When requesting a machining quote, the choice of STEP vs IGES vs PDF affects how fast and how accurately a shop can price your part. Each format carries different information. A 3D model describes shape. A drawing describes requirements. A shop needs both to quote with confidence, and the combination of a STEP model and a PDF drawing with tolerances is the package most machine shops prefer.
STEP vs IGES vs PDF: what each file carries
| Factor | STEP (.stp, .step) | IGES (.igs, .iges) | PDF drawing |
|---|---|---|---|
| What it contains | Solid 3D geometry with faces, edges and topology | Surfaces and curves; solids often come through as loose surfaces | 2D views, dimensions, tolerances, GD&T, material, finish and notes |
| Tolerances and notes | Usually none; AP242 can carry PMI, but few quote workflows rely on it | None | Yes; the controlling requirements document |
| Reliability on import | High; imports cleanly into CAM | Variable; gaps and missing faces are common | Not importable as geometry |
| Effect on quote speed | Fast volume, feature and setup analysis | Slower; may require repair | Needed to price inspection and finish correctly |
| Effect on quote accuracy | Good for geometry; misses tolerance cost drivers | Lower if geometry needs repair | Good for requirements; slower for complex shapes |
| Best fit | Primary model for any machined part | Legacy data when no STEP is available | Always, alongside the model |
Why STEP plus a PDF is the ideal quote package
The model tells the estimator how much material to buy, which machine the part belongs on, how many setups it needs and how long the cutting will take. The drawing tells the estimator what the part must do: which features are tight, what the surface finish is, what material and heat treat are required, what finish goes on after machining and what inspection report is expected. Most of the cost in a precision part sits in those requirements, not in the shape. A part with a 0.0005 in. bore and a CMM report costs more than the same shape with general tolerances, and only the drawing shows that.
When the two disagree, the drawing normally governs. Make sure the revision letters match and that the model is saved at nominal dimensions.
When each format is enough on its own
STEP only
A STEP file alone can support a budgetary price for simple parts with general tolerances. Expect the estimator to ask for material, finish, quantity and any critical features before the quote is firm.
PDF only
A fully dimensioned PDF can be quoted on its own, especially for turned parts and simpler prismatic parts. Complex 3D shapes are slower and less precise to price without a model.
IGES only
IGES works when it is all you have, such as older legacy data. If your CAD system can export STEP, use STEP instead.
Common mistakes
- Sending a model with no material, finish or quantity information.
- Mismatched revisions between the model and the drawing.
- Exporting a mesh file such as STL for a machined part. Meshes do not carry true arcs and planes.
- Leaving the title block tolerance off the drawing, so general tolerances are unknown.
- Applying tight tolerances to every feature when only a few are functional.
A quote package checklist
- STEP model at nominal dimensions, matching the drawing revision
- PDF drawing with title block tolerances, GD&T and surface finish callouts
- Material grade and condition, including heat treat if required
- Finish specification, with masking noted
- Quantities, including prototype and expected annual volume
- Required documents, such as material certs, FAI or CMM reports
How this applies at Wexmar
Wexmar's instant estimator accepts PDF and STEP files. It returns a starting estimate, and a human estimator then reviews the drawing and confirms every quote before it is final. If you only have IGES or another format, email it to ron@backwell.com and we will review it. Our estimators look at tolerances, materials and inspection requirements together, so the confirmed price reflects the actual work on our milling and turning equipment. For more guidance, see our other machining guides.
Getting a quote
For the fastest and most accurate price, send a STEP model and a PDF drawing with tolerances, material, finish and quantity. You can upload a drawing for an instant estimate, or call (315) 400-2654 with questions about your files.