Metric Pitch Timing Pulleys

Metric pitch 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. Metric pitch timing pulleys have a spacing or pitch based on millimeter (mm) measurements and trapezoidal or curvilinear, toothed form. Pitch is the distance from one tooth’s center to the adjacent tooth’s center. Force is transmitted via evenly spaced grooves which mate with the teeth in the belt. 

Pitch and geometry are important specifications to consider when selecting metric pitch timing pulleys.  Pitch choices include T pitch, AT pitch, GT pitch, HTD pitch, and super-torque pitch. T pitch is a trapezoidal pitch available in four sizes: 2.5, 5, 10 and 20 mm. AT pitch is a curvilinear pitch available in three sizes: 5, 10 and 20 mm. GT^® pitch is also curvilinear, but available in 2, 3 and 5 mm sizes. HTD^®, an acronym for high-torque drive, is also curvilinear. Sizes include 3, 5, 8, 14, and 20 mm. Both GT and HTD are registered trademarks of Gates Rubber Company. Super-torque is a metric, curvilinear pitch with sizes ranging from 2 to 14 mm. In terms of geometry, metric pitch timing pulleys differ in terms of the number of grooves, belt width, length, bore diameter and length through bore. 

Metric 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. Metric pitch timing pulleys that use a combination of materials feature plastic teeth with metal inserts. 

Selecting metric 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.  Metric 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.

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