Sawmill belts and Pulleys explained Part 1FLEXIBLE BELTS AND SHEAVES
Flexible belt drives are used in industrial power transmission applications, especially when the speeds of the driver and driven shafts must be different or when shafts must be widely separated. The trend toward higher speed prime movers and the need to achieve a slower, useful driven speed are additional factors favoring the use of belts. Belts have numerous advantages over other means of power transmission; these advantages include overall economy, cleanliness, no need for lubrication, lower maintenance costs, easy installation, dampening of shock loads, and the abilities to be used for clutching and vari-able speed power transmission between widely spaced shafts.
Power Transmitted By Belts.
With belt drives, the force that produces work acts on the rim of a pulley or sheave and causes it to rotate. Since a belt on a drive must be tight enough to prevent slip, there is a belt pull on both sides of a driven wheel. When a drive is stationary or operating with no power transmitted, the pulls on both sides of the driven wheel are equal. When the drive is transmitting power, however, the pulls are not the same. There is a tight side tension T T and a slack side tension, T S . The difference between these two pulls
(T T .T S ) is called effective pull or net pull. This effective pull is applied at the rim of the pulley and is the force that produces work.