Why does my 3D carve have ridges or a washboard pattern on the finish pass?

Why this happens

1. Stepover too large for the ballnose. A ballnose leaves a scallop (cusp) between adjacent passes; the wider the stepover, the taller the ridge.
2. Roughing left ridges too tall for the finish pass to remove. The finish tool rides over leftover terraces.
3. Marks perpendicular to the cut direction appear where the tool steps between contours. With the Offset strategy, the Stepover Retract setting controls this.
4. Steep, near-vertical surfaces cut with a horizontal raster get widely spaced contour lines on the walls.

The fix

1. Finishing stepover of 8 to 12% of tool diameter (for example, 0.02 to 0.03" for a 1/4" ballnose; go smaller for hard, detailed work). The official documentation calls 8 to 12% typical for 3D finishing, and it is what gives a smooth, sandable surface.
2. Reduce roughing pass depth so leftover ridges are small, and leave a modest machining allowance (about 0.02 to 0.03") for the finish pass to clean.
3. If you use the Offset strategy, set a Stepover Retract value so the tool lifts between contours. This can remove the between-contour drag marks. The value must be large enough to clear the cusp height (the form warns if it is too small). Stepover Retract applies to the Offset strategy only; it does nothing for a raster finish.
4. For steep walls: use the Moulding toolpath's "Vary Step Over" option, or run a second raster finish at 90° to the first over just the steep areas.

Pro tips

• A tapered ballnose is stiffer than a straight one at small tip sizes, giving less deflection and a cleaner finish in deep reliefs.
• Time versus finish is a straight trade: halving the stepover roughly doubles finish time. About 10% stepover is a common choice for decorative work.