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Journal for junyingJournal for junying
When CNC lathe is processing thread, because of the change of transmission chain, in principle, as long as the spindle speed can ensure that the cutter moves a pitch along the main feed axis (mostly Z-axis) every rotation, it should not be limited. However, use CNC lathe processing thread will be affected by the following aspects:
1) The pitch (lead) value of the instruction in the thread processing program section is equivalent to the feed rate f expressed by the feed rate (mm / R). If the spindle speed of the machine tool is selected too high, the converted feed rate (mm / min) must greatly exceed the normal value;
2) At the beginning and end of its displacement, the tool will be constrained by the rising / falling frequency of the servo drive system and the interpolation operation speed of the numerical control device;
3) The thread CNC turning must be realized by the synchronous operation function of the spindle, that is, the lathe thread needs the spindle pulse generator (encoder). When the spindle speed is too high, the positioning pulse sent by the encoder (i.e. a reference pulse signal sent out by the spindle every rotation) may cause the thread to thread disorderly due to "overshoot" (especially when the quality of the encoder is unstable).

Therefore, the determination of spindle speed should follow the following principles when thread turning:
1) Under the condition of ensuring production efficiency and normal cutting, lower spindle speed should be selected;
2) When the lead-in length δ 1 and cut-out length δ 2 (as shown in the figure) in the thread processing program section are considered to be sufficient, that is, when the thread feed distance exceeds the length of the thread specified in the drawing, a higher spindle speed can be selected;
3) When the allowable working speed specified by the encoder exceeds the maximum speed of the spindle specified by the machine tool, the spindle speed as high as possible can be selected;
4) In general, the spindle speed (n screw) during thread turning shall be determined according to the calculation formula specified in the machine tool or CNC system manual. The calculation formula is as follows:
In the formula of N screw ≤ n tolerance / L (R / min), n allows the maximum allowable working speed of encoder (R / min);
L- pitch or lead (mm) of workpiece thread.
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