- PDF controls dimensions, notes and revision.
- STEP carries solid geometry; DXF carries 2D profiles.
- STL should not be the sole authority for precision fabrication.
- Every file needs the same part number, units and revision.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
PDF: The Readable Contract Baseline
The PDF should contain dimensions, tolerances, datums, weld symbols, material, finish, deburring, threads, inspection and revision history. Verify text, symbols and views at 100% scale after export and embed fonts. Number multi-page drawings as page X of Y to prevent missing sheets.
DXF/DWG: Keep Only Manufacturable 2D Geometry
DXF/DWG suits laser, plasma, waterjet, stamping profiles and some gauges. Remove duplicate lines, open contours, dimensions, hatching and hidden construction layers. Confirm mm versus inch, 1:1 scale and true arcs rather than thousands of short segments. State whether geometry is the finished profile or a compensated flat pattern. It is often safer for the fabricator to create the flat using its own tooling and bend data.
Prefer STEP; Use IGES for Legacy Compatibility
STEP preserves solids, assemblies and surface relationships and is useful for interference checks, programming and DFM. IGES may import as disconnected surfaces and is mainly a compatibility option. For assemblies, provide a simplified assembly plus individual STEP files and remove unrelated confidential detail. STL is a triangle mesh for visualization or printing and should not be the sole authority for precision sheet metal or machining.
Do Not Assume PMI Will Survive Translation
A PMI-enabled model can carry dimensions and GD&T, but semantic PMI support varies across CAD/CAM systems. Unless both parties have validated an MBD workflow, continue to provide a 2D PDF. Critical requirements must not exist only as CAD colors, layer names or email text.
File-release Check
Reopen the files on another computer or neutral viewer, measure a known dimension and verify normals, hole count, thickness, units and revision. A useful filename is “PartNo_Name_RevB_20260716.step”. Resolve 2D/3D differences before release rather than asking the supplier to guess.
RECOMMENDED PACKAGE
Single sheet-metal part: PDF + STEP; add DXF when a 2D cutting profile is required.
Welded assembly: assembly PDF + assembly STEP + part drawings/models + BOM.
Bent tube: PDF with centerline, tangents and rotations + STEP + tube specification.
Cosmetic part: the above + color/finish sample + cosmetic-face map.