12150

Check arc center calculation

In the NC program, verify that I/J/K values correctly define the arc center. Calculate radius from start point (current position) to center (I,J,K) and from end point to center.

Use SINUMERIK's simulation mode to visualize the intended arc path before execution

Verify coordinate system consistency

Ensure I/J/K values are incremental distances from start point to arc center, not absolute coordinates. Check active coordinate system G54-G59.

Mixing absolute and incremental arc definitions will cause geometry errors

Recalculate arc parameters

Use CAM post-processor or manual calculation to generate correct I/J/K values. Alternatively, use R-word programming with explicit radius value.

R-word programming is often more reliable than I/J/K for simple arcs

Check current tolerance setting

Access machine data via HMI: Commissioning → Machine Data → Channel-specific MD → MD20200 CONTOUR_TOL. Note current value in mm.

Typical values range from 0.001mm to 0.01mm depending on application precision requirements

Calculate actual radius deviation

Manually calculate the radius difference in the problematic arc. If deviation is small but exceeds MD20200, consider adjusting tolerance or improving arc definition.

Increasing tolerance may affect machining accuracy - consult machine documentation

Adjust program or tolerance

Either correct the arc geometry in the NC program or temporarily increase MD20200 if the deviation is acceptable for the application.

Document any MD changes for future reference and quality control

Verify geometric feasibility

Check that the specified R-value can physically create an arc between start and end points. The radius must be at least half the chord length between points.

Use the formula: minimum R = (chord length)/2 for geometric validation

Check for duplicate arc solutions

When R-value creates two possible arcs, SINUMERIK chooses based on sign (positive for minor arc, negative for major arc). Verify correct sign usage.

Wrong R-value sign can cause unexpected tool paths and potential collisions

Convert to I/J/K format

If R-word continues to cause issues, convert to I/J/K incremental format for explicit arc center definition and better control.

Many CAM systems provide both R and I/J/K output options in post-processor settings

Check active transformations

Review current coordinate transformations: ROT, SCALE, MIRROR functions. Access via HMI: Program → Coordinate System → Transformations.

Use SUPA (suppress transformation) to test if arc works without transformations

Verify transformation compatibility

Ensure arc programming is compatible with active transformations. Some combinations of scaling and rotation can invalidate circular interpolation.

Non-uniform scaling will convert circles to ellipses, which cannot be executed as circular interpolation

Reprogram or adjust transformations

Either modify the arc definition to account for transformations or adjust transformation parameters to maintain valid geometry.

Consider programming arcs in the final transformed coordinate system to avoid geometry conflicts

Check coordinate precision

Examine NC program for excessive decimal places or very small coordinate values that may cause floating-point precision issues in SINUMERIK calculations.

Limit coordinate precision to 4-5 decimal places for typical machining applications

Round coordinate values

Round arc coordinates and parameters to appropriate precision for the application. Use CAM post-processor settings to control output precision.

Excessive precision can cause calculation errors while insufficient precision affects accuracy

Verify with fresh calculation

Recalculate arc parameters using fresh geometry data rather than accumulated transformed coordinates to eliminate precision drift.

Use SINUMERIK's built-in geometry functions like CIC (circle interpolation) for complex arc calculations