ONE:In spiral gearing the line of force is at an angle of forty-five degrees with the bearing faces of the teeth, and the sliding movement equal to the speed of the wheels at their periphery; the bearing on the teeth, as before said, is one of line contact only. Such wheels cannot be employed except in cases where an inconsiderable force is to be transmitted. Spiral wheels are employed to connect shafts that cross each other at right angles but in different planes, and when the wheels can be of the same size.Keeping these various points in mind, an apprentice will derive both pleasure and advantage from tracing their application in steam-hammers, which may come under notice, and various modifications of the mechanism will only render investigation more interesting.
