Failure of the electric turret to start is one of the most common and basic faults encountered in CNC machines. When troubleshooting, always follow the principle of checking mechanical issues before electrical issues, and external causes before internal ones. This approach can save a significant amount of diagnostic time.

1. Mechanical Causes (Approximately 60% of Cases)

Excessive Clamping Force

Typical symptoms:

* When turning the worm shaft with a wrench at the worm end, it feels very stiff.
* The shaft can be rotated with considerable force, but the turret still fails to start after clamping.

Recommended solution:

* Reduce the turret motor clamping current by approximately 10–15%.
* Adjust until the worm shaft rotates smoothly while still providing sufficient clamping force for machining operations.

Internal Mechanical Jamming

Typical symptom:

* The worm shaft cannot be turned clockwise at all from the worm end.

Inspection procedure:

Check the anti-backstop locating pin

* If the pin is stuck in the anti-backstop ratchet slot, rotate the connection hole between the anti-backstop ratchet and the screw shaft by 30°–60°, then drill and reconnect.

Check the spindle nut

* If the nut is seized or excessively tight, loosen the locknut and readjust the clearance to 0.02–0.05 mm.

Check lubrication condition

* Lack of lubrication over a long period may cause rotating components to seize.
* Disassemble the turret, polish any damaged surfaces with fine emery paper, and apply suitable lithium-based grease before reassembly.

2. Electrical Causes (Approximately 40% of Cases)

Power Supply and Drive Circuit Faults

Inspection sequence:

1. Check whether any fuse has blown.
2. Verify proper contact of the power switch.
3. Measure the three-phase supply voltage and confirm phase balance (voltage deviation should be within 5%).
4. Inspect the turret cable for open circuits or damage.
5. Check for loose internal wiring connections.

Commonly overlooked issue:

* A misaligned brush-type Hall sensor can cause abnormal power switching and prevent proper turret operation.

Control Signal Faults

If manual indexing works but CNC-controlled indexing does not:

* Inspect the wiring between the PLC and turret controller.
* Check the I/O interface and the turret position feedback signal.

PLC troubleshooting:

* Verify that forward rotation output Y0.0 and reverse rotation output Y0.1 switch to a high state when the corresponding input command is present.
* If either output remains low, replace the associated interposing relay.