Thursday, 8 November 2012
Brians Big Bow + Update
Anyhow I'm pressing on with Brian's bow and it's now at a low brace height and pulling about 19" at 45#
The target weight is about 48#, but I'll make it 50# initially to allow for settling down and finishing, for the moment I'm not going over 45# untill I've got it nice and even.
The upper (right) limb is a tad stiff, and both need to work more in the outer half / two thirds.
The main thing is it's trying to twist and bend slightly sideways, I can't cut the nocks much further to the desired side (nock nearest the camera needs shifting left), so I'll resort to an old trick and glue on a temporary tip overlay and file the nock groove in that (and maybe fill the nock groove on that left edge with epoxy and Yew dust). This will allow me to effectively shift the tip over by about 1/4" to help it all align itself.
Bear in mind the tip will be reduce to a point like a sharpened pencil when it comes to fitting the horn nock, so I've actually got plenty of wood to spare.
I can also remove a little from the left upper edge of the belly to encourage the bow to bend that way.
You can see that the bow is almost a square cross section at the moment so it doesn't really have any great desire to flex one way rather than the other. It needs gentle coaxing, several small changes will pull it into line.
I had a contact from a guy a while back with this very problem and with a bit of advice he sorted it out. It can be rather panic inducing the first time you meet it.
I could just press on regardless and at a higher brace it would find it's own plane of bending, but that might be slightly skewed, much better to get on top of it now.
The potential for sideways bend is much less on flat bows (like my primitives), shorter bows or higher draw weight fatter bows. The combination of a moderate draw weight on a long bow makes it something to watch out for, but conversely it should make a very smooth shooting bow.
I shall try to give it that slightly medieval look with the limbs tapering fairly late in the last 1/3 rather than more evenly along most of the limb.
The whole tillering process can run away with you, and it's about now that I need to slow down and get it really right before moving on.
You can see the sapwood layer is much thinner now and the heart/sap boundary is looking good.
I said the right limb is stiff, that's one of those things that can send you round in circles and cause great confusion... the right tip is pulling down lower than the left one, so surely it's weaker??? Do you see the dilemma? The way I look at it is to imagine what happens if the right limb is rigid, the bow would tilt down at the right tip pivoting on the support like a seesaw (teeter totter if you are in the US) and the more you weaken the left limb the more it will flex up and let the stiff right limb pull down. I can see why some people like to clamp the bow, maybe it makes it clearer, but I like to do it this way. Of course early on in my bow making I got it wrong, reduced the wrong limb and made the problem worse and worse until I worked out what was happening, it's the lessons like these we remember most.
Anyhow, progress is good and I'll be posting quite a bit in the next few days as I hope to get it shooting a couple of arrows by Monday with a bit of luck.
Update:- Thursday evening.
I've shifted the nock and slimmed the tip considerably, it's now bending much straighter and is coming back to about 23" at 50# from a reasonable brace height. The curve of the bow is better too as I've also started rounding the belly as part of the work to help it come back true.
Now it's time to get the back cleaned up pretty much into it's final state and get the limbs back to a lovely even curve as it slowly get back towards full draw.