Ellis why don't you fix the wheel to the shaft in a way similar to the way a drill chuck is fixed to the shaft. I never had a wheel coming off this way. I'm using a metal hub threaded with the same thread as the shaft, the hub will cover the whole length of the thread on the shaft. Then the locking screw will lock everything in place. Its impossible to work loose this way as long as you dont strip the threads or shear off the lock screw