Fig. 2304.
Fig. 2305.
In [Fig. 2304], for example, is a wheel hub w, assumed to be a good fit to the shaft s, while the key k fits at the end a only. If the key be driven tightly home, the wheel will spring over, so that instead of the plane of its diameter standing at a right angle to the axial line of the shaft as at d in [Fig. 2305], it will stand at an angle as at e, throwing the wheel out of true in that direction. This would occur not only on account of the elasticity and compression of the metal of the keyway, but also because the surface of the bore of the wheel and of the shaft is not, even under the best of turning, smooth enough to come into close contact all over, but are covered with slight projections or protuberances, which may occur in spirals because of the turning tool marks, or in localities because of differences in the texture of the metal. In driving the key home these protuberances give way, and they do so most where the contact pressure is greatest, which would be at g in [Fig. 2305], causing the wheel to cant over. If the wheel is not a good fit to the shaft it will not in this case touch the shaft at c, [Fig. 2305].
Fig. 2306.