Engineering Characteristics of a Precision Acme Screw

Christopher Nook by Christopher Nook

Have a mechanical design in the works? It’s likely that you’ll need to consider some type of linear motion control solution for your product. While there are a variety of screws that are available for a mechanical design, an Acme screw has characteristics that separate it from competing hardware, such as roller and ball screws.

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Have a mechanical design in the works? It’s likely that you’ll need to consider some type of linear motion control solution for your product. While there are a variety of screws that are available for a mechanical design, an Acme screw has characteristics that separate it from competing hardware, such as roller and ball screws. The engineering characteristics of a precision acme screw may be just what you need to add value to your design.

Acme lead screws are designed to translate rotary motion into linear motion. They have a trapezoidal thread profile with a standard included angle of 29 degrees (some Helix screws use 40 degrees). The pitch of a lead screw is the distance from one thread to the next. The lead is the distance the nut will move with one revolution of the screw. Pitch equals lead for a single start screw. Unlike roller and ball screws, they operate with sliding contact. Acme lead screws have efficiencies between 20 and 80 percent. Lubrication and material select have an effect on efficiency.

So again, what characteristics of an Acme lead screw make it such a desirable piece of hardware for mechanical design? Here’s a look:

  • No braking system required: When a lead screw is not under power, the load can push against the screw and rotate it; this is called back driving. Unlike other types of screws, Acme lead screws are self locking when the efficiency chosen is below 35 percent. Ball screws usually need some sort of brake to secure their load as they are not self-locking. Consider the cost savings of a brake system and part count reduction when choosing what type of lead screw to use. This self locking property also makes Acme screws ideal for vertical applications.
  • Anti-backlash: All lead screws have some clearance necessary for them to operate. Acme lead nuts can be designed to take up the clearance between the nut and screw when the application requires increased positional accuracy. Anti-backlash nuts can help an Acme lead screw approach the accuracy of more complicated and expensive ball screws.
  • Low maintenance: Depending on the material it’s made of, some Acme lead screws don’t require any lubrication to function. This makes Acme lead screws an especially helpful component in applications where maintenance is difficult. Without circulating balls or other moving parts Acme screws also run quieter than other types of lead screws. They can also be made of corrosion-resistant materials and are less sensitive to particulate contamination.
  • Cost effective: While not really an engineering characteristic, we’d be remiss if we didn’t offer up the cost savings Acme lead screws can provide product developers compared to other types of screws as a big benefit. In fact, it’s estimated that Acme screws cost anywhere from 25 to 80 percent less than ball screws. This cost savings can then be passed along to your customer, to make your product more competitive in the market.

While we’ve covered some of the characteristics that put Acme lead screws in a league of their own, perhaps the biggest one is the fact that they can be custom made, both in terms of lead sizes and diameter. This trait allows designers and engineers much more design flexibility in the product development process. Instead of having to design a product to fit the screw, designers and engineers can design the screw to fit the product. There are literally hundreds of options and different configurations available.

For more information on Acme lead screws and the characteristics they exhibit, contact Helix Linear Technologiestoday. Helix can manufacture precision Acme lead screws via thread rolling, thread milling or thread grinding on diameter sizes from 1/8 of an inch to 6 inches. Download our Engineer's Guide to Identifying Lead Screw Forms for more information: