Author Topic: Sinew backing  (Read 583 times)

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Offline Jakesnyder

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Sinew backing
« on: May 16, 2019, 03:24:11 pm »
I've seen some people take a stave, rough it out to floor tiller and put it in a form (or string it backwards) and sinew back it while its reflexed and others (like me) have heat bent what curves they wanted then sinew. What are the benefits to keeping it reflexed instead of just heat bending it?

Offline Pat B

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Re: Sinew backing
« Reply #1 on: May 16, 2019, 05:43:06 pm »
 It prestresses the wood before adding the sinew allowing the sinew to work harder.
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Online SLIMBOB

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Re: Sinew backing
« Reply #2 on: May 16, 2019, 06:09:40 pm »
I think ...it also helps with the belly on the compression side. The belly will feel less compression than it would if it was heated in.
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Offline Jakesnyder

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Re: Sinew backing
« Reply #3 on: May 16, 2019, 06:20:55 pm »
So if the wood is prestressed it helps the belly with compression issues? So on woods that typically need heat treat wouldnt?

Online SLIMBOB

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Re: Sinew backing
« Reply #4 on: May 16, 2019, 06:49:51 pm »
If the belly is “bent” backwards, then to some degree it won’t feel compression until it returns to its straight position. It can’t because the sinew is holding it in position. So as the bow is drawn, the sinew stretches allowing the belly to begin moving toward what would have been its relaxed position. The theory has it that it won’t feel compression until it reaches that point. That point  that would have been the unbraced position is deep into the draw. There is however some disagreement on this topic.
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Offline Jakesnyder

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Re: Sinew backing
« Reply #5 on: May 17, 2019, 12:04:57 am »
That is real interesting though. It makes sense. Sound like a good experiment. Maybe on a white oak. Is there anyone that prefers that prestressed over heat bending?

Online SLIMBOB

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Re: Sinew backing
« Reply #6 on: May 17, 2019, 06:27:41 am »
It's not a one or the other proposition.  You can heat in some reflex AND bend in reflex.  I have one right now that has been heat straightened and I reflexed a deflexed limb with heat.  I will as well, tie it into some degree of reflex when I sinew it.  I don't necessarily prefer one over the other.  Each renders a different outcome.
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Offline PatM

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Re: Sinew backing
« Reply #7 on: May 17, 2019, 07:39:59 am »
Many are probably doing a combination of both these days.

Offline bradsmith2010

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Re: Sinew backing
« Reply #8 on: May 17, 2019, 09:17:14 am »
I do a combination of both,, not knowing if that is the best or not,,

Offline High-Desert

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Re: Sinew backing
« Reply #9 on: May 17, 2019, 09:18:36 am »
I just sinewed one yesterday that I had heat straightened out some of the deflex, then strung backwards about 5” for sinewing. I thing heat treating with 5” of reflex may cause some compression issues, but I haven’t tried it, so I don’t know, but it may work. I was mostly worried about drying the wood out too much before sinewing since I always seem to get some splitting after sinewing, and this one is greenish wood.
Eric

Online SLIMBOB

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Re: Sinew backing
« Reply #10 on: May 17, 2019, 02:18:58 pm »
Just spit balling Eric, but the heat treating helps.....with the compression issues.  5 inches of reflex or board straight.  Your firming the belly up to allow it to withstand greater compression forces, so I can't see the first part of your statement as regarding compression issues as a concern.  Quite the opposite in fact.  As to the dry wood cracking...mine that I am working on now has cracks just from the heat treating.  It's very seasoned Osage so it's a concern, but a minor one for me.  The greener wood shouldn't absorb as much moisture from the hide glue, or so I would argue, and shouldn't check as bad as dryer wood.
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Offline High-Desert

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Re: Sinew backing
« Reply #11 on: May 17, 2019, 02:28:07 pm »
That a good point slimbob, I might as well try it on my next one if I sinew a well seasoned stave.
I’m guessing it would be necessary to heat treat in the full reflexes position because you wouldn’t want to pull it into tension after heat treating.
Eric

Online SLIMBOB

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Re: Sinew backing
« Reply #12 on: May 17, 2019, 02:34:22 pm »
When I heat treat, I'm tweaking the alignment AND the degree of reflex or deflex all at the same time.  The one I am working on now has 5.5 inches of heated in reflex.  I will still pull it into a bit more reflex when I back it.  Not much, because I'm already at 5.5 inches.  So heat treated or not, you can still pull into reflex for the sinew.
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Offline Jakesnyder

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Re: Sinew backing
« Reply #13 on: May 17, 2019, 03:02:28 pm »
What about heat treating? Would it still be necessary?

Online SLIMBOB

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Re: Sinew backing
« Reply #14 on: May 17, 2019, 08:36:06 pm »
If the bow will benefit from hardening up the belly, then yes. I started out being very selective on which bows I tempered. I temper most all of them now. Osage included. If the back can take the added strain, the bow will benefit from it so far as I am concerned.
Liberty, In God We Trust, E Pluribus Unum.  Distinctly American Values.