The Acme Lead Screw Backlash Survival Guide

So what's so important about perfecting your acme lead screw backlash design and why do you need a survival guide to help steer you in the right direction? Find out everything you need to know about backlash here.

So what's so important about perfecting your acme lead screw backlash design and why do you need a survival guide to help steer you in the right direction? Find out everything you need to know about backlash here.

What exactly is backlash?Acme lead screw backlash

Backlash (lash) is the relative axial clearance between a screw and nut without rotation of the screw or nut. Lash will always increase with use.

The image to the right depicts the differences in force between a standard nut, tension anti-backlash nut and compression anti-backlash nut. 

The importance of backlash design

Backlash is most harmful in precision positioning applications, where small changes in location are relevant.  If a system doesn’t compensate for backlash, it can add up over many cycles resulting in inaccurate positioning and to get the job done right. 

Backlash matters the most in lead screws where positioning, power and accuracy are ofhigh importance. such as; syringe pumps, unmanned robots and other various medical and defense applications – backlash can cause inaccurate positioning.  Doctors, defense officers and other professionals have to rely on their applications for the most accurate positioning. 

For example, small infusion pumps  gradually administer intravenous medications to patients, including pain-killing analgesics, nausea-suppressing medicine, and other drugs. If the design engineer for this application doesn’t compensate for the correct amount of backlash, a patient can receive the wrong dosage of a medication and (taking it to the extreme) may die. 

The more complex the application, the more complex the backlash design.

Designing for acme lead screw backlash

There are several unique ways to reduce or remove the lash between the screw and nut. For screw diameters over 5/8 inch, PowerAc™ No-Lash™ Flanges are available. The PowerAc™ No-Lash™ Flange is identical to a standard flange except for slotted mounting holes. The backlash can be removed by using a nut with a PowerAc™ No-Lash™ Flange in combination with a standard nut and flange. By rotating the slotted PowerAc™ No- Lash™ Flange and nut relative to the other, the thread in the second nut advances until the lash is reduced.

As the nuts wear and backlash increases, loosen the mounting bolts and readjust the PowerAc™ No-Lash™ Flange and nut until the lash is minimized as seen in the image below.

Acme lead screw backlash cut away

CAUTION -  When the uncompensated lash is equal to or greater than times the pitch, the assembly should be replaced.

Antibacklash Nut Designs

Nuts are available in standard and antibacklash designs, with centralizing threads to match your precision acme leadscrew designs. Centralizing threads have the lowest backlash of any nut on the market. Now, with the release of our new NAB / AAB product lines, HELIX™ has even more economical options in the 1⁄8" to 1" diameter range.

If you need Acme, Trapezoidal, or SpeedyR (high lead) threads with a precision low backlash nut, or a state-of-the-art anti-backlash design, we deliver the highest quality and exceptional value to our customers.

Keeping your acme lead screw backlash survival guide in mind

The survival guide to designing your perfect acme lead screw application starts with a backlash design. A good design is key for low friction, minimum wear, long life and clean operation. 

Download this free presentation to learn more about how to compare lead screw nut material: