Summary

This article explains how to include fixture bodies in collision-avoidance calculations for a GibbsCAM milling operation and set safe Entry and Exit Clearance Planes. Fixture avoidance works within an operation; do not rely on it alone to protect positioning moves between separate operations.


Table of Contents


Before You Begin

  • Confirm that the fixture, clamps, jaws, and other workholding are modeled and positioned correctly in the GibbsCAM part.

  • Determine a safe clearance height above the tallest fixture component in the operation's machining coordinate system.

  • Save a backup copy of the part before changing or regenerating operations.

Important: Fixture-avoidance controls vary by process. If the required option is not available, do not assume the process will avoid fixtures.


Procedure

Step 1 - Define the Fixture Bodies

  1. Select each workspace body that represents a fixture, clamp, jaw, or other workholding component.

  2. Open the body properties and designate the body as a Fixture.

  3. Do not use Fixture (Display Only) for a body that must affect toolpath calculation.

  4. If the setup uses Intermediate Tooling (IT) fixtures, confirm that the correct fixture is loaded and positioned for the active setup.

Step 2 - Enable Fixture Avoidance in the Process

  1. Open the process dialog for the operation that must avoid the fixture.

  2. For most supported milling processes in GibbsCAM 2025 and later, open the Solids tab and select Avoid IT Fixtures.

  3. For an Advanced 3D process, open the Boundary tab and select Avoid IT Fixtures.

Step 3 - Set the Fixture and Operation Clearances

  1. If the process provides a Fixture Clearance value, enter the required offset between the toolpath and the fixture.

  2. Set the Entry Clearance Plane above the highest fixture component, including an appropriate safety margin.

  3. Set the Exit Clearance Plane to the same safe height or higher.

  4. Review these values for every affected operation; the settings are operation-specific.

Step 4 - Recalculate and Verify the Toolpath

  1. Recalculate the operation.

  2. Inspect the entry, cutting, linking, and exit moves to confirm that the toolpath maintains the intended fixture clearance.

  3. Simulate the operation with collision checking enabled for the tool, holder, and fixture.

  4. Simulate the full operation sequence and inspect each move between operations separately.

  5. If an inter-operation move does not clear the workholding, raise the Exit Clearance Plane of the preceding operation and the Entry Clearance Plane of the following operation, then regenerate and verify both operations.

  6. Review the posted program and follow the shop's normal prove-out procedure before machining the part.


Expected Result

Within each configured operation, the generated toolpath maintains the specified clearance from the fixture. The tool enters and exits at clearance planes high enough to clear the workholding, and moves between operations have been verified separately.


Troubleshooting

  • Problem: The toolpath does not recognize or avoid a fixture body.

Possible Causes

  • The body is not designated as a Fixture, or it is set to Fixture (Display Only).

  • The wrong IT fixture is active, or Avoid IT Fixtures is not selected for the process.

Resolution

Correct the fixture-body type or IT fixture selection, enable Avoid IT Fixtures in the process, and regenerate the operation before simulating it again.

  • Problem: The operation clears the fixture, but the move to the next operation crosses it.

Possible Causes

  • Fixture avoidance is applied within the operation, but the Exit Clearance Plane of the preceding operation or the Entry Clearance Plane of the following operation is below the required safe height.

Resolution

Raise both clearance planes above the tallest fixture component with an appropriate safety margin, regenerate the affected operations, and verify the complete operation sequence.



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Keywords

Fixture Avoidance, Avoid IT Fixtures, Intermediate Tooling, IT Fixture, Workspace Fixture, Fixture Clearance, Entry Clearance Plane, Exit Clearance Plane, Operation Clearance, Collision Avoidance, GibbsCAM Milling, GibbsCAM Advanced 3D