Fanuc Alarm 49: ILLEGAL OPERATION (G68/G69)

Fanuc Alarm 49: ILLEGAL OPERATION (G68/G69)

Fanuc Control Model: Fanuc 0i, 15i, 16i / 18i / 21i, 30i / 31i / 32i

Fanuc Alarm 49 (PS0049) is a Program / Software (P/S) alarm indicating an improper command execution involving G68 (Coordinate System Rotation) or G69 (Cancel Rotation). This error usually occurs when G68/G69 commands are placed inside restricted control modes or combined with incompatible G-codes.

Official Alarm Description

The commands for three–dimensional coordinate conversion (G68,G69) and tool length compensation (G43, G44, G45) are not nested.Modify the program.

Common Causes of Fanuc Alarm 49

This alarm is triggered when the CNC controller encounters invalid G-code sequence commands. Common reasons include:

1. Commanding G68 during Cutter Compensation: Trying to turn on Coordinate Rotation (G68) while Tool Nose / Cutter Radius Compensation (G41 or G42) is active.
2. Missing G69 Cancel Command: Turning on G68 without canceling it with G69 before switching work coordinate systems or calling specific canned cycles.
3. Invalid G-Code inside G68 Block: Attempting to command specific G-codes (like G27, G28, G29, or G30 zero return commands, or coordinate system changes like G52/G54–G59) while G68 rotation mode is enabled.
4. Incorrect Axis Input: Specifying coordinate rotation values or plane selection (G17, G18, G19) incorrectly within the G68 block.

Step-by-Step Troubleshooting & Solution

Follow these steps on your Fanuc CNC control panel to clear Alarm 49:

1. Identify the Faulty Block: Switch to EDIT mode and review the block (line) highlighted by the cursor when the alarm stopped the machine.
2. Check G41/G42 Status: Ensure G40 (Cutter Compensation Cancel) is executed BEFORE the G68 line.
3. Check G68 Syntax: Verify your G68 syntax matches the required plane and format:
   • G17 (XY Plane): G68 X_ Y_ R_
4. Insert G69 Cancel: Ensure G69 is called at the end of the rotated section before returning to machine zero (G28) or changing work offsets (G54).
5. Clear Alarm: Press the RESET key on the MDI panel to clear the error and restart execution.

G-Code Example (Correct vs Incorrect)

Incorrect Code (Triggers Alarm 49):

G-Code

G01 G41 X20. Y10. F150 (Cutter Comp Active)
G68 X0 Y0 R45.0        (ERROR: Cannot command G68 while G41 is active)
G01 X50. Y30.

Correct Code (Fixed):

G-Code

G40 G00 X0 Y0          (Cancel Cutter Comp FIRST)
G68 X0 Y0 R45.0        (Enable Rotation)
G01 G41 X20. Y10. F150 (Now enable Cutter Comp)
...
G40 G00 X100. Y100.    (Cancel Cutter Comp)
G69                    (Cancel Coordinate Rotation)

Frequently Asked Questions (FAQs)

Q1: Can I use G68 inside a subprogram?

Yes, but you must ensure that G68 is properly canceled with G69 inside or immediately after the subprogram before returning to main machining commands.

Q2: Will turning off the machine clear Fanuc Alarm 49?

Power cycling will reset the alarm state, but the machine will stop again at the exact same line unless you edit the faulty G-code.

Have you faced Fanuc Alarm 49 ILLEGAL OPERATION (G68/G69) on your machine? Share your experience or troubleshooting tips in the comments below to help other CNC operators and programmers clear this error faster!