MANUFACTURING ENGINEERING DEPARTMENT PULLEYS How they work MANUFACTURING ENGINEERING DEPARTMENT

A fixed pulley or class 1 pulley has a fixed axle A fixed pulley or class 1 pulley has a fixed axle. It is used to change the direction of the force and it has a mechanical advantage of 1 only. That means that the force is equal on both sides of the rope.

A movable or class 2 pulley has a free axle A movable or class 2 pulley has a free axle. It means the axle is free to go up and down. A movable pulley has a mechanical advantage of 2. The weight of the load is split between the anchored end and the force pulling.

A compound pulley uses both, fixed and movable pulleys A compound pulley uses both, fixed and movable pulleys. The example below has a mechanical advantage of two.

The combination of several pulleys is called blocks or drums The combination of several pulleys is called blocks or drums. Notice on the example below that the fixed pulleys and the movable pulleys are grouped in pairs sharing the same axle.

The picture below is an example of a compound pulley The picture below is an example of a compound pulley. Notice that the hook supporting the pulleys is bearing a weight of 1 ½ times the load.

The pulley below has a mechanical advantage of four The pulley below has a mechanical advantage of four. Notice that each fixed pulley is bearing the weight of 50 lbs. and the anchored end of 25.

Different pulley arrangements.

An overhead crane uses a hoist and a pulley block to lift the load An overhead crane uses a hoist and a pulley block to lift the load. Notice that one end of the wire rope is attached to the frame and the other end to the winch. The mechanical advantage is 4.

A Lathe with several pulleys, also called sheaves, sharing the same axle. In this case the different diameters are used to transfer different torque to the shaft.

Assortment of pulleys