Self-intersecting vectors: the flaw you cannot see at normal zoom

VCarve's Vector Validator flags "intersections". SheetCAM refuses to offset a part. A fill comes out with a wedge missing. You zoom in where the tool points and see nothing wrong, because the crossing is often smaller than your kerf. Somewhere, the path crosses itself, and at that point "inside" and "outside" stop meaning anything.

Why one tiny crossing breaks the whole part

Draw a figure-8 as a single closed path and ask: which region is inside? There is no answer. The SheetCAM manual puts it bluntly: "There is no rational way to cut this shape." A kerf or tool offset has to move the path a fixed distance to the inside or outside, and at the crossing those directions contradict each other. Fill and engrave algorithms hit the same wall, because the even-odd logic that decides what gets filled flips at the intersection.

Different tools fail differently. Some refuse the operation with an error, some produce a garbage toolpath, and some silently skip the contour. The silent case is the worst one, because you discover it on the machine, with material clamped and half a job already cut.

Where self-intersections come from

Almost never from deliberate drawing. The usual sources are a bad raster trace that loops back on itself at a corner, a sloppy node edit where a handle got dragged across the path, and an overlapped join where two curves were merged so that their ends cross before they meet. All three produce crossings a fraction of a millimetre across: invisible at normal zoom, fatal at offset time.

Finding and fixing the crossing

VCarve and Aspire

The Vector Validator marks intersection points on the drawing. The repair happens in node editing mode, span by span: move or delete the offending node so the path no longer crosses, then run the validator again. Users on the Vectric forum describe the process accurately as tedious but reliable.

Carveco and ArtCAM

Same picture: a validation step flags self-intersecting vectors, and the fix is manual node editing at the flagged spot. There is no one-click repair here either.

SheetCAM

SheetCAM has no vector repair tools. If it refuses to offset a contour or produces a strange path, fix the geometry upstream in your CAD and re-import. The manual documents the figure-8 case explicitly as uncuttable.

The actual repair is nearly always small. Delete the tiny loop, or move one node a hair so the path stops crossing itself, and the shape becomes cuttable again. Finding the spot is most of the work, which is why validators exist.

Why DXF Medic reports it and refuses to auto-fix it

DXF Medic detects self-intersections and reports them as named findings, pointing at the affected contour and the location of the crossing, so you fix one node instead of hunting through the whole drawing. It deliberately does not "fix" them for you. Cutting a self-crossing contour is undefined, and any automatic repair would be a silent guess about which loop you actually designed. A wrong guess means cutting something you did not draw, which is worse than an honest refusal.

That line runs through the whole tool: flaws with one unambiguous repair (contour gaps within your tolerance, stacked duplicate points, zero-length entities) are fixed automatically and itemized. Flaws where a machine would have to guess your intent are reported with their exact position and left for you to decide.