I've had great success in the past attaching sprockets to shafts using a keyless locking device known as a TranTorque Keyless Bushing. I've found them in MSC and they are produced by a company called Fenner Drives (
www.FennerIndustrial.com)
The cool thing about them is that you
don't need a keyway or setscrew and they come in a whole range of sizes in both english and metric. I think the smallest I saw they make fits an 1/8" shaft, but they go all the way up to something like a 3" shaft or so.
Just a thought...???