How do I stop a 3D toolpath cutting too deep around the outside of my model? (The Zero Plane floor trick)

Why this happens

Outside your model's silhouette there is no component, so the area sits at the bottom of the job's height range. With a boundary that extends past the model (Material Boundary, or a generous offset), the tool excavates the surrounding field down to that level. (Community explanation; preview your toolpath to confirm what your project does.)

Fix 1: tighten the boundary

Set the Machining Limit Boundary to Model Boundary or a selected vector, and keep the Boundary Offset modest (about one tool radius). See the finish-boundary entry. Often that alone solves it.

Fix 2: the Zero Plane floor

When you WANT the surrounding field machined but only to a set level, add a Zero Plane component. Create Zero Plane (on the Modeling tools) creates a flat component the size of your job setup with a height of zero. To put the floor at a different level, open the component's Component Properties and change its Base Height. Merged into the composite model, the plane acts as a floor, so the bit dresses the field flat at the plane height instead of diving.

This same approach can fix recessed models sitting "below zero," backgrounds you want at a uniform depth, and imported STLs whose base extends deeper than you want to cut.

Pro tips

• Preview is the honest check. Run Preview Toolpaths and inspect the field areas before cutting.
• Combine both fixes for dished designs: a zero plane for the rim level plus a model boundary for time (see the 3D-speed entry).
• Create Zero Plane and the component behave the same in VCarve Pro and Aspire. This is not an Aspire-only rescue.