How to Select Timing Pulleys (inch)

Timing pulley

Image Credit: Baldor | Belt Corporation of America | Berg

Timing pulleys that are designed with an inch-based pitch designation. Timing pulleys mate with same-pitch timing belts in synchronous drives. Timing pulleys are used in power transmission systems where maintenance of speed ratio is an important design consideration. These synchronous belt drive systems are durable, highly efficient, and suitable for many different applications.

English pitch timing pulleys have a spacing or pitch based on inch (in.) measurements and a toothed, trapezoidal form.

Specifications

English pitch timing pulleys are available in a variety of sizes and geometries.

• Pitch is the distance from one tooth’s center to the adjacent tooth’s center. Most suppliers list belt pitch according to specifications from the American National Standards Institute (ANSI).
  • Choices for ANSI pitch include 0.080 in. (MXL), 0.0816 in. (40 DP), 0.200 in. (XL), 0.375 in. (L), 0.500 in. (H), 0.875 in. (XH), and .250 in. (XXH). English pitch timing pulleys with an MXL, 40-DP, XL, or L pitch designation are designed for light duty applications. By contrast, pulleys with an H, XH, or XXH pitch designation are designed for heavy duty use.

• Force is transmitted via evenly spaced grooves which mate with the teeth in the belt. 

• In terms of geometry, English pitch timing pulleys differ in terms of the number of grooves, belt width, length, bore diameter and length through bore. 

Materials

English pitch timing pulleys are made of metal, plastic and combination materials. Factors such as environmental conditions, design horsepower, operating temperature, and cost determine the best material choice. Typically, metal pulleys are made of aluminum or steel. Plastic pulleys are made of acetal, nylon, or polycarbonate materials. Acetal pulleys provide chemical resistance, but melt at relatively low temperatures. Polycarbonate pulleys have excellent mechanical properties, but can be attacked by solvents and petrochemicals. English pitch timing pulleys that use a combination of materials feature plastic teeth with metal inserts. 

Mouting Options

Selecting English pitch timing pulleys requires an analysis of mounting options.

• Many products include a hub which provides a shaft-attachment mechanism such as a set screw or hub clamping screw.
  • Set screws tighten directly onto the shaft for pulley attachment.
  • Hub clamping screws squeeze the inner diameter of the hub to a tight fit around the shaft. 
• English pitch timing pulleys that do not use hubs are also available. These pulleys may be pressed or adhered onto a shaft, or use a set screw whose thread is tapped into the pulley grooves. In addition, some synchronous drive belt systems use flanges to resist side forces and keep the belt from slipping off the pulley.