Acme screws and ball screws are often used for linear motion applications. Each type of screw has its own advantages that can make deciding which type to use for an application very clear. However, when a design has flexibility, lead engineers may question which screw type is better for the application.
We’ll compare the major identifying features of acme screws and ball screws to help engineers determine which type of screws are best for their specific applications.
Benefits of Acme Screws & Ball Screws
There are several clear benefits of each screw type. These may help to simplify which is best for an assembly.
Acme screws are best suited for high load, industrial applications. They are generally used when low efficiency and positional accuracy are acceptable. In addition, they are better suited for applications with high static loads and those in which noise may be a concern. Since acme screws often have fewer components than ball screws, they are typically lower-priced.
While also used in high load applications, ball screws are generally selected when high efficiencies are required. They provide greater locational accuracy for precision applications. Ball screws also have lower torque requirements, higher load ratings, and a longer life cycle than acme screws.
Manufacturing Acme Screws & Ball Screws
Acme screws use a trapezoidal thread in both the nut and shaft of the screw. While these threads are typically made to an industry class, PST can customize the thread sizes upon request.
Comparatively, ball screws use a custom thread profile for both the nut and the shaft. The ball bearings are loaded using a recirculation method, which allows them to roll through the threads. The load is therefore applied to the ball bearings as well as the shaft and nut.
Acme screw shafts are typically made of carbon steel or alloy steel, while the nuts are made of bronze alloy, brass alloy, or plastic. If the application requires corrosion resistance, acme screws can also be made of stainless steel. The load rating of the assembly is based on the strength of the base material.
Ball screws are also made of carbon or alloy steels, but they can be hardened over HRc 56 to provide the highest available load ratings. Ball nuts are typically made of carburized alloy steels but can also be made from precipitating, hardening stainless steels. Like acme screws, ball screws may also be made of stainless steel to provide corrosion resistance. However, with materials such as 17-4, the hardness cannot reach that of an alloy or carbon steel. This leads to reduced load ratings within the assembly.
Choosing an Acme Screw vs Ball Screw
When there is design flexibility, there will often be a discussion of whether a ball screw or an acme screw is the best choice for the application. Typical factors impacting that decision include:
- Dynamic load rating
- Static load rating
- Life requirements
- Required efficiencies and torque requirements
- Speed requirements
- Noise requirements
- Corrosion resistance
- System cost requirements
- Operating environment
- Design envelope
The decision to choose an acme screw or a ball screw will always come down to a combination of factors in an assembly. It is only after analyzing the entire assembly and the costs and benefits of one screw type over another, that a decision can be made.
Do the screws within your assembly run effectively? Contact our team of acme screw and ball screw experts today to learn how they can help.