Thursday, 23 January 2014

Derbyshire Yew Early Tillering

I spent the morning cleaning up the garage, overhauling the bandsaw after having cut a load of wet Yew., and emptying my dust extractor.
Having done that I got back to the fun stuff, working on the Deryshire Yew warbow. The spec' is creeping up a bit and I'm aiming for 95-100#. This will allow some final tweaking and the bow settling down a bit. I've stuck wedges of Yew onto the tips and filed in temporary nocks. It's just being pulled back with some rope as a string for the moment.
I put the bow up on the tiller and pulled it to 100#, one limb flexed a bit but the other was too stiff. I've worked down that limb a bit and put it up again, as shown in the video.
You can see the left limb is still stiff and the tips of the bow are only coming back about a bricks worth. At least it's bending with no nasty surprises.
I'll work down the left limb some more, check the string alignment and start teasing it back towards brace height. By the time the left limb is flexing the same as the right it will probably be back enough at 100# to brace it. Once braced a bow is well on the way to completion, if it's not bending evenly at that point and still at a good weight, there is a danger of coming in under weight.
video

Further explanation of draw weight on a long string here:-
http://bowyersdiary.blogspot.co.uk/2013/11/warbow-flexing.html

To expand the discussion a bit more.
Say for arguments sake, we knew that on a finished 100# bow it took 60#  on a long string to get it braced.
If wepull 60# on the long string and work on the bow to get it back to brace we won't have any spare wood to play with... If we take off any more wood the bow will go below 60# and end up under weight!
We'd be trying to tiller a bow without ever having seen it flex beyond brace!
Hopefully that illustrates why it's the Devil's own job to get a warbow braced when we first start working on it!
Another problem is string stretch, a couple of guys have found it almost impossible to actually brace the bows they were working on due to the high poundage and string stretch. That's a great reason for making a good quality long string and a toggle to let you shorten it as you progress.
Picture of my string toggle here:-
http://bowyersdiary.blogspot.co.uk/2013/02/left-handed-testing.html

No comments:

Post a Comment