Primitive Archer
Main Discussion Area => Bows => Topic started by: bubbles on June 18, 2014, 05:30:01 pm
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I'm attempting an hickory backed Osage recurve from an osage board. Shooting for 50#@26, 62"ntn, 1/5"wide. I'm at about 50#@23" right now. On the top limb, there are two little clusters of pin knots. I noticed that in the lower cluster, the wood inside the knots seems to be chrysaling. I'd rather not have those spread to the rest of the limb - is there anything I can do? I guess my choice of board wasn't the greatest, but it was slim pickin's. I soaked the cluster in a bit of thin CA, I don't really know what I expected that to do. I thought of drilling out the knots just a bit and filling with Epoxy and sawdust, or will the chrysals stay contained to the wood inside the knot? This is my first attempt with osage, so I'm not sure how venerable it is because of those knots. The limb doesn't appear to be hinging to bad where the knot is, but I'm not at full draw yet. The knot in question is between the fade and the pencil mark mid limb on the top limb.
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That's a toughy. That grain swirl doesn't want to bend straight back naturally so its wrinkling up on you. My suggestion is to continue on and see what happens. Then glue another up! If it holds, great. Some fella's like plugs, not me.
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Finish it out and see. I really don't like to see them that close to the edge.
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You should have left some extra width there. You can grind it out with a drum sander then make a piece to fit the scallop left. Dean Torges has a description of the process on his website. It works when done right.
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What about if I drilled it out to about 1/2 way through the limb and epoxied in an 3/8" osage dowel? That would be easier for me than the torges patch as I don't have a drum sander. Would that have a similar effect? I have tried torges patches before and it was a huge pain to get a good fit.
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I'd saturate it well with super glue and shoot it. Keep an eye out for changes and it they happen then go to plan B.
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If you struggle with the scallop then yes drill it out and replace with a dowel. Remember to leave it proud when cleaning the excess off.
IMO superglue cannot fix this problem. The wood in the cluster of knots has different properties (harder/less flexible) than the surrounding wood hence the problem. If you 'replace' it with sound wood you have a chance!
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Yeah, I rasped out the section and am doing the torges patch. I figured I might as well take care of this now before it (possibly) gets worse and while i'm still tillering. More likely to make weight if I have to make any tiller adjustments after the patch, rather than waiting till I'm shooting it.
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Tiller looking good to that point,hope it works out. :) Keep us posted on how the patch work goes. :)
Pappy
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Here's the patch - I left it a touch proud. I'm probably going to leave it another day, just to be absolutely sure it's safe. I used G2 epoxy from lee valley. Hopefully through more tillering and dropping weight some of the epoxy round the edges will be removed.
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Allright, so, the first patch did not work - as Dean Torges says, "everything beyond Urac and Resorcinol will eventually break your heart". So I ordered some Resorcinol and waited for that to arrive. So I re-did the patch and DID NOT CLAMP.
Well, this time it seems to be holding. I tillered her out to 50-52@ 26", checking the patch every step of the way. At one point it was shooting at 55#@26 before I realized that it was a bit heavy. Got about 30 arrows through it so far. Gotta say, this guy makes me nervous! But it is by far my fastest shooter. Thanks for the tips and advice - I really need to get a drum sander or spindle attachment for my drill - it`s hard to get a perfect "scoop" out of the limb.
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You can buy a sheet of floor sanding sandpaper from Home Depot and stick a piece to a section of pipe of your desired radius. Clamp that in a vice or to a work table top and then push the bow across that to make the scooped out area.
No need for a spinldle sander.
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I kind of did the opposite, clamped the bow and ran piece of PVC pipe back and forth with sandpaper. The edges ended up slightly rounded from my imperfect back and forth motions. Next time I will try the PatM method.
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I much prefer a set-in patch that presents what amounts to a butt joint since the belly is in compression. A plug patch hardly even needs to be glued to work.
Round plugs work too.
Jim
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How do you remove a perfect square of wood from a bowlimb?
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With a very sharp chisel.
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The scallop method is superior because those butt joins eventually fail. I've done four in total and every one has creased at the edges. When you fit a new patch it hasn't been compressed, once you get the patch to fit perfectly and then carry on tillering the patch gets compressed and it's no longer a perfect fit.
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Personally I prefer a longer shallower scallop. Not sure I'd like a square edged insert, although I've done it in a grip so I could introduce a bend more easily. (Cut out a section, bent it and then glued in a block).
Del
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I have done 3 of these patches, one held 3 years, one a couple years and one about 6 months but all eventually failed.
(http://img.photobucket.com/albums/v181/ekrewson/Archery%20%20pics/limb_patch.jpg) (http://smg.photobucket.com/user/ekrewson/media/Archery%20%20pics/limb_patch.jpg.html)
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How do you remove a perfect square of wood from a bow limb?
That "square" patch extends through the left edge of the limb.
As far as the new wood not being compressed, not so. I made the patch a tight fit with the limb flexed backward a little bit. You can do the same with a round/dowel type patch--flex the limb while drilling the hole and while inserting a tight dowel. Then the dowel is compressed when the limb is in the unstrung mode.
Just have to think about the dynamics when planning such a repair.
The bow is still shooting after three years with no issues around the edges of the patch. There are also two round plug patches in the limbs. I turned the plugs in the lathe such that the grain runs straight across the diameter of the plug so the grain could be oriented in line with the grain of the limb.
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Well, if it lasts a year, ill be happy, then if it fails, ill just re-do it. How did they fail on you Eric? Was it slow or sudden and catastrophic?
Ash arrow - so when you install the patches, you're flexing the limb slightly backwards? That way the limb is exerting compression on the patch at all times correct?
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Exactly. I make the plug a very snug fit with the limb flexed back slightly--it's a bit subjective about how much flex.
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My failures started with a cracked patch which eventually started breaking out and led to a hinged limb, nothing catastrophic. Superglue wouldn't stop the crack.
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I assume the cracking was the glue line?
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I have done 3 of these patches, one held 3 years, one a couple years and one about 6 months but all eventually failed.
(http://img.photobucket.com/albums/v181/ekrewson/Archery%20%20pics/limb_patch.jpg) (http://smg.photobucket.com/user/ekrewson/media/Archery%20%20pics/limb_patch.jpg.html)
Do you know of any that survived.? Makes sense to me for a patch that size, kind of like taking someone elses skin graft
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Here is my most radical patch on an bamboo backed osage elb, this one only lasted a few months. I patched the bow for a friend who loved the bow and wanted to save it from a failure around a huge knot.
(http://img.photobucket.com/albums/v181/ekrewson/bow%20making/joesbowpatch_zps9a949e7e.jpg) (http://smg.photobucket.com/user/ekrewson/media/bow%20making/joesbowpatch_zps9a949e7e.jpg.html)