Primitive Archer
Main Discussion Area => Bows => Topic started by: jeffp51 on April 18, 2015, 11:17:27 pm
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Will this crack doom this sinew backed juniper bow? The crack only goes the pin knot just below the surface, which should stop it from going further. The know is maybe 1/32" below the surface. I filled it with thin CA glue, and I have drawn it a few times. My gut says it will be okay, but it scares me a little.
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Its hard to say but I'd do as you did by adding super glue to the knot and proceed with the sinewing.
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the back is already sinewed with 3 layers. Tiller is mostly where I want it, drawing 29" for 60" I was working on the finish when this appeared.
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Keep watching the know. If the crack continues I'd put a sinew wrap around the limb over the knot.
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Pat thanks for the advice. I am always impressed at how you are patient and willing to help out the beginners.
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It looks like it will get worse over time to me. Personally I wouldn't expect much from it then I wouldn't be too disappointed when it goes.
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Yep....that's just going to keep getting worse. I would rasp out the entire knot and patch it. The reason its doing that is that the grain of the knot is running perpendicular to the grain of the bow. Wood resists pressure differently when its applied from different angles in relation to the grain. Knots across the belly are usually trouble because wood is not as resistant to crushing when the pressure is perpendicular to the grain as it is when the pressure is applied with the grain. With the the grain resistance is called compression strength. Across the grain is called crushing strength. So if you decide to patch it, make sure the grain of the patch runs true with the grain of the bow. Otherwise it will just crush out again. Josh
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I would guess you have a corresponding lump on the back side of the bow. I doubt it is really doing much there. If I did anything at all I would lightly rasp out the cracked area and possibly not do anything else. Just pull it back slowly excersizing and check it for hinges. I think it is just non flexable knot cracking.
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I think it is a good chance nobody really knows what it will do,, I like to think on the positive,, it is worth a try for sure,, I would leave that area a little stiffer,, ,and sinew wrap it as suggested,, I agree with Badgers observations as well, if you sinew wrap it ,, it well make that area a bit stiffer,, and a sinew wrap sure wont hurt anything,, I think it will make a bow,, :)
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With the the grain resistance is called compression strength. Across the grain is called crushing strength.
They are both the same thing but just different grain configurations.
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They are not the same thing due specifically to the different grain configurations. That was the point. Wood is much stronger in compression strength than it is in crushing strength. As evidenced in this case where the crack runs along the belly where the knot compromised the the structural integrity of the wood. If that section is not doing much, then why do you suppose it cracked? Rasping out the crack will only make a weak spot weaker. Half the width of the belly is already compromised. It's only a matter of time before the other half chrysals and fails.
As far as the sinew wrap goes, it certainly won't hurt anything. Of course it won't help either, except to help contain the pieces. A sinew wrap doesn't do anything to stiffen a weak spot, it only hides the crack. It would be as helpful structurally speaking as an ace bandage on a broken arm. Good luck with your bow Jeff. That juniper sure is pretty. Josh
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sinew can stiffen a whole bow,,, so it definitely has some effect when applied to any part of the bow,, whether it can help this bow or not remains to be seen,, what effect a sinew wrap would have,, would definitely depend on the thickness,, the sinew becomes the back of the bow at that point,, and does strengthen the back,, and so would stiffen that part of the bow,,allowing it to work less,, so it is more than an ace bandage,, or there would be ace bandaged backed bows,, :)
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sinew can stiffen a whole bow,,, so it definitely has some effect when applied to any part of the bow,, whether it can help this bow or not remains to be seen,, what effect a sinew wrap would have,, would definitely depend on the thickness,, the sinew becomes the back of the bow at that point,, and does strengthen the back,, and so would stiffen that part of the bow,,allowing it to work less,, so it is more than an ace bandage,, or there would be ace bandaged backed bows,, :)
Yes, sinew backing will stiffen a bow. Of course a sinew backing has the fibers running the length of the bow parallel to the grain. A sinew wrap is just wrapped around the limb which offers no stiffening properties to the bow. I hope that I don't have to explain further. Josh
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They are not the same thing due specifically to the different grain configurations. That was the point. Wood is much stronger in compression strength than it is in crushing strength.
I mean that you have decided that different grain configurations warrant different definitions of what is happening to them. They don't.
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I would heat flow some thin super glue in it, lightly sand and wrap with sinew. I think it would be alright. I'm dealing with one right now and I'm just gonna wrap it with sinew to be on the safe side.
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Josh is right, sinew does nothing in compression but hide the crack.
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Agreed...a sinew wrap ain't gonna do jack for that...and I can't believe the best solution hasn't been mentioned yet....PLUG IT!!! Easy peasy,and a peace of mind.
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The debate here has been very informative. I think the question for me is, 1) which solution adds strength in a way that doesn't create a new weakness? and 2) Left untreated, (beyond superglue) would the crack grow beyond the region where it is now? It seems to just affect the area immediately above the knot where it is, and to be contained by the knot.
Can some of you post pictures or links to the various repair methods--patch, plug, or wrap?
Thanks again for the input.
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Is that a tension crack from sinew pulling the bow into reflex or is it a compresion fracture?
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If I had to guess, tension crack. I was experimenting with what pulling a little more reflex back into it. I heard a tick. I didn't see anything at the time, but found this a day or two later.
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If its a tension crack i would probably just soak it with glue and keep an eye on it.