G69 Coordinate System Rotation Cancel: Modals, Alarms, and Setup

If an operator presses reset or performs manual handwheel jog adjustments while G68 mirror coordinates are active, coordinate registers shift by the cutter distance. If automatic operation is resumed without verifying these offsets, the tool post travels along a shifted trajectory, driving the turret directly into table clamps, workpiece fixture vise jaws, or the rotating jaws of the spindle chuck. This sudden positioning error results in a catastrophic hard collision, shatters the cutting tools, throws high-current overload alarm codes such as M01 1036, and converts the workpiece into a completely ruined scrap part.

Technical Summary

Quick Read

• G69 deactivates coordinate mirroring and returns registers to the base turret.
• G14 cancels balance cut mode synchronization.
• Parameter #1202 mirofs defines the distance between base and facing turrets.
• Mitsubishi allows mirror activation directly via the T command.
• Never switch program compilers (G188) while mirror image mode is active.
• Manually shifting axes during active mirroring requires absolute coordinate verification before restart.

Basic Concepts

Implementing the modal G68 mirror image function on turning centers provides programmers with coordinate flexibility when machining symmetrical parts on facing turrets. By automatically reversing the coordinate sign of the X-axis and shifting the program coordinate system to the opposed turret side, G68 allows operators to use programs written for the base turret to cut parts on the facing turret without recalculating coordinates. Similarly, G15 balance cutting synchronizes the start of the cutting feed on both turrets.

When machining long, thin workpieces, applying cutting tools simultaneously from both sides of the raw stock prevents workpiece deflection, suppresses structural slack, eliminates vibrations, and significantly reduces cycle times. Prior to starting automatic cycles, the setup operator must physically position and secure the raw stock within the workpiece workholding—such as clamping it in a machine vise jaw, table clamp, or the rotating jaws of a spindle chuck.

Command Structure

The G69 command cancels the active mirror image mode established by G68. This shifts the coordinate framework from the opposed facing turret back to the base turret. The syntax operates as a standalone preparatory code and does not require additional axis definitions on the block.

Balance cutting modes follow a separate structure, requiring G15 to activate synchronization and G14 to deactivate it. The synchronization operation number is specified using the L address. Operators must ensure that appropriate parameters are configured for tool selection masking and coordinate shifting.

G69 ;
G14 ;

Brand Applications

Fanuc

Fanuc controls handle facing turret mirrors using explicit G68 and G69 preparatory blocks. The control relies on the active G69 command to restore standard coordinate processing.

G68 ;
G69 ;

Fanuc lacks direct T-command mirroring integration, requiring the programmer to insert standard G-code blocks.

Siemens

Siemens processes coordinate rotations and mirrors using active frame management. When cancelling frames, the native frame rollback completely deselects active modals.

G68 ;
G69 ;

Siemens completely deselects active frames and modals during native frame rollback.

Mitsubishi

Mitsubishi permits the mirror image of facing turrets to be turned ON and OFF directly via the tool selection (T command) rather than preparatory G-codes. Guided by parameters like #1119 Tmiron and #1203 TmirS1.

G68 ;
G14 ;

Mitsubishi dynamically integrates G68/G69 turning modals with its manual arbitrary reverse run (G127) function to track tool compensation accurately.

Brand Comparison

Technical Analysis

Three key programmatic and coordinate behaviors clearly distinguish Mitsubishi’s mirror image and balance cut handling from Fanuc and Siemens controls during turning operations. Mitsubishi permits the mirror image of facing turrets to be turned ON and OFF directly via the tool selection T command rather than preparatory G-codes. Guided by parameters #1119 Tmiron, #1203 TmirS1, and #1204 TmirS2, selecting a designated tool number dynamically shifts the workpiece coordinate systems and wear offsets. Fanuc and Siemens controls lack this T-command mirroring integration, requiring explicit G68/G69 preparatory blocks in the part program.

Mitsubishi dynamically integrates G68/G69 turning modals with its manual arbitrary reverse run (G127) function. When manual arbitrary reverse run is active, the operator can manually turn the handwheel backward to retract the tool. During this reverse tracing, Mitsubishi’s motion kernel successfully tracks and maintains the active G68 coordinate shifts, tool direction compensations (#1118 mirr_A), and offsets using its specialized modal information storage block, preventing axis drift and maintaining coordinate safety. Siemens completely deselects active frames and modals during native frame rollback.

Mitsubishi enforces a parameter-locked validation flag for bimodal program format switching under active mirroring. If a G188 command is issued in a part system that is actively in T-code mirror image mode, the control immediately blocks the compiler switch and generates Program Error (P29). This ensures coordinate tables are clean and initialized before shifting compilers, a protective register lock not monitored by Fanuc or Siemens controls.

Program Examples

Fanuc Example

O1001
G68 ; Turn ON mirror image for opposed turret
T0202 ; Call tool
G69 ; Cancel mirror image

dry run: Execute the block without physical stock. Verify that the coordinate shift activates on G68 and fully drops after reading G69.

Siemens Example

N10 G68 ; Activate mirror image
N20 T2 D1 M6 ; Call tool and offset
N30 G69 ; Cancel mirror image

dry run: Step through the cycle in a safe machine state. Ensure active frames revert smoothly after G69 execution without residual offsets.

Mitsubishi Example

G68 ; Turn ON mirror image for facing tool posts
T0202 ; Facing turret selection
G69 ; Cancel mirror image
G15 L10 ; Activate balance cut mode
G14 ; Cancel balance cut mode

dry run: Simulate the cycle using graphics. Confirm that T0202 triggers the parameter-driven shift and that G14 successfully cancels path synchronization.

Error Analysis

Application Note

A critical cause of program failure during balance cutting is assuming that the controller maintains path synchronization throughout the cycle. The balance cut command only synchronizes the start of the cutting feed; it does not dynamically coordinate axis movements or overrides thereafter. To prevent catastrophic failures, the programmer must ensure that travel distances, feedrates, override states, and interlock keys of both turrets are programmed identically.

Related Command Network

• G68: Activates the mirror image coordinate shift.
• G14: Cancels the balance cut synchronization.
• G188: Switches program formats which must not be executed during mirror modes.

Conclusion

Always verify coordinate shifts and active modals before restarting automatic operation, especially after manual handwheel adjustments.

FAQ

How do I cancel a mirror image offset without a G69 command?

On Mitsubishi controls, you can configure parameter #1119 Tmiron to allow the T command to directly manage and cancel the mirror image when selecting a tool from the base turret.

Why does the machine generate a P29 alarm during a tool change?

Commanding a G188 program format switch while the tool system is still running in active T-code mirror image mode will immediately halt the operation and generate a P29 alarm. You must disable mirrors before switching compilers.

What causes the turret to crash after pressing reset during a balance cut?

If an operator performs manual handwheel jog adjustments while G68 mirror coordinates are active, coordinate registers will shift. Resuming automatic operation without verifying offsets drives the turret into the chuck.