Sunday, 26 January 2014

Derbyshire Yew Update

I was in danger of running out of heartwood as I was taking wood off the belly, so I took the back down a growth ring or two. To some extent this is because the sapwood looks much thicker on one edge of the bow.
This took most of the day off and on in burst and probably removed about 1 maybe 1.5 mm off the back. I've put it back on the tiller and taken a tiny bit off the belly of the right limb to get the limbs balanced. All of a sudden it's winching back to a 25" draw at 80#...
Blimey! Am I going to make the draw weight now?
A quick calculation:-
80# at 25" is actually 80# at 19" of string movement from brace top draw. E.G Draw minus brace height.
This gives 80#/19" which is about 4.2# per inch. So working that out for a 31" draw which is the target draw length (31-6) x 4.2 =105
Whew, you can see, despite it seeming like I was building a monster and pulling far too much weight, I was pretty much on the money. In fact my estimate of how far it would draw at 100# once braced was far too low, although to be fair, I didn't just winch it straight back as I've been checking the tiller.
In fact you may have noticed I've quoted it's current state as 80# at 25", that's to say I haven't actually taken it back to 100# yet. that's because I need to get the tiller spot on and start actually finishing it and making sure there are no flaws in the back.
I'm not actually worried about coming up short on draw weight as I can always loose an inch of each end if necessary. there is a tiny bit of discolouration at one end which will probably disappear under the nock, but I don't want to risk any rot near the tips.
The point I'm try to make here is, getting a warbow to brace is actually probably 80% of the job.
Hopefully I'll post some video and pics tomorrow.
Just for the record the target for the bow was originally 90# at 31", this was increased to 95-100# at 31"

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