Summary

If small corner radii are not being output when Cutter Radius Compensation (CRC) is enabled, the behavior is typically expected and is a limitation of edge-based cutter compensation.

When the tool radius is larger than the distance from the center of the tool to the programmed contact point, the tool edge cannot physically produce the programmed radius. As a result, the CNC control may omit the small radius or interpret it as a sharp corner.

Table of Contents

Before You Begin

Before troubleshooting this behavior:

  • Verify that Cutter Radius Compensation (CRC) is enabled.

  • Confirm the programmed corner radius and tool diameter.

  • Review the posted NC code to determine whether the radius has been omitted or modified.

Note: This behavior is not caused by GibbsCAM. It is a limitation of edge-based cutter compensation performed by the CNC control.

Cause

Why Does This Happen?

With edge-based Cutter Radius Compensation, the CNC control calculates the path of the tool center, not the cutting edge.

If the cutting edge is positioned inside the programmed feature by more than the corner radius, the edge cannot physically produce the desired arc.

Because multiple tool edge shapes can produce the same compensated centerline path, the control is free to interpret the motion differently. Depending on the control, this may result in:

  • A sharp corner.

  • A blended radius.

  • The omission of very small corner radii.

This is a fundamental limitation of edge-based cutter compensation rather than a software defect.

Common Causes

This behavior typically occurs when:

  • The programmed corner radius is smaller than the effective tool radius.

  • CRC is enabled on very small features.

  • The selected cutter is too large for the programmed geometry.

  • The CNC control applies its own compensation logic.

Symptoms

You may experience one or more of the following:

  • Small corner radii are missing from the posted toolpath.

  • Rounded corners become sharp corners when CRC is enabled.

  • The NC program does not contain the expected corner arcs.

  • The same geometry outputs correctly when CRC is disabled.

Procedure

Step 1 – Verify Cutter Radius Compensation

Confirm that the operation is programmed to use Cutter Radius Compensation (CRC).

If CRC is disabled, this article does not apply.


Step 2 – Compare the Tool Radius to the Corner Radius

Review the programmed geometry and compare:

  • The tool radius.

  • The corner radius being machined.

If the tool radius is larger than the distance from the tool center to the programmed contact point, the tool edge cannot produce the programmed corner.


Step 3 – Review the Posted Code

Inspect the posted NC program.

When CRC is enabled, the CNC control determines the compensated toolpath. If a corner radius cannot be represented by the compensated edge path, the control may:

  • Output a sharp corner.

  • Blend the corner using a larger radius.

  • Omit the small radius entirely.


Step 4 – Evaluate Possible Solutions

If the programmed corner radius is required, consider one of the following:

  • Use a smaller cutter.

  • Reduce or eliminate the use of CRC for that operation, if appropriate.

  • Modify the machining strategy to accommodate the required feature size.

Expected Result

You understand why small corner radii may disappear when Cutter Radius Compensation is enabled and can determine whether a tooling or programming change is required.

Best Practices

  • Select a cutter that is appropriate for the smallest feature being machined.

  • Review posted code whenever CRC is used on small radii.

  • Consider programming without CRC when extremely small corner features must be preserved.

  • Verify the expected toolpath through simulation before machining.

Troubleshooting

  • Problem: Rounded corners are output as sharp corners.

Possible Cause

The tool radius is too large for the programmed corner while using CRC.

Resolution

Use a smaller cutter or modify the machining strategy.


  • Problem: The posted code does not contain the programmed corner radius.

Possible Cause

The CNC control cannot generate the required edge path using cutter compensation.

Resolution

Review the programmed geometry and tool size. Consider disabling CRC for the affected operation if appropriate.


  • Problem: The toolpath appears correct in GibbsCAM but differs on the machine.

Possible Cause

The CNC control is performing cutter compensation differently than expected.

Resolution

Review the posted NC program and machine controller documentation to understand how CRC is applied.

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Keywords

CRC, Cutter Radius Compensation, Corner Radius, Rounded Corners, Sharp Corner, Tool Radius, Edge Compensation, Posted Code, Small Features, Toolpath