Author Topic: Heat treating belly of sinew backed bow.  (Read 6027 times)

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Offline maitus

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Heat treating belly of sinew backed bow.
« on: March 20, 2019, 04:42:09 am »
Any experience, included bad and advises?

Offline simk

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Re: Heat treating belly of sinew backed bow.
« Reply #1 on: March 20, 2019, 05:56:49 am »
I did some heat corrections on my latest (and first) sinewed bow. I therefore was advised to continously check the temperature of the sinew layer by infrared thermometer and to take care that the sinew layer didn't heat up more to than 60 degrees and the belly to not more than 120 degrees (celsius). I protected the sinew with a silver paper. I had mixed feelings doing that but it worked fine.
I can imagine that you could do a heat treating of  the belly  that way. In this case I'd heat treat the belly rather hot but short, so that not too much heat goes alltrough the limb. A slighter heat treating should be doable like that. Still I see some risks...
Cheers
« Last Edit: March 20, 2019, 06:00:35 am by simk »
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Offline Pat B

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Re: Heat treating belly of sinew backed bow.
« Reply #2 on: March 20, 2019, 06:04:10 am »
I wouldn't attempt it. Not worth the risk for me.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline maitus

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Re: Heat treating belly of sinew backed bow.
« Reply #3 on: March 20, 2019, 06:33:58 am »
Thank You guys!
 I have heat treated rawhide backed bows a lot. There is no risk but im not sure with sinew. The next bow i will tiller and heatreat before sinewing. Im stupid :D...
 I think simk-s idea with folium tape could work, if to tape edges on belly level.
Lets wait for more posts :).....

Offline DC

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Re: Heat treating belly of sinew backed bow.
« Reply #4 on: March 20, 2019, 08:48:32 am »
If you heat hide glue does it soften and reharden as good as new or does it degrade?  Could you dampen the sinew/ hide glue a bit.

Offline simk

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Re: Heat treating belly of sinew backed bow.
« Reply #5 on: March 20, 2019, 09:18:56 am »
Quote
If you heat hide glue does it soften and reharden as good as new
True, but Hide glue and sinew also are made of proteins - they both soon denaturate if getting too hot - not reversible. I'd be careful somwhere above 60 degree ceslsius
(fish glue should be better and resists temperatures up to 160 degree celsius - says a book of mine)
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Offline DC

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Re: Heat treating belly of sinew backed bow.
« Reply #6 on: March 20, 2019, 09:42:17 am »
It wasn't with hide glue(it was epoxy) but I managed to twist a laminated bow with a heating pad. I wrapped it around the limb and (most important) I put a thermometer in there and adjusted the pad until it was 150°f (65°c) inside. That softened it enough to twist. That said if it's just a bit out I wouldn't risk it. I guess you could strip the sinew off the offending limb and start again

Offline maitus

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Re: Heat treating belly of sinew backed bow.
« Reply #7 on: March 20, 2019, 09:47:02 am »
If you heat hide glue does it soften and reharden as good as new or does it degrade?  Could you dampen the sinew/ hide glue a bit.
No, dry hide glue will not soften with heat, it will bubble :D . The question is: is it possible to keep heat away form the sinew and does the heat go thru the limb and reach to the sinew. There is no way that sinew coult resist heat.
« Last Edit: March 20, 2019, 09:50:35 am by maitus »

Offline sleek

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Re: Heat treating belly of sinew backed bow.
« Reply #8 on: March 20, 2019, 09:54:48 am »
I have used a very damp but not dripping rag on sinew with no ill effects. Just heat the belly slowly and hold the heat source further away to avoid burning the sinew.
Tread softly and carry a bent stick.

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Offline simk

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Re: Heat treating belly of sinew backed bow.
« Reply #9 on: March 20, 2019, 10:10:48 am »
Quote
The question is: is it possible to keep heat away form the sinew and does the heat go thru the limb and reach to the sinew.
Yes, you can: Just heat heat the belly not too long but intense and make sure the hot airflow doesen't directly affect the sinew. That way only the wood close to the belly will be heat treated. Check temp of sinew with a cheap infrared thermometer.
Any liability excluded.

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Offline maitus

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Re: Heat treating belly of sinew backed bow.
« Reply #10 on: March 20, 2019, 02:41:25 pm »
Thank You for advises. I think i will take a risk to try :). I have an experience with heat treating elm selfbow which took some 15 cm set during tillering  . After heat treating was the set 3cm and it keeps this set until today. So it worth to try.

Offline sleek

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Re: Heat treating belly of sinew backed bow.
« Reply #11 on: March 20, 2019, 02:53:19 pm »
Quote
The question is: is it possible to keep heat away form the sinew and does the heat go thru the limb and reach to the sinew.
Yes, you can: Just heat heat the belly not too long but intense and make sure the hot airflow doesen't directly affect the sinew. That way only the wood close to the belly will be heat treated. Check temp of sinew with a cheap infrared thermometer.
Any liability excluded.

[sleek: congrats to your 5000-post-anniversary!]

Oh, wow. And i spent it giving some dubious advice. Lol.
Tread softly and carry a bent stick.

Dont seek your happiness through the approval of others

Offline sleek

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Re: Heat treating belly of sinew backed bow.
« Reply #12 on: March 21, 2019, 03:57:56 am »
Seems some folks advocate for a quick heat, and im the only one saying do it slow. I guess I will explain why i say do it slow so i dont look stupid.

With a slow heat, its harder to overheat and burn the belly. Also, the heat soaks in deeper. A good deep heat treat is always ideal. Now of course you want the back to stay cool and thays what the damp rag is for. Of course that only helps so much, so you dont want to heat as long as you would without sinew. Just keep feeling the back and when it starts to get to the point of it being uncomfortable to hold your hand there for a solid min, you are at the threshold.  When Im done putting heat to a belly, I take a wet not damp, rag and wipe the belly. With the belly facing up ( heat rises ) to cool it off as fast as possible. I feel doing less than this just doesnt make the effort worthwhile, the belly just doesnt get heat treated enough.
Tread softly and carry a bent stick.

Dont seek your happiness through the approval of others

Offline Pat B

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Re: Heat treating belly of sinew backed bow.
« Reply #13 on: March 21, 2019, 08:34:53 am »
If you've ever dipped sinew in glue that is too hot it will immediately shrivel. How it acts in a matrix with hide glue I don't know.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline DC

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Re: Heat treating belly of sinew backed bow.
« Reply #14 on: March 21, 2019, 09:26:44 am »
I was reading about tillering horn bows last night and it's all about heat and wood and horn on finished bows. They heat and bend all the time. Maybe use their methods.