Made up of a nut, screw, and ball bearings, ball screw drive systems work like typical power screws but the rolling friction replaces the sliding friction. As the screw rotates, the machine moves.

What does it do well?

When done correctly, ball screws have exceptional accuracy and are friction-free, sliding smoothly with the motion. There are also more mounting options. Racks have to be bolted to something for their entire length, where ball screw may be a better fit for some machine designs. Ball screws systems are also easier to use in the manufacturing process, where rack and pinion may require more processes to be built correctly.

What are its weaknesses?

As stated above ball screws are known for being accurate and friction-free. However, on a longer axis, vibration can worsen as increased speed is needed, hence making the screw rotate faster. This issues is coined as “screw whip”. A ball screw driven system may need bigger motors or more gearing compensation for “screw whip” and to maintain machine positioning speeds, making the use of a ball screw on axis over 1500mm in length not ideal. Ball screw systems are best suited for height positioning or the Z axis because of the short travel distance.

In regard to speed, ball screws cannot accelerate as quickly nor can they maintain the higher speeds as efficiently. Their stiffness is lower and less constant. Their transfer of power, or efficiencies, is in the 80-85% range.

Serviceability is also trickier with ball screw systems, usually requiring specialized skills to replace which isn’t ideal being that ball screws can be very sensitive. Ball nuts are very sensitive to misalignment, especially when opposing nuts are used. Ball screws are also more susceptible and less forgiving to contamination and harsh environments (like stone shops) which can lead to catastrophic failures.