Author Topic: Post For Tim Baker ( Sinew)  (Read 53572 times)

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Offline Badger

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Post For Tim Baker ( Sinew)
« on: April 12, 2018, 11:44:00 am »
  Tim is having problems with the registration process so asked me to post for him until he gets the problem resolved.
Experimenting With Sinew.

Sinew is useful for keeping short bows from breaking, but is not good at increasing the cast of mid-length and longer wooden bows. This is largely because sinew is lightly strained in such situations, and has high mass.

The idea here is to cause the sinew to be far more strained than typically, making it do far more work per mass. Elevating the sinew well above the bow back would accomplish this by  increasing it's percentage of stretch.

This first experiment elevated the sinew by placing a filler of hide glue-soaked cotton string between the back and the sinew. The goal was to see to what degree draw weight could be increased while raising mass by small amounts.

The belly is bamboo, 46" long, weighing 5.5 ounces.
The dry weight of the sinew and glue is about 2 ounces.
Once in place the bow was twice as thick as the bamboo alone.
The bow was held in 5" of reflex when sinewed, holding 6" of just-unbraced reflex.
Draw weight rose 400% of that of the bamboo alone!
Some touch-up tillering is needed, so corrective amounts of sinew will be added in a couple of areas before going to full draw, and a visit to the chronograph. My guess it that it will well outshoot same-draw weight conventionally sinewed wooden bows, and Asiatic composites. We'll see.

Meanwhile, please let me know of other efforts to get more work out of sinew by elevating it above the bow back.  And your results, and details, if you do something along these lines yourself.

Arguments, comments and suggestions welcomed.

Tim Baker

Offline DC

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Re: Post For Tim Baker ( Sinew)
« Reply #1 on: April 12, 2018, 01:22:12 pm »
I like the idea of raising the sinew but I'm wondering if the hide glue soaked cotton is heavier than wood. Maybe a layer of some light wood would accomplish the same thing with a little bit less mass gain?

Offline PatM

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Re: Post For Tim Baker ( Sinew)
« Reply #2 on: April 12, 2018, 01:47:29 pm »
  This has already been done with a light crowned core. Really it's just a composite of simpler materials but the principle is the same.

Offline willie

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Re: Post For Tim Baker ( Sinew)
« Reply #3 on: April 12, 2018, 02:06:09 pm »
  This has already been done with a light crowned core.

Pat, do you have any more details about the arrangement of core and sinew in that example? Or know what the core was constructed from? It seems to me that if the sinew is going to stretch or work very much, that the core has to be able to withstand almost the same amount of stretching as the sinew, or core will fail under the sinew. This rules out any woods that I know of.

Offline PatM

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Re: Post For Tim Baker ( Sinew)
« Reply #4 on: April 12, 2018, 02:39:31 pm »
  The core remains intact generally in  composites with  tips touching reflex and long draws.
   
  To use sinew effectively in mid to longer bows you just limit it to hard working sections and make sure the bow is drawn farther.

 Seems like Tim has brought up the old solution in search of a problem.   This topic came up on here about 15 years ago. Not sure why Tim is bumping it again?

 The weight of the glue soaked cotton needs to be factored in as well. It won't get a free ride.

Offline Badger

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Re: Post For Tim Baker ( Sinew)
« Reply #5 on: April 12, 2018, 04:02:38 pm »
 Tim Baker says

DC:  Yes, light wood will be better. The cotton/glue just reduced the mount of sinew needed.

PatM: Can you point me to details on the version you mentioned: the % of sinew to total bow mass, the height of the sinew above the NP, draw weight increase,etc.  Any idea where I can find the mentioned 15-year old related posting?

This version elevated the sinew enough to double the thickness of the bow, used about 2 ounces of sinew, compared to the bamboo's 5.5 ounces  The fact that draw weight rose by 400% with a relatively small mass increase  is what's encouraging so far.

Tim

Offline bradsmith2010

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Re: Post For Tim Baker ( Sinew)
« Reply #6 on: April 12, 2018, 04:03:18 pm »
thank you for posting, great to have the chance to hear your ideas,, great to have you here, B
and thank you Badger :)

Offline Badger

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Re: Post For Tim Baker ( Sinew)
« Reply #7 on: April 12, 2018, 04:12:14 pm »
  Maybe one of the mods could look at Tims Account. it says he is logged in but when he goes to post it puts him back through the registration process.

Offline BowEd

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Re: Post For Tim Baker ( Sinew)
« Reply #8 on: April 12, 2018, 04:28:14 pm »
Interesting post.Glad to see Tim running some projects by he's been fooling with.Thanks Steve for posting it.I've fooled with borderline projects like this.Crowned sinew with lots of reflex/on working portion of limbs/light weight outer limbs.Just on 60" & 58" bows though.They do shoot outstanding.I would think with shorter less mass weighing limbs not quite as much reflex should be needed with the same or more result depending on poundage also.
BowEd
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Ed

Offline PatM

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Re: Post For Tim Baker ( Sinew)
« Reply #9 on: April 12, 2018, 06:05:31 pm »
"PatM: Can you point me to details on the version you mentioned: the % of sinew to total bow mass, the height of the sinew above the NP, draw weight increase,etc.  Any idea where I can find the mentioned 15-year old related posting?"

   Pretty sure the old posts are long gone.    The idea back then was pretty identical.

  Not sure of the actual masses of things and draw weight bumping since I don't weight the stuff or bend things much before assembly.

 The basic idea is a  wood backing strip shaped so that the center is a higher ridge and the sinew sits mostly on that.  Basically like the Kasan ridge of a Turkish bow but running up the limb more.

 

Offline BowEd

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Re: Post For Tim Baker ( Sinew)
« Reply #10 on: April 12, 2018, 07:16:32 pm »
Tim and Steve,
                       Enjoying this as a new post, wasn't here 15 years ago...I thought of flax linen+sinew...Is there a reason Tim used cotton...What does this do to the neutral plane with the cotton layer...Does this also take some compression stress off the belly...
                                                                     Thanks, Don
Combed flax would be a better choice yet.
BowEd
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Ed

Offline Badger

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Re: Post For Tim Baker ( Sinew)
« Reply #11 on: April 12, 2018, 07:29:11 pm »
 Tim Baker says:

Burchett--Don:

" Is there a reason Tim used cotton...What does this do to the neutral plane with the cotton layer...Does this also take some compression stress off the belly..."

It's only job was elevating the sinew, to judge the effect The bamboo was 50% of finished thickness, the cotton/glue about 25%, the sinew the top 25%. Chose the cotton assuming it would be fairly neutral in tension and compression, not throwing off measurement of the elevated sinew's performance by any large degree.  Another reason for using cotton was to prevent having to make a perfectly smooth surface on the bamboo, as when preparing a surface for wood core.


PatM:

Yes, similar idea. Sinew on a higher ridge would work harder. This highest, hardest working portion would have a small cross section, not raising draw weight substantially. To raise draw weight/energy storage by several times requires a lot of sinew, placed way above the NP, and as close to rectangular as feasible, making all of the sinew work equally hard.


Tim

Offline Marc St Louis

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Re: Post For Tim Baker ( Sinew)
« Reply #12 on: April 12, 2018, 08:03:25 pm »
  Maybe one of the mods could look at Tims Account. it says he is logged in but when he goes to post it puts him back through the registration process.

Steve
He is just having to do what every other new members has to do.  Once he post 3 or 4 times the questions will stop

As to his "idea".  Why use cotton?  Just mound the sinew in a high crown down the center of the limb, that is what I always did.
Home of heat-treating, Corbeil, On.  Canada

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Offline DC

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Re: Post For Tim Baker ( Sinew)
« Reply #13 on: April 12, 2018, 08:15:43 pm »
Has anyone ever had sinew break in tension? How about without breaking the bow? I'm thinking about a little sinew spaced away from the belly versus a lot of sinew closer to the belly.

Offline willie

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Re: Post For Tim Baker ( Sinew)
« Reply #14 on: April 12, 2018, 09:06:06 pm »
Tim,
Exploring new ideas about energy storage on the tension side seems worthwhile.

Don, you are from yew country, is there something special about yew sapwood?

Seems like it's a necessary part of the thicker than usual bows, possibly a good candidate for a core in the rectangular design?