New Turkish hornbow

mikekeswick · Post by **mikekeswick** » Fri Jul 19, 2013 5:11 pm

Bede - I think you may be right as it only made the noise when I drew it to take photos of the tiller. I normally shoot with quite a cant to the bow so perhaps the act of drawing it straight up and down caused me to tourque it slightly?
Scemdonmez - Thanks, I finally feel like I am starting to get to know what i'm doing with these bows.
Kviljo - I haven't drawn it far enough yet to know where it starts to stack. I've had it back to 24 and there is no stack yet. I suppose really it should be drawn to 28. I'm going to take it slowly now.
The other bows i've made have any been too reflexed and thick at the kasan eyes so the limbs have more string follow than this bow and also had stability problems - I still haven't quite tamed the first successful bow yet!
I have been a little lucky with this bow as it has needed very little correction or tillering.

Bede · Post by **Bede** » Mon Jul 22, 2013 1:30 am

Sometimes accidents of one's physiology can cause some interesting experiences drawing a bow. Since I am five foot four, if I draw an arrow to my earlobe with a thumb draw, the length works out to be twenty eight inches. This caused some amusing exchanges between Adam Karpowicz and me because he had measured a bow I was using and it started stacking at 26 inches. When I drew it to 28, it seemed incredibly smooth. Adam was right of course since he had made objective measurements with a ruler and a scale. What I had experienced is the subjective feeling caused by the change of physical geometry when my shoulders started to form a straight line with my upper arms. This increased stability gave me the impression the bow was as easy to draw as in the earlier part of the process.

I think there might be an important design criterion for recurved, eared bows. Many bows made with modern materials end their draw with the ears almost vertical and the angle to the string between 45 and 55 degrees to the tips. As the bow approaches full draw on traditional bows like Turkish and Persian bows, the string angle inches up towards 80 degrees, sometimes the full 90 degrees where the leverage stops further drawing on all but the lightest bows. This combined with the straightening of the shoulders and lining up of the arms produces a very stable body shape to hold the bow at full draw. Because the archer is not being stressed by perceived stacking, aiming and releasing are made easier. There maybe other advantages to this physical geometry that bowyers and experienced archers have noticed.

mikekeswick · Post by **mikekeswick** » Mon Jul 29, 2013 6:13 pm

I have had another tillering session on this bow and I have found a patch in the sinew that hasn't bonded properly. When you tap it with your finger you can hear that there is some sort of delamination in the sinew layer.
I am at a loss for what to do next.
Obviously I need to get some glue in there...but how? There are no cracks or other ways to get glue in there. I don't think it's delaminated from the core itself more just a minor delamination between sinew layers. Maybe some glue gelled before the sinew was correctly laid down or it was starved of glue. I really don't know.
The hollow sounding patch is about 2 inches long and only appears to be in the center of the limb.
Any ideas?

M Hardman · Post by **M Hardman** » Mon Jul 29, 2013 6:31 pm

Use a syringe!

I was advised by someone to inject glue using a syringe, into a bit of sinew back that had started to delaminate. I didn't bother, since the bow had failed for other reasons by that stage. An idea though perhaps?

mikekeswick · Post by **mikekeswick** » Tue Jul 30, 2013 6:30 am

Yes I know but the sinew layer is to compact to get a syringe into the 'unstuck' bit. I've already tried and the needle just gets bent.

Adam Karpowicz · Post by **Adam Karpowicz** » Tue Jul 30, 2013 10:07 am

An small incision can be made (with a sharp knife or scalpel) into the sinew to reach the pocket. Cut along the fibers, parallel to the arms. Then it should be possible to deliver the glue with a syringe.

Adam

mikekeswick · Post by **mikekeswick** » Tue Jul 30, 2013 1:37 pm

Thank you. I've been hoping there was a way to fix this as apart from this problem the bow appears, to me anyway, to be perfect.
How long should I leave it to dry? Presumably it will depend on how deep the unbonded section is? I intend to make a 'bath' that the limb can fit in and then I can immerse the limb and flex it to suck the glue in.

mikekeswick · Post by **mikekeswick** » Tue Jul 30, 2013 1:38 pm

Oh and it appears to be bending a little too much at the unbonded section. If I am sucessful in getting this section glued do you think that perhaps it will 'stiffen' this area?

Adam Karpowicz · Post by **Adam Karpowicz** » Tue Jul 30, 2013 11:27 pm

If this section became weak, then the repair must really be successful. First it is necessary to make sure the pocket is indeed open under the incision, You can try to lift the edges of the incision to make way for the glue.

When the section is dipped in glue and the flexing shows the bubbles coming in and out, there is a good chance of success. I usually clamp with some kind of padding that conforms to the surface of the section and does not create a dent (the sinew and glue, now wet, are quite soft). I once made an epoxy mould for a section of kasan, or carved a good match of wood. A few pieces of thick paper will provide more padding under the mould. The paper will stick, but it can later be scraped off.

I suggest to keep the clamps in place for one day, then replace the paper and clamp again for several days. Then at least a month to dry before tillering.

Adam

mikekeswick · Post by **mikekeswick** » Wed Jul 31, 2013 6:51 am

Thanks again.
I did the repair last night and am hoping that it will be sucessful.
I scored some lines in the sinew and then flexed the limb, the unstuck section started to lift when I flexed the limb. Then I applied some glue and again flexed the limb and the glue was sucked in well. I think that I have got all of the loose section. I used some leather shims to make sure I got good contact/clamping and I used a small piece of rope wrapped around and around for the clamping pressure as clamps weren't going to be so effective.
I will let everyone know how it went when I bend it again! I really hope this has fixed it as this is my first bow with zero stability problems.