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FANUC Controller
Overtravel/Limit · Intermediate · 15-30 minutes
Fanuc Alarm 204 - ILLEGAL AXIS OPERATION
Alarm 204 occurs when the NC detects axis movement commands between the rigid tapping preparation block (M29 or similar rigid tap M-code) and the actual tapping cycle execution block (G84 or G74). The rigid tap synchronization requires these blocks to be consecutive without intervening axis motion to maintain spindle-axis lock integrity.
204
Fanuc Alarm 204 - ILLEGAL AXIS OPERATION
Axis Overtravel HW
In rigid tapping, an axis movement is specified between the rigid M code (M29) block and G84 (or G74) block.
Root Cause Summary
Alarm 204 occurs when the NC detects axis movement commands between the rigid tapping preparation block (M29 or similar rigid tap M-code) and the actual tapping cycle execution block (G84 or G74). The rigid tap synchronization requires these blocks to be consecutive without intervening axis motion to maintain spindle-axis lock integrity.
Safety
- Check for crash damage before continuing
- Ensure the machine is in a safe state before attempting any troubleshooting. Disconnect power if necessary.
- Be aware of potential pinch points and moving parts when working around the machine.
- Exercise caution when jogging the axis away from the limit. Use low jog speed and be prepared to stop the machine immediately if necessary.
- Electrical hazards exist when working with limit switches and wiring. Disconnect power before inspecting or repairing electrical components.
- Refer to the machine's safety manual for specific safety precautions and procedures.
- Always check for potential crash damage before attempting to move the axis
- Wear appropriate personal protective equipment during inspection and troubleshooting
Causes and Fixes
- 1
Review the NC program at the alarm occurrence point. Press RESET, then navigate to PROGRAM > check the active program line number displayed when alarm triggered. Look for any G00, G01, G02, G03, or other axis move commands between M29 and G84 (or G74) blocks.
- 2
Modify program to remove all axis positioning between M29 and G84/G74. Correct format is either: separate consecutive blocks 'N10 M29 S___ ; N20 G84 X_ Y_ Z_ R_ F_ ;' or combined single block 'N10 G84 X_ Y_ Z_ R_ F_ M29 ;'. No G-code motion commands between these.
- 3
Verify parameter 5200 bit 6 (RGT) = 1 to enable rigid tapping mode. Check SYSTEM > PARAM > search parameter 5200, confirm rigid tap function is enabled for the machine configuration.
- 4
After program correction, reset alarm with RESET key, return spindle to position mode if necessary (M19), and restart cycle from a safe block before the rigid tap sequence.
Ensure spindle orientation is correct before re-executing rigid tap cycle.
Call a technician if:
- ·Parameter 5200 series changes required
- ·Custom macro modification needed
- ·Persistent alarm after program corrections
Prevention
- Always position axes before M29 command
- Use G80 to cancel active canned cycles before rigid tapping
- Avoid subroutine calls within rigid tap sequences
- Verify modal G-code states before tapping operations
Common Mistakes
- Programming Z-axis retract between M29 and G84
- Leaving G41/G42 compensation active during rigid tapping
- Using G00 rapid positioning after M29 command
- Calling tool change macros within tapping sequence
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