STEP vs STL vs DXF: Which File Format for Which Process?
A file in the wrong format delays your quote. The differences between STEP, STL, DXF, IGES and PDF, and which to use for CNC, 3D printing, laser cutting and sheet metal.
Table of contents 6 sections
The same part carries very different information in different file formats. Choosing the right one lets the manufacturer quote and produce your file without having to ask questions.
In short: send STEP for CNC and sheet metal, STL or STEP for 3D printing and DXF for laser cutting. Always add a PDF drawing for tolerances, threads and other details.
Format comparison
| Format | What it carries | Best for | Limitation |
|---|---|---|---|
| STEP (.step, .stp) | Precise 3D solid geometry | CNC, sheet metal, injection molding | No tolerances or surface data |
| IGES (.igs) | 3D surface geometry | Compatibility with older systems | May lose solid information |
| STL (.stl) | A mesh of triangles | 3D printing | No true curves; unsuitable for CNC |
| DXF (.dxf) | 2D lines and curves | Laser, plasma and waterjet cutting | Flat geometry only |
| Technical drawing | Every process, as a supplement | Cannot be used directly for production |
STEP: the standard for CNC and sheet metal
A STEP file (ISO 10303) carries the part’s true mathematical geometry: cylinders are cylinders and holes are holes. The manufacturer can create a CAM program directly from it and calculate machining time and material. SolidWorks, Fusion 360, Inventor and other CAD tools can all export STEP.
STL: the language of 3D printing
STL approximates a surface with small triangles. 3D printer software slices this mesh into layers. In an STL, however, a hole is a polygon rather than a true circle, which makes it unsuitable for CNC machining. When exporting, keep the resolution (triangle count) high enough; otherwise curved surfaces come out faceted.
DXF: the format for flat cutting
DXF describes two-dimensional lines, arcs and curves. Laser, plasma and waterjet machines follow this geometry directly. For sheet metal parts, the flat pattern of a bent part can also be sent as DXF, but a 3D model or dimensioned drawing should be added for bend information.
Watch out: converting an STL to STEP does not restore the lost mathematical geometry. For CNC, always export STEP directly from your CAD software.
Why is a drawing still needed?
3D models carry geometry but do not tell the manufacturer which dimensions are critical, the tolerances, thread types, surface roughness, material or finish. Adding a PDF drawing prevents misunderstandings and revision loops.
What to send for each process
- CNC machining: STEP + PDF drawing
- Sheet metal: STEP (bent state) or DXF flat pattern + dimensioned drawing
- Laser cutting: DXF (1:1, mm) + PDF if needed
- 3D printing: STL or STEP, with notes on fit dimensions
- Injection molding: STEP + material and surface texture information
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