Why the format question exists at all
Your designer works in SolidWorks, Fusion, Inventor or Creo. Your supplier's CAM system may be none of those. Native files carry version and licence problems across that gap; neutral formats exist to close it.
STEP (ISO 10303, files ending .step or .stp) is the neutral 3D format the industry settled on. It carries exact solid geometry that any CAM system reads cleanly, which is why it is the standard request for machined parts. IGES is its older sibling: still readable, more prone to broken surfaces; send STEP where you can.
DXF is the 2D exchange format for flat profiles: the laser, plasma, waterjet and punch world runs on it. One closed outline per part, internal cut-outs as closed loops, drawn at 1:1 in stated units.
STL describes a mesh of triangles, not true geometry. It is the right file for a 3D printer and the wrong one for a machine shop, because CAM needs exact faces and edges, not an approximation of them. If a machinist receives an STL, someone ends up remodelling your part, at your cost and their interpretation.
The file is not the specification
A STEP file describes shape perfectly and intent not at all. It carries no tolerances, no material grade, no thread callouts, no surface finish, no revision. Every one of those lives on the drawing, which is why the pair matters: CAD for geometry, PDF drawing for everything the geometry cannot say. Our RFQ pack guide covers the full send-list; the short version is that a STEP file without a drawing gets quoted on assumptions, and assumptions are how goods-inward arguments start.
Threads deserve a special mention. CAD models usually show threads as plain holes, modelled at drill or nominal diameter. Without a drawing callout, M8x1.25 to a stated depth, the machinist cannot know a thread was intended at all. The same goes for tolerances and fits: an H7 bore looks identical to a clearance hole in the model.
The file errors that stall quotes
| Error | What happens | The fix before sending |
|---|---|---|
| Wrong or unstated units | A 100 mm part arrives quoted as 100 inches, or the supplier stops to ask | State units in the file and on the drawing; export metric |
| Open contours in a DXF | The laser nest software rejects the profile or closes it wrongly | Check every outline and cut-out is a closed loop |
| Stray geometry and duplicate lines | Ghost cuts, double cuts, rejected files | Purge construction lines, text and duplicate entities before export |
| Assembly instead of a part | The supplier must extract and guess which body you want priced | Export one part per file, named to match the drawing number |
| Mesh (STL) instead of a solid | Remodelling at your cost, or a refused quote | Export STEP from the original CAD, not from the mesh |
| File name chaos | Wrong revision gets made; nobody can prove which file was quoted | Name files with part number and revision, matching the drawing |
The send-it-right checklist
- Machined part: STEP file plus PDF drawing with revision, tolerances, material, finish and thread callouts.
- Laser or waterjet profile: DXF at 1:1 in stated units, closed contours, plus a PDF stating material, thickness, quantity and any bend lines. The process choice itself is covered in our cutting comparison.
- Folded sheet part: STEP of the finished part plus the PDF; let the fabricator generate the flat pattern, because bend allowances are theirs to own.
- No CAD at all? A dimensioned sketch or sample part is workable: that is reverse engineering, and the output includes the STEP and drawing you were missing.
Send that pack to TrueNorth and the DFM review comes back within 48 hours, including any file problems found, fixed or flagged rather than silently guessed. One quote, one price, for the delivered and inspected part.