I've been on a kick this fall of focusing on finishing up a few stalled projects before starting anything new. Almost two years ago I started a weapon designed to fire small throwing knives. You can probably come up with a long list of reasons that was a bad idea without thinking too hard, and you'd be right! I couldn't make it work, I think my fabrication skills weren't quite up to par with my noobish enthusiasm. I put a lot of time into designing and building parts, though, and didn't want it to be a total waste, plus I needed a test bed for my first lock mechanism that doesn't use a roller nut. So I converted to fire regular bolts.
I didn't do much in-progress photography, but I wanted to get a photo of it before I broke it down one last time for final tweaking and finishing.
When I get it broken down I'll post pictures of the components. The body is cut from a retangular alumium tube, the prod is two 80# fiberglass pistol prods, the nock ends and pulleys are carved from Delrin, as are the trigger mech components. The bolt tracks are UHMW plastic, attached to wooden inserts for rigidity. There are two tracks, over and under, a remnant of the original sliding-truck design. I guess that technically makes this a slurbow? I'm not convinced that it's truly a compound, though, despite the pulley action, since the string ends are attacked to the tiller rather than the limb ends. Anybody care to weigh in there with an opinion?
Thanks to Zidar for the turnbuckle idea. It's pretty cool to be able to experiment with adjusting brace height versus power stroke on the fly. As currently configured the brace height is 2.5" and the powerstroke 8.5". I think I'll go try maximizing the powerstoke by making larger diameter cams and lengthening the string. I haven't bothered measuring muzzle velocity yet, as I've still got it rigged up with paracord until I make a real string for it.
It fires full size crossbow bolts, albeit the smallest commercially available: MTech 14" long, 5/16" diameter shafts. If you have experience with these or have read reviews, you know they're crap, at least if you go into it thinking they will be useful out of the box for a medium powered prod. These shafts are much too flimsy to be fired from a 150# prod more than once, and the substance they use to attach the components to that shaft cannot be called "glue" without insulting a host of hard-working adhesives across the globe. They were perfect for this project, though, since I wanted something lighter and was planning on taking them apart and reworking them anyway.
More later,
Gnome
I didn't do much in-progress photography, but I wanted to get a photo of it before I broke it down one last time for final tweaking and finishing.
When I get it broken down I'll post pictures of the components. The body is cut from a retangular alumium tube, the prod is two 80# fiberglass pistol prods, the nock ends and pulleys are carved from Delrin, as are the trigger mech components. The bolt tracks are UHMW plastic, attached to wooden inserts for rigidity. There are two tracks, over and under, a remnant of the original sliding-truck design. I guess that technically makes this a slurbow? I'm not convinced that it's truly a compound, though, despite the pulley action, since the string ends are attacked to the tiller rather than the limb ends. Anybody care to weigh in there with an opinion?
Thanks to Zidar for the turnbuckle idea. It's pretty cool to be able to experiment with adjusting brace height versus power stroke on the fly. As currently configured the brace height is 2.5" and the powerstroke 8.5". I think I'll go try maximizing the powerstoke by making larger diameter cams and lengthening the string. I haven't bothered measuring muzzle velocity yet, as I've still got it rigged up with paracord until I make a real string for it.
It fires full size crossbow bolts, albeit the smallest commercially available: MTech 14" long, 5/16" diameter shafts. If you have experience with these or have read reviews, you know they're crap, at least if you go into it thinking they will be useful out of the box for a medium powered prod. These shafts are much too flimsy to be fired from a 150# prod more than once, and the substance they use to attach the components to that shaft cannot be called "glue" without insulting a host of hard-working adhesives across the globe. They were perfect for this project, though, since I wanted something lighter and was planning on taking them apart and reworking them anyway.
More later,
Gnome
Last edited by Gnome on Sun Nov 10, 2013 9:17 am; edited 1 time in total (Reason for editing : pulleys, not cams)