Should I rough with Z-Level or 3D Raster, and why does my finish pass plunge too deep?

The difference that matters

• Z Level roughing uses a series of 2D pocket-style passes at stepped depths, so it leaves stepped shelves of material between the terraces and the model surface.
• 3D Raster roughing passes over the whole model surface. The official documentation says it leaves a more even amount of material for the finish cut to remove, but it may take significantly longer on deeper parts.

On deep shapes (a 2" dish, a deep relief), Z Level's leftover terraces can be thicker than your finish bit expects, so the finishing pass suddenly takes a deep bite on those shelves. That can overload the bit and snap tapered ballnoses.

The decision

The official guidance is that Z Level is usually more efficient on deep parts, and 3D Raster suits shallow ones (where roughing only takes one or two passes). 3D Raster leaves a more even skin for the finish tool, so some users accept the longer roughing time on deep curved, bowl-like shapes when the finish bit is fragile. If you use Z Level on a deep part, reduce the roughing pass depth so the leftover steps stay small.

• Deep, curved, bowl-like shapes with a fragile finish bit: consider 3D Raster roughing for the more uniform allowance, and accept the longer time
• Blocky or shallow reliefs: either works, and Z Level terraces stay small
• Either way, set a real machining allowance (about 0.5 to 1 mm is a common starting point) so finishing always has a consistent skim, and preview the ROUGHING result. Look at what's left, not just the final pass.

If the finish pass still plunges

1. Check the roughing actually ran or recalculated after model edits.
2. Reduce roughing pass depth so terraces shrink.
3. Verify the finish preview against the roughed state (preview toolpaths in order).

Pro tips

• This pairs with the rest-machining entry: a big-tool rough plus multi-tool finishing is a safe deep-relief approach.
• Deep dishes: also confine the finish with a boundary so the walls aren't machined with a horizontal stepover (see the ridges entry).