W = width in inches.
H = AV⁄66,000 A = 66,000 H⁄V. W = A/L, where L = length of belt on driven pulley in inches.
Another authority simply says H = {70 to 80} × WV⁄33,000.
And a third says W = 36,000 H⁄6VL, where L is here in feet.
Evan Leigh’s rule is W = 66,000 x IHP⁄L x V.
L = length of arc of contact upon smaller pulley in inches.
V = velocity of rim in feet per minute.
A belt transmits its motion solely through frictional contact with the surfaces of the pulley. The lower side of the belt should be made the driving side when possible, as the arc of contact is thereby increased by the sagging of the following side. Increase of power will be obtained by increasing the size of pulleys, the same ratio being retained. Wide belts are less effective per unit of sectional area than narrow belts. Long belts are more effective than short ones. The proportion between the diameters of two pulleys working together should not exceed six to one. Convexity of pulleys to receive belt = ½ inch per foot wide. The width of pulley should equal 1·2 times width of belt.
Speed of Belts.
Belts have been employed running over 5000 feet per minute. Nothing, however, is gained by running belts much over 4000 feet per minute. About 3500 feet per minute for main belts agrees with good practice; lathe belts from 1500 to 2000 feet per minute. The life of a belt may be prolonged and its driving powers increased by keeping it in good working order. To ensure this it should be dressed on the back with castor oil every few weeks, more or less according the dryness of the atmosphere in which it works.