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When designing or manufacturing Power Transmission or Linear Motion Screws having a Trapezoidal thread profile, PST follow the conventions of ISO 2901, 2902, 2903 & 2904. The original intent of the trapezoidal thread was for holding large loads and/or accuracy. An early typical application for a "trap" thread would have been a bench vice where the screw thread was used to hold large compressive loads. In order to do this the lead angles of the screw thread were kept low to prevent back driving. Now trapezoidal threads are found in Power Transmission or Linear Motion Screws more often than static load situations. And although the ISO convention is still standard for design, keeping the lead angle low is no longer of paramount consideration. In practice today trapezoidal threads are seen as the "Acmes" of the metric world with faster leads, multiple starts, centralizing profiles and other modified profiles. The difference between Trapezoidal and Acme threads are relatively minor. Other than using metric metrology for dimensioning the thread geometry is different only in the included angle. An Acme thread has a 29.5° included angle (14.5° flank angle) and the Trapezoidal thread has a 30° included angle (15° flank angle). Trapezoidal Power Transmission or Linear Motion Screws are very robust and yield a large level of static and dynamic capacity in a relatively small design envelop. Because Trapezoidal threads are sliding friction screw threads the typical efficiency of the design is in the 30-40% range. PST has custom manufactured trapezoidal Power Screws with improved efficiencies that will perform in the 40-55% range. These high efficiency "trap" threads are present and show little or no increase in radial or axial play after what used to be call "run-in". Usually the features that make it necessary for a trapezoidal thread to be customized are the things like: Contact PST for hardware solutions that can't be found in the catalog and application answers that need to be resolved.
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