ACME Lead Screw Efficiency and Life

For the CNC router builder or buyer, some of the utmost concerns with the ACME lead screw are efficiency and life. Both of these aspects can make or break a quality machine. Unfortunately, it is impossible to give an exact life or efficiency for ACME screws, but we can make some decent estimation on both. The best way to obtain this information is from the manufacturer.
Life

The life will depend on maintenance, environment, lubrication, friction, and proper usage. On many CNC machines, the ACME nut is made of a high strength polymer plastic increasing the life of the screw significantly. With proper maintenance and lubrication, the lead screw will probably outlast many other parts of the CNC router. If the nut is bronze or steel, the wear on the screw will be much more significant, but this is rare in modern machines.

Screws with plating may have less life as the plating can chip and wear. However, most screws used in CNC machines are polished, not plated. For the CNC router builder, keep this aspect in mind. In most cases, the ACME screw will outlast the ball screw. If you like, you may use this lead screw life estimator, but keep in mind it is the ONLY estimation. The metric version may be found in the calculator’s section.
Efficiency

The efficiency of ACME thread form has increased significantly over the years and will continue to improve as new materials and thread forms are created. The efficiency of a screw and nut assembly is determined by the lead, nut material, and friction. There is a wide range of acme screw efficiency percentages, it can be anywhere from 10% to 80%.
For the CNC Router Builder

To maximize the efficiency of the assembly you choose, try and design your system with the highest lead as possible. Increasing the lead greatly improves efficiency. For a Stepper Motor system, a high lead setup also maximizes power output as most torque is at low RPM.

Also, always choose a plastic nut when possible. This will help reduce friction and increase screw life. If the efficiency of the screw is not provided by the manufacturer, use the Efficiency Estimator

The calculator is based on data of over 200 ACME screws and their efficiency percentage. The formula used is based on diameter for friction estimations and lead. It assumes that the lead screw is steel or steel allow and that the finish is of good quality (centralizing threads).

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