CAD file formats for manufacturing confuse a lot of first-time product developers. You finish a design, a vendor asks for “a STEP file,” another asks for an STL, and a laser shop wants a DXF. Sending the wrong format can mean delays, lost detail, or parts made incorrectly. Our product design team in Los Angeles handles file conversions every day, so here is a practical guide to the formats that matter and when to use each one.
Native CAD Files vs. Neutral Formats
Every CAD program saves its own native format: SolidWorks uses SLDPRT and SLDASM, Fusion 360 uses F3D, Inventor uses IPT, and so on. Native files keep the full feature history, sketches, and parameters, so they are the best format for continuing design work in the same software.
The problem is that native files usually only open properly in the program that created them. That is why manufacturing relies on neutral formats that any shop can read.
STEP (.step, .stp): The Universal Manufacturing Format
STEP is the most widely accepted format for sharing solid 3D models. It preserves exact geometry, meaning true curves and surfaces rather than approximations. Machine shops, mold makers, and engineers prefer STEP because they can measure it, program toolpaths from it, and modify it in their own software.
Use STEP for CNC machining, injection molding, sheet metal fabrication, and sharing designs between engineers. If someone asks for “a 3D CAD file” without specifying, STEP is usually the safe answer.
IGES (.igs, .iges): The Older Surface Format
IGES predates STEP and is still requested by some vendors and older software. It works well for surfaces but sometimes arrives as loose, unjoined surfaces instead of a solid body, which can require repair. If a vendor accepts STEP, choose STEP.
STL (.stl): The 3D Printing Standard
STL describes a model as a mesh of triangles. It is the standard input for most 3D printing workflows and slicer software. The tradeoff is that STL approximates curves with flat facets and contains no unit information or feature data. That makes it fine for printing but poor for machining or further engineering edits.
When exporting STL, choose a fine enough resolution that curved surfaces look smooth, and confirm the units (millimeters vs. inches) with your printing service.
OBJ and 3MF: Meshes with Extras
OBJ supports color and texture data, which is useful for full-color printing and visualization. 3MF is a newer printing format that packages units, materials, and color in one file and is increasingly supported by modern printers.
DXF and DWG: 2D Profiles for Cutting
DXF is the go-to format for 2D profiles used in laser cutting, waterjet cutting, plasma cutting, and CNC routing. It stores lines, arcs, and polylines at true scale. DWG is AutoCAD’s native 2D/3D format and is common in architecture and facilities work. For flat parts, a clean DXF with closed contours at 1:1 scale is exactly what a cutting shop needs.
PDF Drawings: The Missing Piece
A 3D file shows shape, but a 2D drawing communicates tolerances, threads, materials, and finishes. For machined or molded parts, send both a STEP file and a PDF drawing so the shop knows which dimensions are critical.
Quick Reference: Which Format Should You Send?
- CNC machining: STEP plus a PDF drawing.
- Injection molding: STEP (and native file if the tooling engineer requests it).
- 3D printing: STL or 3MF, with STEP as a backup.
- Laser or waterjet cutting: DXF at 1:1 scale.
- Collaborating with another designer: native files if you use the same software, otherwise STEP.
Common File Problems We Fix
We often receive meshes that need to be machined, STEP files with missing faces, DXFs with open contours or duplicated lines, and models drawn at the wrong scale. Our team can repair, convert, or rebuild models as clean parametric CAD so every vendor gets what they need.
Need Help with Your CAD Files?
eCadCam has more than 22 years of experience preparing manufacturing-ready CAD. Visit us at 4212 San Fernando Rd, Glendale, CA 91204, call 213.489.1173, or request a quote and send us your files.