DXF, DWG or SVG: which file a laser cutter, CNC machine or print shop wants
The same drawing can be perfect on screen and useless on a machine. From people who work with CNC every day: which format to send, and how to prepare it so it cuts first time.
Three formats, three origins
- DWG is the native format of AutoCAD: rich, versioned, and what engineering offices work in. It is a closed format, and machine controllers rarely read it directly.
- DXF (Drawing Exchange Format) was created by the same company to move drawings between programs. It is the common language of cutting machines: almost every laser, plasma, waterjet and CNC CAM package imports it.
- SVG is the vector format of the web, written by design programs such as Illustrator and Inkscape. It is ideal for logos and graphics, and many hobby lasers and vinyl cutters accept it — but it knows nothing about millimetres unless you tell it.
What the machine actually needs
A cutting machine follows lines. It does not care about colours, fills, shadows or how good the drawing looks; it cares about four things:
- The right scale and units. A part drawn 100 mm wide must arrive as 100 mm — not 100 inches, not 100 pixels. A DXF can carry its unit, but many programs ignore it, so draw at 1:1 and state the unit when you send the file.
- Closed contours. An outline that misses its starting point by a hair is not a shape to the machine: it may skip it, or cut it in the wrong order. Lines that should meet must really meet.
- No duplicates. Two lines on top of each other look like one on screen, but the machine cuts twice: slower, with a wider kerf and sometimes burnt edges.
- Sensible geometry. Lines, arcs and circles cut cleanest. Curves exported as thousands of tiny segments make the controller stutter, because it cannot look far enough ahead.
Our DXF node optimizer takes care of the last point: it reduces polylines to far fewer points while keeping the shape within a tolerance you choose. To check scale and contours before you send anything, open the drawing in the DXF viewer.
Layers and colours carry meaning
In a cutting file, layers and colours are instructions, not decoration. A common convention is one layer for the outer contour, one for inner holes, one for engraving or marking and one for bend lines. Ask your supplier which convention their machine uses; many reserve one colour for cutting and another for engraving.
Convert text to outlines, or use a single-line engraving font. Otherwise the machine either ignores the text or cuts out every letter as a hole.
Kerf, small holes and fine detail
Every cutting process removes a strip of material — the kerf — from a fraction of a millimetre on a fibre laser to a millimetre or more on plasma. Do not compensate for it in the drawing: draw the finished size, and let the operator's CAM software offset the path. If you shrink your holes yourself and the machine compensates too, the parts end up wrong twice over.
Small details have limits. As a rule of thumb, holes smaller than the material thickness are hard to cut cleanly, especially with plasma, and very thin bridges between holes can burn through or warp. Ask your supplier for their minimum hole size and minimum web width for your material and thickness before you finalise the drawing.
From SVG, PDF or a picture to DXF
Logos and drawings often arrive from a designer as SVG, EPS, AI or PDF. Those already contain vectors, so they convert to DXF directly: use SVG to DXF, EPS to DXF, AI to DXF or PDF to DXF. Always check the size afterwards: a graphic drawn in pixels has to be scaled to real millimetres.
A photo or a scanned sketch has no vectors at all. Image to DXF traces its outlines into lines, which works well for clean, high-contrast artwork and poorly for photographs. A traced drawing is made of many small segments, so run it through the node optimizer before it goes to the machine.
When the customer sends DWG
If an engineering office sends DWG and your machine wants DXF, convert it with DWG to DXF. The other way round, DXF to DWG produces a file an AutoCAD user can open. If your CAM software is old, ask for — or save — an older DXF version: newer ones are not always understood.
Casting, shrinkage and print shops
Patterns and moulds for castings, and parts in some plastics, must be drawn larger than the finished part, because the material shrinks as it cools. The shrinkage scaler enlarges a DXF or STL by an exact percentage for that reason.
Print shops and sign makers usually prefer PDF or EPS with real vectors and text converted to outlines; plotters and vinyl cutters often want DXF or SVG. When in doubt, ask for their preferred format and a sample file — five minutes of questions saves a wasted sheet.
A checklist before you send
- Drawn at 1:1, with the unit stated.
- Every contour closed, no duplicate lines.
- Text converted to outlines or to a single-line font.
- Layers and colours as your supplier expects.
- Checked once in a viewer.
- A file name with the part number, material and thickness.