How Plastic Acme Nuts Resolve Lead Screw Challenges

Christopher Nook by Christopher Nook

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Acme Nuts

While lead screws provide cost, performance, and dependability advantages for many of today’s linear actuation requirements, some motion control applications present challenges that require the use of plastic acme nuts, which are engineered to provide internal lubrication, to make lead screws operate more smoothly, quietly, and reliably.

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While lead screws provide cost, performance, and dependability advantages for many of today’s linear actuation requirements, some motion control applications present challenges that require the use of plastic acme nuts, which are engineered to provide internal lubrication, to make lead screws operate more smoothly, quietly, and reliably.

Lead screws utilize the helix angle of the screw thread to convert rotary motion into linear motion and rely on the coefficient of friction between the nut and screw to position loads. The acme thread form—the original trapezoidal screw thread—has a 29° thread angle with a thread height that is half of the pitch. Because the tooth shape of an acme thread has a wider base, it is stronger than a similarly sized square thread and capable of carrying larger loads.

Acme lead screws are available in a variety of materials, such as carbon steel and stainless steel, and can be paired with a bearing-grade bronze or internally lubricated plastic acme lead nut. This article will examine the operating conditions that require the use of lubricated plastic acme and lead nuts.

plasticacmenut

In the past, many design engineers believed that the characteristics inherent to lead screws made them unsuitable for high-temperature, high-load, or high-duty-cycle applications, often opting instead for costly ball screws for these types of applications. Or, if they did use acme lead screws, they would require frequent lubrication and maintenance to counteract frictional effects. However, a new generation of lead screws are made from engineered plastics and polymers that reduce friction—and the heat, noise, and wear that it creates—with built-in, internal lubrication, making the combination of a lead screw and plastic acme lead nut a viable, more cost-effective option.

Acme lead screws utilize friction to convert rotary motion into linear motion, their operation can create heat, noise, and wear. These characteristics present additional performance challenges in applications that operate in high temperature environments, position heavy loads, or perform with a high duty cycles. Examples of these types of operating conditions include rapid prototyping machines, which utilize liquid plastics at high ambient temperatures; factory automation systems, which repeatedly move heavy loads; and lighting systems, which move frequently under the heat generated by powerful lights. 

Advanced Materials for Acme Nuts

A range of advanced nut materials has been developed, including custom-engineered polymers, which integrate lead screw technology into applications that previously would not have been possible. Helix acme lead nuts are available in several types of plastics, including PEEK, polyester, acetal, Torlon®, Vespel®, PVDF, UHMW, and Ertalyte®, as well as customer-supplied specialty materials.

A range of plastic types for nuts is necessary because of varying pressure velocity (PV) and thermoplastic characteristics. For example, while an acetal plastic blended with 15 percent PTFE lubricant is cost-effective for lighter loads, its PV value—a measure of a material’s ability to be dynamically loaded—is insufficient to support higher loads without overheating and deforming. Blends of Torlon, Vespel, and PEEK provide might higher PV values that when blended with PTFE lubricant form bearing-grade materials that are much better suited for higher temperatures and heavy loads.

Choose Helix Linear for Acme Nuts Made from Engineered Materials

When your application presents linear actuation challenges—whether related to the operating environment, load, or duty cycle—Helix Linear Technologies can provide an effective, affordable solution. By combining lead screws with Acme nuts made from custom-engineered materials, HELIX Linear can develop lead screw configurations that resolve performance challenges related to heat, stress, and wear, enabling you take advantage of cost-effective lead screws for applications that heretofore were not possible.

To learn more about how lead screws and advanced plastic acme nuts can make lead screws a suitable option for linear actuation challenges, download this free presentation comparing lead screw nut materials: