Author Topic: Advice needed: siyah belly lam, tension/compression branch, sinew heat treat  (Read 2266 times)

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Offline gfugal

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So I'm working on a Juniper bow for the bow trade. I added Siyahs, and am planning on sinewing the back, but I'm running into a couple of problems that I would like advice on.

Problem 1) So I spliced the siyahs onto the bow already, but am debating whether I should add a belly laminate near the siyah to add extra support. I forgot to take a picture of it this morning but it looks similar to this bow.

I'm conflicted. Part of me says the extra support would be good, but part of me thinks that it would add too much mass.

Problem 2) the bow is a spliced billet. the two billets came from opposite sides of a tree branch. Turns out that depending on the orientation of the wood determines how easy it is to bend, like there is a compression and tension side. For example, the bottom limb is thicker than the top limb. Originally I thought this was because the top limb was denser and thus stiffer. But I was going to try and reverse brace the bow and found the bottom limb was much stiffer when you tried to bend it the opposite direction, about as more stiff as the top limb is stiffer the bottom limb in the original draw direction. Now I have a dilemma. If I leave it tillered as is, then the sinew will reflex the top side more than the bottom because of this anomaly. If I thin down the bottom limb so it bends as much as the top in reverse brace then it will be much weaker when I get back to tillering it, potentially target weight ruining weaker. What would you do? have unbalanced reflex or risk having a weak bow?

Problem 3) I want to sinew this bow, but I also want to heat treat it. I figure heat treating would be bad after sinew, so logically it must be done before the sinew process. But I heard dry heat makes wood brittle and less able to handle tension. If I heat treat it would a reflex induced by reverse brace and sinew drying of about 3" potentially crack the belly, due to compromised tension from heat treating it? Should I risk it or forgo heat treatment.
« Last Edit: October 07, 2017, 12:25:15 pm by gfugal »
Greg,
No risk, no gain. Expand the mold and try new things.

mikekeswick

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No belly lam is needed if your splice is good.
Forget heat treating juniper. It is amazing in compression with a sinew back.
Tiller it for even strain showed by what set the limbs take. Uneven limbs are no big deal unless you want that 'picture perfect' full draw.

Offline willie

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Quote
the two billets came from opposite sides of a tree branch.
top and bottom of a horizontal branch?

if so, do you recall if the top limb came from the top of the branch?

Offline gfugal

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Quote
the two billets came from opposite sides of a tree branch.
top and bottom of a horizontal branch?

if so, do you recall if the top limb came from the top of the branch?
It was a horizontal branch. I can't say for sure which came from the top and the bottom, but I'm pretty convinced the top limb of the bow was the top of the branch, and the bottom limb was the bottom of the branch.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline gfugal

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No belly lam is needed if your splice is good.
Forget heat treating juniper. It is amazing in compression with a sinew back.
Tiller it for even strain showed by what set the limbs take. Uneven limbs are no big deal unless you want that 'picture perfect' full draw.
Thanks! Exactly the advice I was looking for!
Greg,
No risk, no gain. Expand the mold and try new things.

Offline willie

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the top of the branch may have a lot higher ringcount, and the bottom of the branch may have wood  with a higher lingin content. If so, the bottom of the branch may need more backing to be safe. this presumes that the oldest ring just under the bark is the back on both the top and the bottom. Almost like making a bow with two different kinds of wood.
The bottom, if it has compressionwood, may recover from more strain (without taking permanent set) than the top, and may be more sensitive to moisture changes as it liner expansion is quite a bit different from normalwood.

Offline gfugal

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Yeah it's definitely not a situation I plan on repeating cause the two limbs are acting like they are from two separate trees.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline gfugal

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So to get the bottom limb to reflex like I wanted I used my tillering stick to put most of the tension on that side of the bow.



Here's a picture of the Siyhas. It has a 3-inch splice, and the lever is 5 inches in length. It's longer so I could put in a reverse nock for reverse bracing. I plan on cutting it down to 3-4 inches after the sinew dries.

« Last Edit: October 10, 2017, 03:13:06 pm by gfugal »
Greg,
No risk, no gain. Expand the mold and try new things.

Offline turmoiler

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Hi, I can't see the pictures, just a forbidden sign  :'(

Offline gfugal

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You should be able to now. I'm still trying to figure out how to post pictures from google photo that gives anyone permission to view.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline turmoiler

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Thanx!

Offline BowEd

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An easier way to get the same thing is to just use the string alone.Then put a bike innertube[correct name is a barshak] on the weaker limb 1/3 of the way down from the tip or your right limb to pull the stronger one or left limb into more reflex.Just like balancing horn bows after first tiller.Although I think you might run into some extra tillering doing that in the end.If you've already tiller balance it to brace.Good luck.
« Last Edit: October 11, 2017, 09:37:49 am by BowEd »
BowEd
You got to stand for something or you'll fall for anything.
Ed