Primitive Archer
Main Discussion Area => Bows => Topic started by: jeffp51 on December 03, 2014, 02:04:25 am
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We were so close on this. I had it tillered out to 15lbs at 15 inches. Mountain maple, steamed recurved tips, heat treated belly--most of this for practice--and a little boy more excited than there are words. He helped me scrape it and was talking about hinges and flat spots like he had been doing it his whole life. He had plans for snake skin fabric (cotton diamond back? nylon python?) and wanted to dye it blue. It was going to be a beautiful little snakey bow.
When I went to make the string, it was too short and the brace too high. When I went to remove the string to try and fix it, the bow exploded. I don't know if the knot had anything to do with it, but I am glad it happened on me and not on my son. I would appreciate any opinions on cause of death. could the heat treating have made it brittle? We had tears (he is eight) for a whole night.
Next question: I have quickly turned a hickory board into a new stave, but the back isn't pristine. I am debating what to back it with. I know the wallboard tape (glass) will make it safe, but it is ugly. I am not going to use sinew on this. What other options will make a safe bow for a child? Brown grocery paper? old silk ties? Have to make this work for him.
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and here are the after pictures. In the tillering picture above the broken side is on the right. The picture is not from the final tiller, which I think was a little better than what this shows.
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Total bummer man. Super cute pic of the little man on the shaving house, gotta love that.
Keep at it :)
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Could be a natural weak spot in the wood, too dry, or too stressed. Its a good lesson, though, and the reason I don't make selfbows for anyone not old enough to drive. A laminated bow is a different matter and the only "backing" I would consider for a kid's bow.
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Jeff, Looks like a grain violation by the way the break is running from the outside inward...Can't tell without a closer pic. I know the little fella is sad so try again...
Don
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Jeff, Keep at it. I have been lucky and not broken one yet. I have made 3 competed board bows so far, 2 for kids. My first had the handle pop (Thanks Tyke), but other than that they have held fast. What does the grain look like on the hickory?
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Every bow I made to give a kid was backed with bamboo to make them bomb proof, probably given away a dozen or more, none have failed.
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Unless you chase a ring on a board it's gonna have violated rings if its not quartersawn as long as the grain is straight on the edges and runs good front and back you should be ok, can ya post a pic of the board
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Will you post a close up pic of the break on the back?
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On a 15# bow the limbs are going to be very thin. Is it possible the heat treating penetrated to deep?
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Looks like a grain runout. You have to follow that radial grain when laying out the profile.
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I will try to post some closer pictures of both the old bow and the new one. I tried really hard to follow the longitudinal grain and give the knots extra meat around them. The grain in the break itself is not straight at all, but there doesn't seem to be any sign of that on either the back or the belly. With this maple, grain is hard to read at all. there was a back violation, but on the other limb.
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It looks to me like (in the tiller pic) that the right limb is a little thicker at the knot and the area toward the fade (where it broke) is a little thinner (if I'm seeing the pic right)....might be just thickness taper....That would make it stiffer on the nock side of the broken area. The same thing causes frets. I have found in my own learning (breaking) process that leaving knots thicker and stiffer doesn't work for me. They have to bend a tiny bit with the rest of the limb or you'll have a high stress area on the backside and a high compression area on the belly side. Kind of like bending a stick over the edge of a counter top. JMHO. I've found that if I stick to thickness taper religiously (even through the knot) I have much better success. That might mean scooping out the belly side of the knot if the knot forms a hump on the backside. That would allow the tension and compression forces on the knot to flow around the knot onto the extra wood left on the sides of the knot and not the crown of the knot (if that makes any sense) Think Simson's hollow limb designs....
The little guy is disappointed now (and might be a few more times) but oh the lessons learned and the sweeter and more exciting for him when he finally succeeds. The stuff that builds character........
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i would save the heat treating and reflex for a different project,, on the kids bow a straight stave will work great,, and reduces the chance of over heating or damaging the wood when bending,,, a bow that is reflexed it under alot of pressure when first being strung,, and straight bow is not,, the straight bow is just a little more forgiving to make and not as likely to break if there is some unseen flaw,, rawhide backing would be my first choice if the grain on the back is in question,, but better yet,, a nice straight grain board would give you better odds of success,, :)
also I have a feeling when you were unstringing the bow may have accidentally put uneven pressure on that part of the bow,,???
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Brad, I probably did put uneven pressure on it, and that was probably the final straw. The stave was naturally reflexed, I didn't add that. Rand, you are right, the knots were thicker on the back and that may have contributed too.
the hickory is pretty straight, with only a couple of shallow runoffs. TBB suggests that you can get away with that with hickory. I just want to be sure. Does rawhide add a lot of draw weight? this is going to be a thin bow as it is, and I am looking for something that adds strength without adding too much pull.--and and there is no reflex in this one, although the little guy still wanted recurved tips like dad's
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the rawhide will not add weight,, just make the back a little more durable,,and it is a good skill to have,, and I think makes the bow less likely to break if there is an inperfection on the back,, it can also be very beautiful when sanded and finished,,
I highly recommend it,, the thinner the better for your project,,,deer hide or thin goat etc,, the recurves should be fine,, :)