Thursday, 4 September 2014

First Flexing

I glued on some scraps of offcut Yew for temporary nocks, the bamboo isn't as long as the Yew belly, so I bevelled the end of the bamboo and matched the Yew offcut onto the bevel, that gave me maximum length of limb. Always best to maintain maximum length, after all, it can always be cut off later, but its hard to gain length later if you need it.
The horn nock will just cover the end of the bamboo when it's all finished. I put on a slack string and flexed it while looking at the reflection in the patio doors. It felt strong enough and looked reasonable. I spent some time checking limb thickness to take out any thick spots so that it slowly tapered towards the tips.
I tried to mark a centre line, but it's tricky on a curved bow, I need to reduce the width along the whole bow to stay within the 5/8 thickness/width ratio of the longbow definition.
I wish I'd had thicker belly billets so that I could have had a bit more taper, but you have to work with what you have.
The brief was 40# maximum, so I can always drop a few pounds to get the tiller right.
There was a long discussion on Primitive Archer about different tillering methods. I like to get it braced ASAP but one guy said that if your short string just slips onto the bow the draw weight/draw length figures actually line up pretty well with the finished product. If that's right then I'm about 40# at 25" which gives me some elbow room to get it right. I've already adjusted one limb to get the 5/8 ratio and a better string line, but I've done enough for today. If I'm short of draw weight I can always come back in an inch on each nock (not that it will make much difference).
video
My marking out just didn't look right so I didn't take off any wood, instead I tightened the string and got it to a low brace, this allowed me to look at the string line and I could immediately see I needed to push the string across a little at one end. This gives me a centre position for the tips and I can mark out and tentatively start narrowing the bow.
First I wanted to see it on the tiller. It looks ok, but most bend is on the inner limbs, the tips need tapering in width, which is what I'll do next. Slow and steady, I've done probably 80% of the physical work on the bow, but I'm still only half way there in terms of tillering.

3 comments:

  1. What do you mean by the short string just slipping on and the draw weight/draw length figures adding up? Do you have a link to the PA discussion you mentioned?

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  2. If I find the thread I'll post a link. It was an empirical thing with no mathematics, physics or geometry to it, a couple of people used the fact that with a 'slip on' string what you lost in 'leverage' due to to the longer string you made up in the fact that it dangled down further and it just worked out that the "draw length" as measured just reading off the scale on the tiller tree, and the poundage on the scale came out pretty close to the final figure with a short sting. Personally I don't use the method with staves, but with this bow it almost made and assembled as the heat treated belly couldn't be reduced much once it was all glued up for fear of rasping through the heat treated layer.

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  3. Ah, got it... took a bit of trawling through. There was a similar thread going on at about the same time too.
    http://www.primitivearcher.com/smf/index.php/topic,47101.msg643390.html#msg643390

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