THE PROBLEM OF “END-THRUST.”
The objection of “end-thrust” is raised against the bevel-driver. If the reader will look at a cut showing the shaft in position with the two axles, he will understand that the large beveled wheel on the crank axle tries to push the pinion and shaft backward, so that it may free itself and turn as the rider is forcing it to do. This backward pressure is because the face of the tooth is sloping, and before the load can be moved this pressure back must be resisted solidly somewhere. So (it is said) the rear pinion of the shaft is liable to be forced hard against the one on the hub, thus causing friction and possibly “bind,” especially on hills and bad roads. But this peculiar action between the interacting teeth at the crank shaft is necessarily duplicated at the other end of the shaft, so that the backward thrust at the front is met by a forward thrust at the rear, the two thrusts thus counteracting each other.
It should be said here that the pin-roller gear, already described, as used on the Monarch and others, is free from any possible objection of “end-thrust,” as there is no tendency to shove the shaft either backward or forward.