The sprocket can't be put around the drill shaft. The boss of the sprocket is literally the same size as the drill shaft. Physically impossible to put the sprocket over it!

The sprocket has a bore the same size as the reverse screw. We clamped it between the shaft (with the nut pulled from the chuck) and the reverse thread bolt. Really tight. With loctite. We then cotter-pinned the nut, shaft, and bolt (not sprocket) so that they couldn't loosen. The sprocket had a setscrew which went onto the bolt. It was seriously solid.

That worked well for a while, but as the setscrew loosened a little the reverse bolt got mashed (the sprocket could turn with the torque despite being compressed to hell between the bolt and the shaft as well), and so it didn't grip. We decided to cotter the sprocket through the bolt too. This worked well, until our first pin sheared completely. Out second stronger pin should have been the final fix, but after lifting about 6kg of Tormenta 1 the reverse thread bolt twisted and broke in two. We have strengthened parts and so moved the weak point from the setscrew, to the cotter pin, to the bolt.

That is where we are at now. I'll try and get a pic together but it's in pieces now! This is a very old picture but you can sort of see it here: http://s1088.photobucket.com/albums/i32 ... 012433.jpg