Friday, March 23, 2012

Cheiroballistra, Pt.3

There I was, sitting at the bench with three bolt throwers at various points of completion. It's not that I don't want to finish them, it's that with every one I start, I find a better, more efficient way to make one. And don't forget, I wanted them smaller. So the first, bigger thrower I made will be the only one that size. I guess now was as good a time as any to finish it off.

The first thing I wanted to do was cap off the ends of the upright (torsion) tubes.  On the historical unit these caps were dome-shaped with a center nub. This hole punch with interchangeable punches and dies has no problem going through brass sheet. And while playing around one day, I discovered if you  use the correct size die for the hole you want, but use a punch one size smaller, it makes a perfectly domed circle, even having the nub.

Here they are glued in place. Next I wrapped thin wire around  the windlass and attached it to the ratchet/trigger mechanism. That little devil took the most time of the project. I tried several designs with different materials before settling on this one. It was the simplest, and I think I can duplicate it for the others. The bow string is brass, a little larger than scale, cause I never wanna see no droopy string. I pre-bent the wire, fed it through the trigger, and cut it to length. Confession Time! One of the reasons I went through so many trigger designs was they were too long. The bow string went straight across, with no bend in it. It didn't look like the string was drawn. Even after shrinking the trigger as small as possible, it was barely bent. The arms were bent back at a sharp angle, so I broke the glue bonds, and moved the arms forward. But they were so long, that even at the shallower angle, the string still didn't look right. Finally I clipped 1/4" off the ends that go in the tubes, to get this passable pose. How many people would have even noticed this? Well, I would have.

The bolt is brass rod hammered to a wicked sharp point. The fleches are styrene. (One got knocked off.) The wire at the front is there to steady the thrower while I took these pictures. Not sure if it's staying.

The latest, smallest yet, v.3. The torsion tubes are shorter (only 5/8"), closer together, with more delicate cross-pieces. The bolt trough and the arms are also shorter.  Here you can see it next to the down-sized v.2.

I figure I'll pre-cut the pieces for 3-4 more of each.  Construction goes pretty fast as a production line process.  Don

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