Cut the holes first, or the part moves
The order a machine cuts in is not cosmetic. Cut the outline before the holes and the part drops, tilts or shifts, and everything after that is wrong.
What goes wrong
While a part is still attached to the sheet, it is held. The moment the outline is finished, it is a loose piece of material sitting in a hole, held by nothing but friction and whatever the honeycomb is doing.
If any cutting remains, it now happens on a part that can move. On a laser the piece tips and the beam goes out of focus. On a router it is worse: the bit catches the loose piece and throws it.
The rule
Inside features first, outline last. For nested parts, innermost first, working outward. A contour inside another contour is an inside feature, which is the same nesting test kerf compensation uses.
Tabs, when the part is heavy
For thick stock, ordering is not enough on its own: the part still drops at the end. Small uncut tabs hold it in the sheet until you break it out by hand. They leave a mark you have to sand, which is the trade.
Travel time is the other half
Ordering is not only about safety. A machine that cuts the contours in the order they happen to appear in the file spends most of its time travelling between them. On a sheet of fifty small parts that is minutes per sheet, every sheet.
Ordering by nesting first and then by proximity cuts the travel substantially, because work that is near itself gets done together. It costs nothing at export time and it is why the option is on by default.
Lead-ins, on a plasma or a waterjet
A thermal cutter cannot pierce on the line: the pierce blows a crater wider than the kerf. It has to start off the part and travel in, which is a lead-in, and leave the same way. That is a CAM decision rather than a tracing one, but the geometry has to support it: a contour with no room inside it for a lead-in cannot be cut that way at all.
What ordering cannot fix
- Parts that are smaller than the honeycomb cell will fall through whatever order you cut in.
- Material that is cupped is out of focus before you start.
- Very thin bridges will snap on the last pass regardless. Thicken them in the editor.
- Overlapping duplicate contours get cut twice. That is a file problem, not an ordering one.