HAYING MACHINERY l6/ 



large gear wheels in the drive wheels are more positive 

 in their action and hence are preferred in foreign coun- 

 tries where very heavy swaths are to be cut. 



234. The pitman in the mower corresponds to the con- 

 necting rod in an engine. Its function is to change cir- 

 cular motion into rectilinear motion, the reverse of the 

 connecting rod. The crank pin and sickle should always 

 be at right angles with each other, but this feature is not 

 so essential when the pitman is connected to the sickle 

 with a ball-and-socket joint. 



Pitmans are made of wood and steel. Wood rods are 

 the most reliable, because steel, due to the excessive 

 vibration, becomes crystallized and weak. The steel pit- 

 man, however, may be so constructed as to be adjustable, 

 and enables the operator to adjust the length until the 

 knife acts equally over the guards at each end of the 

 stroke. The pitman should be protected from being 

 struck by any obstruction from the front. 



235. The cutter bar is the cutting mechanism, exclusive 

 of the sickle. It has a hinge coupling at one end and a 

 divider and grass board at the other. The bar proper to 

 which the guards are bolted should be stiff enough to 

 prevent sagging. It is the practice in some machines to 

 make the bar bowed down slightly and to straighten it by 

 carrying the greater part of the weight at the hinge end, 

 the weight of the bar itself causing it to straighten. 



Some arrangement should be provided to take up the 

 wear of the pins of the hinge joints in order that the 

 cutter bar may be kept in line with the pitman. 



236. Wearing plates. Best mowers are now equipped 

 with wearing plates where the sickle comes in contact 

 with the cutter bar. They may be renewed at a small 

 cost. The clips to hold the sickle in place are now made 

 of malleable iron and are bolted in place to facilitate 



