This is the way I do it. The first thing you need to do is center drill the ends of the crank shafts. Now mount it between centers and turn the shafts to about +.010. I do it this way but you could cut it to the finished dimension if you like. Now make up 2 blocks, one to clamp on each end of the shafts. The blocks can be steel or aluminum. The blocks will have a through hole to fit the diameter of your shaft and another hole that is center drilled to locate on your centers. The center drilled hole will be offset from the through hole by whatever dimension your throw distance is. Each block should be made identical, size, hole location and spacing. The reason for this is because when you clamp the shaft into the blocks you will have to lay them on a flat surface to make sure that the offsets are on the same axis centerline. With the blocks machined you will now cross drill through the side opposite the throw hole. Drill for a tapped hole all the way through and drill a clearance hole half way through. When this is done saw a split from the end of the block into the crank hole. Now you can put a bolt into the cross drilled hole and clamp the block onto the crank. Now mount the blocks with the assembled crank back into you centers and turn the throw shaft. Take light cuts and use a bifurcated tool. That's a necking/cutoff type tool with a groove ground into the tip. This keeps the tool load down to help prevent chatter. The reason I leave .01 on the shaft is in case there are any marks from clamping etc. I can then put it back between centers and clean it up. If you do it this way you can add a packing piece, filler block, between the webs to stiffen everything up so you don't get any flex when finishing the shafts. Here again if you have a good set of collets you can grab one end of the shaft with the collet and support the other end with a live center and finish the crank this way.
gbritnell
