Pitch is the distance between
groove centers and is measured on the pulley pitch circle. On the
belt, pitch is the distance between tooth centers and is measured on
the pitch line of the belt.
Pulleys are designed to accept
belts of a certain diameter. There is often a range of operational
belt sizes for a given pulley; any overlap in the specified range and
the pulley range will produce a match
Pitch or datum diameter for a
pulley is the diameter of the line of action. Typically it is at or
near the center of the circular pulley groove.
Full diameter to outside of
Diameter of center hole for shaft
Shaft Mounting Style
Set Screw / Keyway / Weld or
Press-On / QD Hub / Taper Bushing / Clamp Hub
The pitch you choose will depend on
the application’s load and speed. Timing belts must be run with timing
pulleys of the same pitch. When running sets of pulleys the smaller pulley
of the set is usually flanged. If three or more pulleys are in a drive,
every other should be flanged. A pulley’s pitch diameter will always be
greater than its outside diameter. Timing pulleys have evenly spaced axial
grooves in order to make correct positive engagement with the mating teeth
of the belt.