Author Topic: Sinew cross section question (Read 7007 times)

possum · « **on:** August 14, 2007, 04:24:36 pm »

I have a short sinew backed osage bow in the works. I had it floor tillered somewhat then sinewed the back. Of course I'm guessing it is about 200@3" right now.

I do have to wonder at this point about the belly shape.

Does a short sinew-back bow prefer a rounded or flat belly? My own instinct would be a flat belly but I would defer to some of the ideas coming from more experienced bowyers. Jump in with ideas soon. My tillering fingers' itchin'.

possum

Pat B · « **Reply #1 on:** August 14, 2007, 04:48:10 pm »

In my experience, an osage bow, whether it have a sinew backing or not, prefers a slightly rounded belly. Pat

tom sawyer · « **Reply #2 on:** August 14, 2007, 06:18:52 pm »

I generally try and make the profile of the belly somewhat similar to the back, maybe just slightly less round than the back. I think this keeps the bow limb edges from trying to curl up or down. But it really doesn't matter too much, because with sinew you can really bend an osage bow a long way before it will fail.

mullet · « **Reply #3 on:** August 14, 2007, 11:04:28 pm »

If it's short I would go with a more flat belly.I believe with it being short and the sinew would have a tendency to start chrysaling if it was rounded.

a finnish native · « **Reply #4 on:** August 15, 2007, 01:47:06 pm »

FLAT! a sinew backed bow is drawn further than a self one and thus the belly has to handle more compression. and not only the woods own compression but also the compression of the sinew and dry glue.

Badger · « **Reply #5 on:** August 15, 2007, 04:01:18 pm »

Sinew is about 10times more elastic than wood, I prefer slightly rounded to make the sinew work more. Steve

possum · « **Reply #6 on:** August 15, 2007, 04:54:48 pm »

The bow is 52" ntn. It is also 1 1/2 inches wide, narrow handle section. I have the back crowned pretty good with the sinew. It was pretty flat before hand. It is still about 150@ 6" maybe.

But I did notice it move.

Does anyone have a similar bow that they can give me the low-down on it's performance?

possum

Badger · « **Reply #7 on:** August 16, 2007, 03:00:23 am »

Possum, I wouldnt recomend you pull it past it's intended draw weight even though it is barely moving. I have made several bows such as you describe and they perform pretty well, lots of fun to shoot. Steve

Pappy · « **Reply #8 on:** August 16, 2007, 07:40:40 am »

possum : I don't have one that short but I do have one at 57 n-n.It has 2 lairs of sinew
and is 52@26 it is 1 1/2 to mid limb then tapered to the tips.I did turn up the last 6 inches of the tips.It shoot hard.Never shot it through a cono. but it is pretty fast.I went all the way to the tips with the sinew but some have said it is better to stop short of the tip to save weight,don't
know how much that matters but is is something to think about.Mine has a flat belly.The back
is pretty flat ,it came out of a big tree.I usually do the belly like Tom Sawyer said he dose
to keep the limb thickness the same all the way across.
Pappy

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Marc St Louis · « **Reply #9 on:** August 16, 2007, 09:27:50 am »

I would go with a flat belly and a high crown to the sinew. I would also reduce the width to 1 3/8" or a bit less.

This bow is 53" N to N. It's not Osage but HHB and has 4 courses of sinew, is a bit less than 1 1/2" wide and is flat bellied. I made this bow for flight shooting and it pulls about 70# @ 27". Steve (Badger) has it now.

possum · « **Reply #10 on:** August 16, 2007, 11:34:02 am »

The reason it is 1 1/2 inches it has quite a few knots that I wasn't able to get out. Some are big. Now that I think about it I could've probably removed them since I sinew backed it. Can I take down the sides if the sinew went down over the sides a bit? I really don't know about removing the knots. A couple are fairly good sized. I'll have to see about getting a few picks of them.

possum

possum · « **Reply #11 on:** August 16, 2007, 12:30:28 pm »

here are some pics

belly shot of knots

back shot of knots (little blurry)

profile. little more reflex since I thinned the belly a little. It was quite thick at first.

tips, to keep string on.
The sinew doesn't come down the sides as much I thought.

I could narrow it some. Will I need to wrap the sinew?
thanks for all the help.

possum

Badger · « **Reply #12 on:** August 16, 2007, 04:32:56 pm »

Mark, that bow still has maintained its draw weight very well, going to bring it to the flight shoots again this year, I have had some trouble matching arrows for good flight, I have some real good shaft material now. Steve

Marc St Louis · « **Reply #13 on:** August 17, 2007, 08:57:11 pm »

Steve
That bow should shoot an arrow out there far. I remember I got about 240 fps with 300 grain arrows out of it. That should be good for at least 350 yards

Primitive Archer