2OO FARM MACHINERY 



worm gear drive, the feed being regulated in the latter 

 case with a face gear or cone gears and a flexible shaft. 

 The ratchet drive (Fig. 152) has an advantage in offering 

 a great range of speed. As many as ten speeds for the 

 apron, or in reality ten rates of feed, may be obtained. 

 However, the motion is intermittent and heavy strains 

 are thrown upon the driving mechanism by the sudden 

 starting of the heavy load. The ratchet drive is liable 

 to breakage and does not prevent the load from feeding 

 too fast in ascending a hill owing to the tendency of the 



FIG. 153 THE WORM GEAR DRIVE TO THE APRON. ALSO FACE GEAR FOR 

 VARYING THE FEED 



load to run back. To prevent this a brake is used, but 

 must be unsatisfactory. 



The worm drive, on the other hand, gives a constant 

 motion to the apron, but does not offer a great variety of 

 feeds, and unless carefully attended to wears out quickly. 

 Fig. : 53 shows a worm drive with a face gear for vary- 

 ing the feed. The worm drive must be greased several 

 times each day or it will cut out. It has been known for 

 a worm gear to wear out in a single day's work. The 

 cone gear for varying the speed is very little used, but 

 seems to be a satisfactory drive. 



