Top 10 Common CNC Spindle Troubles and Solutions

Machine Spindle

As one of the core components of CNC machine tools, the main shaft is mainly used to drive the rotation of workpieces or tools on machine tools. It usually works in high humidity, heavy dust and large temperature difference working environments. Not only does it need to "work day and night", but it also needs to ensure accurate processing accuracy. CNC machine spindles usually consist of spindle, bearings and drive components (gears or belts), which are important guarantees for high-precision machining of CNC machine tools. However, some troubles may occur over time.

Spindles are mainly divided into two categories in practical applications: one is the high-speed electric spindle with zero transmission, and the other is the spindle combining variable frequency motor and mechanical speed changing mechanism. The former has the advantages of integrated structure with motor and precise dynamic balance calibration, although it has some limitations on output torque and power; the latter has fewer limitations on output torque and power, but its rotation accuracy and stability are relatively poor.

Therefore, common troubles of CNC spindles generally include damage of spindle components, loose bolts between spindle box and bed, belt slackening, incorrect direction of oil pump rotation, clogged oil pipes, damaged hydraulic valves, damaged electrical components, no detection signals in control system, etc. The corresponding solutions can be further divided into the following ten categories:

Spindle without braking

1. Abnormal brake circuit or damage of strong circuit components: check whether bridge stack, fuse, AC contactor are damaged; check whether strong circuit is interrupted;

2. Braking time is not long enough: adjust braking time parameter of system or converter;

3. System has no brake signal output: replace internal components or send to factory for repair;

4. Converter control parameters are not properly set: check converter manual and set parameters correctly.

Spindle stops immediately after starting

1. Pulse time output by system is not enough: adjust M code output time of system;

2. Converter is in point-to-point state: refer to converter manual and set parameters properly;

3. Damage of control components in spindle circuit: check whether contacts of all relays are in good condition, check whether DC relays, AC contactors are damaged, causing non-self-locking of contacts;

4. Short circuit of spindle motor causes thermal relay protection: find out reason of short circuit and reset thermal relay.

Spindle cannot stop rotating

AC contactor or DC relay is damaged and remains engaged for a long time, failing to control: replace AC contactor or DC relay.

Spindle starts rotating immediately after power-on

1. AC contactor or DC relay is damaged and remains engaged for a long time, failing to control: replace AC contactor or DC relay;

2. IC2803 in system is punctured: replace IC2803 or system mainboard.

Spindle without VFD does not rotate

1. Mechanical transmission fault causes: check belt transmission for breakage or check if machine is in neutral gear;

2. Three-phase power source for spindle lacks phase or is reverse phase: check power source and swap any two power lines;

3. Circuit connection error: carefully refer to circuit connection manual and ensure correct wiring;

4. System has no corresponding spindle control signal output: measure system signal output terminal with multimeter, if no spindle control signal output, internal IC components need replacing or send to factory for repair;

5. System has corresponding spindle control signal output but power supply circuit and signal output circuit have interruptions or component damage: check power supply circuit and signal control circuit between system and motor with multimeter; check contact condition of all wires; check if AC contactor or DC relay is damaged; check thermal relay for overcurrent; check if fuse is burnt, etc.

Spindle with VFD does not rotate

1. Mechanical transmission fault causes: check belt transmission for breakage or check if machine is in neutral gear;

2. Three-phase power source for spindle lacks phase: check power source and swap any two power lines;

3. Converter control parameter of CNC system is not opened: refer to system manual to understand parameter setting of converter and modify it;

4. Connection error between system and converter: refer to wiring diagram between system and converter to ensure correct wiring;

5. Abnormal analog voltage output: check system analog voltage output with multimeter; check if analog voltage signal wire connection is correct or contact poor; check if analog voltage received by converter matches;

6. Strong circuit control part has interruption or component damage: check reliability of contacts in spindle power supply circuit, check for interruptions or damage of DC relay, check if fuse is burnt;

7. Converter parameter is not properly set: converter has control mode selection between converter panel control spindle and NC system control spindle modes, failing to select NC system control mode disables system control of spindle, modify this parameter; check rationality of relevant parameters.

Spindle speed controlled by VFD is uncontrollable

1. Mainboard used has no VFD function: replace mainboard with VFD function; 2. System analog voltage has no output or connection to converter has interruption: first check system for analog voltage output, if no output, it is system fault, if has output, check for interruptions in wiring; 3. Wrong connection between system and converter: refer to connection diagram to check wiring; 4. System or converter parameter is not properly set: open system VFD parameter and adjust converter parameter; 5. Axis speed display error caused by system software: when converter changes from S500 to S800, display is still S500, need G04 delay in programming for software improvement.

Spindle without VFD (gear-changing spindle) speed is uncontrollable

1. System has no S01-S04 control signal output: check system for gear-changing control signal output, if none, it is system fault, replace IC or send to factory; Wiring fault: if system has gear-changing control signal output, check wiring for interruptions or poor contact, check DC relay or AC contactor for damage; Spindle motor damage or short circuit: check spindle motor; Gear not engaged: engage gear position.

Spindle with electromagnetic clutch does not rotate

Coil of electromagnetic clutch is not powered to close gear engagement, causing spindle failure to rotate; short circuit or interruption of coil may also cause spindle malfunction: check if clutch coil is powered normally; check if fuse is damaged; check if clutch coil is damaged, replace qualified components.

Spindle with magnetic brake coil does not rotate

Coil of electromagnetic clutch is not powered to close gear engagement, causing spindle failure to rotate; short circuit or interruption of coil may also cause spindle malfunction: check if clutch coil is powered normally; check if fuse is damaged; check if clutch coil is damaged, replace qualified components.

In summary, the troubleshooting order in CNC machine tool maintenance work should be: First, list possible causes that may cause troubles and preliminarily determine the troubled part before repairing. In general, spindle troubles are quite common in CNC machine tools. As long as mastering the mechanical structure of spindle, analyzing and finding out the cause of troubles, repair and troubleshooting, the spindle can be restored and machine runs normally!