What is the best speed for turning external threads on a CNC lathe

When machining threads on a CNC lathe, due to the changes in the transmission chain, in principle, as long as the tool can make one revolution along the spindle (mainly the Z axis), the speed should be limited. However, when the thread is processed by the CNC lathe, it will be affected by the following aspects:

1) The pitch (lead) value of the thread processing block command is equal to the feed speed f expressed by the feed amount (mm/r). If the spindle speed of the machine tool is selected too high, the feed rate (mm/min) after conversion must be much higher than the normal value.

2) The tool will be limited by the up/down frequency of the servo drive system and the interpolation speed at the start/end displacement of the numerical control device. Since the lifting frequency characteristics cannot meet the processing requirements, the pitch of some helical teeth may not meet the requirements due to the "advance" and "lag" produced by the main feed motion.

3) Turning thread must be realized by the synchronous operation of the spindle, that is, turning thread requires a spindle pulse generator (encoder). When the spindle speed is too high, the positioning pulse (ie the reference pulse signal sent by the encoder for each revolution) may cause the tightening of the workpiece thread due to "overshoot" (especially when the quality of the encoder is unstable).

Therefore, when the vehicle is threading, the determination of the spindle speed should follow the following principles:

1) In the case of ensuring production efficiency and normal cutting, a lower spindle speed should be selected.

2) When the lead-in length and cut-out length of the thread processing block are considered sufficiently, that is, when the thread feed distance exceeds the thread length specified in the drawing, a higher spindle speed can be appropriately selected.

3) When the allowable working speed specified by the encoder exceeds the maximum spindle speed specified by the machine tool, the highest possible spindle speed can be selected.

4) Under normal circumstances, the spindle speed (N screw) when turning threads should be determined according to the formula specified in the machine tool or CNC system specification. The calculation methods are mainly as follows:

In the n-type screw, the maximum working speed allowed by the n-type encoder (r/min) <the n-type allowed/l (r/min);

L——workpiece pitch (or lead, mm).