Set Safe Travel Heights in FreeCAD Path Operations

Defining safe travel heights in the FreeCAD Path Workbench (renamed to CAM in recent versions) is crucial for preventing machine collisions with workpieces, fixtures, and clamps during rapid transit moves. This guide explains how to properly configure clearance and safe travel heights globally for an entire machining job as well as locally for individual operations, ensuring your CNC tool moves efficiently and safely across the workspace.

Understanding Travel Height Parameters

FreeCAD utilizes specific terms to control Z-axis transit levels:

  • Clearance Height: The absolute safe level where the tool can perform rapid (G0) lateral movements across the entire workpiece or between different operations without hitting clamps or fixtures.
  • Safe Height (Retract Height): A lower elevation situated just above the cutting surface where the tool retracts between adjacent cuts within the same operation to reduce cycle time.

Method 1: Setting Global Heights in the Job Setup

Setting travel heights at the Job level creates default parameters that apply automatically to every operation created within that job.

  1. In the Tree View, double-click your Job object to open the Job Edit panel.
  2. Select the Setup Values tab.
  3. Locate the Clearance Height and Safe Height fields.
  4. Enter your desired values relative to the job's defined Z-zero coordinate:
    • Clearance Height: Set this higher than any clamps, vises, or stock protrusions (e.g., 10 mm or 0.5 in above the highest obstruction).
    • Safe Height: Set this slightly above the top of the stock surface (e.g., 2 mm or 0.1 in).
  5. Click OK to apply the changes to the entire job.

Method 2: Adjusting Heights per Individual Operation

You can override global height values for specific operations, such as deep pocketing or clearing specific obstacles.

  1. In the Tree View, double-click the specific operation (e.g., Profile, Pocket Shape, or Helix).
  2. Go to the Depths tab in the operation dialog.
  3. Adjust the values for:
    • Start Depth: The top level of the material for this cut.
    • Clearance Height Expression / Safe Height Expression: Enter a specific numerical value (e.g., 15mm) or modify the default formula to raise or lower the transition path.
  4. Click OK to save the changes and regenerate the toolpath.

Method 3: Using the Property View Panel

If you prefer editing parameters directly without opening dialog boxes:

  1. Click on the operation or the Job in the Tree View.
  2. Go to the Data tab in the Property View panel (usually in the lower-left corner).
  3. Scroll to the Depths section.
  4. Edit the values for properties such as ClearanceHeight and SafeHeight.
  5. Right-click the operation and select Recompute to update the toolpath.

Verifying Travel Heights

Before exporting your G-code, always visually verify the rapid traverse planes:

  1. Select your Job in the Tree View.
  2. Click the CAM Simulator (CAM Simulation) tool on the toolbar.
  3. Observe the green/red travel lines: rapid travel movements (G0) should visibly clear all stock geometry and clamping mechanisms.