboo is grass and not wood.
I wonder if Marc is thinking of Dick Baugh?
Here's the bamboo tests:
http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf
Yes it was Dick who did the testing.
I think it's time for Tom to say goodbye
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I have heat treated bows were the back is very hot to the touch with no ill effects. I do it ,because I feel I am getting the full benefits of the heat treating method. May not be right in many bow maker's eyes, but it works, and that is really what counts.
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The experience of Bamboo flyrod builders seems to mirror our experience. Of course we know bamboo is grass and not wood.
I wonder if Marc is thinking of Dick Baugh?
Here's the bamboo tests:
http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf
Yes it was Dick who did the testing.
I think it's time for Tom to say goodbye
I already don't miss him!
Now that the housecleaning service has dealt this the matter, shall we get back to work?
To my mind, there are two extremes of heat treatment, both being of zero value. First would be toasting a bow until the entire thickness of the bow has reached the same temp as the belly and the bow is ruined because the back now will not handle the tension. The other would be toasting so rapidly that only the very thinnest surface layer of the limb actually has change, as often signified by the change of color, yielding virtually no measurable change in the behavior of the wood under bend.
How to heat to a consistent depth along the entire belly of the bow without compromising the back of the bow is where the skills part of the equation comes into play. Whatever means you choose, you need to control both time and temperature, with each of the two variables affecting the other in real time! I think having a clock on the bench as well as one of those fancy infrared temperature sensor guns would go a long way to helping someone generate some consistency, but a lot of us are going by keeping a slow count in our heads and watching the color change.
Patently ridiculous claims for the purposes of creating drama notwithstanding, no one here (well, certainly not now that housekeeping has serviced the room) claims that heat treating bow bellies isn't a useful tool in the toolkit.
As I have been following this thread and mulling things over in my mind, I am curious about doing a laminated bow of two layers consisting of one raw slice for the back, and another baked in a controlled temp oven for the belly. Zero chance of overtoasting and far more consistent results across the belly. Now, where can I buy a six foot wide oven???
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The experience of Bamboo flyrod builders seems to mirror our experience. Of course we know bamboo is grass and not wood.
I wonder if Marc is thinking of Dick Baugh?
Here's the bamboo tests:
http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf
Yes it was Dick who did the testing.
I think it's time for Tom to say goodbye
I already don't miss him!
Now that the housecleaning service has dealt this the matter, shall we get back to work?
To my mind, there are two extremes of heat treatment, both being of zero value. First would be toasting a bow until the entire thickness of the bow has reached the same temp as the belly and the bow is ruined because the back now will not handle the tension. The other would be toasting so rapidly that only the very thinnest surface layer of the limb actually has change, as often signified by the change of color, yielding virtually no measurable change in the behavior of the wood under bend.
How to heat to a consistent depth along the entire belly of the bow without compromising the back of the bow is where the skills part of the equation comes into play. Whatever means you choose, you need to control both time and temperature, with each of the two variables affecting the other in real time! I think having a clock on the bench as well as one of those fancy infrared temperature sensor guns would go a long way to helping someone generate some consistency, but a lot of us are going by keeping a slow count in our heads and watching the color change.
Patently ridiculous claims for the purposes of creating drama notwithstanding, no one here (well, certainly not now that housekeeping has serviced the room) claims that heat treating bow bellies isn't a useful tool in the toolkit.
As I have been following this thread and mulling things over in my mind, I am curious about doing a laminated bow of two layers consisting of one raw slice for the back, and another baked in a controlled temp oven for the belly. Zero chance of overtoasting and far more consistent results across the belly. Now, where can I buy a six foot wide oven???
Might I suggest using billets for the belly? You’d only need a 3’ oven instead of a 6’
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As I have been following this thread and mulling things over in my mind, I am curious about doing a laminated bow of two layers consisting of one raw slice for the back, and another baked in a controlled temp oven for the belly. Zero chance of overtoasting and far more consistent results across the belly. Now, where can I buy a six foot wide oven???
I tried this on my last couple laminated bows but made the bellies too thick and the heat didn’t seem to penetrate enough. I think if you started out with a 3/8” belly piece you could heat the crap out of both sides with a heat gun for similar results.
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I think DC has been dabbling with fully heat treated belly pieces. The two wood bows of Eurasia used heat treated belly lams. I'm sure you could improvise an oven of sorts in an outdoor setting by making a long bed of coals and covering it with a metal box or similar.
Personally I don't find it hard to just toast the belly of a stave and get the heat into the stave to a sufficient depth without going through to the back
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Of course very consistent heat treating will yield the best results.
Like all my bowmaking I just do things by what feels good to me, heat treating included, I don't measure much or time myself and often just say "that's good enough".
Works for me, 27 years of experience might come into play as well though.
If Tom is gone it will be a breath of fresh air, I had to bite my tongue to keep from responding in a negative way to his caustic posts.
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I typically use bow woods that benefit from heating like Ash and Elm.
A few years ago, I had a yew sapling seasoned and ready to go.
The problem was that it was thin, (33mm) at the center.
So I decided to make a longbow, 33mm x 27mm at the center with normal taper to the tips.
This created a flat belly, but not enough wood was removed to expose the heartwood except in the final 300mm - 400mm of the limbs.
So I decided to heat treat the sapwood belly to hopefully harden it up, to be able to cope with the compressive forces.
This worked very well and it is a nice shooting bow of 80lbs at 30 in draw.
In fact the heated sapwood became so hard, I had real trouble stamping my usual bowyers mark at the arrow pass point.
I use a leather stamping tool and normally have no issues producing a nice clean mark on hard woods such as Oak, Hawthorn and Yew heartwood.
So I guess most people know Yew sapwood is the best there is for a bows back, even when the rings are severally violated.
I would never have guessed that the sapwood heat treated could transform into a robust, compression resisting belly as well!
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Even Osage can benefit from heat treating.
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In Europe, research is being carried out at various universities on and with "thermowood".
At ETH Zurich, for example, I have found many things on this subject.
That was years ago but there were some very interesting statements about heat treatment of wood and the effects on the wood properties.
- The so-called equilibrium moisture content decreases. This means that microbes and fungi can only decompose the wood much more slowly. This is especially important in wood construction. Untreated pine may last up to 5 years outdoors. As thermowood, pine lasts 15 years and more under these conditions. Ash is offered thermo-treated as a floor for bathrooms....
- The wood becomes harder and lighter (less residual water in the cells) but at the same time more brittle (it is similar with steel). If you make the wood too hot or treat it with too high heat for too long, the wood can be spoiled, if you make too little (in extreme nothing), you will not achieve any change.
One must try to find the optimal compromise between the properties to be achieved and the treatments used.
There is also worldwide evidence that our ancestors used heat / fire to harden wood. The burial sticks and the first spears were not provided with stone tips, but the wood tip was hardened in the fire ....
The posts of pasture fences also often have fire-hardened tips, which moreover also last longer than the non-thermally treated posts....
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Interesting Andrew. I think it helps at the 350-400 degrees so I will keep doing it that way. Arvin
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I have only worked with a hot air gun so far. Even this can be done in very different ways: Low or high temperature setting, distance of the nozzle to the wood and the time interval for how long I temper the wood.
I have tried a lot and sometimes even deliberately worked on the borderline.
In the meantime, I tend to temper more slowly (minimum: 1 hour per limb), not with the maximum temperature (low temperature setting of the hot air gun) and a distance of the hot air gun of about 10 cm from the wood. About 130 - 150° C should result on the wood...(260 - 300° F).
I had best results with elm, hickory, cornus, hazelnut and bamboo.
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I finally found the document Dick sent me on heat-treating experiments he organized. If anyone is interested they can read it here...(link disabled)
sites.google.com/site/marcsbowsandarrows/home/documents-and-files?authuser=0