from each other by the use of positive clutches, a friction clutch always connects the engine with the machinery so that the shock is taken up there. The teeth, notches, or projections of positive clutches require to be very carefully and accurately cut and properly hardened, for if they are not they are very apt to be chipped and to wear by the action of engagement.
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Fig. 11
Rough edges denote chipping, and rounded edges much out ot shape indicate wear. When this is the case the gear becomes very noisy in action, and much movement of the parts is noticeable when the actuating lever is moved to and fro. In these circumstances they will require facing or re-cutting, and this should be done at once when such a condition of things is discovered,
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Fig. 12.—SectionFig. 13—End Section
or the condition of the parts will rapidly go from bad to worse. These latter remarks also apply to the teeth of gear wheels.
Having now briefly considered the principal details of simple transmission, we pass on to the means whereby the ratio of the gears may be altered as required by the road conditions, and in so doing have to combine the speed-varying
