FANUC cutter-compensation interference alarms: an oversized tool or a reversed compensated path?
The cutter compensation C chapter of the 16i/18i-MB manual distinguishes geometric inaccessibility, compensation data and path-reversal checks. An internal-fillet example explains why reducing the offset value is not a valid way to clear an alarm.
Contents
After an interference alarm associated with G41 / G42, simply reducing the compensation value may let the program continue while placing the tool center incorrectly. A better starting point is to compare the design contour, actual tool and compensation data used by the CNC within the same geometric model.
What this interference check examines
The scope here is cutter compensation C on 16i-MB and 18i-MB / MB5 machining-center systems. The public mirror of original manual B-63534EN/02 (cover designation GFZ-63534EN/02), §14.6.5, pages 326–330 explains that the check concerns overcutting and changes in the compensated path; it cannot detect every interference. Some contours without actual overcutting can also trigger the check. An alarm alone therefore does not prove a collision has occurred, and no alarm does not establish complete spatial clearance.
First make a dimensional check that cannot be bypassed
Original two-dimensional example: an end mill machines a finished internal fillet from the inside. The required fillet radius is R=4 mm, and the actual cutter radius is r=6 mm. In an ideal model without wear, runout or elastic deformation, the tool-center arc radius would be R−r=−2 mm. That cannot form the required inward offset arc.
| Actual cutter radius | R−r | Geometric assessment |
|---|---|---|
| 6 mm | −2 mm | The tool is too large to produce this internal fillet |
| 3 mm | 1 mm | A positive-radius tool-center arc exists, but entry, exit and adjoining contours remain unverified |
Keeping the 6 mm radius tool installed while falsely entering 3 mm in the compensation data does not change its actual cutting edge. Likewise, a 12 mm diameter tool cannot fit fully into a 10 mm wide straight slot. This is a dimensional constraint that cannot be resolved by adjusting parameters.
Then distinguish physical dimensions from path-calculation issues
Section 14.6.6, page 331, of this edition describes overcutting when an internal corner radius is smaller than the cutter radius. Section 14.6.5 also addresses checks for a compensated-path direction that differs from the programmed direction. Separate the investigation into three steps:
- Determine whether CAM outputs a finished-part contour or an already offset tool-center path. Applying the same compensation to both can produce a duplicate offset.
- Check the actual tool size against the compensation record selected by the program. Correct genuinely incorrect data; if the dimensions are inherently unsuitable, choose a different tool or process.
- If dimensions permit the operation but the alarm remains, inspect the alarm block and surrounding contour. Compare compensated intersections, connecting directions and entry/exit clearance instead of examining only the line at which the alarm appears.
Cutter-compensation checking is not whole-machine collision protection
This analysis addresses the specified compensation mechanism. It does not cover a complete three-dimensional model of toolholders, fixtures, rotary tables and machine structures, nor does it treat single-block operation as a guarantee against overcutting. Confirm basic G41 / G42 and extended interference-function configuration boundaries separately. For three-dimensional models, see the 3D interference-checking article.