Timing pulleys mate with same-pitch timing belts in synchronous drives. Some timing pulleys are designed with an inch-based pitch designation. 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

Pitch

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)
• 0.250 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

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

Geometry

English pitch timing pulleys differ in terms of the number of:

• Grooves
• Belt width
• Length
• Bore diameter
• 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

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.

Standards

BS ISO 5294 - Synchronous belt drives - pulleys

JIS B 1856 - Synchronous belt drives - pulleys

ISO 9011 - Synchronous belt drives - automotive pulleys

Image Credits:

Baldor Electric Company | Belt Corporation of America | Berg W.M., Inc.