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The ACME Lead Screw System

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Learn more at www.igus.com/leadscrews The ACME Lead Screw System by Matt Mowry Product Manager, drylin ® linear systems, igus ® Inc. Introduction Lead screws are a common technology used to convert rotary motion into linear motion, and are often used to provide actuation to a set of linear bearings. Lead screws and plastic nuts are excellent lower-cost alternatives to ball screws and metallic nuts when used in applications where extreme precision (micron level) is not required. One of the most common lead screw geometries in North American manufacturing is the ACME lead screw system. ACME lead screws were developed in America in the mid-1800s and have been routinely utilized since. Designed with a trapezoidal shape, a flank angle of 29 degrees and a higher pitch than fastening screws, they were made for applications requiring frequent positioning, including power transmission applications moving high axial loads. High-performance plastic ACME nuts are ideal to use in an ACME system. igus ® triboplastic iglide ® ACME nuts from the drylin ® product line are made of composite plastic materials, which offer lower friction and wear values than many other materials across a wide range of applications. The triboplastics operate free from oil and grease, and they do not require maintenance. They are also able to operate on traditional ferrous lead screws, as well as light-weight aluminum lead screws. Furthermore, they can handle high axial loads, they are insensitive to dirt and dust, they are corrosion-resistant, they have lower wear than other plastics, and they handle vibrations and impact loading better than bronze nuts do. Speeds and Loads Due to the tight pitch geometry of ACME systems, they are best suited for low-speed positioning applications. For designs requiring a high linear feed rate, we recommend higher helix lead screws such as dryspin ® technology. For even higher cycle applications, we recommend belt-driven actuators. For more information on how to choose between lead screws or belt drives, please read our tech talk, "3 Tips for Selecting a Linear Slide Table." The maximum RPM typically recommended for an ACME lead screw is dependent on the radial and axial support from the radial bearings or bushings. For applications exceeding 100 RPM, it is highly recommended that the lead screw be supported by ball bearings. Many radial ball bearings are also capable of carrying the axial load generated by many applications. For those applications under 100 RPM, plastic bushings like iglide ® bearings may be used, which do not require lubrication and are ideal for many industries.

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