How To Choose Ball Screw？

Ball screw is the ideal product for converting rotary motion into linear motion, or converting linear motion into rotary motion.

Ball screw is the most commonly used transmission element in tool machinery and precision machinery, and its main function is to convert rotating motion into linear motion, or to convert torque into axial repeated force, while having the characteristics of high precision, reversibility and high efficiency. Because of its small friction resistance, ball screws are widely used in various industrial equipment and precision instruments.

In simple terms, ball screw is a mechanism that can be converted from rotational motion to linear motion or from linear motion to rotational motion, but the general application of it is converted from rotational motion to linear motion.

How to select ball screw type

1, Screw shaft diameter

Common specifications are (unit: mm) : 8, 10, 12, 14, 15, 20, 25, 32. Generally, the larger the shaft diameter, the greater the load.

The load size of the screw with different shaft diameters can be viewed in the manufacturer's sample book, and the relevant parameters are dynamic rated load and static rated load. Static rated load refers to the rated load that the screw can withstand in the static state, but we can't make it static with the screw, so here, we basically only care about the dynamic rated load. Then, the smaller the ratio between the actual load and the rated load, the longer the theoretical life of the lead screw. (Note: The rated load does not represent the maximum load, but generally do not exceed the rated load, otherwise it will reduce the service life of the lead screw)

2, Lead 

Lead refers to the screw rotation one week, the nut straight movement distance (this many engineers do not know, so focus on the mark). Common leads are (unit: mm) : 2, 4, 5, 8, 10, 20, 25, 32. It is important to mention that there is no special relationship between the lead and the axial clearance, and the size of the lead is determined by the linear speed of the transmission. 

3, Accuracy 

Accuracy is expressed as follows: no matter how long your ball screw is, any 300mm, the error is within the accuracy represented by the grade, the accuracy represented by each grade is as follows:

In general, ordinary machinery uses C7, C10 level, CNC equipment generally uses C5, C3 level (C5 more, most of China's domestic CNC machine tools are C5 level), aviation manufacturing equipment, precision projection and coordinate measuring equipment generally use C3, C2 accuracy.

In addition, C7, C10 grade is generally manufactured by rolling method, and C5 grade and above are manufactured by grinding method.

In summary, the accuracy level of the ball screw commonly used in non-standard design is C7 (rolling method manufacturing or some people call it conversion), and the accuracy level of the ball screw has higher requirements, C5 (grinding method manufacturing) is also sufficient.