Saturday, 24 August 2013

Boo Yew On the Tiller

The initial tillering is a bit tricky as, at a low brace, just an inch or so the bow will try to bend sideways. This is especially noticeable with this bow as it's rather narrow. At some points on the limb it's as thick as it is wide, so it doesn't really care which way it bends. Heavily recurved bows can flip over on the tiller in the early stages and give you a nasty whack.
So it's a bit of a race, to get it back to a reasonable brace and exercise it  to get it bending in the right direction whilst getting the bend even. At the same time adjusting the nocks sideways a bit to try to help avoid the sideways bend.
It's a mistake to over react to problems. A little off one side of the nock and pulling the string to one side can be enough to keep it in line at the early stages. Don't be fooled into thinking a bow has any respect for straight lines marked down the back of the bow! It may well settle down to flex smoothly and consistently on a slightly skewed plane.
It's the old game of successive approximation and slowly slowly. As the bow is tillered more the thickness will be slightly reduced and the bow will settle to become more stable.
I don't actually like the phrase 'it will "learn" how to bend'  I'm not sure quite sure why I don't like it. Maybe 'the wood will slowly become conditioned to bending in one plane' is better... I don't want to get pedantic or pretentious about it... so whatever works for you.
People say a bow should be exercised by pulling it 20 times every time a little wood is removed. I think it's down to common sense and feel. I'm certainly exercising this one to try and get it stable as early as I can.
It's standing in the corner braced to 5" at the moment.
The rain has been steady all day, so I've been in and out of the garage slowly getting it tillered. the draw weight feels pretty high, but it should as I'm aiming for 55# at 26" which would feel pretty heavy at 28"
It's not quite making it at the moment as it's 50# at 26" mind I've left it slightly long and it's still a lowish brace of about 5". If I lop and inch off each end and brace it to 6" it should be close enough, I didn't have enough width of wood to get any higher without ending up with a bow thicker than it was wide. That would be a recipe for nasty instability. At the moment it's about 70" long, but I want a fairly short bow to suit the archer. If I end up about 68" nock to nock, it will still be about 70" overall allowing for the horn nocks.

You can see the tiller is a bit asymmetric at the moment.
Criticism of tiller:- Slight weak point middle of left limb, and the outer third of each limb a whisker stiff.
The lower (left) limb went from being a bit strong to how it is in the pic just by cleaning up some slightly thick areas as I checked along the limb!
I shall adjust the tiller a bit, and then take 1" off each limb (maybe a whisker more of the left) and then check it again. Not sure how much more I'll do today tho'
Funny, zooming in the draw weight looks nearer 45 than 50# in that pic, mind the bow had been sitting there.
No point worrying, it will come out how it comes out and the proof of the quality will be how it shoots. On primitive Archer people are always asking how to recover lost draw weight and I usually advise it is a waste of time and you end up chasing your own tail. the best way is heat treating, but obviously I can't do that due to the glue line. Lopping some off the ends can help but not if it compromises the design of the bow. I usually allow an extra inch either end, but by the time I've take that off and re-tillered I expect it will be about 50 @ 26" I won't beat myself up about it and it will be a matter of trying it out, if it does the job fine, if not I'll tiller it out to 28", use it myself or find it a home.

I've just gone out to the garage and sawed 1 1/4" off the lower limb and 1" off the upper... no point messing about! New temporary nockshave been glued on with spuperglue and strapped with rubber.

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