Saturday, 12 December 2015


A guy from the club came over for "a bit of a tutorial" as he put it.
It was specially interesting for me in a couple of ways, he had a big piece of American White Ash, (AWA) it had lovely straight grain and was just over 2" square. I've never used AWA and never made a board bow... so what do I know?
(I've just edited this... I'd put AW Oak... I think it was AW Ash)

He had a set of plans, you know the sort of thing from an old magazine, which are pretty much a standard layout. We used those as a rough guide and tried to work out the best way to cut the board to give one solid bow and a couple of bits which could be spliced up to make a second.
I suggested rough out dimensions which would give plenty of room for error and he marked it out and ran it through the band saw. It cut quite sweetly and ran fairly true. (the cut being 90 degrees to the table, which you can't always take for granted, especially with wood as the rings can pull the blade)
It was cut with the growth rings running from belly to back to avoid the whole "following a growth ring ion the back" thing.
It was flexed floor tiller style, but was obviously too stiff so we decided to take it down with another run through the bandsaw. Normally I wouldn't have done that, but with limited time we were aiming to get it on the tiller. Of course trying to do it quick is pretty much a guarantee of causing problems.
The first saw cut was a tad off giving a slight thin point about mid limb, the the other limb was more even and a tad fatter, so we called that one the lower limb. We were glad we hadn't cut out the grip at this point as it gave us some wriggle room. We'd have had even more wriggle room if the stave had been left with an extra inch either end, as is my usual practice... but more of that later.

The front profile shape was then sawn out (still leaving the handle full width) and some of the thick spots on the limbs taken down with draw knife, spoke shave and rasp. It was good to have a go with the various tools and try the shave horse. Cutting temporary nock grooves allowed us to get it on the tiller with a long string and see where we were.
The thin point (already marked with "L" for leave) was showing as weak and the lower limb was way too stiff even at a low poundage, so we didn't pull to full target weight. We measured limb thickness every 6" to see how much wood we needed to remove to get the lower limb roughly the same as the upper and marked a rough pencil line. This was a good move as we could see that tiny shavings with the spokeshave just weren't going to get there, instead the drawknife worked carefully along the edges of the belly down to the pencil line, and then taking off the remainder in the centre would get us there quicker.
Some more work taking wood off the belly on the lower limb gradually got it more even as we put it up and down on the tiller.

We eventually had it on a low brace and looking reasonable. We'd been aiming for about 45-50# but of course the perils of working fast (trying to show all the processes involved) took it's toll. We never pulled it to full weight, just to about 35# but the lower limb is still a tad stiff so we didn't go further. I can't remember what draw length that was, probably about 20-22" ish? But that's a a good illustration of the technique.
You always pull to full target weight unless there is a problem .
In this case the problem was the potential hinge at the thin point in the upper limb and the over stiff lower limb.
We discussed ways of gaining some draw weight like sawing and inch and a half off the upper limb. I'd have done it like a shot, but I recognised I was getting tired, two and a half hours of intensive tooting had left my head spinning, and as I always say. It's the wise man who knows when to quit.

We had quick try out with a 30# bow (bark on Hazel of TV fame) after we'd shot it I asked if he could see which limb was longer he couldn't really tell, but when measured it showed the lower limbs is about 3" longer than the upper and yet it shoots beautifully. The point of that was to show that plans and measurements are there for guidance they are not set in stone (or even wood) and sawing an inch or two off the upper limb wouldn't be a problem.

He's going to build himself a tiller rig and press on with the bow. I think it will just about make 40# and he's got the offcuts which will make a spliced bow.
All in all a great session I got to play with some new wood (and a few bottles of beer for my trouble) and he got to cram in a few years experience into a few hours. He's welcome back to do some more as it's always a pleasure to meet people who share this passion and actually want to get stuck in.

I woke this morning with the tillering still going round in my head, so maybe writing it down will let my poor old brain let it go!

No comments:

Post a Comment