Why does my 3D finish toolpath waste hours machining flat empty areas?

Why this happens

The 3D Roughing and Finishing forms have a Machining Limit Boundary option. If it is set to Material Boundary, the boundary of the entire material block is machined, flat background included. On a small model in a big blank, most of the runtime is the ballnose skimming an empty, zero-height plane at finish stepover.

The fix

1. In the 3D toolpath form, set Machining Limit Boundary to Model Boundary. The toolpath stays inside the combined boundaries of the components in the job (the area of the composite model that has components on it).
2. Or choose Selected Vector(s) after drawing or selecting your own boundary vector for precise control (for example, the model plus a border you actually want machined). Selected Level limits the toolpath to the components on a named level.
3. Use the Boundary Offset field to push the limit outward by roughly the tool radius so edges get fully machined without the tool shank rubbing the boundary walls.

Pro tips

• Create Vector Boundary (from selected components) generates the silhouette vector in one click. Offset it and reuse it for both roughing and finishing.
• Check the time estimate before and after changing the boundary. On small-model-in-big-blank jobs it is common to cut hours off the finish pass.
• If the background should be machined (a dished panel), keep Material Boundary but rough it with a larger tool first.