G50 Scaling Cancel (Milling): Fanuc, Siemens & Mitsubishi Guide

Production Risks and Safety in Coordinate Scaling

Shifting or resetting coordinate transformations on the shop floor without clearing active scaling coordinates causes the spindle to descend using uncompensated trajectories, driving the tool directly into table-mounted clamps, fixture vise jaws, or the rotating chuck. Under Fanuc, Siemens, and Mitsubishi CNC rules, executing a program reset, commanding M02 or M30, or triggering an emergency stop while in scaling mode automatically forces the control back to scaling cancel (G50) mode. If the setup operator resumes machining after a reset without re-calling the G51 block, the tool will travel at full 1:1 scale instead of the programmed reduction. This sudden increase in coordinate dimensions drives the tool path far beyond the expected workpiece envelope, resulting in a catastrophic hard collision that shatters the carbide cutting insert, damages the machine axis, and converts raw stock into a ruined scrap part.

Attempting to program circular interpolation (G02 or G03) while scaling is active on only one axis of the plane configurations triggers immediate control lockouts. The interpolation preprocessor requires equal scaling multipliers on both plane axes to resolve the path radius. If this constraint is violated, the machine ceases motion, throws axis overload alarm codes (such as Program Error (P70)), and aborts the machining cycle. Operators must maintain absolute vigilance regarding active modal states and verify coordinate limits before restarting execution.

Technical Summary

Property	Specification
Command Code	G50 (Fanuc, Mitsubishi, Siemens ISO Dialect) / SCALE (Siemens Native)
Modal Group	Group 11 (Fanuc/Mitsubishi modal), Group 18 (Siemens ISO Dialect modal), or native Siemens frame deactivation (SCALE)
Supported Brands	Fanuc, Siemens, Mitsubishi
Critical Parameters	Fanuc Parameter No. 3401 (Bits GSC/GSB), Parameter No. 8072 (SCALING P); Siemens MD 22914 ($MC_AXES_SCALE_ENABLE), MD 18800 ($MN_MM_EXTERN_LANGUAGE); Mitsubishi Parameter #8072 SCALING P, Parameter #1151 rstint
Main Constraint	Scaling does not apply to cutter compensation amounts (tool length offset or tool radius compensation). Program G50 in a separate block at a safe clearance position. Circular interpolation (G02/G03) is restricted when active scaling is unequal or on only one plane axis, triggering program errors. Feedrates (F) and spindle speeds (S) remain unscaled and must be manually recalculated.

Quick Read

• Program G50 in a separate block at a safe height to cancel all active G51 scaling coordinates before executing machine home returns.
• Recalculate and scale programmed feedrates manually during active scaling, as G51 only affects geometry axes and leaves F-values unscaled.
• Apply equal scaling factors to both axes of the plane before executing circular interpolation (G02/G03) to prevent G-code program errors.
• Ensure the external language parameter MD 18800 is activated before programming G50 or G51 on Siemens SINUMERIK controls.
• Always cancel active cutter compensation (G40) before activating coordinate scaling to avoid path calculation faults.
• A program reset, M30 command, or emergency stop automatically forces the controller to revert to G50 Scaling Cancel mode.

Basic Concepts of Coordinate Scaling

Activating G51 scaling on a milling machine center provides a powerful mathematical tool to enlarge or reduce programmed workpiece geometry. By specifying a pivot center and a scaling factor, programmers can adapt a toolpath to accommodate material shrinkage or machine nested identical features without recalculating coordinate points. The G50 command cancels this coordinate transformation, restoring coordinate calculations to a standard 1:1 scale.

Scaling centers and scaling factors are defined through specific addresses in the G51 block. The coordinates of the scaling pivot center are entered relative to the active coordinate system (G54 to G59). Scaling factors can be applied globally to all axes or independently to individual axes using parameters P or I, J, K. Minimum command increments vary by control resolution systems, typically supporting up to six decimal places for precise scaling factors.

Tool radius and length compensations are calculated on the physical shape after the scaling calculation is completed. This means that scaling factors do not apply directly to offsets like G41/G42 cutter radius compensation. Standard programming practices dictate that all cutter radius offsets must be canceled using G40 before entering scaling mode, and reloaded once G50 restores standard dimensions.

Command Structure and Syntax

The syntax for coordinate scaling cancellation is straightforward, but its operation depends on the active compiler mode and brand configuration. On Fanuc, Mitsubishi, and Siemens in ISO Dialect mode, G50 cancels Group 11 or Group 18 modal scaling. In native Siemens SINUMERIK mode, absolute scaling cancel is performed by issuing the SCALE command without parameters.

When G50 is programmed, it terminates the active scaling mode globally for all axes. The G51 command must have been previously active to declare the scaling center and factors. For best results on the shop floor, G50 should always be programmed in a separate block at a safe clearance location before returning to reference positions or ending the program.

• G50 ; - Scaling mode cancel (Fanuc, Mitsubishi, Siemens ISO mode)
• G51 X__ Y__ Z__ P__ ; - Scaling ON with common factor P at center X, Y, Z
• G51 X__ Y__ Z__ I__ J__ K__ ; - Scaling ON with axis-specific factors I, J, K
• SCALE ; - Native Siemens absolute scaling cancel (resets all scale factors back to 1:1)
• SCALE X__ Y__ Z__ ; - Native Siemens absolute scaling ON
• ASCALE X__ Y__ Z__ ; - Native Siemens additive scaling ON

Command parameters and address registers configure the scaling center and factors during program execution:

• X: Absolute coordinate of the scaling center on the X-axis.
• Y: Absolute coordinate of the scaling center on the Y-axis.
• Z: Absolute coordinate of the scaling center on the Z-axis.
• P: Common scaling factor multiplier applied to all basic axes (minimum input increment is 0.000001).
• I: Scaling factor for the basic 1st axis (X-axis).
• J: Scaling factor for the basic 2nd axis (Y-axis).
• K: Scaling factor for the basic 3rd axis (Z-axis).

Brand Applications and Parameter Configurations

Fanuc

Fanuc controls rely on G-code Group 11 modal commands to manage coordinate scaling. The active G-code system is configured by Parameter No. 3401 (Bits GSC/GSB), and Parameter No. 8072 sets the default background scaling factor P. Setting Parameter No. 1013 configures the increment system for scaling calculations.

Activating scaling uses G51 with scaling center coordinates and factor address P, while G50 cancels the active scaling mode. If a circular interpolation command (G02 or G03) is executed while scaling is active on only one of the two active plane axes, the control halts with Program Error (P70).

• Parameter No. 3401 (Bits GSC/GSB): Selects G-code system A, B, or C, which determines G50's modal group.
• Parameter No. 8072 (SCALING P): Default scaling factor if P or I/J/K is omitted from the G51 block. Value range: -99999999 to 99999999 (representing -99.999999 to 99.999999 times).
• Parameter No. 1013: Defines the increment system for scaling coordinate calculations.
• Program Error (P70): Circular interpolation (G02/G03) programmed when scaling is active on only one axis of the plane.
• Program Error (P35): Commanded scaling factor exceeds limits (outside -99.999999 to 99.999999).
• Program Error (P350): G51 scaling commanded but option not installed.
• Lathe vs. Milling Difference: In lathes, G50 is Group 00 unmodal for spindle speed clamping or coordinate presets. In milling, G50 is Group 11 modal scaling cancel.
• Series 15 Program Format: Parameter No. 0001 Bit 1 (FCV) set to 1 enforces Series 15 format, which overrides scaling parameter evaluations during repetitive canned cycles.

Executing zero-return commands (G28 or G30) during active scaling causes Fanuc controls to scale the intermediate point vector. Always program G50 before home returns to prevent axis crash.

Siemens

Siemens SINUMERIK controls manage coordinate scaling as an independent component of a dynamic frame memory structure. Programmers switch the interpreter to ISO Dialect mode via G291 to enable G50/G51, requiring machine data parameter MD 18800 to be set to 1. Native scaling is managed via SCALE and ASCALE blocks, where a naked SCALE deactivates scaling factors.

Calling zero offset suppression commands (G53, G153, SUPA) will suppress tool offsets depending on MD 10760. Ensure offsets are reloaded before calling technology cycles to prevent program aborts.

• MD 22910 $MC_WEIGHTING_FACTOR_FOR_SCALE: Defines the base unit of the programmed scaling factors.
• MD 22914 $MC_AXES_SCALE_ENABLE: Set to 1 to enable axial scaling factor functionality for specified axes.
• MD 10760 $MN_G53_TOOLCORR: Suppresses or retains tool length and radius offsets during coordinate frame suppression (G53, G153, SUPA). Value range: BYTE (2 to 4, default 2).
• MD 18800 $MN_MM_EXTERN_LANGUAGE: Set to 1 to activate external NC compiler for G291, G50, and G51.
• Alarm 12080 "Syntax error": Programmed G50 block in native Siemens mode (G290), or programmed block skip characters or illegal formatting during scaling.
• Alarm 14800: Programmed a path velocity (feedrate F) that evaluates to less than or equal to zero.
• Alarm 14011: Commanded G10.6 rapid retract but the retraction subroutine CYCLE3106.spf is missing from the NC memory.
• Alarm 61800: Attempted to switch to G291 or program G50/G51 commands when MD 18800 is disabled.
• SINUMERIK 840D sl vs. 802D sl: Dynamic adjustments for block skip levels and DryRun behaviors are available in 840D sl but are hard-locked in 802D sl.
• Hardware Features: High-end 840D sl features multi-touch panels with minimized sidescreens and a dedicated "Collision avoidance" option not supported on compact/legacy models.

Calling a naked SCALE command to cancel only scaling in native mode will reset all frame components, immediately clearing active zero translations (TRANS) and coordinate rotations (ROT).

Mitsubishi

Mitsubishi controls execute scaling cancel according to active format parameters and reset settings. The modal reset behavior is governed by Parameter #1151 rstint and #1210 RstGmd, which determine if the scaling cancel modal G50 is initialized on reset. Setting active input units is managed via Parameter #1003 iunit and Parameter #1041 I_inch.

Activating scaling uses G51 with scaling center coordinates and factor address P, while G50 cancels the active scaling mode. System variables for scaling offsets are mapped to variables #30080 to #30097, which are disabled on lathe systems.

• Parameter #8072 SCALING P: Default background scaling factor if scaling factor is omitted from the G51 block. Value range: -99999999 to 99999999.
• Parameter #1151 rstint: Reset initial configuration: 0 (retains modals) or 1 (cancels modals).
• Parameter #1210 RstGmd: Modal G-code reset setting: controls if Group 11 scaling status is initialized or retained on reset.
• Parameter #1003 iunit: Selects the command resolution system and active input unit system.
• Parameter #1041 I_inch: Selects active input unit system (metric/inch dimensions).
• Program Error (P350): Commanded G51 scaling when the scaling software option is not installed or enabled in the control system.
• Program Error (P35): Programmed a scaling factor value outside allowable limits (outside -99.999999 to 99.999999, or between -0.000001 and 0.000001 excluding zero).
• Program Error (P70): Commanded G02 or G03 circular interpolation when scaling is active for only one of the two active plane axes.
• Lathe vs. Milling Difference: In lathes, G50 is Group 00 unmodal for spindle clamp speed or coordinate settings. In milling, G50 is Group 11 modal scaling cancel.
• M800/M80 Series Variables: Scaling system variables mapped to #30080 to #30097 are fully enabled in milling (M) systems but completely disabled (marked with ×) in Lathe (L) systems.

Performing a workpiece coordinate preset (G92) during active scaling shifts the physical scaling center by the exact offset amount, causing subsequent toolpath deviation.

Brand Comparison

Topic	Fanuc	Siemens	Mitsubishi
Scaling activation G-code	G51 (milling Group 11)	Native: SCALE/ASCALE; ISO Dialect Mode: G51 (Group 18)	G51 (milling Group 11)
Scaling cancel command	G50	Native: SCALE (axial or global deactivation); ISO Dialect Mode: G50	G50
Lathe G50 mapping	Spindle clamp speed limit setting or coordinate system setting (Group 00 unmodal)	— (no source)	Spindle clamp speed limit setting or coordinate system setting (Group 00 unmodal)
Integration with manual reverse run	— (no source)	— (no source)	Active scaling vectors remain valid and are successfully recovered using the modal information storage block (G127)
Bilingual Program Format Switch compiler	— (no source)	Switch interpreter via G290/G291	Toggles turning and milling format via G188/G189 G-codes
Global suppression control	Suppressed at the intermediate point during reference returns (G28/G30)	Suppression via G53, G153, SUPA frames, governed by MD 10760	Suppressed at the intermediate point during reference returns (G28/G30)

Technical Analysis of Brand Variations

Analyzing coordinate scaling cancellation reveals three distinct architectural methods for managing G-code transformations. First, Fanuc and Mitsubishi controls rely on G-code Group 11 modal G-codes (G50/G51) to switch scaling modes, meaning that G50 cancels only scaling without impacting other modal groups or offset registers. Siemens SINUMERIK controls bypass G50/G51 in native mode, treating scaling as an independent frame transformation (SCALE or ASCALE). Canceling scaling in native Siemens mode via a naked SCALE command resets all frame components of the active programmable frame, meaning active zero offsets (TRANS) and coordinate rotations (ROT) are cleared simultaneously.

Second, interpreter switching methodologies divide Siemens from Fanuc and Mitsubishi. Siemens utilizes a bilingual compiler model, switching the interpreter to ISO Dialect mode via G291 to compile G50 and G51 blocks. Toggling the interpreter back to native SINUMERIK mode requires a G290 command, where pocket cycles and high-level frame calculations are executed. Mitsubishi achieves format shifts through standard G-code switches G188 and G189 to toggle between lathe and machining center code layouts, which dynamically resets G-code tables. Fanuc lacks single-program compiler switching of this kind, relying strictly on background parameters (Parameter No. 3401) to hardcode G-code system modalities.

Third, integration with advanced machine functions highlights Mitsubishi's unique modal handling during manual interventions. When manual arbitrary reverse run (G127) is active, Mitsubishi's motion kernel retains and restores active scaling vector coordinates using its specialized modal information storage block to prevent axis drift. Siemens suppresses frames globally during SUPA, G153, or G53 moves, governed by machine data MD 10760. Fanuc suppresses coordinate transformations strictly at the intermediate point during G28 or G30 home returns, with no integrated handwheel rollback recovery for unmodal coordinates.

Program Examples and Dry Run Walkthroughs

Fanuc G-Code Program Example

N10 G90 G00 G54 X-100.0 Y-100.0 ; Rapid traverse to absolute start position
N20 G51 X-100.0 Y-100.0 P0.5 ; Activate scaling at center X-100 Y-100 with factor 0.5
N30 G01 X0 Y0 F150 ; Machine profile at 50% scale
N40 G40 G50 X0 Y0 ; Cancel cutter compensation and scaling mode before return coordinates
N50 G91 G28 X0 Y0 Z0 ; Return to reference home position

Dry Run Walkthrough

• Block N10: Rapidly positions the axes to the absolute coordinates (X-100.0, Y-100.0) in the G54 coordinate system.
• Block N20: Activates coordinate scaling with a factor of 0.5 (reducing the programmed toolpath size by half), centered at the physical pivot point (X-100.0, Y-100.0).
• Block N30: Moves the tool to target coordinates (X0, Y0) in a straight line at 150 mm/min. Because scaling is active with factor 0.5, the actual physical travel is 50 mm instead of 100 mm.
• Block N40: Cancels tool radius compensation (G40) and scaling mode (G50), restoring coordinate multipliers to a standard 1:1 ratio.
• Block N50: Performs an incremental machine reference return to the Z, X, Y home position, ensuring that the intermediate coordinate calculation is unscaled.

Siemens G-Code Program Example

N10 G17 G54 T01 D01 M03 S1500 ; Select plane, zero offset, tool edge, start spindle
N20 TRANS X15 Y15 ASCALE X0.7 Y0.7 ; Native mode: Shift zero offset and scale XY contour by 0.7
N30 SCALE ; Native mode: Cancel scale factors and reset active programmable frame
N40 G291 ; Switch interpreter to ISO Dialect Mode to compile legacy codes
N50 G51 X0 Y0 P0.5 ; ISO mode: Activate scaling at center X0 Y0 with factor 0.5
N60 G50 ; ISO mode: Deactivate scaling and restore 1:1 path calculation

Dry Run Walkthrough

• Block N10: Selects the active working plane XY (G17), activates G54 workpiece zero offset, loads tool edge D01, and starts spindle rotation at 1500 RPM.
• Block N20: Shifts the current zero position by 15 mm in X and Y, and adds an axial scale factor of 0.7 to both geometry axes.
• Block N30: Clears the scaling factor and resets the programmable frame coordinate transformation (clearing the translation offset programmed in N20).
• Block N40: Switches the SINUMERIK control compiler interpreter to ISO Dialect mode.
• Block N50: Activates scaling centered at (X0, Y0) with a scaling factor multiplier of 0.5 (reducing toolpath dimensions by half).
• Block N60: Commands G50 to deactivate scaling and return the control to a standard 1:1 path calculation in ISO Dialect mode.

Mitsubishi G-Code Program Example

N10 G90 G00 G54 X-100.0 Y-100.0 ; Rapid traverse to absolute coordinate clearance values
N20 G51 X-100.0 Y-100.0 P0.5 ; Activates scaling at center X-100 Y-100 with factor 0.5
N30 G01 X0 Y0 F200 ; Machine profile at scaled size
N40 G50 G40 X0 Y0 M30 ; Cancels scaling and cutter compensation, returns to original coordinates and ends program

Dry Run Walkthrough

• Block N10: Executes a rapid traverse positioning movement to absolute clearance coordinates (X-100.0, Y-100.0) in the G54 system.
• Block N20: Activates coordinate scaling with a scaling factor multiplier of 0.5 (reducing toolpath travel distances by half), centered at the coordinate pivot point (X-100.0, Y-100.0).
• Block N30: Executes a linear feed move to target coordinate (X0, Y0) at 200 mm/min. The physical tool movement path is scaled to 50% size.
• Block N40: Cancels active scaling mode (G50) and tool radius compensation (G40) while resetting the coordinates to a standard 1:1 ratio, ending program execution (M30).

Error and Alarm Analysis

Brand	Alarm Code	Trigger Condition	Operator Symptom	Root Cause & Resolution
Fanuc	Program Error (P70)	Circular interpolation (G02/G03) commanded while scaling is active on only one axis of the plane.	Cycle halts immediately with plane calculation alarm display.	Cancel scaling mode using G50 before arc commands, or program equal scale factors for both plane axes.
Fanuc	Program Error (P35)	Programmed scaling factor exceeds control limits (outside -99.999999 to 99.999999).	Controller displays command limit exceeded message and stops program.	Correct the scaling factor multiplier to fall within allowable limits.
Fanuc	Program Error (P350)	Command G51 scaling called in program when scaling option is not enabled on the control.	CNC halts with program error code display.	Enable the scaling software option or remove scaling blocks from program.
Siemens	Alarm 12080 "Syntax error"	Programmed G50 block in native Siemens mode (G290), or programmed block skip characters or illegal formatting.	Spindle stops and syntax error warning displays.	Program G50 only in ISO Dialect mode (G291), or correct formatting syntax.
Siemens	Alarm 14800	Programmed a path velocity (feedrate F) that evaluates to less than or equal to zero.	Program execution halts with path velocity warning.	Ensure a non-zero feedrate F is commanded and active in the program.
Siemens	Alarm 61800	Executed G291 or G50/G51 commands when MD 18800 (external language compiler) is disabled.	NC halts with missing external language interpreter message.	Set machine data parameter MD 18800 to 1 to enable the ISO Dialect compiler.
Mitsubishi	Program Error (P350)	Command G51 scaling called when the scaling option is not installed or enabled.	Machine cycle stops with option missing alarm.	Enable the scaling software option or modify program files.
Mitsubishi	Program Error (P35)	Programmed a scaling factor value outside allowable limits (outside -99.999999 to 99.999999, or between -0.000001 and 0.000001 excluding zero).	Control halts with factor parameter out of range message.	Adjust scaling factor to fall within safe boundaries.
Mitsubishi	Program Error (P70)	Commanded circular interpolation (G02/G03) when scaling is active for only one of the two active plane axes.	The program execution aborts and alarm display appears on the screen.	Apply equal scaling to both plane axes or command G50 to cancel scaling before arc interpolation.

Application Note

Shattering carbide tool inserts, bending machine spindle axes, or fracturing solid carbide cutters occurs when a setup operator fails to execute G50 scaling cancel at a safe clearance height before returning the spindle to the home position or tool change location. If a program reset, emergency stop, or program end (M02 or M30) is executed, the control automatically reverts to Scaling Cancel (G50) mode. If the operator resumes the cycle without re-calling the scaling block, the tool will travel at full 1:1 scale instead of the reduced scale, shifting coordinate boundaries and driving the tool path far beyond the expected workpiece envelope. If these unexpected movements occur near physical fixtures, the tool can plunge directly into table-mounted workpiece clamps or the rotating spindle chuck. This sudden impact results in a severe hard collision, shatters the cutting insert, damages the machine axis, triggers an overload alarm code (such as Program Error P35 or P70), and converts the raw stock into a completely ruined scrap part.

Related Command Network

• G51: Activating coordinate scaling (milling Group 11 for Fanuc/Mitsubishi, Group 18 for Siemens ISO Dialect) to enlarge or reduce workpiece geometry relative to a pivot center.
• SCALE / ASCALE: Absolute or additive programmable coordinate scaling commands in native Siemens frame transformations.
• G290 / G291: Native SINUMERIK mode or ISO Dialect mode interpreter switch commands on Siemens controls to compile legacy G-codes.
• G188 / G189: Change command format between turning and milling G-code systems on Mitsubishi controls.
• G28 / G30: Reference point returns that temporarily suppress active scaling factors at the intermediate point coordinates.
• G52 / G92: Local coordinate system setting and coordinate preset commands that shift the active scaling center register.
• g40-compensation-cancel: Deactivates tool radius compensation, which must be executed prior to starting scaling. Link: g40-compensation-cancel
• g41-cutter-radius-compensation: Applies cutter radius compensation to the left, which is calculated based on the scaled toolpath coordinates. Link: g41-cutter-radius-compensation
• g49-tool-length-compensation-cancel: Cancels active tool length offsets, another critical cancellation G-code that must be executed at safe clearance positions. Link: g49-tool-length-compensation-cancel

Conclusion

Systematically programming G50 at the end of every coordinate-scaled machining sequence ensures that subsequent programs and coordinate transformations execute with predictable 1:1 scaling. Checking parameters—such as Fanuc No. 8072 or Siemens MD 22914—prior to machining prevents scaling errors and alarms during automated cycles. Maintaining a clear protocol for safe tool retraction before deactivating active scaling protects expensive machine spindles, fixtures, and workpiece materials from unexpected movements.

Frequently Asked Questions

Why does my machine alarm when performing G02 or G03 while scaling is active?

This alarm occurs because circular interpolation requires identical scaling factors on both plane axes to generate a perfect arc. Programmers must check the active plane (G17, G18, or G19) and ensure that equal scaling values are programmed in G51 (or that SCALE factors match exactly). If unequal scaling is needed, convert the arc move to linear segments (G01) or cancel scaling using G50 before calling G02/G03.

What happens to tool radius and length compensations when G50 is active?

Coordinate scaling cancels only geometry path movements and does not apply to active tool length offsets (G43/G44) or cutter radius compensation (G41/G42). The controller calculates compensations on the physical shape after the scaling calculation is completed. Standard operating procedures dictate that programmers must cancel active cutter compensation (G40) before commanding G51, and reload tool data before resuming 1:1 machining after G50.

Does G50 automatically execute on a control reset?

Yes, on standard Fanuc, Mitsubishi, and Siemens ISO settings, an emergency stop, NC reset, or program termination (M02/M30) automatically forces the control back to G50 (Scaling Cancel) mode. Programmers must verify that the modal status has been re-called (G51) if a program is aborted and restarted mid-cycle. Verify control parameters No. 1210 (Mitsubishi) or MD 20150 (Siemens) to customize modal retention behaviors for your specific machine.