FAQ Friday: Top 15 Acme Screw and Lead Screw Questions Answered Here

by Christopher Nook

Acme lead screws convert rotary motion into linear motion by turning either the screw or the nut. Lead screws and nuts are highly customizable. Helix Linear offers a custom shop where engineers and manufacturers can use the largest collection of options available to build the best lead screw to fit their needs.

Acme Screw and Lead Screw Products

1. Will a long lead screw assembly bend? If so, is there a solution to eliminate bending?

Under specific loading scenarios, a long lead screw can bend. One possible solution when using long lead screws is to use intermediate supports, such as a spring-loaded arm with a plastic sleeve that supports the screw during operation but drops away from the assembly as the nut passes.

2. Do Lead Screws and Nuts need to be Lubricated?

Yes, we offer high quality lubricants for your acme screw application. We offer several greases that are designed for specific uses like military and aerospace, semiconductor and medical applications. We also offer high-performance dry lubricants like our H10X™ PTFE coating and several different ceramic coatings for applications that need to be “clean”.

3. What is the Difference Between Pitch and Lead?

Pitch is the measurable distance between screw grooves. Lead is the linear travel the nut makes per screw revolution. The pitch and lead are equal with single start screws. The pitch is ½ the lead in two start screws.

4. For Extra Strength, Should I Use an Extra Long Nut Instead of Standard Nuts?

In theory, yes it would be better, but in practical terms it wouldn't. The standard length nuts that are offered in the Helix Linear Technologies catalog offer the best price/performance ratio. When using extra long nuts, special gauging and tooling is required for them to work properly. Fit up problems typically occur when using extra long nuts, which creates hot spots that have the ability to expand thermally under load and also bind locally on the screw. However, larger diameters should be considered if capacity is a major concern.

5. Are Alloy ACME Screws Better Than Medium and Low Standard Carbon Steel Screws?

The Alloy 4140 Heat Treated Screw is favorable only with certain applications and is frequently "over specified." This is typically attributed to the fact that it is an extremely popular material for fastener threads and bolts. Numerous users specify Alloy 4140 HT with the intent of extending the screws wear life; but the majority of screws are used with either plastic or bronze nuts and there is a large hardness differential between these materials and all steels meaning that the performance of the nut materials is not changed.

6. Are End Machining Services Offered at Helix Linear Technologies?

Yes. Helix Linear has a 40,000 sq-ft manufacturing facility located in Cleveland, Ohio, with multi-axes CNC machines dedicated to machining lead screws and linear actuators.

7. What Materials are Used to Manufacture Helix Screw Products?

Helix Linear Technologies utilizes materials that efficiently produce superior thread finish while also integrating excellent machinability. Acme, Trapezoidal Lead, and Hi-Lead screws: Screws can be manufactured from low carbon alloy, high carbon heat treated alloys , aluminum, tutanium, bronze, plastic and ceramic materials.

8. What are the “C” and “G” Class of Fit for Lead Screws?

The two classes of fit described in the ANSI standard for ACME screw threads are “Centralizing (C)“ and "General Purpose (G).” The General Purpose fit allows for the nut and screw contact interface to take place on the thread flanks while simultaneously providing clearance on the minor and major diameters. On the other hand, the Centralizing fit allows for contacting on the major diameters while also maintaining the same thread flank contact as the generalizing fit. There are minor differences between C and G when being used for applications solely of axial loading.

9. Are There Any Distinctions Between a Left or Right Handed Thread?

Typically, unless stated otherwise, lead screws are right handed. There are occasions where a left and right hand screw will be used simultaneously to permit travel in both directions concurrently. Helix Linear manufactures Twin-Lead^TMscrews as a standard product in sizes from 2mm - 75mm diameters.

10. Is It Possible to Determine if a Lead Screw Is Ground and Rolled by Looking at It?

Yes, the simplest way to do so is by examining the lead screw’s outer diameter. There may be a fold or line (known as the witness line or crest line) present where the material has been dislocated for formation of the screw. If so, then the lead screw is rolled.

11. How Often Should I Lubricate a Lead Screw?

Regularly. Regularly checking for adequate lubrication levels and lead screw integrity can help prevent premature wear and extend the life of the screw assembly. It is important that the lead screw remain lubricated. If there is a lack of lubrication on the screw additional quantities should be applied. Lubrication frequencies are very application specific and should be established to eliminate the chance of running a screw assembly without lubricants.

12. How Do I Decide Which Type of Screw Product to Use? Acme vs. Ball Screw for My Application?

Screw selection is dependent on many factors that include but are not limited to, application load, desired speed, accuracy/repeatability requirements, and application environment. For help in selection please contact The Helix Application Engineering or visit our Linear Custom Shop^TM to build a custom screw for our team to evaluate.

13. Can Acme Screws be Used in Vertical Applications Without Back Driving?

Yes, lead screws can be used in vertical applications as long as the screw efficiency is below 40% and the screw does not experience any vibration. All applications moving people and flight-critical surfaces on airplanes and UAVs should be reviewed by Helix Application Engineers.

14. Are Lead Screw Products Able to be Used in Harsh Environments?

Helix PowerAc™ acme screws and nuts do not utilize any rolling elements and are therefore can perform well in harsh environments. Lead screws perform well in industries such as paper, material handling, wood, and metal cutting, and food processing.

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