466 



ENGINEERING ON THE FARM 



After International Harvester Co. 



Fig. 356. An adjustable end-thrust ball 



bearing at the end of shaft supported 



by roller bearings 



TRANSMISSION OF POWER 



Shafting. A shaft is a rotating medium through which 

 power is transmitted and distributed. It is supported by 



and rotates in bearings 

 held in the frame of the 

 machine or by boxing 

 held by supports or hang- 

 ers. The part of the 

 shaft which enters the 

 bearings is frequently 

 known as the journal. 

 Jointed sections of shaft- 

 ing have been used to 

 transmit power for a 

 considerable distance, as in the tumbling rod of the horse- 

 power grain dump. Shafting is usually made of cold rolled 

 steel. The formula for finding the safe maximum horse 

 power transmitted by a shaft of a given diameter is as follows: 



d*N 

 n. p.= 



50 

 where d = the diameter of the shaft in inches and iV = the 



number of revolutions per minuter (r. p. m). 



The power is applied to the shaft by one of several well- 

 known methods. 



Pulley. The pulley for the transmission of power to the 

 shaft through a belt is one of the most common forms. 

 Pulleys are made of wood, cast iron, and steel. The wood 

 pulley is cheap and can be had in two parts which make it 

 convenient to attach, but it is not very lasting and will not 

 transmit much power. Metal pulleys may be made in two 

 parts, are long-lived, and the surface may be covered with 

 leather to increase the friction. The one supplying the 

 power is known as the drive pulley, the other as the driven 

 pulley. To find the velocity of a pulley in feet per minute, 

 multiply the circumference in feet by the number of revolu- 

 tions per minute. To find the speed of a driven pulley, 



