Primitive Archer
Main Discussion Area => Bows => Topic started by: Lee Lobbestael on December 02, 2014, 07:04:40 am
-
Hey guys. I'm finishing tillering an elm self bow and it has an exposed knot in the center of the top limb. It was actually a branch at one time. I trimmed it down short and a small crack formed during tillering. I sanded it down a little and the crack disappeared bu re-appeared as I finished the tiller. It is a tiny crack but extends past the knot on one side and is perpendicular to the grain. Sorry the picture wouldn't turn out on my phone camera. Can I patch it somehow?
-
Super glue! The crack could have started as a check which is a common occurrence in knots. Is this crack on the back or belly?
-
Super glue da-dah! Love that stuff.
-
it is in the back
-
Bummer. Not a good thing unfortunately, especially the crack running across the grain. Like said, fill it with SG and just shoot it.
-
Is it possible that the bow will hold together long term? Its my second elm bow and it seems to crack around knots a lot
-
And it is cracking against the grain? Have you heated the wood at all?
-
yes I have heat treated it twice
-
Is it possible that the bow will hold together long term? Its my second elm bow and it seems to crack around knots a lot
Not likely. The crack will likely continue to grow and eventually fail. It might hold with CA glue, but I wouldn't trust it. Common in elm. I don't use elm much anymore as backing wood. It makes fine selfbows, but I've had bad luck using it as backing wood.
-
The way I handle knots is when tillering I want that area to not bend as much as the rest of the limb by just a little bit. I just want to take a little of the strain from that area.
Now I tell you ha, Lee. :)
Jawge
-
Yeah thats what I should have done! So a sinew wrap over a rawhide patch or something like that won't hold it together?
-
Wraps will never hold a tension issue. Tension pulls so a wrap around contains nothing. Post a picture before you call it dead.
-
Would a rawhide or linen patch hold it together?
-
Rawhide would work dandy, do the whole bow.
-
what about a rawhide patch with a snake skin over it so you don't see it?
-
what about a rawhide patch with a snake skin over it so you don't see it?
I make elm saplings with knots and lumps on the back into flatbows and mollies, probably more than any other type of wood or bow, and I know this problem well. You probably know why, but to cover it thurougjly, the issue is that the lump is narrower AND stiffer than the limb around it would be (due to thickness).
In the future, try to make that highest point of the bump (I usually have 5-8 on each limb) not bend. It's a tad tricky, because you need the flats between bumps anto bend, and you need as much limb as you can get bending, so you kind of have to fade the bend in and out at every knot, and as close to the knot as you can get. BUt your crack happened because the little peak just couldn't take the strain. (It's one of those nipple looking knots with a small, dark branch smaller than a pencil, isn't it?) Cool? So, if it doesn't bend there, you are safe. If it does bend as much as the rest of the limb, or even less, it can be in danger.
NEVER sand a crack down, or or level a bump on the back of a bow. Rawhide stretches too much for a patch like this, and so does sinew, unless you put a LOT on. Linen cloth is your best bet. If you patch with linen, DO level the knot or at least smooth it. Use Titebond II or III. Add like a 2" long patch across the whole limb, and make sure the edges fray out lengthwise as you lay it down. Let it partly dry, and add a second longer patch, at least 3-4" over the first patch. Smooth it out and let it dry. When dry, retiller, but keep your draws short, just enough to check it. Then, using TB or QUALITY superglue (not dollarstore stuff) wrap over your whole patch with small diameter string or thread. Lots of surface area contact between patch and wraop, and lots of glue.
THIS WILL USUALLY WORK JUST FINE. But don't be surprised if it doesn't. I have bows I gave away maybe 8 years ago going strong with this treatment, but some of them don't get shot much. i just finished doing this on a black locust bow that had a funny diagonal hollow dip on the back I wanted to reinforce. It works, but not every time. This is my closest approximation to Baker's method of using raw linen. IF the bow breaks, elm's toughness usually allows the rings mid way through the limb thickness to stay intact and the bow will fold rather than snap and hit you.
Good luck.
-
i think sinew is stronger than rawhide
-
I wouldn't waste a snake skin on it. Save that for a another bow.
-
Thanks guys. Springbuck thanks for the in-depth response. What about a linen (fake) snake skin? I heard those have some backing properties
-
i think sinew is stronger than rawhide
Sinew is stronger than rawhide, almost certainly. And he could shorten the bow and sinew the whole thing, letting it dry into reflex. The problem is not its breaking strength. It is that sinew and rawhide both stretch like a rubber band about 10 % of it's length. That much stretch will allow the wood fibers under the patch (where we already have a crack or leveled knot) to experience enough tensile force to give up, breaking the bow under the patch.
Vegetable fibers will stretch 1-2%. Slightly more for fabric. Elm wood fibers stretch about like hemp or linen, so a linen patch is in order. The first linen layer makes the top layer feel more tension than the first layer does, which is more than the surface of the wood does.
The trick, the hard part, is getting the patch to hold without linen backing the whole bow. And sometimes they don't. :-(
A long as it is linen cloth, made from flax, or something like hemp, you can use it, so if you have some printed stuff, use it. Just make sure it isn't nylon or something. Plain linen is also a cool as heck blank canvas for painting/staining geometric patterns on.
Don't waste a real snakeskin on a knobby, crowned piece of elm, though.