The answer to "We sent the drawing, when will the quote arrive?" usually depends on the file that was sent. A drawing that arrives as a screenshot, a 3D model without dimensions or a PDF with missing tolerances extends the quotation process by days and increases the risk of incorrect pricing. This guide explains what each file format does for CNC turned and milled parts and the ideal package you should send to your supplier. It can be read as the detailed version of the technical-file section of our RFQ guide.
Formats and Their Roles in CNC Manufacturing
| Format | Content | Use in CNC | Pros | Cons |
|---|---|---|---|---|
| STEP (.stp/.step) | 3D solid model, neutral format | CAM programming, volume/chip calculation, fixture design | Opens in all CAD/CAM systems; lossless geometry | Usually no tolerance, surface or material data (except AP242 PMI) |
| PDF technical drawing | 2D views, dimensions, tolerances, surface, material, notes | Quotation, inspection, FAI, contract reference | Binding document; everyone can read it | Geometry must be remodelled; ambiguity if dimensions are missing |
| DXF/DWG | 2D vector drawing | Laser/plasma/waterjet cutting profiles, 2D milling contours | Transferred directly to cutting machines | Insufficient for 3D parts; thickness and tolerance must be communicated separately |
| IGES (.igs) | 3D surface/solid, older neutral format | Alternative when STEP is unavailable | Wide support | Surface errors and unclosed solids are common; STEP is preferred |
| Parasolid (.x_t/.x_b) | 3D solid kernel format | Between SolidWorks/NX/Solid Edge | Very accurate geometry | Not every CAM opens it |
| Native CAD (.sldprt, .prt, .ipt, .catpart) | Parametric model | Suppliers using the same software | Full information, feature tree | Version incompatibility; risk of sharing know-how |
| 3MF/STL | Triangulated surface mesh | 3D printing | — | Not suitable for CNC: no tolerances and no true surfaces |
The Ideal Package: STEP + PDF
For CNC contract manufacturing the standard and sufficient package is a pair:
- STEP file (AP214 or AP242): the 3D solid model of the finished part; the supplier derives the CAM program, the raw-material size and the clamping strategy from it.
- PDF technical drawing: all functional dimensions and tolerances, the general tolerance standard (for example ISO 2768-mK), surface roughness, material grade and standard, heat treatment/coating, thread definitions, edge-break note, revision number and part name.
The PDF is the technical annex to the contract and the reference for the inspection report; if the STEP and the PDF conflict, the rule the drawing governs is the industry standard. Stating this explicitly in the RFQ removes any ambiguity.
What to Add in Which Case
- Sheet and plate profiles: in addition to STEP + PDF, a 1:1-scale DXF (with thickness and material note).
- Models with PMI: STEP AP242 carries the tolerances on the model (MBD – Model Based Definition). If you use it, say so; but still include the PDF drawing, as not all suppliers can read PMI.
- Assembly parts: the model of the mating part (for reference) makes fits and function easier to understand; valuable for DFM recommendations.
- Reverse engineering: if there is no drawing, a physical sample + photographs + critical dimensions; the supplier creates the model and submits it for your approval.
- Cutting and machining combined: for laser-cut + CNC-milled parts, the DXF cutting contour and the STEP final geometry are sent together.
Common Mistakes
- Unit confusion: STEP files carry the unit, but some exports lead to inch/mm confusion. Make sure the drawing states unit and scale; for US-sourced drawings state that they are in inches.
- Revision mismatch: STEP Rev C, PDF Rev B. Include the revision in the file name:
12345-C_flange.step,12345-C_flange.pdf. - PDF without dimensions: a drawing containing only a 3D view and the note "per STEP" does not define tolerances; if not even the general tolerance standard is stated, price and inspection are undefined.
- Screenshot or photograph: a quote can be given but is not binding; a drawing is requested before the first order.
- Before/after coating ambiguity: if there is anodising or coating, state in which condition the tolerance applies.
- Conflict between model and drawing: R2 in the model, R3 on the drawing. If the "drawing governs" rule is in place, the problem is solved; if not, production stops and waits for an answer.
- Password-protected or edit-locked PDF: makes ballooning and inspection-report preparation difficult; keep printing/measuring permission enabled.
File Security and Sharing
Technical drawings contain know-how. Sending a STEP instead of the native CAD file does not share the feature tree and the design logic; it is common practice to send only the files needed for the quote before an NDA is signed. Sending files via secure transfer or the supplier's quote form rather than as e-mail attachments reduces version confusion. Tornelle's quote form accepts STEP, DXF and PDF files directly.
What Happens on the Supplier Side?
A contract-manufacturing workshop that receives a STEP + PDF package does the following: imports the model into CAM, determines the raw-material size, works out the operation and clamping plan, calculates the cycle time, converts the tolerances and surfaces on the drawing into an inspection plan, obtains material and coating prices and notes any DFM recommendations. With a complete file set this process takes 1–2 days; with incomplete files it can take a week of question-and-answer loops. In our DFM article you will find the typical recommendations that come up at this stage.
Frequently Asked Questions
Can I get a quote if I send only a STEP file?
You can get a preliminary quote, but tolerance, surface and material are priced on assumptions; a binding quote and production require a PDF drawing.
Is a PDF drawing alone sufficient?
For simple turned parts, yes; for complex milled parts the supplier remodels the part, which brings time and risk of error. Adding a STEP always speeds things up.
What is the difference between STEP AP203, AP214 and AP242?
AP203 carries basic geometry, AP214 colour/layer/product data, and AP242 carries PMI (tolerances and notes). For CNC, AP214 is sufficient; if MBD is used, AP242 is preferred.
What scale should the DXF be?
Always 1:1, in mm, and containing only the cutting contour (dimension lines and frame on a separate layer or deleted).
Conclusion
The ideal package to send to your CNC supplier is STEP + PDF; for sheet parts, add a DXF. If the revision, the unit and the "drawing governs" rule are clear, the quote arrives within 24 hours and production starts without questions. Send your files via our quote form; if any information is missing, we let you know as a list in our first reply. For process details see our how we work page.
