Below are some useful terms and definitions related to Fenner Precision's pulleys:
Terms & Definitions
Anodized - Is a technique used to coat the surface of a metal with an oxide layer.
Bore - The inside diameter of a pulley.
Concentricity - This term refers to the measurement of the distance between the center of rotation of a pulley and the center of rotation of the outside surface of a pulley.
Face width - Of a pulley is the width between flanges or in a non flanged pulley the width of the tooth surface.
Face width / belt width clearance - This is the clearance between the width of a belt and the space between flanges.
Flange - Is a protruding rim or collar attached to a pulley to stop a belt from tracking off the pulley.
Hub - The center part of a pulley.
Mounting method - In reference to a pulley this is the method used to attach the pulley to a shaft.
Outside diameter - Of a pulley is the maximum diameter of the pulley as measured using a caliper.
Pitch - The distance between two adjacent teeth centers as measured on the pitch line of the belt.
Pitch diameter - Of a pulley is the outside diameter plus 2 x the pitch line differential.
PLD (Pitch line differential) - Is the perpendicular distance from the outside diameter of a pulley to the pitch circle. The P.L.D. varies depending on the belt type.
Pitch Circle - Of a pulley coincides with the pitch line of a belt. The pulley pitch circle is always greater than the outside diameter of the pulley.
Pitch Line - The neutral axis of a belt. In a timing belt, the center of the reinforcement is positioned at the pitch line by the cord support.
Route Diameter - Of a pulley is the outside diameter minus two times the tooth depth.
Surface finish - A measurement of the roughness of a part's surfaces after the final product is formed; usually relating to the profile (grooved) and/or flanged faces for pulleys. It can be specified using several methods depending on the material used for the pulley. Machined pulleys should have a finish that is at least RMS 63. Injection molded pulleys should have a finish of at least SPI B3.
Taper - The gradual change in Outside Diameter over the axial-length of the part resulting an a subtle conical or convex tube shape. Often occurs on injection molded pulleys due to shrinkage or draft angle, but can occur on machined pulleys.
TIR (Total Indicator Reading) - Is the amount of eccentricity measured in a rotating pulley using a dial indicator.
Torque - Is the measure of the force applied to a pulley to produce rotational motion. Torque is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied. Imperial units of measure include foot pound-force inch and metric units include Newton meter.
