Thursday, 24 March 2011

When is a Mistake a mistake?

A guy on one of the forums (fora?) had looked at this blog and asked if I still make mistakes after my years of experience or if I hide them.
It's a very good question but it rather depends on what you consider a mistake!
The longbow I'm working on at the moment has some natural twist and a few wiggles, now with hindsight I'd have left the sapwood thicker along one edge rather than following the growth ring, this wood have made the back of the bow flatter rather than sloping such that one edge of the bow is thinner than the other due to the twist.
Having one side thinner tends to make the limb twist even more and it tries to bend sideways.
This begs the question 'did I make a mistake'?
Well I s'pose it depends on if the bow turns out well.
It's not an exact science where 2+2=4
Sometimes 2+2 can equal 1+1+2 as there are many ways of achieving the desired result, some will be prettier than others, some will give a faster bow, some maybe a more rugged bow.
As a (rather contrived) example if a limb is exactly 6 growth rings thick, but the rings aren't uniform and the bow is 0.5" thick on one side and 0.7" thick on the other what can you do? well you can thin the 0.7" side down to 0.5, this could be done on the back or the belly.
You could make the limb narrower to minimise the discrepancy as presumably somewhere in the middle it's 0.6" thick! But if you make the limb V narrow it will be even more likely to bend sideways.
Anther thing would be to move the centreline of the bow across to try to counteract the tendency to bend sideways, this is done by shaving away one edge of the bow and re filing the nock groove as necessary... ah, but both these solutions involve narrowing the limb tip, thus any narrowing may well be doing two jobs at once and produce a dramatic effect (on the other hand it may do nothing!)
So you see often it's a matter of making small changes, each trying to rectify the problem, sometimes one change will have an effect elsewhere or a more dramatic effect than anticipated.

Of course there is always more drastic action, say cut 3" off the offending limb tip and move the grip along to compensate (I usually make a bow 2" longer than the target length to allow some room for maneuver).
As a final resort sideways bend can be removed with heat.
I believe some twist can also be removed with heat, but it is generally considered to be more trouble than it's worth.
A bit of twist isn't a problem as long as the bow draws back smoothly in a consistent plane, what you don't want is a limb which moves progressively sideways through the draw, although I daresay it would still throw an arrow!

So have I made a mistake with the longbow?
I don't know yet!
It's pulling back to 50 pounds at about 22" at a low brace height. It's behaving fairly well but I'm having to keep an eye on the sideways shift, the one thing in my favour is that as I work the bow down the irregularities and imperfections are being reduced at each stage.
In fact a tiny bit of asymmetry in the bow can be useful, if the string tracks slightly to one side this can be an advantage if it's nearer the arrow pass and thus giving a bit more of a centre shot, the bow would be said to be right handed or left handed.
There was much discussion of this on one of the archery sites where some people though this was a lot of nonsense, however, these were generally people who weren't used to making self bows and having to accommodate the peculiarities and whims of the stave.
I hate the term 'expert' but if I'm forced to define it I'd say an expert is the person who can put right their own mistakes.

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