What is 'Separate Last Pass' on a profile toolpath, and when should I use it?

What it does

In the Profile toolpath form, Do Separate Last Pass makes every depth pass cut slightly AWAY from the final line (leaving a thin skin of material, the allowance you specify, for example 0.02" or 0.5 mm), then takes one final full-depth pass that shaves that skin off the true line in a single continuous cut.

Why that helps

Normal multi-pass profiles can leave faint ridges or witness lines where each pass meets the next, and the loaded cutter deflects slightly on every pass. Both show on the finished edge. The separate last pass is a light, low-load skim, so there is less deflection and no per-pass ridges, giving an edge that often needs little or no sanding. It is the profile-toolpath cousin of the climb-rough plus conventional-finish trick (see the climb-vs-conventional entry). The official documentation also notes that the Reverse direction option reverses the cutting direction of the last pass, which can help minimize witness marks on the edge.

When to use it

• Visible edges on finished work (signs, trays, boards): ON, with an allowance of about 0.02" (0.5 mm) as a starting point. The software warns if the allowance is more than one third of the tool diameter, and it should ideally be much smaller.
• Fuzz-prone material (plywood edges, softwoods): ON, because the skim shears cleanly
• Waste cuts, jig parts, anything getting edge-routed afterward: skip it (it adds a full extra perimeter pass of machine time)

The interactions to know

1. Tabs still work. The last pass respects them.
2. The final pass cuts full depth in one go along the line. This is fine, because it is only removing the thin allowance.
3. Pair it with a downcut bit and the top edge gets even cleaner (see the bit-selection entry).

Pro tips

• If edges STILL show marks with the separate last pass on, check bit sharpness and machine rigidity (see the dull-bit and cut-quality entries).
• On thick hardwood cut-outs, a separate last pass plus a slightly reduced final-pass feed is a clean edge that many hobby machines can produce (shop advice).