Primitive Archer
Main Discussion Area => Bows => Topic started by: make-n-break on March 06, 2015, 01:49:28 pm
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Happy Friday everyone.
Been makin' em and breakin' em for a while now. This forum has been an invaluable resource in my journey. I look up to all the amazingly talented bowyers on Primitive Archer. Another invaluable resource has been the Traditional Bowyers Bible series and Bows and Arrows of the Native Americans. I've got a small handful of long-term shooters under my belt, most of which were given away to family members and friends. One recent development that I've been having trouble with is pyramid bows that break at the fades.
The three that have broken recently let loose after shooting in, finishing, and 500+ shots. One was a rift saw oak board at 55#, and I can see where the grain orientation might have caused that break. The other two were a decrowned hickory stave pulling 90 pounds, and a flat saw hickory board pulling 70 pounds.The lower weight bow had a slightly bendy handle and the heavy ones have glued on handle risers. I leave plenty of thickness near the handle, and have never had one pop off, so I'm sure the riser area isn't bending. I've only used rift saw or flat saw boards and decrowned staves up to this point. I haven't got any seasoned staves ready for a single ring back just yet. I use an eliptical tiller. I try to keep the first 6 inches or so out of the fades bending minimally, majority of stress focused in mid limb, and the last 6 inches near the tips stiff.
I broke enough of them due to bad tillering in the beginning to have a pretty good general idea of the tillering process. I'm not developing crysals or hinges anymore, so as far as I can tell my tillering is satisfactory enough to keep them together. (I don't have any tiller pictures of the bows that have broken as I'm out of town for the weekend)
Here are the 'general' specs for the lighter bows:
64-68"
2 inches wide limbs straight fading to 1/2 or 3/8 tips
4 inch handle, 1-1/2 deep
2 inch fades, with the fade going into the working part of the limb and always past the widest portion
Here are the specs for the heavier bows:
66-68'
2.5 inches wide taper to 1/2 or 3/8
4 to 6 inch handle, 1-1/2 deep
2 inch fades, same principal as above
They're lifting massive splinters that are half the dept of the limb and 6-8 inches long, always right on the top limb's outside points of the fade. All three in the same spot and all three rendering the bow useless.
I've borrowed a photo I found on google that's linked to PP to show the tiller shape I use, so I hope no one minds my borrowing it for illustration purposes. I'm also drawing up a sketch of the breaks which I'll post in a moment. Hopefully once I've got the illustrations up you guys can give me some guesses as to what's happening. I'm clueless.
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If you ask me? id say the fades in this picture are too stiff for a pyramid profile. Or any for that matter.
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Got any pics of the bows in question?
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I do keep the fade area a little stiff cuz I had a few handles pop off in the beginning of my building and got a little gun shy. My tiller usually looks exactly like the pic. I'm just confused why they're letting loose in the fade where it isn't bending.
No photos at the moment bubby , out of town for the weekend.
Here are illustrations of the break and it happened in the same spot on all three.. Top limb.
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If they don't bend evenly they become a fulcrum. That fulcrum is right at the fades. That's my guess as to why they are breaking.
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As a note...you say " minimal bend at the fade...most of the stress at midlimb". Sounds like that may be perception and not reality.
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The whole idea of the pyramid design is to evenly distribute the stress, one reason why they last a long time, could be as simple as fades to stiff and not rounding over enough, without pics it's pretty hard to accurately diagnose the cause
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It's because of the abrupt step in for the handle coupled with the short fades. Basically the same reason we caution against cutting sight windows and a shelf in a self bow.
You need to make your fades longer and more gradual.
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Two inch long fades should be fine, 2-1/2" wide seems a bit wide though
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Sounds to me that with that weight, the bend is running up into the fade until it runs out of limb.
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The outer third don't seem to be doing much but going for a ride :)
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Even stiff handled bows bend in the handle. Albeit slightly but they do bend. Looks like you need to make your fades longer and round them significantly more.
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Ok. All makes sense. Thanks for the info fellas. The fades are 2" long but they do seem to make a rather abrupt change from the 1 to 1-1/4 handle width to 2.5" limbs. I can see the limbs in my mind and I know already from the info you've all provided that I haven't been rounding them enough or tapering them gradually enough. Any general recommendations for Max width of a 70, 80, 90 pound pyramid (I enjoy rather heavy bows)? Is 2.5 too wide for a heavy hickory? I've grown to like using hickory for its availability and durability (except in my case on the last few) so that's what I'm usually hunting for.
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Sounds to me that with that weight, the bend is running up into the fade until it runs out of limb.
Thats what I am thinking, @68" long 70# will flex over 3/4 thick of wood near the handle, I think you are just running out of room for it to bend. Once it starts to narrow there just isn't enough wood to hold it.
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I somehow get the feeling that the fade is too short, but the stiff inner limb section is too long. Fades should be long enough that the limb isn't starting to bend until well out from where the handle starts to narrow. But, in a pyramid bow, you really want the limb bending as soon as the fade ends, to accomplish your cirular tiller.
My best thinking on this tells me that, in trying to protect the handle, you have actually stiffened the first few inches of the limb so much that the handle, right where it narrows, is experiencing more strain than it can take. Your stiff inner limb is forcing the handle to bend slightly. And rememeber, it could be trying to bend slightly to the side...
Try hard for that circular tiller, make the fade end 1.5" past the handle-shoulders, and see what happens.
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if the bows are breaking there, then there is too much bend there or the wood is not thick enough.. you will need to rethink the design for the heavier bows,,
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Thanks for all the advice. I'll be applying you guys' recommendations to the next one.
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I somehow get the feeling that the fade is too short, but the stiff inner limb section is too long. Fades should be long enough that the limb isn't starting to bend until well out from where the handle starts to narrow. But, in a pyramid bow, you really want the limb bending as soon as the fade ends, to accomplish your cirular tiller.
My best thinking on this tells me that, in trying to protect the handle, you have actually stiffened the first few inches of the limb so much that the handle, right where it narrows, is experiencing more strain than it can take. Your stiff inner limb is forcing the handle to bend slightly. And rememeber, it could be trying to bend slightly to the side...
Try hard for that circular tiller, make the fade end 1.5" past the handle-shoulders, and see what happens.
+1
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The cut in from the limb into the narrow part of the handle is far to steep - that's just asking for trouble...