Saturday, 17 January 2015

Yew Primitive on the Tiller

It's coming on quite nicely. I re-did the recurves with a little more curve and more heat to heat treat the belly. There is still a long way to go and the left (lower) limb is a tad stiff, just inboard of a knotty area about 1/2 of the way from the grip. The right limb seems to working nicely, but maybe stiff mid limb?  (it looks a tad thick there maybe). The recurves are uncoiling nicely
I've had to adjust the width at the tips and grip to centralise the string line.That shows the wisdom of leaving wide tips and grip in the early stages.
Here's a composite pic of the unbraced and draw shot from the video. It's pulling 50# at 23"
The repeated flexing helps me to see what's actually moving dynamically. With the static pictures it's easy to mistake bends in the stave for flexing. The classic case in point is the knotty area half way along the left limb, is it stiff or is it flexing? You can decide for yourself...

The sapwood has been reduced on this bow, and it's at this stage I'm going over it meticulously trying to make sure it's smooth and to follow a ring where possible, or to make any exposed rings blend gracefully in, ideally at an angle rather than straight across the back of the bow. There is some adjusting of the tiller by removing sapwood but not much.
Say there is a raised bulge on the back, that will make the limb stiffer there. Do you remove wood from the belly if there isn't much heart wood, or do you reduce the sapwood on the back? Well it's a little of each, trying to get the right compromise without weakening the back.

The things you don't do are as important as the things you do!
The string line still looked off. Peering down the bow whilst doing some armchair bowyering I thought, this limb is off by a good half inch, it's twisted too... If I heat it and twist it I can bring it in line.
I started to jig it up and the more I looked at it the more I thought, no, it's fine! A little off one side of the grip and the edge of the limbs and it will be good. Taking some off the width will also help get the limbs bending more. I slackened my temporary string so it was just taut and looked at the centreline. An 1/8" off here and there and it's looking better, it's coming an inch further back on the tiller too.
Another thing I've decided not to do is to leave a hole through the limb as "character". It wasn't a big hole and to be honest looked a bit of a pathetic attempt at character. It also meant I was leaving extra wood round the hole for security and worrying about the strength of the limb.
I've fitted a Yew peg, it will make the final tillering less nervy.

video



3 comments:

  1. Hi Del Thanks for a little more depth one reducing sapwood. Looking at the video I noticed that just out of the fade on the right limb it seems to hump up as you draw the bow. I've noticed this on one of mine. do you know what causes that?
    Thanks

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  2. Hi, yes, the bow rocks on the tiller as you start to draw it. But that is mimicking what happens in your hand, (you don't normally notice it in your hand). It's because the bow is supported at it's centre but the string is being pulled from about 1" above (right of centre). If the bow is supported dead centre on the tiller and drawn from dead centre, you don't get that effect, but you also end up with a weak lower (left) limb when it's actually drawn in the hand.
    that's also why the bow tilts down on the right tip at the start of the draw.
    Hope that makes sense.

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