Sunday, 19 February 2012

Onwards and Upwards

There were a couple of suggestions that the wood in the exploding bow was possibly too dry.
Too dry in our climate? Surely not. I got my moisture meter and could hardly believe it, the moisture content barely registered on the heartwood where it had broken, reading 7-8%, yet the sapwood measured about 12% which is typical of any wood in my garage.
Strange, I reached for my 'Traditional Bowyer's Bible Vol 1' where they discus moisture content, below 5% is considered fatal, so maybe the heartwood was fine. After all the big 90# bow was from the same timber.
It's daft to leap to conclusions, far better to just concentrate on the facts. The interesting thing being that the heartwood can be at 7% while the sapwood is at 12% despite a year seasoning.
I confirmed this on some of the other Yew on the shelves. Maybe this is all tied up with the different properties and feel of the heart vs sap wood? (Note:- A week later and all the wood is reading 12% ! The weather has changed from the couple of cold dry weeks we'd had. I'm not drawing conclusions here, just reporting what I measured)
Oddly I checked a bit of the Oregon Yew and the heart wood on that wasn't so dry.
Anyhow, time to look at the Oregon billets so I cleaned up one edge of one of the shorter thinner billets and marked it out for sawing.
Looking at the sapwood on a billet is deceptive as it is wider than the rest, once the edges are cleaned up and you allow for the width of a saw cut, it can be very tight trying to squeeze a pair of limbs from one billet. What I did was to always aim for one good billet and if I could get a second or third, that was a bonus. It's also a mistake to saw one and then assume the saw line is straight and mark off that for another. You are drawing lines on an undulating curved and probably twisted surface, then running it through a saw without a smooth flat reference edge or face... it isn't going to be straight.
You can see in the first pic how I've cleaned up the left edge (which had been split from the log, the right edge had been sawn) and marked my limb. (about 28mm at the wide end and 18mm at the narrow, I allowed more for a warbow on one of the bigger billets)
Of course a commercial saw mill would square everything up, ruin the sapwood and waste a ton of material. You can see the twist on the right piece.

I've just noticed the 'explain more' box ticked on the previous post.
Ha! If only I could explain it all, then maybe it wouldn't have blown on me. I expect a forensic laboratory could possibly work out where the failure originated...
The bottom line is it blew, I don't think I made any glaring mistakes, the usual mistake is rushing, and I certainly didn't do that.
As one of the guys on Primitive Archer said. 'I guess that piece of Yew just didn't want to be a bow'
I think that's what I enjoy about making bows, you can't know what's going on inside the wood without slicing it open and having a look, you can't always analyse it, some wood will just twist for no obvious reason. It's not an even homogeneous material that lends itself to computer simulation and machining by numerically controlled robots. It's about feel, the anxiety in the pit of your stomach as you turn the handle of the winch. The elation of the first arrow and the sheer joy of that exquisite parabola as the arrow soars through a clear blue sky.
Whoops, getting a bit poetic there, pull yourself together old chap... have a nice cup of tea.

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