Sunday, 22 June 2014

Removing the Twist from Yew Primitive

The twist on the Yew primitive was getting a bit problematic as it was twisting in the same direction as the sideways waggle in the limb was trying to twist the bow. Two out of line forces acting in the same direction was a bad thing.
There is no way to remove the sideways waggle, so I steamed out the twist. The pics (one from each end of the set up show how I did it. An off cut of square plastic drain pipe contained the steam along most of the limb and a length of 2x1 was made into a wrench to hold the limb tip and apply the twist. A length of rubber strapping applied the force, held in place by my inertial restraint device (or Anvil as it's sometimes called!) The steam is from a wallpaper stripper and it is going into the drainpipe through the black flexible hose. The ends of the drainpipe are loosely closed off with foam plastic offcuts to contain the steam, I've left a drain hole at one end for the water to run out where the steam condenses. The workmate is blocked up at one end on bricks to ensure the water runs out rather than soaking the wood.
The last pic shows the result. There is still some twist near the grip, but the rest of the limb has been eased round to keep the belly of the two limbs pretty much parallel. You can see the place where the string line gets very near the edge of the limb, which of course tends to twist the limb. It's looking more like a bow now, and I've remove a bit more wood at the grip, this was helpful for clamping the bow onto the jig.
The Yew went soft with the steam remarkably quickly, probably because the limbs are relatively thin and have plenty of surface to absorb the heat. Also the steam and twist was spread out over a good length of limb.
I was very pleased how it went. I followed my first rule of heat bending.
Spend as much time planning and jigging it up as you do heating.

As well as removing the twist, I applied a little force/movement to remove a small deflex bend, which was by the sideways waggle. I'm not sure how much that took out, but I didn't want to over stress it as there are some knots in that area.

It's now 60# at 22" and I've heated out an ugly bit of deflex from the tip of the lower limb, I haven't gone mad with it and flipped the tip, just straightened it..

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