The FANUC OT0505 alarm typically occurs when the machine exceeds the negative stored stroke limit due to incorrect work coordinate offsets or restrictive parameter settings. The most likely fix involves verifying and adjusting the G54-G59 offsets or checking the stored stroke limit parameters (1320-1327) for accuracy. Quick resolution often comes from resetting offsets or jogging the axis back within limits. CRITICAL: Always ensure machine is in EMERGENCY STOP before making any parameter or offset changes.
FANUCOvertravel/LimitIntermediate20-60 minutes
OT0505
Fanuc OT0505 - Overtravel alarm: soft limit -3
OVERTRAVEL ALARM: SOFT LIMIT -3
The machine has exceeded the software stored stroke limit in the negative direction on one or more axes. The control detected that commanded position has moved beyond the negative stored stroke limit defined in parameters 1320-1327, which creates a protected zone to prevent collisions with fixtures, tombstones, or machine structural limits. This is a safety interlock that prevents potential machine damage.
Root Cause Summary
The FANUC OT0505 alarm typically occurs when the machine exceeds the negative stored stroke limit due to incorrect work coordinate offsets or restrictive parameter settings. The most likely fix involves verifying and adjusting the G54-G59 offsets or checking the stored stroke limit parameters (1320-1327) for accuracy. Quick resolution often comes from resetting offsets or jogging the axis back within limits. CRITICAL: Always ensure machine is in EMERGENCY STOP before making any parameter or offset changes.
Safety
Before jogging axis back into travel range, visually confirm no obstructions, fixtures, or workpieces in path of movement - collision may have already occurred
If alarm occurred during crash or unusual noise, inspect ball screw, linear guides, and axis coupling for damage before moving axis under power
Do not disable stored stroke check (parameter 1300 bit 4) to bypass alarm - this removes critical collision protection and may void machine warranty
Causes and Fixes
1
Verify Active Offset Values
Press the OFFSET button on the control panel and navigate to the active work offset (G54-G59). Check for large negative values that could push the axis beyond the stored stroke limit. Compare against the setup sheet or known good values.
Take a photo of the offset screen before making changes for reference in case of further issues.
Do not modify offsets without confirming the correct values to avoid further mispositioning.
2
Reset Offset if Necessary
If the offset values are incorrect, manually input the correct values based on the setup sheet or machine zero return position. Ensure the values align with the physical setup of the workpiece and fixture.
Use small incremental changes to test the effect of offset adjustments before running the program.
Ensure the machine is in a safe state before altering offsets to prevent unintended movement.
3
Test Movement with Dry Run
After correcting the offset, perform a dry run of the program in single block mode with feed override set to 0-25%. Monitor the POSITION screen to ensure the axis does not approach the negative stroke limit during the cycle.
Keep a log of offset changes to track recurring issues with specific setups or programs.
Stop immediately if the axis approaches the limit again during the dry run.
1
Access Stored Stroke Parameters
Navigate to SYSTEM > PARAMETERS on the control panel. Locate parameters 1320 (X-), 1321 (Y-), 1322 (Z-), etc., for the negative limits of the affected axis as indicated in the alarm message.
Document the original parameter values before making any changes for future reference.
Ensure parameter write enable (parameter 0000 bit 0=1) is set before attempting changes.
2
Compare Against Manufacturer Specs
Cross-check the parameter values against the machine’s travel specifications provided in the manufacturer’s manual. If the negative limit is set more restrictive than the spec, adjust it to match the recommended value with a small safety margin (10-20mm).
Consult with the machine builder if specs are unclear to avoid setting limits beyond safe travel.
Incorrect parameter changes can disable safety protections; proceed with caution.
3
Test Adjusted Limits
After adjusting the parameter, disable write enable (parameter 0000 bit 0=0) and reset the control. Jog the axis slowly in the positive direction to confirm it moves without triggering the alarm, then run a test program to verify operation within the new limits.
Use a slow jog speed (1-5%) during initial testing to minimize risk of overshoot.
Visually inspect for potential collisions before jogging the axis after parameter changes.
1
Review NC Program Code
Open the NC program on the control panel or offline editor. Locate the line or block where the alarm occurred (noted in the alarm log or during operation) and check for G53 commands specifying absolute machine positions.
Use the control’s search function to quickly find G53 commands in large programs.
Do not run the program again until the issue is identified to avoid repeated alarms or crashes.
2
Check Commanded Position Against Limits
Compare the G53 commanded position for the affected axis against the negative stroke limit in parameters 1320-1327. If the commanded position is beyond the limit, modify the program to stay within the safe zone with a 10-20mm margin.
Add comments in the program to note safe limits for future reference by other operators.
Ensure no fixtures or workpieces are in the path if testing movement after edits.
3
Simulate Program Execution
Run the modified program in simulation mode or dry run with single block active and feed override at 0-25%. Monitor the POSITION screen to confirm all commanded moves remain within the stored stroke limits throughout the cycle.
Use graphic simulation if available on the control to visualize the tool path before actual execution.
Stop immediately if the simulation shows the axis approaching the negative limit.
1
Check External Offset Values
Access the OFFSET/SETTING screen and navigate to the extended offsets (G54.1 P1-P48). Look for large negative values that could contribute to exceeding the negative stroke limit when combined with other offsets.
Cross-reference with fixture setup documentation to confirm intended offset values.
Do not clear offsets without documenting current values for traceability.
2
Adjust or Reset External Offsets
If the external offset values are incorrect or excessive, adjust them to reasonable values based on fixture setup or reset them to zero if not in use. Ensure the cumulative effect with work offsets (G54-G59) stays within limits.
Test small offset adjustments incrementally to observe their impact on machine position.
Confirm no program is running while adjusting offsets to prevent unexpected movement.
3
Validate with Incremental Jogging
After adjusting offsets, use incremental jogging (minimum feedrate 1-5%) to move the axis in the positive direction back within limits. Then, run a dry run of the program to ensure no further limit violations occur.
Monitor the POSITION screen during jogging to track progress toward safe limits.
Visually inspect the axis path for obstructions before jogging to prevent collisions.
1
Inspect Tool Offset Values
Go to the OFFSET/SETTING screen and review the tool length offset values for the active tool. Check for large negative values that, when combined with G43 and work offsets, could push the axis beyond the negative limit.
Compare tool offsets against historical data or setup sheets for discrepancies.
Do not alter tool offsets without confirming the correct tool setup to avoid crashes.
2
Review Program for G43 Usage
Open the NC program and locate instances of G43 (tool length compensation) near the faulted line. Verify if the combined effect of tool offset and other offsets exceeds the negative limit for the axis.
Temporarily comment out G43 in the program to test if it resolves the issue during simulation.
Ensure the program is not running while reviewing or editing to prevent unintended movement.
3
Adjust or Test Without Compensation
If the tool offset is excessive, adjust it to a smaller value or temporarily disable G43 in the program for testing. Run a dry run in single block mode with low feed override (0-25%) to confirm the axis stays within limits.
Use a shorter tool or mock offset during testing to isolate the compensation effect.
Stop the test immediately if the axis approaches the limit to avoid triggering the alarm again.
DIY Feasiblehigh confidence
Call a technician if:
·If the alarm persists after checking offsets and parameters, indicating a potential control or hardware issue.
·If there is evidence of a crash or mechanical damage (unusual noise, visible wear) before or during the alarm.
Prevention
Always double-check work and fixture offsets before starting a program to ensure they align with the machine’s safe travel limits.
Regularly review and update NC programs to avoid G53 commands that exceed stored stroke limits, adding safety margins.
Train operators on proper offset entry and parameter handling to prevent accidental changes during setup.
Maintain a backup of machine parameters to quickly restore correct stroke limit settings if altered.
Common Mistakes
Ignoring small offset discrepancies during setup, leading to cumulative errors that trigger the alarm.
Attempting to bypass the alarm by disabling stored stroke checks in parameters, risking machine damage.
