Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on April 11, 2018, 01:35:33 pm
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I just had something happen(again) that I have only noticed on backed bows. I was happily tillering away, everything going fine, put the bow on the tree and gave a couple of pulls and one section of the bow just gave a little. I saw it jump a bit as it went. It was fine and then it just hinged. Is this something I should be watching for with backed bows or is this just a coincidence? I had two inches to go. I might save it but it's basically gone I think. This is on my Maple backed Locust. It is a couple thousands thinner where it hinged. There is 1/3 backing and 2/3 belly.
PS No visible chrysals---yet.
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Could it be a glue problem DC?
Bjrogg
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That was one of my first thoughts but the join looks good. Any ideas what to look for? By the time I caught up to the hinge the bow was 30# and with the glue there I can't even use it to cook brats :D :D
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visible in the tiller, but no apparent damage otherwise? Has it taken set at the hinge?
could be the "hidden damage" that precedes the obvious, if so, good catch
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I'd say its an under-exercised issue. Just a guess. A few thousandths thickness variation is nothing. A human hair is .003".
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I'd say its an under-exercised issue. Just a guess. A few thousandths thickness variation is nothing. A human hair is .003".
+1 How many times do you exercise/draw the bow after you remove wood?
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Willie--Yes it took a lot of set in the hinge and the other limb is the same just not as bad. I think I was scraping too much in one spot. It's an RD an the hinge(s) are about a foot out from the handle. Seems to me the last time this happened it was the same. I'll avoid that spot next time.
PD-- Good thought, I've kind of gotten away from the 30 pulls thing. Time to back up a bit.
Has anyone ever glued a veneer on the belly. I was thinking that I could correct the tiller and then glue a veneer on the belly and live with what happens. There wouldn't be enough to tiller so that would be it. Ahh, it's just a stick, I'll throw it away and start again.
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I have glued veneers on belly's with good success.
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DC, I have had that happen on R/D bow more times than I like to admit. That is one of the reasons I started going to full draw weight after each wood removal. Did it happen in an area where you started the reflex?
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I had an osage recurve fret badly(uncommon for osage, not seasoned enough) so I ground down the belly and added an Argentine osage lam to the belly. Re-tillered and all was good.
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I agree about excersising the limbs. I find that with backed bows (bamboo especially) it is resistant to change so excersising is more so important to not have hinges pop up.
I do think thousands of an inch are important. I have read, calculated, and tested that .003-.005” of thickness on a dense belly is equal to about 1 lb difference in draw weight. So if you had one limb a pound or 2 stronger than the other one I think you would notice the imbalance in your hand or have your pull hook sway one way or the other. When you make that adjustment and scrape a few times to balance the limb you are making thousandths of an inch adjustments.
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Here's some pics. It looks worse in person. Doesn't look like I took any wood off the outers. Not really proud of this. It started out so nice. The reflex went from 1 3/4 after glueup to 2 1/4" after tillering out to about 18" and then all of a sudden it dropped to an inch.
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"Has anyone ever glued a veneer on the belly. "
I never have just glued on a bit as a patch, but I have ground down and added a thin belly lam to save a bow. I did almost the whole limb, though.
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How is the whole thing constructed? Is it all one piece plus a backing, or is it a backing, belly stock, a handle block, power lam, etc....
The similar experiences I had were the result of something "giving" near the fades when I had too much going on.
Like I had a power lam, bellys fishtailed at the handle, then I had thin slats making up the handle and dips, plus my backing was 2" too short, so I cut it and let it gap near the handle. So the backing at the middle stubbed out on the back, then I ground it flat, covered it with an overlay. The fades or something buckled or slipped.
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It looks complex but nothing extends beyond the fades but the belly and backing. The hinge is a foot out the limb.
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Yup, it's not that, then, I don't think.......
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DC.....I did'nt see this yet,but from doing bamboo backed wood board pecan bows D/R I'd say people are right.It's a not excersized enough issue.That glue line is tougher than you think too.Especially with a lot of reflex to excersize they are very touchy.
It's up to you to add belly lam wood to increase poundage.It'll work,but you might be better off starting over.It's up to you though.
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Sorry to see that, it looks really nice unstrung! If I where you I would save the energy and sart over.
But if you want to fiddle with it some more... This is what I tried ones and worked out really well:
I had a bamboo backed ipe with about the same fades as your bow. Cut a thin bamboo backing in half and heat bend one end of each piece to roughly match the curve of the handle fades. Glued both pieces of bamboo to the belly going up the fades. Make sure the boo is thin because it will add a lot of draw weight! (Mine added about 30 lbs but I glued in some extra reflex for fun;-) )
(https://farm1.staticflickr.com/792/40046283965_1ff015284c_c.jpg)
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That's an interesting fix leonwood. I'm guessing you don't have much room to tiller such a bow after the bamboo is glued on.
If you didn't tell us, I would have thought it was designed that way. How did it perform?
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I made a bamboo back osage that came in under weight and added bamboo on the belly. I then came in way over and decided why not tiller just like I would a wood belly bow. I had seen where a lot of folks said it wouldn't work but wondered how many had actually tried it. I proceeded to begin tillering as if the nodes we're not even there and made what was probably as good shooting a bow as I've ever made. Reluctantly put a shelf on for a left handed shooter and gave the bow to the intended recipient. Bow is still shooting fine.
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Looks really cool, Leon.