Saturday, 31 March 2012

Full Draw

I took some video of me flexing the bow on the tiller and winching it back to 55#.
Viewing it actually flexing rather than static seemed to show a lot of movement at one point about 5" along from the grip on the upper limb followed by a slightly stiff section. It didn't look so obvious in the bit of video where it was winched back more slowly.

Maybe I should get a long rope on the tiller so I can stand back and flex it, mind it's hard to get far enough back across the width of the garage. That's why the video function on the camera comes in handy.
I marked the place with some masking tape and checked with calipers, I could see it was slightly too thick either side of that point, especially where it approached the grip.
One advantage of making a longbow tillered full compass rather than in the Victorian style with a built up stiff handle section is there is no intentional 'fade' from grip to limb which is a potential problem area. The grip does end up being a little thicker but only because the thickest point of each limb meets there.
I eased off the belly with a little judicious rasping to even out the taper (also eased off the tip of the lower limb) and put it back on the tiller. It had gained about another inch of draw and looked much smoother.
I winched it back to 55# and it was nearly at 28" inches now, so I took it the rest of the way.
58# at 28" which is great as it leaves me some leeway to narrow the tips and clean the bow up some more without coming in under weight.
I've shot a dozen arrow through it now, it feels great, very smooth and it groups well.

Here's a video of it being flexed by pulling on the rope, it's nearly there and may look fine at first glance but you can see most of the bend is in the central third of the bow and the centre section of each limb isn't doing much flexing. Stiff tips are ok, but the centre of each limb needs to work just a tad more and that will take some off the load from the centre section. It will also get rid of the extra 3 pounds of draw weight.

On one of the the websites a guy was worried that he'd spent 3 hours tillering a bow and it was all over the place and ended up breaking. I offered some advice, most of which was slow down and don't try to do it all at once.
What looks great today, doesn't necessarily look quite so good in the cold light of morning. I don't often do more than say half an hour and take a breather. I'm still tinkering with the tiller on this bow, but it's using a scraper mostly now.
BTW. The start position of the bow is skewed, because it is supported where my hand grips it in use and is being pulled from where my fingers will draw it, this gives a more accurate view of the tiller than mounting it up all square. Some people clamp the bow onto the tiller, which in my view is a mistake.
Blimey this tillering has been driving me mad, I've been taking endless videos and even got my wife to video me actually shooting it. It's this 'the lower limb should be a bit stiffer' idea which I'm slightly ambivalent about. Anyhow to me it looked as if the top limb (right) was doing all the flexing and the outer half of the left limb was too stiff. So I've been fiddling about with a rasp and scraper on and off all day driving my wife mad talking about it.
Here's the final pic (grabbed from video)before I put horn nocks on it.

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