Why CNC Lathe Machine Can Not Make Thread?

 

System working principle: The working principle of CNC lathe thread processing is the interpolation between the spindle rotation and the Z-axis feed. When the thread processing command is executed, the system starts thread processing after receiving the one-rotation signal from the spindle position detection device, and performs Z-axis interpolation control according to the spindle position feedback pulse, that is, the spindle rotates once, and the Z-axis feeds a pitch or a lead.

 

Cause of failure:

 

(1) The connection between the spindle encoder and the system is poor.

 

(2) The position signals PA, *PA, PB, and *PB of the spindle encoder are defective or the connecting cables are disconnected.

 

(3) The one-rotation signals PZ and *Z of the spindle encoder are defective or the connecting cable is disconnected.

 

(4) The system or spindle amplifier is faulty.

 

Troubleshooting:

 

For the cause of the fault (1), the fault can be found and repaired by checking the connection cable interface and the calibration line of the cable.

 

As for the cause of the fault (2), it can be judged by whether there is a spindle speed display on the system display device. If there is no spindle speed display, it is this type of fault.

 

For the cause of the fault (3), it can be judged by switching between the processing command G99 (feed processing per revolution) and G98 (feed processing per minute). If the G98 feed cutting is normal but the G99 feed is not executed, it is this type Fault. If the above faults are eliminated, the system itself is faulty, that is, the system storage board or main board is faulty.

 

2. Unstable pitch in thread processing and its solution

 

Working principle of the system: During thread machining on a CNC lathe, interpolation control is performed when the spindle rotates and the Z-axis feeds, that is, the spindle rotates once, and the Z-axis feeds a pitch or a lead.

 

The reasons for the failure are as follows.

 

(1) If the pitch error is random: The possible causes of the failure are poor connection of the spindle encoder, dirty interior of the spindle encoder, poor Z-axis position encoder, and loose connection between the Z-axis motor and the Z-axis.

 

(2) If the pitch error is fixed: the possible cause is that the transmission ratio between the spindle encoder and the spindle is set incorrectly or the system software is bad.

 

3. Faults and solutions of "random buckling" during processing

 

Working principle of the system: General thread processing can only be completed after several cuts, and the position where the tool starts to feed must be the same every time the cutting is repeated. In order to ensure that the repeated cutting does not mess up, the numerical control system starts the calculation of thread cutting after receiving the one-turn signal from the spindle encoder.

 

 

Causes of failures and solutions: When the first-rotation signal obtained by the system is unstable, the phenomenon of "disorderly buckling" will occur. The cause of the failure is poor connection of the spindle encoder, poor one-turn signal or signal cable of the spindle encoder, dirt inside the spindle encoder or poor encoder itself. If the system still buckles randomly after the above troubleshooting, you need to check the system or the spindle amplifier.