Encoder wheel loose on shaft

We put the encoders on the gearboxes last night. One of the wheels is loose on the shaft. Has this happened to anybody else? The wheel on the other gearbox was fine. Next question is what to do about it? Nurl the shaft? Rough it up with somethign else?
Thanks,
Brian

This is actually a fairly common problem. Take the disc off of the shaft, then using light pressure and a pair of pliers, squeeze the bands that hold the disc to the shaft in and close the gap between them. The disc should fit on the shaft snugly.