284 APPLIED SCIENCE 



alloy increases according to the amount of tin which it con- 

 tains, the usual proportion being 8% tin and 9% copper. 

 The resistance to wear is sometimes increased by the addi- 

 tion of 2% phosphorus. The 

 speed of shafting, that is, the 

 number of revolutions per min- 

 ute (abbreviated R. P. M.), is 

 governed by the type of machine 

 run by the shafts. This speed 

 varies from 125 to 150 R. P. M. 

 in metal-working shops to more 



than 250 R. P. M. in wood- 

 FIG. 140. Heavy Head Shaft . , . , 



Hanger. working shops. 



322. Formula for Horse-Power a Shaft Will Transmit- 

 To find the horse-power which a shaft of a given diameter will trans- 

 mit, multiply the cube of the diameter in inches by its revolutions 

 per minute and divide by 92 for steel shafts and by 190 for wrought 

 iron shafts. The quotient is the horse-power. To find the revolu- 

 tions per minute necessary for a shaft to transmit a given horse- 

 power, multiply the given horse-power by 92 for steel and 190 for 

 wrought iron and divide the product by the cube of the diameter 

 of the shaft expressed in inches. The quotient is the required 

 revolutions of the shaft per minute. 



Considerable power is lost by the use of shafting and the average 

 loss would be about as follows. For each 100 H. P. generated, 10 

 H. P. is consumed by the friction of engine, 15 H. P. by the line- 

 shafting, 15 H. P. by the belts and pulleys, 15 H. P. by non-produc- 

 tive machinery, and only 45 H. P. goes for productive work. There- 

 fore every effort is made to reduce friction and waste to a minimum, 

 and shafts are usually adjusted every ten or twelve hours. 



323. Setting Line-Shafting. There are two points to be 

 considered in setting line-shafting in line. One is that it 

 should be either horizontally or vertically in line with its 



