Primitive Archer
Main Discussion Area => Bows => Topic started by: kbear on August 08, 2019, 10:10:40 pm
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So, this happened......
(https://live.staticflickr.com/65535/48492675137_e8e5f07959_k.jpg) (https://flic.kr/p/2gT8CRP)2019-08-09_12-39-44 (https://flic.kr/p/2gT8CRP) by korey Aitkenhead (https://www.flickr.com/photos/155311393@N06/), on Flickr
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(https://live.staticflickr.com/65535/48492371571_597cf77f22_k.jpg) (https://flic.kr/p/2gT75BV)Hickory explosion...... Tip (https://flic.kr/p/2gT75BV) by korey Aitkenhead (https://www.flickr.com/photos/155311393@N06/), on Flickr
Hickory, 66" ttt, 40# at 22 inches on the short string, with a fairly even tiller about to go to brace when Bang!
The stave had some pretty bad violation due to having the bark removed, and planed flat. It also, had some bug damage just out of the fade on the bottom limb (limbs 100% sapwood). This was a suspect area. I filled the bug track with CA, but the tunnel went under the surface and can be seen coming out on the side of the handle.
I knew this would be tricky. The plan was to finish the tillering, heat treat, then back with rawhide. Had already heat treated it at floor tiller, with about 3" reflex, anticipating some set (several days ago). I had already sized the back with gelatin glue whilst waiting for the moisture to stabilize. Should probably have backed it before the short string! It probably would have exploded anyway.........
This is the first time I have used Hickory. It is quite dry in the shop at the moment, about 26% RH, so I knew it would be "snappy".
I half expected a tension failure resulting from the bug damage, but had my fingers crossed.
I didn't expect it to explode like this though! Wow. Multiple failures on both limbs! How does that happen?
Do you think my gelatin glue became brittle and caused the failures?
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I had a red oak bow one time blow into 9 pieces, handle was the largest piece.
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Honestly it's no surprise with what you told us. You don't plane the back..just leave it as is once the bark is off ridges and all. The bug damage didn't help either.
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Bug damage on the back = firewood :)
A planed back is disaster if you don't follow the grain.
It almost looks like a laminar separation, probably the break following the bug damage though.
Only choose next to perfect wood for bow making. Just thinking about what you are asking it to do!
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Never seen hickory behave like that before. Yes it had some bug damage, but you might get a break on that limb, and the other would still be okay, as it was only drawn 22" but broke comprehensively in tension.
I can only guess, but that the stave might of had dry rot through it. There appears to be some grey areas on the back that could be a fungal infection( or they could be pencil marks).
Perhaps it had an incredibly low moisture content. I had a board of tropical wood, made a really nice bow from it. I cut out another stave from the same board, got it braced, part tillered. I put it into a drying box, where I kept some part green staves 38-40 degrees Celsius. It was about 2 weeks before I had a chance to work on it again. I tried to string it and the lower limb just snapped. I put it down to the drying box, drying it out too much.
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Bug damage on the back = firewood :)
A planed back is disaster if you don't follow the grain.
It almost looks like a laminar separation, probably the break following the bug damage though.
Only choose next to perfect wood for bow making. Just thinking about what you are asking it to do!
Too true! In my defense, I did not plane the back, that is how the stave came. I've never used hickory before, I thought it nearly unbreakable in tension, apparently. I've made numerous board bows that held up better actually........
I am not surprised it failed at the bug damaged section...... half expected it, but the rest? Boy, spectacular!
Why the laminar separations? Just a dud stave?
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Never seen hickory behave like that before. Yes it had some bug damage, but you might get a break on that limb, and the other would still be okay, as it was only drawn 22" but broke comprehensively in tension.
I can only guess, but that the stave might of had dry rot through it. There appears to be some grey areas on the back that could be a fungal infection( or they could be pencil marks).
Perhaps it had an incredibly low moisture content. I had a board of tropical wood, made a really nice bow from it. I cut out another stave from the same board, got it braced, part tillered. I put it into a drying box, where I kept some part green staves 38-40 degrees Celsius. It was about 2 weeks before I had a chance to work on it again. I tried to string it and the lower limb just snapped. I put it down to the drying box, drying it out too much.
Dry rot huh? You might be onto something there Hamish. The stave was cut in March this year, and I only removed the poly and roughed out the stave about 3 weeks ago. I heat treated it a few days ago. I thought I'd left it long enough.......
I was expecting a lot more from it, despite the bug damage.......
I have another one of those staves. It has been violated the same as the first, and looks much the same. Maybe I should go down closer to the heartwood, and just build up the handle?
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Sound hickory doesn't break straight across the back, at least I've never seen it in 30 years of bow building.
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Bug damage is often more serious than you can see on the surface.
My exploding hickory from bug damage;
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Sometimes when a bow explodes, within all of the ultimate damage that results, there is a cause, or two or three, the bug damage for instance... and/or how the design may have put more strain there in that area of obvious weakness... and the ring violations... and then everything else is cascading collateral damage due to the violence and extreme strains that ensued elsewhere in that 'split' second of failure. Sometimes 99% of the damage is collateral and I don't think we should waste too much time trying to analyze that part of it. Sometimes it's impossible to tell where the failure started, or what the cause actually was, but in this case I think you already covered it pretty good.
29% is pretty dry, but I've stored bows in that r.h. for months at a time without a problem. That's where my house stays in the winter with the furnace running.
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You could tie a hickory bow in a knot at 29% moisture.
I agree with Eric about the hidden bug damage. Powder post beetles enter the wood by a small(1/16")hole but destroys the internal integrity of the wood. And, violated back rings don't break across the grain but usually follows the violations.
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Hickory is well capable of being planed flat if the stave is a typical straight grained one. That's the same principle as any decent board or backing.
It seems likely that the wood has fungal breakdown that isn't always readily apparent. The heat treating then exacerbated that weakness.
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How was the stave prepped and handled from the stump?
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How was the stave prepped and handled from the stump?
I would bet it had just the right amount of time in a too warm, too damp, left in log form for too long scenario before it was split up.
Drying wood is not too different from drying meat. You gotta hustle if you want it to work.
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Yep,,.bow elfs,,,
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The job of fungi is to break down natural materials back into the environment and it is very good at it. Whitewoods will be infected pretty rapidly and as long as there is any moisture in the wood the fungi will thrive.
I cut backing strips from a log that had been in a garage for 2 years. The first one I used failed because of fungi. The moisture in the log didn't have enough time to dissipate before the fungi worked itself throughout the log.
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someone seny me a nice piece of pecan,, it was wrapped in plastic,, I did not take it out, the bows I made exploded,,,my bad,,on not taking it out of the plastic,,
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How was the stave prepped and handled from the stump?
Not really sure. The stave was an ebay purchase. It was cut 03/19, so fairly recently. I guess now I can probably speculate it may have been already dead. I have got a dozen or so staves from this seller. This is the first to let me down. No matter.
Since we don't have Hickory in Aus, I was real keen to try. Dashed!
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That might be your answer. How long did it take for the stave to arrive and how was it shipped?
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Thanks for posting this this.
I think the rot, dry rot, bugs, are affecting my white oak boards. Meaning, they break. A sinew backed bow broke,with a 57 " length for 24 " draw.
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My first bow was a red oak board bow. At 30# with the long string the limb blew off with such force I found it clear across my basement after 15 minutes of searching. It snapped across the limb closer to the handle just like your picture. The grain was very solid, I really think it was the moisture content being too low. I had just picked it up from Menards. I made my second bow with the same design, same type of wood, not as solid grain from a board that had spent two years in my basement and it turned out great.
Dry wood doesn't just fail, it snaps like a pencil. Might have been the issue with both our bows.
Just an observation from a newbie.
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That might be your answer. How long did it take for the stave to arrive and how was it shipped?
Postage was by USPS Priority Mail from Tecumseh to Sydney. By air I'm sure, because it was here in like three weeks. Surprisingly quick.