Monday, 13 August 2012

Hazel Primitive

It's coming along nicely. I always say that Hazel is a good wood to have a go with as it's so common.
However there's still a lot of work in making a decent bow.
I've de-crowned it so that I can maintain maximum width and I'm taking care to keep the decrowned surface pretty much following along a ring, nice and flat and parallel to the belly. Holding a couple of arrows across the limb, one pressed against the belly and one against the back is a quick check for parallelism.
An arrow held across each limb also checks the limbs are flat relative to each other.
Not the sort of job you can rush at if you are after perfection, but one that can be acheived with an axe quite quickly to have a go... hmmm that old balance between perfectionism vs utilitarianism.

The sketch below shows how de-crowning reduces thickness substantially whilst retaining width.
The area inside the rectangle represents the cross section of the bow about 1/3 of the way from the grip.
The red dots show where growth rings have been cut, this will give lines running along the length of the bow, so they don't weaken it. (The sketch has been improved from one in an earlier post).
If we remove wood from the belly (lower edge in sketch) instead of de-crowning, to get the same thickness we would have to cut away up to the blue line, which you can see gives a narrower limb.

Thin and wide works well for woods like Hazel as there is less compression stress on the belly.
Imagine a nice thin low stressed bow say 1/4" thick and 1/2" wide, it will be pretty feeble, say 10#. If we make it thicker it will bring up the draw weight but the wood may chrysal. Ah, but if we make two identical bows and stick them side by side, the stress is the same as it was but we have twice the draw weight!
So If we put four such bows side by side we have a bow 1/4" thick 2" wide of 40# draw weigh but no more stressed than the original!

Maybe I'm being a bit fussy with this bow, but I think I'm pushing it quite hard to get a good 45# from this style of bow without recourse to heat treating, which is how I want to do it.
I'm aiming for pretty much a replica of my little Hazel bow but a couple of inches longer, higher draw weight and without the several inches of set which that bow has.
There is often discussion about do you tiller the inner limbs first or the outer limbs. To be honest I think it's a slightly flawed concept, you need to get it all working together to some extent pretty much from first putting a long string on it. Ok you can concentrate on one area, but you must always keep the overall picture in mind. It can be fatal to get sucked into a small area of the bow (say a knot, the grip or the fades) and forget the rest.
The other big problem is, say you work too much on the inner limbs and get the draw too far back, when you then work down the rest of the limb you end up too weak.

Sorry if that's a bit rambling. The real point is, there is no magic recipe or list, do A then B the C and you'll get a bow. It's a bit of everything, slowly homing in on the desired result whilst reacting to what's happening as the work progresses. It has a slight S shaped waggle, I've retained this, as it would have reduced the width to have straightened it out.

Here's a video tour of what it looks like so far, the limbs taper in width from about 2"  to 1" and in thickness from about 17mm to 12mm. It pulls back to about a low brace height, and still has it's reflex.
I managed to get a tight string on it which pulls it back to straight, and really shows the string line and the wiggles in the bow. (The stone by the grip shows the arrow pass.)

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