Primitive Archer
Main Discussion Area => Bows => Topic started by: aero86 on September 06, 2010, 07:14:02 pm
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it broke. i pulled it to almost 25 and it broke. was shooting for about 40lbs@27. might be too much to ask for red oak, or too much to ask for my tillering skills. i had thined it down, than started tillering it, mostly working on the outer limbs. even reduced the sides of it on the limb ends.
with stiff outter limbs, maybe its hard for me to tell on the tillering where its bending too much or not enough..
this was at 20 inches..
http://i157.photobucket.com/albums/t49/whiteneon98/bow%20stuff/013.jpg (http://i157.photobucket.com/albums/t49/whiteneon98/bow%20stuff/013.jpg)
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got a pic of the break?
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Hmmm, red oak is capable of handling a 40 pound bow... Did the break occur near the fades? Seems from your pic it's doing most of the bending from mid limb to fades, putting a lot of stress at that area. From mid limb to tip looks to be resting easy comparatively.
-Prof
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I am with Tim on this...Get Us a few Pictures of the Bow..and the Break...Red Oak is capable of a 55-60 pound Bow...if designed correctly...
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i know at lengths, they are good for decent poundage. but this one was 48 inches long. 4 inch handle, 1 inch fades. the siyahs are only about 2.5 inches long. the ends of the limbs where the siyahs are glue, are 3.5 inches.
after looking at the break, the belly seems to have failed first, but maybe not. i havent broken enough to be able to tell.
(http://i157.photobucket.com/albums/t49/whiteneon98/bow%20stuff/015.jpg)
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It looks like you didn't radius (i.e round) your edges before tillering. You need to be sure to do that to both the back and belly. I get them nice and smooth and then burnish them. It'll save you a lot of heartache. Also, I think the design was pushing it for red oak. Hickory could probably handle it if everything went nearly perfectly. But, with the added leverage of the siyahs and the stiff handle, you were left with a short working limb doing a great deal of work. But, all in all, I bet it was a great learning experience! :)
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so, rounding the edges will help? i tried to keep as flat as possible to make sure the force was distributed evenly along the back. i guess the belly is a bit different. maybe i dont understand the compression force, as i kinda understand the forces on the back.
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Aero86, I've done better than a couple dozen Red Oak bows, anywhere from twenty five pounds to fifty five pounds. Mostly pyramid, some rigid handle, and some bending in the handle. With a few failures along the way, the majority of them have launched hundreds, and even better than a thousand arrows. Most are still preforming well. Don't discount Red Oak yet, and definitely radius those edges. Don't give up on the red just yet, try again.
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lombard, i have two that have hundreds of shots on them as well. but they are better than 65 inches tall.. this one was 48 inches. i just dont know if my tillering skills are up to something that short with the draw length id like to use. i might have to bite the built and build the next one a couple inches longer.
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Aero
Check your PM's
Ron
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My skills would not be up to that design on any wood for a self bow. Jawge
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so, im thinking i will try it again. the tiller was looking good i thought, even if it is kinda bendy towards the handle. when i made my lines for the belly wood removal, i made it horizontal. next one ill make it thicker at the handle. i was trying to get as much material working as possible.
after removing that wood, maybe i should get it bending and then move towards the handle.. it just seems like after a certain draw length, the outer limbs will quit bending. maybe not, im just thinking out loud, as ive never tillered this kind of bow before
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im thinking maybe the problem was that the grain ran off there and the flex made it split. kens design seems like it would flex a little bit in the handle, which is probably why he used the dowels to hold it from popping off. he also used a backing, which im sure helps. not saying its not possible with red oak but insurance is just that. good luck, if i get mine started soon ill post my results as well.
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Yeah, you must round the edges on any working part of the bow, especially on the back. Any sharp edge will succumb to the strains induced on it and pop.
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there might have been a run off there. i couldnt see one. so, can i just burnish the corners round? say with a screwdriver or something harder than the wood?
maybe the next one i try will have a bendy handle, though i have yet to make a bow with a bendy handle. the reason i dont is the wider handles are uncomfortable for me, and i like the thicker, less wide handles better, if yall know what im trying to say..
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...so, can i just burnish the corners round? say with a screwdriver or something harder than the wood?...
I usually give 'em a good rounding over with a coarse, then fine file, then sand smooth. I think you'll want a significant radius on before you smooth and burnish. I usually try for 1/16"-1/8" at least.
Frode
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alrightie then. ill keep that in mind next time!
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its not really a bendy handle so much as the handle flexes to a certain point. if you read the posts on short bows many of the bowyers mention tillering so that it flexes into the handle just a bit at full draw. this helps to get longer draws out of the shorties. as for burnishing, i use the bottom end of a large combination lock on my bows, works pretty well.
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alrightie. i wish i was good enough to narrow the handle a bit and tiller it that way.. ill figure out something!
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i think the way ken approaches it is probably the easiest, by using a limb thickness thats consistent, then attaching the handle and pinning it with dowels. this is a trick for board bows that flex too much for a glued on handle to normally stay. for me, replication is the easiest way to learn something, and then after i get something successful i just add the changes i want to. as with almost everything involved in making bows, patience and perseverance are key.
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Too short. Go longer. Jawge
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well, i did do almost the same thing, with a thin board. so i tried to go with the design i had, with a thicker board. just had to tiller it.
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i think the design would be hard to do with a stave you would have to tiller due to the leverage the siyahs impart upon the limbs. it almost goes against what we know about making bows because there is really no taper, and very little change in thickness down the limb. your first one looked like it turned out well, with the exception of being a little on the light side. ken used a backing which would add some weight, as well his siyahs were longer which would increase leverage and add weight as well.
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yeah, id like to add longer siyahs, but i was practicing a couple different ways.. but im wondering if longer siyahs help any? i mean, i know what they are for, but i wonder how they affect stress..
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im certainly not the authority on the subject, but im guessing that the longer the siyah the greater the leverage and therefore greater stress. much like reflex or recurves.
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thats what i was thinking too. that book everyone says to get, does anyone know if it goes into siyah length and tillering and such? sounds like i need to read it