Automating Outer & Inner Contour Selection for CNC Nesting in Fusion 360

Preparing flat-panel sheets for CNC routing requires classifying outer part boundaries and inner cutouts. If you want to batch select contours Fusion 360 CAM or implement automatic cutout selection Fusion 360 workflows, manually picking edges on nested sheets is a major bottleneck. Selecting inner cutouts before outer boundaries is essential to prevent part movement on vacuum tables.

In this guide, we show how inner outer contour recognition CNC algorithms automate contour selection with tool-diameter awareness.

Why Manual Contour Selection Fails on Vacuum Tables

On a CNC router vacuum table, inner cutouts (such as sink openings, cable grommets, and handle slots) MUST be cut before the outer boundary is severed. If the outer perimeter is cut first, vacuum hold-down pressure is lost, causing the part to shift when the tool cuts internal openings.

“Cutting order discipline on vacuum beds is non-negotiable. Automating inner cutout recognition guarantees that internal features are machined while full vacuum sheet clamping is active,” highlights Viktor Unipessoal, a CNC programming expert.

Production Benchmark: 95% Faster Contour Selection

In a time-study evaluating flat-pack furniture panel preparation:
– Manual Contour Selection: 22 minutes to select inner and outer loops across 26 panels.

  • SmartCAM Auto Add Time: 35 seconds to detect all 26 outer perimeters and 58 inner cutouts.

  • Vacuum Shift Incidents: Reduced from 3 part shifts per month to 0.

How Auto Add Contours Operates

Inside the CONTOURS → Auto Add panel:
1. Define Zone: Select the sheet boundary edge.
2. Set Tool Diameter: Enter your active endmill diameter in document units (MM or IN).
3. Filter Mode:
– IN+OUT: Separates inner cutouts from outer perimeters.
– OUT: Collects outer boundaries exclusively.
– IN: Collects internal cutouts exclusively.
4. Staging & Review: Items load into Picked Items where you can preview IN/OUT classification before applying to CAM.

   [Zone Edge] ──> [Tool Diameter Filter] ──> [IN / OUT Loops] ──> [CAM Execution]

This guarantees correct cutting order and flawless vacuum table hold-down performance.