Acme Screws Come in a Variety of Flavors

Christopher Nook by Christopher Nook

There are a lot of reasons why acme screws are the preferred choice when it comes to linear motion applications. The popular trapezoidal screw with a 30-degree thread angle, which works to convert rotary motion into linear motion, boasts attractive features such as quiet operation, affordability, precision and a reduction in regular maintenance compared to the alternatives.

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There are a lot of reasons why acme screws are the preferred choice when it comes to linear motion applications. The popular trapezoidal screw with a 29-degree thread angle, which works to convert rotary motion into linear motion, boasts attractive features such as quiet operation, affordability, precision and a reduction in regular maintenance compared to the alternatives.

But one additional benefit of going the acme screw route for your application over competing technologies is how diverse the screws truly are. For starters, acme lead screws come in a wide range of diameters and lead sizes. Diameters range from 1/8 of an inch all the way up to 6 inches. Leads are available from less than 1/32nd of an inch up to 4 times the diameter. Based on that alone, you could say that acme screws come in many “flavors”, but there's more to acme lead screws than just diameter and lead sizes. Other options include end machining, thread types, coatings and materials.

Here's a closer look at some of the many flavors you have available with acme lead screws:

Acme Thread Forms: There are options within the acme thread geometry itself depending on the application, accuracy, and size constraints of your application. There are two main varieties - general purpose, and centralizing. The general purpose acme thread is the standard 29-degree angle (40 degree angle in smaller sizes), which is available with a series of diameters and related pitches. Centralizing acme threads are characterized by their manufactured properties, as they're generally made with tighter tolerances and reduced clearance on the major thread diameter. This type of thread reduces the chances of the nut thread wedging on the screw. Generally, the thread depth of a single start Acme screw is one half of the pitch. Stub acme threads are characterized by their thread depth being less than standard. This results in a lower profile thread for space-constrained applications.

Materials: When it comes to lead screws, the materials with which they can be constructed are diverse - and this should be a careful consideration in the product design and engineering process. Just some of the factors to be considered when choosing screw and nut materials are load, speed, duty cycle, operating temperature, chemicals present, accessibility and maintenance interval. The most common types of materials used in the manufacture of lead screws are carbon steels, alloy steels, heat-treated alloy steels, stainless steel, aluminum, titanium and other space-age metals. At Helix, we specialize in fabricating acme screws with 300 Series Stainless and 4140 Series materials. Lead screw nuts are also diverse in their material availability, ranging from self-lubricating plastic, high impact plastics, high temperature co-polymers and bronze.

 

End Product: The application will obviously dictate what size and "flavor" of acme screw is necessary. At Helix, we create nearly all of our screws via thread rolling. This process is fast, efficient, and produces a very precise screw, so screws can get to you more cost-effectively and quicker than ever. In the rare case that you may need greater accuracy we can produce milled or ground threads. Acme screws are available in standard length and cut to length and we also offer standard and custom end machining.

Coatings: Performance of the lead screw has a lot to do with its characteristics - and this can span more than just materials and nut type. Specifically, we’re talking about how the right coating can really enhance performance. Helix uses black oxide coating on alloy screws as a standard coating to protect against corrosion. Another higher performing coating option is PTFE, a durable fluoropolymer that provides a dry film lubrication. PTFE also has excellent salt spray and abrasion resistance. Furthermore, PTFE is chemical resistant, water and heat resistant and offers a no-stick surface. This coating can be applied to all Helix lead screws as a means of increasing the efficiency of lead screw assemblies through a reduction in the coefficient of friction.

No matter the application, there's an acme lead screw for it. As you can see, these types of screws come in many different "flavors" - all it takes is a little bit of analysis to discover which one is right for you.