Primitive Archer
Main Discussion Area => Bows => Topic started by: simk on April 03, 2018, 05:56:04 am
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Hi All
May I ask you a question:
I was just finishing a bow when I noticed some little compression-cracks @ a knot on the belly. (You best see it in the middle-pic; its not the cracks directly @ the knot I mean, but the one that starts on the belly and goes down sideways)
How can I cure/avoid this?
Is it usually better to drill out such a knot and fill it with epoxy? Would this generally reduce the risk of such cracks? (Maybe because the epoxy better resist the compression than the rest of the old branch???)
Or should I remove wood @ the back to relieve compression/force @ the belly? (Because maybe the extra-wood around the knot caused too much force on the belly?????)
Or should I just remove wood before an after the knot, what means weaken the whole bow to relieve the spot?
How do you deal with such spots?
I'ts my second bow with this problem up to now and I don't want more of them...
Thanx for your advice and have an very nice day!
Simon
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Is it a stiff handle? If it's not bending there it doesn't seem like it should be a problem. If knot is lose and it is bending there it could be a problem. I have zero experience with yew. My gut says it's ok but I'm not the one holding it and watching it bend and don't want to give you bad advice. I'm thinking Del is your man. He's handled some pretty iffy knots in yew.
Bjrogg
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simk....The one pic shows to me what I would call a compression crack.Very insidious things.The cracks in the knot are of no concern but I'm afraid the stiff area there caused your compression crack beside it.
It looks like you heat treated the belly of the limb too.That does retain form but does not make a limb more elastic if the design is'nt compatible.I do not know what type of wood/length of bow/width of bow etc. that you have there.You have a combination of things coming together here to cause all of this.Design/tiller/length and width of bow.In all asking too much from the wood for the design you chose along with a stiff area that caused your compression crack.
It looks like a sapling bow.Going for a lighter bow weight or a longer bow also might have helped here.Sometimes we learn more from our failures than our successes especially for a certain type of wood.
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Hi Bjrogg
It's an elb-design but not yew - i used my common rowan-wood and flattend the belly a bit. The knot is in the middle of the main bending-zone. I put one more photo of the whole bow...
Hi BowEd
You are maybe right, that the extra wood around the wood made a stiff spot which caused the crack. If so, would it be wise to remove wood on the back, where there is extra wood around the knot to make the spot less stiff? Still it's not too deep/late i think.
What if I remove more wood @ the belly, where the crack is? Major disaster?
Thanks for your advice.
Cheers
[It's 68 NtN & pulls around 60-70 pounds @ it's heat treated]
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My luck with compression cracks is'nt very good myself but possibly making a lighter weight bow removing wood overall on the belly from your rowan wood with a good tiller might save it from reappearing.Time will tell.
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Probably best to just leave it alone. The cracks in the knot are no problem, but it's probably some flexing at the knot (maybe caused by the weakness on the back where the knot comes through that has allowed it to chrysal. It's probably stabilised by now...
I hate chrysals as much as the next man but that's a difficult place to do any fix.
Answering your other question. The knot looks sound on the belly... BUT... you can't tell how far in they go from the back and if there is any rot there. Personally I'd probably have dug it out from the back to see how deep and if there was a cavity or pocket of rot... You can always put in a decorative plug for the back afterwards, but it will add zero strength.
However filling any cavity that is deep past the center into the belly (the compression side) could have maybe helped prevent the chrysal.
The only way to strengthen the back is to put an overlay about 1/8 - 3/16" over the knot area having taken out a loooong shallow flat curved scoop. I wouldn't do it generally as it looses the character, leaving a little extra width normally suffices.
A total permanent repair would be to rasp out the chrysal and patch it. Dig out and fill the knot then patch an overlay on the back.... :o
Or just leave it alone like I said at trick one ;D
Easing everything else off just a tad should help stop it getting worse.
Del
PS. Chrysal don't happen where it's too strong/stiff ::) They happen where it is bending too much for the strength of the wood.
If you remove wood from that area it will certainly get worse (or snap)
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Hi Folks
You are great - thanks for fast advice.
@Del: It's not the cracks @ the knot that worry me, but the one on the belly, that goes down sideways - you can see it @ the 2nd pic.
Probably I have to weaken the whole bow - but that's always the last (but maybe only) possibilty. Making a patch and so seems very very complicated, have never done this and i'm not sure if it lasts.
For future projects the most important question still is for me: What caused it? Was it a too stiff or a too weak spot? If it was a stiff spot, I now could still remove some @ the edge of the back, left & right of the knot, to make it bend....
Cheers from a poor B-wood bowyer (--)
Edit: Del, just saw your Edit - it's clear now, it was a weak spot - i will not remove more wood...thanx
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One way chrysals can occur is because the limb is bending too much in that area. Looks like you have a bit too much wood removal at the knot's area ( foreground in that photo).
I like to tiller knots slightly stiffer than the rest of the limb.
You could retailer that limb to make the knot stiffer and retiller the other limb to match it in strength.
Left as is the bow will eventually fold at that area like a book closing.
Don't ask how I know that. :)
Jawge
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That's pretty much what I meant with a stiff area next to an over bending area.
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I usually soak the belly side of a knot like that with CA. Use the thinnest glue you can get and fill the cracks right up. That "may" have avoided the chrysal.
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For the future, I'd rather have a good stave of second rate wood than a poor stave of first rate wood.
A poor stave of second rate wood is hardly worth the effort.
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Oops wrong thread please disregard.
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I would have left a little more width around the knot too. Measure the diameter of the knot and add that to the width.
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I am not sure I would stress an already stressed stave (chrysals) by recurving.
Jawge
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So, I meanwhile decided to get out the rest of that knot and don't fill it with anything. Then I will remove some wood all over the bow - there's plenty of poundage left for me, so there hopefully will be a bow.
Further I'll leave a little more width around knots with future bows, but i can't change the wood i have, no osage here )P(.
Thanx for advice - im pretty sure now, that the problem occured, because i didnt left enough wood around the knot, neglected rule Nr 5.
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Rule No. 5- Never say you're sorry, it's a sign of weakness???? ;D ;D ;D ;D
Sorry, that's rule number eight.
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Really? DC, are you married? :) Jawge
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I make bows with knots like this that fade in and out of stiffness all along the limb........and it's always a craps-shoot. Usually that extra stiffness, created by the extra thickness, gets me through, creating a stiff spot by itself that fades in and fades out of the rest of the bend in the limb. BUT! Sometimes, if it bends anyway, this happens. The cure WOULD have been extra width around the knot, or enough extra thickness so it can't break.
If you still have a lot of draw weight to reduce, then mark that area, stay out of it and leave it stiff. It it doesn't bend it won't break......unless it just blows suddenly.
The only ways I know to PATCH this kind of thing, or splint it are kind of ugly. Del said, "The only way to strengthen the back is to put an overlay about 1/8 - 3/16" over the knot area having taken out a loooong shallow flat curved scoop." That's it there. And I have the best luck just binding these on rather than messing with glue. You COULD shave that knot a LITTLE flatter, and get a scrap piece with an intact ring (just like you would have used for the back), about 3-4 inches long. I might heat this in the microwave, reflex it into a curve, like Del said, a "scoop", and then clamp and bind this splint down firmly with strong twine, which you then soak in glue.
Ugly but works.