Monday, 19 December 2016

Chasing a Mirage

Ah! The automaton is a bit like a mirage which vanishes just when it appears to be within your grasp. Fortunately I like problem solving!

At one point he was catching onto the string nicely but as it drew back all the force was bending the upper bow limb and the string became slack below his hand and came off the lower nock. It took a while to work out what was going on.
There are so many changing angles and variables in timing and position between the two movements. Even when it works successfully, there is no guarantee it will work right next time.

I'm slowly taking the slop out of the mechanism and designing in stuff to make it work correctly. Firsly I've made the bow pivot in the bow hand which ensures even tension on the string both above and below the hand. (Yes that's yet another bow...)
The control rods are being uprated again to steel cut from sheet, fortunately the bandsaw will manage thin mild steel (not finished yet). I'll be improving all the pivots by drilling tighter tollerance holes with a nice set of drills which I've got Santa to order from Axmister tools . I've also ordered some tiny self tapping screws (size 0, from E-bay), the plan is to remove the slop and then make the hand that catches the string adjustable so that it can be set in the correct position to reliably catch the string.

I'm pretty sure I'll get there in the end, and I've made one more crucial piece... the nock on the string which the hand catches onto was made of linen thread with superglue soaked ito it, which I'd then tried to file into a conical shape. The conical shape allows the hand to slip past it in one direction and then snag on it as it pulls back. Now I'm sure you can imagine that trying to file something like that is nigh on impossible, so, I thought I'd turn a cone on my little lathe, but from what material?
Trying to drill a 1mm hole in something hard is tricky, then I thought maybe horn, then, even better antler!... it turned brilliantly and even parted off cleanly, it was fine up to the point when I dropped it on the floor never to be seen again! Oh well the lathe was still set up and the antler still in the chuck so I just made another. I haven't tried it yet, but I've threaded it onto some of the linen thread I use as the bow string.

I'm enjoying this and it will give me something to tinker with over the holiday period. No pics now, I'll save 'em (and hopefully a working video) for my end of year review.

Talking of which, I looked at last years review and what I had planned for 2016 I was a bit optimistic when it cam to flight shooting, but I did gain a few yards!


  1. Hi Derek, i have really enjoyed following your exploits on here this year. Well done on your successes which have been many and interesting to watch from bough to bow. Keep up the good work and all the best for the approaching festive season. Kind Rgds Adrian from warrington.

    1. Cheers, thanks for the comments/feedback.
      Have a good 'un! :)