ENGINES, MOTORS AND TRACTORS 195 



in the average floor, especially if heavy storage should be above. Line 

 shafting hangers should not be over 8 feet apart and if the shaft is light, 

 not more than 6 feet apart. The horse power of a good shaft may be 

 figured in the following manner: 



Multiply the cube of its diameter by the number of revolutions per 

 minute and divide the result by 82 for steel and 110 for iron. In other 

 words, "The amount of power that can be transmitted by two shafts of 

 similar quality varies directly with the speed and with the cubes of their 

 diameters.' 



The twisting strain on a shaft is greatest near the main drive; there- 



ENGINE OPERATING PUMP JACK. 1 



fore, the nearer the main drive is to the hanger, the more nearly will 

 its strain be counteracted. A disregard of any of the above principles 

 is calculated not only to waste power, but gives an unsteady energy to the 

 machine driven and affects both the efficiency and life of the machine being 

 driven by it. 



Speed of Shafting. If only one machine is to be driven by a shaft 

 the problem of shaft speed is very simple. With the operation of a cream 

 separator at a speed of 60 revolutions per minute and a wood saw at a 

 speed of 400 to 600 revolutions per minute as well as other varied speeds, 

 the problem is more difficult. It is at this point that many very large, 

 expensive pulleys and a number of very small pulleys upon which belts 



1 Courtesy of The Christensen Engineering Company, Milwaukee, Wis. 



