Cross Bow II

http://www.instructables.com/id/Pump-Action-Hex-Nut-Slingshot-Rifle/

Description

Diverging from the "classic" crossbow, I want to use a pulley as the force multiplier (or in this case, reducer). The main mechanism is 2 parallel bars, the front fixed and the back slides, attached to the spring. the drawstring is wrapped around the bars a few times (with force = 90lbs/wrappings and distance = 3in*wrappings). I suggest 4 wrappings, this gives a pull force of 22.5 lbs and draw distance of 12", making it suitable for a handgun design.

Trigger

I plan on using a similar trigger mechanism as in Cross Bow I but instead of a single string catch, I want two smaller catches spaced wide enough apart that I can knock a bolt between them.

Alternatively, the trigger could be connected to the moving pulley bar, which gives some flexibility in design (moving the handle up).

Bolt

Again, similar to Cross Bow I, I want to use a slightly smaller size dowel rod, (1/4 to 1/2 inch). The bolt will have two sections glued together with a fin. The main body of the bolt will simply be dowel rod a few inches long (sized to fit the cross bow) with a rounded front and the back slit to fit the fins.

The fins are cut from a pop bottle and are angled to cause the bolt to spin in flight. Past experience says paint the fins orange so they are easy to find.

The knock is a small piece glued on the end so the string doesn't split the bolt along the split cut for the fins. This is where I want to get a little more complex. The previous knock design was simply a groove for the string. This time I want to drill a small hole 1/4 from the back end of the knock. Cut a small opening from the back to the hole, with tapered sides. The objective is that the tapered edges will guide the string into the hole but once it's in, the opening will be small enough to prevent the bolt from falling off easily but still allow a smooth release when firing.