Primitive Archer
Main Discussion Area => Bows => Topic started by: upstatenybowyer on February 03, 2017, 05:04:15 pm
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Bummer!! I had this one sooooo close. It was pulling 58# at 27" and I was loving the muscular look on the back. Unfortunately, I believe those irregular wavy grooves are what killed it. They weren't as extreme as on some I've seen, so I thought I might be okay. I used PatM's spoon method for removing the cambium, which worked great, so I'm sure it wasn't a knick that caused the splintering. Oh well, such is life in a day of a bow maker. :-\
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That's too bad but when you think of those ridges in the context of being multiple really high crowns it's a wonder any bow with those survives.
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Don't worry; you've turned out enough bows lately to make up for this single loss.
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Oh man that sucks I always keep a couple of ruffed out bows hanging on the wall so when that happens I can just jump to the next one. Eases the pain !
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Pat, you're right sir. I think they were holding up until I heat treated, then they just couldn't take it any more. Someone who shall not be named made one from AH, so I thought perhaps I could.
Dictionary, this is the only loss I've posted ;) lol
SB, I'm on to the next one already!
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Sorry for your loss. Looked like a great bow but can you exlain to me what younmean by irregular grooves?
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Sorry for your loss. Looked like a great bow but can you exlain to me what younmean by irregular grooves?
American hornbeam's most characteristic feature is it's "muscle-like" appearance on the outside of the tree. It's also called Musclewood. If you do an image search for it you'll see what I mean. Because the outside of the tree was used as the bow's back, where all the tension is, the tension is not distributed evenly, it's concentrated on the highest part of the grooves, and that's where it split. :)
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If you think the ridges were the culprit, you can always sand the back smooth and add a rawhide or fabric backing.
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Whatever the specific failure, you just asked too much of the wood. I guess all my bows are "overbuilt" in that they are thinner than most people make them and consequently, lower weight. I always aim for no more than 50# with a thickness of around 9/16".
Lots of you get more weight and more performance out of your bows, but breaking one now and then is the result.
Here's a small hornbeam I made for a young woman friend of my daughter.
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Hey Upstate
I have had great luck with Ironwood if you do a sinew backing. I made a 60 inch 50 pound bow with some pretty hefty recurve on the tips and it shot great but I think it would have done the same if it wasn't sinew backed.
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Jim, that looks more like HHB. Is it?
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Greenriver, sounds like a sweet bow. Probably should have backed mine.
Jim, that's a beautiful little number. I see the logic in overbuilding them for sure.
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The only american hornbeam bow I have seen in person was made by a friend of mine. On it he draw knifed the back flat, ignoring all violations. He and his son have been shooting it for several years. Don't think I could ever get myself to try that though.
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Jim, that looks more like HHB. Is it?
Yes Pat, I overlooked the American moniker in the OP. Sorry all. Haven't tried American hornbeam for the very reasons you are all talking about. I have a couple of them on my property and think about it now and then, but have not cut one. Well, now that I think about it, I have a stave I cut while clearing an area, but it's only about 2" in diameter. I only saved it because it's a rare variety on my land.
Jim
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Hi there, sorry for the break. Here is my take on it:
1) I think you ended up with too short of an area that was actually bending with the added recurves
2) I believe the ridges did not contribute to it. To the contrary, I actually believe [no scientific observation] that the multiple ridges on summer harvested HHB if not violated might actually increase the surface area of the back. I believe it only becomes an issue if you have a heavily crowned stave. My HHB bow I made (Sudbury style) has extreme ridging and has so far not experienced any failures. It has however other than the ridges a flat back.
3) Backing will in my opinion transfer the problem to the bow's belly where you would increase the likelihood of chrysals if not careful. I had issues with that in the past, especially on shorter HHB bows (which this would be when counting the stiff recurves)
Cheers,
Phil
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Hi there, sorry for the break. Here is my take on it:
1) I think you ended up with too short of an area that was actually bending with the added recurves
2) I believe the ridges did not contribute to it. To the contrary, I actually believe [no scientific observation] that the multiple ridges on summer harvested HHB if not violated might actually increase the surface area of the back. I believe it only becomes an issue if you have a heavily crowned stave. My HHB bow I made (Sudbury style) has extreme ridging and has so far not experienced any failures. It has however other than the ridges a flat back.
3) Backing will in my opinion transfer the problem to the bow's belly where you would increase the likelihood of chrysals if not careful. I had issues with that in the past, especially on shorter HHB bows (which this would be when counting the stiff recurves)
Cheers,
Phil
Interesting thoughts for sure. See the Short and Simple HHB thread ;)
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Hi there, sorry for the break. Here is my take on it:
1) I think you ended up with too short of an area that was actually bending with the added recurves
2) I believe the ridges did not contribute to it. To the contrary, I actually believe [no scientific observation] that the multiple ridges on summer harvested HHB if not violated might actually increase the surface area of the back....
Phil
Don't want to hit too hard here, but "[no scientific observation]" is the factual part of that idea. The ridges take the strain first and the lower parts don't contribute until the ridges have stretched, or broken. This is pretty straightforward geometry and mechanics. A lamination at the height of the ridge would take all the tension strain. About 90 % of the tension and compression forces are handled by material within 10% of the surface. That's where the ridges are.
Jim Davis
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to asharrow: maybe I should expand a little on my thoughts. The ridges will add to stiffness of the bow (just fold a piece of paper harmonica style to confirm). I do recognize that the peak of the ridge takes the strain first. But the more ridges you have the more this strain is divided up between those ridges. Hence my observation that it is more the higher crown of the stave than the ridges that are the culprit on that bow braking. I think the ridges themselves contribute little to nothing to the bow having failed. I have observed this myself on my own HHB bow that has been harvested from summer cut wood and is heavily ridged but with a flat crown. It is by far my best shooting bow to date (Sudbury style) with 75# draw weight at 26" and I have to date after hundreds of arrows no evidence of any cracking (not even a tick).
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Ridges are just gang of high crowns. I'm not making this up. I did study physics and mechanics.
If there were more stretch to wood, the ridges could stretch and the lower areas would take up some of the strain as they began to be stretched. BUT, wood only stretches about 1% before it breaks. That's not enough to start the lower areas adding to the effort.
Your image of folded paper is correct in the idea of making a form more rigid, but that only means it will bend less before it fails.
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to asharrow: maybe I should expand a little on my thoughts. The ridges will add to stiffness of the bow (just fold a piece of paper harmonica style to confirm). I do recognize that the peak of the ridge takes the strain first. But the more ridges you have the more this strain is divided up between those ridges. Hence my observation that it is more the higher crown of the stave than the ridges that are the culprit on that bow braking. I think the ridges themselves contribute little to nothing to the bow having failed. I have observed this myself on my own HHB bow that has been harvested from summer cut wood and is heavily ridged but with a flat crown. It is by far my best shooting bow to date (Sudbury style) with 75# draw weight at 26" and I have to date after hundreds of arrows no evidence of any cracking (not even a tick).
Note that the bow in question is American Hornbeam, not HHB. HHB tends to have multiple more evenly distributed ridges. American Hornbeam has fewer and more defined ridges.
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to PatM: thanks for the clarification, my mistake :) I should read the posts more carefully!
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to asharrow: maybe I should expand a little on my thoughts. The ridges will add to stiffness of the bow (just fold a piece of paper harmonica style to confirm). I do recognize that the peak of the ridge takes the strain first. But the more ridges you have the more this strain is divided up between those ridges. Hence my observation that it is more the higher crown of the stave than the ridges that are the culprit on that bow braking. I think the ridges themselves contribute little to nothing to the bow having failed. I have observed this myself on my own HHB bow that has been harvested from summer cut wood and is heavily ridged but with a flat crown. It is by far my best shooting bow to date (Sudbury style) with 75# draw weight at 26" and I have to date after hundreds of arrows no evidence of any cracking (not even a tick).
Note that the bow in question is American Hornbeam, not HHB. HHB tends to have multiple more evenly distributed ridges. American Hornbeam has fewer and more defined ridges.
Thanks Pat. I was really trying to get this point across!
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to asharrow: thanks for your reply. I found your note of the percentage of elongation prior to failure interesting. I was wondering whether you have the percentage of elongation for different wood species. I have found these logarithmic charts on ductility, but it lists only a small number of wood species.
http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-ductility/basic.html
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Ouch!! At least it's bringing up some good discussion. I wonder sometimes if the stave just has to many problems to solve and the one we over look is the one that spells CRACK!!! Do you think American hornbeam should be avoided unless backed?
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To bad that one didn't survive, especially since you were so close to full draw. Muscle wood makes an interesting looking bow with the loads of character on the back but it is a challenge to get to bend without breaking. I've attempted 3 in the past, one broke at floor tiller, one broke on the tiller tree at around 27" draw and one survived and made a bow. The one that made 27" then broke was riddled with tiny worm holes. I knew it was very likely doomed from the get go but was curious to see if it could be pulled off. The one that broke at floor tiller I had nicked the back on one of the ridges while removing the bark. The one that survived was given to a brother since the wood came off his property and it still shoots although I don't think he takes it down to shoot often. This one did have the flatter back with less ridges than the other two.I have to admit it scared the crap out of me when I first gave it to him and watched him crank it back to 29" as he shot arrows in the target.
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BB, glad to hear that one of them survived. Gives me some hope, although it'll probably be a while before I try AH again. If I do, it'll probably be a less stressed design.
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The problem with ALL bows we make is that, the whole time, it's looking for a weakness. And, it only HAS to find ONE. ;D
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Sounds like having a little sinew around when making American Hornbeam bows could be useful.Orrr.... some skins.I horde all kinds of skins here.flat head catfish/grass carp/sturgeon/deer.All these are all a little thicker than your average snake skin for holding splinters down good.
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Phillip, Asharrow would be a better source for specific numbers than I am, but I can tell you from experience (as well as the chart you posted, which was cool) that the differences in elongation potential between different species aren't huge. The differences in tensile strength, which to us= backs that don't break, is huge.
If you notice, the chart is for wood AND wood products, and while only a few are named, many others MUST be included in the main bubble. NO wood tested is outside bubble. See how the bubble for the wood"s numbers basically straddles 1% ? And see how on the far right edge the "stretchiest" wood product is paper (which is basically bonded felt made of wood-fiber, with fibers running every direction rather than parallel)?
Next note that BALSA, which is a ridiculous amount WEAKER than oak, stretches just barely less. Likewise, notice that oak stretched in it's STRONGEST dimension (along the fibers) stretches only about twice as far (+/- 2%) as when stretched in it's weakest dimension, across the grain (+/- 0.8-0.9%). So, even strong wood, in it's strongest tensile application, isn't very stretchy.
Though they weren't named, they must have tested other woods, but note how close oak is to the top of the bubble. This means that even woods much more dense and "stronger" (in other practical senses), than oak aren't a lot stronger than oak in perfectly longitudinal tension (break resistance). AND note that since paper, an engineered product, dominates the right side of that bubble, we can guess that those more dense strong woods don't ELONGATE much more than oak, either. Oak stretches only a smidgin more than pine and a tad more than balsa. I'm guessing ipe stretches only a tiny bit more than oak, then.
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Hi Springbuck: interesting observations for sure! From what I have read, tensile strength of wood is primarily related to the density of the wood and the MFA (microfibril angle) of the S2 layer in the wood cell. I have in some other discussions posted some articles on the subject. But would gladly do it again. I am by no means an expert but like to read up on things once I take an interest in something. This is of course with the risk of sometimes misinterpreting things as well...lol
At the end though curiosity drives knowledge :)
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Lots of good points above and good summaries of what we are up against.
Posting that chart because it is good. Too bad for us that few tests of tensile strength have been recorded or published.
http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-ductility/woods.jpg (http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-ductility/woods.jpg)
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The wood database lists tensile strength for numerous species, particularly ones useful to us.
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Where are you finding that Pat? I looked at Yew and Osage, no tensile strength. Are they calling it something else?
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I also just looked at Osage and Oak on the Wood data base--no tensile numbers.
Once again, I want to point out that the Wood Data Base, while very useful and easy to use, is a secondary source for all the data. He explains that it all came from other places such as the Forest Products Laboratory.
It is possible to extrapolate tensile strength from the other numbers. I don't re call which sets of figures, but tensile strength fall about midway between two of the sets. I have been to lazy to ever work that out.
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Hi all,
I found this paper. Have not had a chance to digest it yet, but tons of information in here! It will take me a while to make sense of it all :)
http://www.conradlumberco.com/pdfs/ch4-Mechanical-Properties-of-Wood.pdf
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I was mistaken on which website had some of the info. Hunt around via google though. You can track a lot of them down. It will mostly confirm what you already know.
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This:
http://www.conradlumberco.com/pdfs/ch4-Mechanical-Properties-of-Wood.pdf
has some tension numbers, but they are for perpendicular too the grain...
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This page has some hints with Hickory and Elm numbers. http ://basiccarpentrytechniques.com/The%20Mechanical%20Properties%20of%20Wood/The%20Mechanical%20Properties%20of%20Wood%201.htm