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CNC lathe Trip off when spindle motor running forward

Problem: CNC lathe machine trip off when spindle running forward, but normal when it is running backward in high and low speeds.

CNC lathe specification: GSK980TD/DA98A, double speed spindle motor, 4 station tool post

How to solve the problem:

1, Problem detail:  The CNC lathe was 2 years old, there was no such problem before, now when input spindle motor run forward command in low speed M3 S1 or high speed: M3 S2, the isolating switch for spindle motor in electric box will trip off.


2, Check if the problem is same as described by user: Input M3 S1 under MDI mode, to run spindle motor forward in low speed, the isolating switch of spindle trip off. Then input M3 S2, the same thing happened.

Then Input M4 S1 under MDI mode, to run spindle motor backward in low speed, the isolating switch of spindle trip off. Then input M4 S2, no problem.

Now the problem is confirmed as description, check other functions like tool post, coolant pump and 2 axes, all is fine. From


3, Diagnose: According to above situation, the trip off is happened only when the spindle motor runs forward, no matter low or high speed, so the spindle motor is fine.

The isolating switch of spindle motor trip off can be checked by below steps:

Step 1-The contact terminal or mechanical part of the contactor is stuck, that makes short circuit of the forward and backward phase sequence.

Step 2-The forward contactor lose phase or the wire phase sequence in short circuit.

Step 3-Machanical transmission overload or spindle forward is stuck.


In this case, we found that the forward contactor lose phase, change the contactor and then the CNC lathe machine is working fine again.


Conclusion: Forward contactor lose phase causes 3 phases imbalance, so the isolating switch overload to protect itself.

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