The Shop > Wood & Stuff
A Crooked Bow
vtsteam:
Notise that the above left limb is a bit smoother in profile thickness than the first tiller photo. That's because a fair amount of wood has been shaved off while tillering.
The goal in using the long string is to get the bow to the point where it can be "braced" -- that is, flexible enough that you can put on a proper length bowstring with the bow bent to its normal strung curve, at rest. Tillering then follows with the bow braced. It's a lot of back and forth checking and removing wood, until the bow finally draws to its intended draw length. You also gradually increase the draw pull until when near your draw length, you are also near your intended draw weight.
Here's the bow fully drawn to it's draw length and weight. It looks a bit uneven, but there are many knots requiring thicker areas. The tip on the right looks a little flat, but that one has natural reflex, more than the other. Some of this will be evened out by heat treating later.
vtsteam:
After tillering, I smoothed the edges and sanded the bow, being careful to do the minimum possible to the back -- the natural side of the bow. This is the tension side when the bow is drawn. And black birch seems to fail first in tension, in the sample test stick I tried. So we try not to disturb the back of the bow too much. It has a lot of irregularity, knots and deep camber.
That's typical of a bow made from a sapling. as opposed to a board bow, made from sawn straight wood. Or even a "stave" bow which comes from a larger tree, split into staves. Those generally have less camber on the back, though may also show grain irregularities, depending on the stave.
Some people call this kind of thing a "character bow", but I don't particularly like that name. I think of it as a natural bow, where you've worked with the natural growth pattern of the sapling it came from. It's tricky -- you have to read it and undestand the wood flow lines, like it was water flowing along the length of the bow and around obstacles, like knots. You have to kind of feel for the strength of the wood as you go along. Because you're going to stress it to near its limits.
vtsteam:
Here's the edge view of the bow. I've shot about 200 arrows through it at this point just to make sure it would stand up. They say a thousand arrows determines its true worth. You can see some set in the limbs -- they curve up in deflex -- towards the belly, and the archer. That's not desirable, it reduces the power of the bow and the speed. Flat or some reflex when unbraced would be better. I think there was about 3" of "string follow" -- the distnce between the bow and the tips in their permanently set deflex.
You can also see some reflex in that left tip -- where it bends back. the right tip is relatively straight in this view.
vtsteam:
Here's the right (lower) tip -- you can see the big knot and curved grain flow around it and flowing in a crescent shape past. Yet that tip isn't recurved like the other, it's straight in the side view. That's what the grain wanted to do. There's also a little twist toward the nock (where the string goes)
vtsteam:
Too much set and string follow and uneven tips, some twist, all can be remedied to some degree by applying heat to the belly -- toasting it and applying pressure. This also has the effect of stiffening the bow a little. I used a heat gun and very lightly toatsed it -- I don't know how much is good and how much is detrimental -- no experience with that.
Here is the belly toasted. You can see the limbs slightly browned from the heat..
It did even out the bow quite a bit, and cut the string follow in half. It also increaased the draw weight a couple pounds, so it was a definite advantage.
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