TRANSMISSION OF POWER 37 



in order that the up stroke of the pump will be made with 

 the up stroke of the windmill. 



55. Gearing. Spur gears are wheels with the teeth 

 or cogs ranged around the outer or inner surface of the 

 rim in the direction of radii from the center, and their 

 action is that of two cylinders rolling together. To trans- 

 mit uniform motion, each tooth must conform to a definite 

 profile designed for that particular gear or set of gear 

 wheels. The two curves to which this profile may be 

 constructed are the involute and the cycloid. Gear wheels 

 must remain at a fixed distance from each other, or the 

 teeth will not mesh properly. 



Fig. 24 illustrates some of the common terms used in 

 connection with gear wheels. Bevel gears have teeth 



AoatHow cncu. 

 PITCH CIRCLE: 



TOOTClRCLt 



FIG. 24 SPUR GEARING 



similar to spur gears, and their action is like that of two 

 cones rolling together. 



The teeth of gear wheels are cast or machine cut. 

 Most of the gear wheels found on agricultural machines 

 have the teeth simply cast, as this is the cheaper method 

 of construction. Where smoothness of running is de- 

 sired, the teeth are machined in, and the form of each 

 tooth is more perfect, insuring smoother action. Th^ 



