Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on April 01, 2019, 01:38:15 pm
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When you heat treating and then glue a surface is there any special care with the joint?
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Freshen up the gluing surface.
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May depend on the wood species. HHB benefits quite a bit from heat-treating on hard backed bows. I only prep the surface of the HHB for gluing after heat-treating
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The question is if the belly needs tillering after heat treating and gluing lams... wont You tiller the treated part off?
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Similar, related question, aimed at Marc really ;D :-
I'm making a flight bow, heat treated Yew belly, 'Boo back.
I've done a good slow heat treat on what will be the back face of the Yew which is about 1/2" thick mid limb. I felt the other side as I was doing it and it was too hot to keep my finger on.
How far into the wood does the heat treating go? Is it worth heat treating the other side too (the side which will have the Boo back glued onto it).
Sorry if this is an unanswerable Q and I don't mean to hijack the thread... I just don't want to glue it all up and then wish I'd heat treated more thoroughly ::)
Del
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Not a hijack Del, just stating my question a little clearer than me. That's exactly what I am doing
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The question is if the belly needs tillering after heat treating and gluing lams... wont You tiller the treated part off?
In my experience, yes. That's why you delay the heat treat as long as you can or do it twice.
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with a laminated bow, couldnt a glueline be considered a workable moisture barrier? my thought is to give a nice thorough (maybe longer at a slightly lower temp?) heat treat to the belly lam. The back could be glued to it a bit green even.
If the belly treat is thorough, one might not have to worry about removing some of it during tillering
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Del. I've found that with a slow heat-treat the effects travel perhaps 1/8".
I've never tried treating both side of the core and I don't think there would be much advantage since the back side of the core wouldn't be doing any work but on the other hand it wouldn't hurt
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The question is if the belly needs tillering after heat treating and gluing lams... wont You tiller the treated part off?
In my experience, yes. That's why you delay the heat treat as long as you can or do it twice.
I have seen video about making yumi bow. They smoke (i would say heat-treat)their lams for a long time in the special smoking houses. There must be some point :)...Maybe to use some metal pipe over the fire to get even and long treating thru the material?
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another approach:
why in that case not use epoxy that resists heat? eg
https://www.shop.swiss-composite.ch/shop/resources/downloads/t-LY5210_HY5210_HY5211_HY5212_e.pdf (https://www.shop.swiss-composite.ch/shop/resources/downloads/t-LY5210_HY5210_HY5211_HY5212_e.pdf)
or natural fish glue that resists temps of 160C celsius?
Cheers
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Thanks Marc:-
This thread really sums up the problem with trying to heat treat a bow that is laminated or backed.
Got to get it almost spot on right before glue up .
Regarding lower temperature and longer.... it needs about 200C (390F) degrees to heat treat, and that's more than any glues I'm found can cope with. It would need extreme care to keep the heat off the glue line.
Must admit I was surprised how hot the underside of the piece I was heat treating had got. I think heat treat a 2nd time for good measure, as it's been cleaned up a tad on the belt sander.
I think this has been the prob with mk1 bow, I've gone through the heat treating on the top limb >:(
Del
I think
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Thatīs a very difficult question. There is one possible solution I can think of (Iīve never tried it):
At first, you take the belly lam alone and reduce it close to the measurements youīre looking for. You can compare the measurements with other laminated bows. You tiller the belly lam alone without the backing on it. Of cause you should not pull it too far, as the belly lam might crack. Maybe you can pull until the belly lam reaches brace hight? Of cause, the wood should have a streight grain then. When youīre happy with the tiller, you can heat treat the belly. After that you glue on the bamboo backing. Hopefully the bow wonīt be out of tiller too much after that, so you can correct the tiller without removing too much wood on the belly.
An other possibility might be using hickory instead of bambo. You could correct the tiller in the end by removing wood from the hickory backing.
lonbow
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There might be a second solution:
You glue on the backing with hide glue, and tiller the bow to a draw length of about 20". When youīre happy with the tiller, you put the bow in the water for some hours until you can remove the backing from the belly. Then you wait for one or two weeks until the wood is dry again. Now you can heat treat the belly and glue the backing on the bow again. Then you can tiller it to your draw length. I donīt know if this works! Itīs just an idea that might be worth trying!
lonbow
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There might be a second solution:
You glue on the backing with hide glue, and tiller the bow to a draw length of about 20". When youīre happy with the tiller, you put the bow in the water for some hours until you can remove the backing from the belly. Then you wait for one or two weeks until the wood is dry again. Now you can heat treat the belly and glue the backing on the bow again. Then you can tiller it to your draw length. I donīt know if this works! Itīs just an idea that might be worth trying!
lonbow
Good idea but a bit labour intensive.
I'm hoping to get mine close first time, but I have extra length to play with and can do some tillering on the width.
Del
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Regarding lower temperature and longer.... it needs about 200C (390F) degrees to heat treat, and that's more than any glues I'm found can cope with. It would need extreme care to keep the heat off the glue line.
Del
Del, my comment to use a lower temp for longer was not phrased well. The thought was to treat the belly stock before glue up.
As far as the heat, 200C should work fine, the idea was to avoid excessive heat that might cause scorching of the surface. one could get heat thorough out the belly lam no matter what the thickness if the heat was delivered in some sort of hot box or oven and the temps were raised slowly, The belly stock could be resurfaced before glue up if needed, and reduced any amount if required, as the treatment would be the same throughout.
this would be a treatment that would certainly over dry a back, if the back were involved, hence the post heat treatment glue up. one might even have a different finish on the belly than the back if they wanted to try to maintain different drynesses in the overall limb, the glueline serving as a moisture barrier of sorts.
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@willie.
Yeah, I get it, a big oven/temperature controlled hot box that could cook through the whole thickness without scorching would be good.
Now if only I had a bigger workshop ::)
Mind it would just get filled up with more machines and I'd loose the fun of doing stuff by hand ::)
Del
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you could probably pull it off with a couple of pieces of stovepipe and some insulation. just something I have always wanted to try.
often I read comments about how heat treating is supposed to operated on a different principle from drying,
but of course any heat treatment job is going to involve some of both. heat treating might be a process that could be explored more.
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Maybe heat treat the whole belly lam in an oven like they do for bamboo. If the oven was set for 400°f you could leave it in there for an hour or so and the heat treat would go all the way through, hopefully. You could do the billets before any glue up. I just measured my kitchen oven and its 27" diagonally. That would have accommodated the billets that I used on the Molles with spliced on tips. I may try a test piece ;)
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I think we all had the same thought at the same time.
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The use of a pizza type oven is well known as a heat treating method.
What actually happens with heat treating is as well documented as we need it to be and it's certainly much more than just super drying wood.
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And here we are reinventing the wheel-again ;D ;D In a fully treated belly is there any danger that having heat treated wood past the neutral zone would cause cracking under the backing?
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Any links to that documentation Pat? I have read opinions based on subjective experimentation, but don't think I have ever seen anything quantitative
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It's out there but every time someone links to it others tend to try to shoot it down or it's quickly forgotten.
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And here we are reinventing the wheel-again ;D ;D In a fully treated belly is there any danger that having heat treated wood past the neutral zone would cause cracking under the backing?
Bamboo flyrods indicate no. All bamboo bows like those made by Schulz and Miller have fully heat tempered lams.
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One hour at 400°f. Before and after. 3/8"thick, same colour all the way through.
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Here's the one on Bamboo.
http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf
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Thanks for posting that Pat.
DC have you independently verfied the temp? Oven dials can be quite a ways off. And what wood is that?
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No and it's Yew. I took a slice off each piece with my pocket knife. The cooked one is noticeably harder. It did make the house smell a bit burnt woody. I'm going to try a bow sized piece at 350 tomorrow.
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No and it's Yew. I took a slice off each piece with my pocket knife. The cooked one is noticeably harder. It did make the house smell a bit burnt woody. I'm going to try a bow sized piece at 350 tomorrow.
Good experiment, watching with interest.
I might Have to persuade Mrs Cat we need a bigger oven >:D
Del
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I've often toyed with the idea of building a tube oven. I was thinking of a six inch diameter metal duct with a long heating element. I just wasn't sure if the radiant heat from the element that close to the stave/billet would be a good idea. Maybe an 8 or 12" tube would be better but being bigger it would be harder to heat I imagine.
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Wohooo! This might really take laminated bows to a new level!
1. The heat treatment reaches the inner parts of the wood. So the effect is much stronger than with selfbows.
2. The inner frictioof the wood will be reduced to a minimum due to the heat treatening.
3. The mass of the bow will be also really small.
4. Heat treatment can be combined with perry reflex.
I am certain your bow will rock, Dell!
lonbow
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I have cut up the limbs of a heat treated bow and if done properly the heat easily penetrates to the full depth of the limb which takes the compression.
The cross section ends up looking remarkably like either an ideal yew limb sap/heart ratio or a typical backed bow with a bit less of a distinct margin obviously.
The belly is browned to within about 1/4 inch of the back through the depth of the limb.
The Finno Ugrian bowyers already did the heat treat the belly first separately and then laminate in Perry reflex.
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Have you treated wood in an oven? If so, what temp and how long? I just did a triangular piece at 350°f for an hour. The outside has gone a nice brown, not as brown as the 400°, but nice. When I cut across it and sanded the ends it doesn't look like it penetrated much. Not sure what to make of this. It's back in the oven a 350 for another hour.
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I think I'm heating them too long. I did a roughly 2x2" piece at 350 for an hour and I can't see a line. I'll try 15 min next.
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http://www .westwoodcorporation.com/what.html
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Not sure what to make of this.
the typical thermostat on a kitchen range, in addition to being not regulated well for accuracy, also suffers from a high differential. so when a call for heat is made, a surface exposed to the radiant heat from the element may get quite a bit hotter than the air near the oven temp probe. the large differential between off and on leads to long cycles.
I use a digital unit like this...and set my oven dial so that the cycle tops out at the desired heat. I shade the wood from the element with tinfoil also.
as pat points out, the commercial guys use an oxygen deprived chamber. heat treating is used in place of chemical treating more in europe and is well documented
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Why don't you just heat the belly lam and remove the wood as you tiller? So long as you evenly apply heat, this shouldn't be a problem. I saw a carbonized composite boo bow made this way years ago. Heated the belly boo till it turned black, glued it up, then tillered normally. Plenty of heat still got through the lam. Lams are thin so you aren't really having a transition of heated material as in a self bow. It is more conistent due to how thin it is. Really, you are creating a heat treated lam, not a heat treated bow. No need to over think it. The yumi smoking thing is just to preserve the bamboo by the way. I read some info on it years ago and that is what they mentioned, although there may be more benefits to smoking. Boo grows mold easily.
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I was thinking more about hard backed bows where the belly piece(lam? I wasn't sure what to call it) is maybe too thick to get a good heat treat with a heat gun.
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A heat gun will cook right through an inch of wood.
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In order to go that deep how far would you hold the gun from the wood and how dark wood you let the wood get? Ballpark is close enough. I usually do 3 1/2-4" until it noticeably darkens and I could still hold my hand on the back of a half inch thick limb
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The use of a pizza type oven is well known as a heat treating method.
What actually happens with heat treating is as well documented as we need it to be and it's certainly much more than just super drying wood.
Ah.. it may be well documented , but the interweb isn't always good at finding stuff! ???
There's a place in the UK called "Sale" ... try searching for that >:D >:( :o ::)
I found it eventually!
Del