Saturday, 2 November 2013

Warbow Tillering 120# 5" Brace

The warbow is at a low brace and moving nicely. The cambium layer is beginning to crack and pop in an alarming fashion, so it's all a bit nerve wracking.
I have decisions to make:-
Do I leave the back untouched and have very little heartwood at the tips?
How do I cope with that weird dip near one tip? The surface of the back and the heart/sap boundary dips along one edge such that it's sloping at about 45 degrees or more.
I could just square it off and ignore the flow of the wood, but I'd be really cutting across growth rings at an unacceptable rate.
If I follow the wood exactly it will end up wanting to bend sideways.
Like most things there's the compromise, maybe I can aim for a sort of oval section with the axis of the ovality being slightly on a slope. I can relieve the high edge of sapwood a tad if it's done over a long gentle line and maybe allow the heartwood to get a bit thin along one edge of the belly.
Maybe I should reduce the sapwood thickness over the whole bow?... a laborious process if I'm going to maintain the integrity of a single growth ring.
It would all be much easier on a low poundage bow.
The answer is to tread slowly and carefully, tease it back and see how it progresses. If I do have to reduce the sapwood thickness over the entire back, then do it slow and steady over a few days.

After lunch I went over it checking the thickness taper, looking, feeling and measuring, and teased it back to 5" brace. I had to winch the long string back to 140# to get the string on it, yet once braced it drew back to 19" at 120#. All a bit counter intuitive and that's why so many beginners make under weight bows.
This means I'm ok for draw weight and the there's a fair bit of wood to remove to get the tiller spot on.
I still have the various problems to solve, but I'm on the right track.

The lighting for the pic is a bit harsh and the shadows make the limbs look rather different. Holding a CD up to the pic shows the outer 1/3 of each limb isn't doing much flexing. This is going to be problematic for the right (upper) limb where it has the weird dip.... maybe that will become the lower limb. It's still early days.
That raises an interesting point about the 'Lower Limb is always stiffer' mantra. On casual examination of the Mary Rose bow dimensions, that seems to be true, but I happened upon several bows where the upper limb is actually wider and thicker. The real answer is, what does it look like on the tiller? Never believe the figures rather than your eyes.

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