136 SCIENCE OF SUCCESSFUL THRESHING 



of an inch up and down play at any point. As the web 

 between the upper and lower cogs of the bull-wheel varies 

 in thickness, it is best to locate the thickest place and mark 

 it. This part may be then turned between the bull-pinions 

 and the shaft bearings adjusted so that the gears mesh as 

 deeply as possible and at the same time allow the bull- 

 wheel to pass freely between them. In building powers at 

 the factory leather packing is placed between the box of the 

 upper short bull-pinion shaft and the main frame. It is 

 the intention to shave down this leather packing from time 

 to time as the bearings wear, thus allowing the bull-pinions 

 to be kept in proper mesh by means of set screws. The 

 box of the lower short bull-pinion shaft has no leather be- 

 tween it and the main frame ; however, it can be set deeper 

 in gear at any time by turning its set-screw from below. 

 The main spur-wheel shaft is not adjustable and the set 

 screws bearing against its boxes are used only to prevent 

 them from becoming loose in their slots. Adjustable 

 slides are placed above and below the bull-wheel. Those 

 below have set-screw adjustment, and should be adjusted, 

 as they wear, so that the bull-wheel just clears the lower 

 bull-pinions. The top slides prevent the up and down 

 movement of the bull-wheel, and should be set down as 

 they wear. The traverse-rollers prevent the bull-wheel 

 from crowding endwise on the bull-pinions. They should 

 be set out by the key adjustment as they wear. The spur- 

 pinion frame is secured by four five-eighths inch bolts in 



