## Factors to be considered in ball screw bearing selection

1. Determine the diameter by load

There is output torque in the motor performance parameters. If it is also equipped with a reducer, it should be counted in (considering efficiency). Calculate how much thrust is needed in the actual working conditions. The ball screw bearing sample (with the manufacturer) has load parameters (ie thrust parameters, Generally marked as dynamic load and static load, see the former), select the nominal diameter of the ball screw bearing.

2. Determine the lead screw bearing lead at linear speed and rotational speed

When the motor is determined, the output speed is known. Consider the maximum linear speed you need. Multiply the motor speed (if the speed reducer is divided by the reduction ratio) by the lead screw lead value is the linear speed. This value is greater than the required value. can.

3. Determine the length of the ball screw bearing according to actual needs

Total length = working stroke + nut length + safety margin + installation length + connection length + margin. If additional protection, such as a sheath, is added, it is necessary to take into account the expansion ratio of the sheath (typically 1:8, ie the maximum elongation of the sheath divided by 8).

4. Determine the accuracy of ball screw bearing with actual needs

Generally, the machine can be selected below C7, and the number of CNC machine tools is more than C5 (corresponding to the domestic standard is generally P5~P4 and P4~P3, see the sample for details).

5. Determine the ball screw bearing nut form according to the installation conditions and size structure.

The nut has many structures, and the different nut structure sizes are slightly different. Depending on the situation, it is recommended not to choose too special, in case there is no problem with the repair and replacement of the parts.

6. Choose to determine the installation method (end)

This mounting can be designed by yourself or it can be purchased ready-made with a standard mounting. The design of the self-designed attention should be made to the force state. The bearing is best to choose the 7000 or 3000 series, because the screw bearing is mainly subjected to the axial force when working, and the radial force should be avoided as much as possible.

7. Consider guides and mounting capabilities

It is recommended to select the ball linear guide for the guides matched with the ball screw bearing. Of course, the combination of linear and linear bearings is a relatively economical choice.

8. Drawing the ball screw bearing drawings according to the above determined conditions

Mainly the end mounting dimensions, this is to be detailed, to provide the shape dimensions and tolerances.

DN value:

D: the nominal diameter of the ball screw bearing pair, also the diameter (mm) at the center of the ball;

N: limit speed (rpm) of the ball screw bearing pair

The DN is limited. The smaller the diameter, the higher the rotational speed. Because of the first determined feed rate, when the screw bearing speed calculated by the feed rate is too high, the DN value can be satisfied by increasing the lead to reduce the rotational speed.