How to prepare DXF files for laser cutting

A clean DXF is the cheapest quality step in laser quoting. This guide covers closed contours, duplicates, open polylines, millimetre units, curves, layers, text, and holes — then shows what AllTerra Calculator does when a file cannot be nested.

Why DXF prep matters before nesting

Nesting and costing software does not “guess” a part from a sketch. It needs closed outlines that define the metal you will cut, plus closed inner loops for holes. Messy drawings — open lines, stacked duplicates, mixed units, or decoration on the cut layer — produce wrong areas, wrong cut length, or a hard stop before nesting starts.

For job shops, that failure shows up as a delayed quote or a wrong price. Fixing the drawing once in CAD is usually faster than debugging a bad nest. The habits below are general shop practice. The AllTerra section states only what the live service at calc.1cterra.ru does today.

Closed contours are the cuttable part

A laser path for a blank needs a continuous outer boundary that returns to its start. In DXF terms that is typically a closed LWPOLYLINE or POLYLINE, or a CIRCLE / closed ellipse treated as a polygon. Open strokes alone do not define a sheet-metal blank.

Inner closed loops that sit inside the outer outline are usually holes or cut-outs. Small decorative closed loops may be treated as graphics rather than cut holes in some tools — including AllTerra’s hole-versus-engraving classification. Keep cut geometry on clear layers and avoid mixing dimension balloons into the cut outline.

Open polylines and missing closures

An almost-closed polyline with a tiny gap is still open. CAD export settings, exploded blocks, or hand-drawn arcs that never meet will leave gaps. Zoom to endpoints and close them, or use a join/close command before export. If the file contains only open geometry, nesting tools cannot invent a blank.

In AllTerra Calculator today: if the parser finds no closed polygons, the upload fails with error code dxf_no_closed_contours. The English UI message is: “The DXF file contains no closed contour — there is nothing to cut.” The underlying parser message is “No closed polygons found in DXF”.

Duplicates, overlaps, and double lines

Two identical outlines on top of each other inflate perimeter and confuse hole detection. Overlapping almost-identical contours can look fine on screen but produce self-intersections after import. Delete duplicates and check for coincident edges left from copy-paste.

Also watch for construction lines left on the same layer as the part. If they close into a loop, a tool may treat them as a second part or as an inner contour. Keep construction on a separate non-cut layer or delete it before export.

Units: work in millimetres

Laser shops in this product’s market quote and nest in millimetres. A drawing saved in inches or unitless “drawing units” without a clear millimetre scale will place parts at the wrong size. Set the CAD document to millimetres and verify a known edge length before export.

AllTerra’s nesting and costing pipeline treats geometry numbers as millimetres (sheet formats, gaps, and cut length are mm-based). There is no automatic inches-to-mm rewrite on upload. Wrong units mean wrong sheets and wrong money.

Splines, arcs, and bulges

Arcs and polyline bulges are normal in good DXF parts. Splines are harder: some importers flatten them into line segments. Prefer arcs and polylines for production outlines when you can. If you must use splines, flatten at a tolerance your shop accepts for edge quality.

AllTerra’s parser can flatten SPLINE entities when tracing outlines from line/arc soups, and it respects bulge on LWPOLYLINE / POLYLINE for curved edges. Extremely dense spline tessellation can still make files heavy — keep production drawings practical.

Layers, text, and engraving

Put cut geometry on a dedicated layer. Put dimensions, title blocks, and notes elsewhere. Text that is drawn as closed outlines can be mistaken for tiny parts or holes if it sits inside the blank. Prefer true text entities on a non-cut layer, or move them outside the part.

In AllTerra, open LINE/ARC strokes on layers whose names hint at engraving, plus small closed loops classified as non-hole graphics, can be stored as engraving lines. Those lines are kept with the part data but are not added into cut length or pierce formulas the way cut holes are, and they are not painted into the mini preview today.

Holes and cut-outs

Each true cut hole needs its own closed contour inside the outer outline. Circles for fasteners should be real CIRCLE or closed polyline holes, not sketched open arcs. Slot-shaped cut-outs should be closed loops as well.

Holes add cut length and pierces. A plate with three openings is not priced like a solid blank of the same outline. In AllTerra, part area is outer area minus hole areas; perimeter for cutting combines outer and hole paths; pierce count for a part includes the outer start plus holes.

In AllTerra Calculator

Orders start from one or more DXF uploads on the order form. The server parser looks for closed polygons. Without them, nesting does not start. With them, the service classifies an outer contour, cut holes, and engraving-style geometry as described above.

• No closed polygons → error dxf_no_closed_contours (message above).
• Closed outer + qualifying inner loops → nestable part with holes.
• Small / decorative closed loops may be classified as engraving graphics, not cut holes.
• Open engraving-layer strokes may be stored as engraving lines; they do not drive cut length or pierces like holes.

After a successful parse, true-shape nesting places the outlines on your sheet format with the gap and edge rules you set. Metrics from that nest (sheets, utilisation, cut length, pierces) feed costing. See also the DXF nesting and nesting engine pages for the commercial product view.

Pre-export checklist

1. Document units are millimetres; a known edge measures correctly.
2. Outer outline is closed; zoom endpoints if needed.
3. Every cut hole is a closed inner loop (or CIRCLE).
4. No duplicate stacked contours on the cut layer.
5. Dimensions and title block are not on the cut layer.
6. Text is not exploding into tiny closed loops inside the blank.
7. Splines flattened or replaced if your shop standard requires it.
8. One clear part per file when possible; multi-part files only if your process expects them.

When the checklist passes, upload at calc.1cterra.ru and confirm the preview shows the outer shape and holes you expect before you trust the price. If the service reports no closed contour, fix the DXF — the calculator will not invent a blank.