When CNC lathes process threads, due to changes in the transmission chain, in principle, the speed should only be able to ensure that the tool displaces one pitch along the main feed axis (mostly the Z axis) every time the spindle rotates, and should not be restricted. However, when CNC lathes process threads, they will be affected by the following aspects:
1) The pitch (lead) value commanded in the thread processing block is equivalent to the feed speed F expressed in feed amount (Mm/R). If the spindle speed of the machine tool is selected too high, the converted feed The speed (Mm/Min) must greatly exceed the normal value;
2) At the beginning/end of its displacement, the tool will be constrained by the up/down frequency of the servo drive system and the interpolation speed of the CNC device. Because the frequency up/down characteristics cannot meet the processing needs, etc., the main feed may The "advance" and "lag" produced by the movement cause the pitch of some threads to not meet the requirements;
3) Thread turning must be realized through the synchronous operation function of the spindle, that is, thread turning requires a spindle pulse generator (encoder). When the spindle speed is selected too high, the positioning pulse sent by the encoder (that is, a reference pulse signal sent every time the spindle rotates once) may be caused by "overshoot" (especially when the quality of the encoder is unstable). Causes random threading of workpiece threads.
Therefore, when turning threads, the determination of the spindle speed should follow the following principles:
1) Under the condition of ensuring production efficiency and normal cutting, it is advisable to choose a lower spindle speed;
2) When the lead-in length Δ1 and cut-out length Δ2 (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, you can choose an appropriately taller spindle. Rotating speed;
3) When the allowable operating speed specified by the encoder exceeds the maximum spindle speed specified by the machine tool, you can choose a spindle speed as high as possible;
4) Normally, the spindle speed (N screw) when turning threads should be determined according to the calculation formula specified in the machine tool or CNC system manual. The calculation formula is mostly:
N screw ≤ N allow / L (R / Min) where N allow - the maximum working speed allowed by the encoder (R / Min);
L-The pitch (or lead, Mm) of the workpiece thread.