Belt Auction

regarding V-belts and pulleys what is "pitch", "pitch-line", and "pitch-line length?

I need to understand these terms in reference to V-belt drives and pulleys. what is "pitch", what is "pitch-line" in a V-belt and a Timing belt, what is "pitch-line length" in a V-belt and a timing belt. what is a pitch circle regarding a pulley. I am going through a millwright text book where i came across these terms but couldnt' find their defintions anywhere. Please help me understand these terms.

Public Comments

1. Pitch, is the mean diameter of the pully. It is not important what radius is used for the pitch diameter, just that it will match the belt. For example, if you have a 12 inch diameter sheave, then the pitch diameter is 12 inches. The sheave may actually measure 12.5 inches. belt pitch length is the total length of belt required to encircle two sheaves, and the distance between them. The distance of the belt pictch length is the length of each straight line tangent to each sheave's belt pitch diameter, as well as the portion of the belt pitch diameter which is in contact with the actual sheave's. That measurment is most easily done in cad software.
2. Pitch line: If you cut a v-belt and look at the end, you'll see a row of fibers near the outside surface. This is the tension carrying part of the belt; the rest of the belt exists only to carry the forces from the pulley to and from these fibers. The plane passing through this row of fibers is called neutral axis plane, where there is neither compression nor tension as the belt runs over the sheave. The line passing through the plane is called pitch line. Pitch: Pitch refers to the neutral axis diameter size of the belt as it moves over the groove in the sheave. Pitch line length: Pitch line length is the total length (circumference) of the belt measured along the belt pitch line.