A CNC machining RFQ should identify one approved design package, explain how the CAD model and drawing work together, and resolve contradictions before a supplier prices or cuts material. A file that opens successfully is not necessarily complete. Geometry, units, revision, material, finish, tolerances and inspection requirements must tell the same story.
This guide gives engineering and purchasing teams a practical release process for outsourced parts. It focuses on document consistency, rather than repeating a general design-for-manufacture checklist. Use it before asking FUMING about CNC machining services, particularly when several people have prepared files or a design has changed during quotation.
Decide what defines the part
Start by identifying the governing product definition. A drawing-led package may use a 3D model for nominal geometry while the drawing controls dimensions, tolerances and notes. A model-based package may contain product and manufacturing information within the digital data set. Neither arrangement should be assumed simply because a STEP file is attached.
ASME Y14.41 addresses digital product definition practices. It is a useful framework for a company that uses model-based definition, but citing its name does not resolve a specific conflict between two files. The design authority still needs to identify the approved data and applicable requirements.
Write a short precedence statement in the release note. Identify the governing model and drawing by part number and revision, and tell the supplier how to raise discrepancies. Do not ask the supplier to choose whichever interpretation is easier to manufacture. When the files disagree on a functional feature, obtain a controlled engineering answer before releasing that feature for production.
Build a release register before comparing prices
A release register can be a small table in the RFQ email or controlled cover sheet. Its purpose is to remove uncertainty about which files belong together. Include assemblies and reference-only files separately so that a supplier does not quote a component from an obsolete assembly model.
| Item to identify | What to record | Reason to stop release |
|---|---|---|
| Part identity | Part number, description and quantity | Model and drawing show different parts |
| Revision | Approved revision of each controlled file | A changed feature appears in only one file |
| Units | Model units and drawing units | Imported overall size differs unexpectedly |
| Material and condition | Specification, grade and required condition | Purchasing note contradicts drawing note |
| Finish | Finish specification and masked surfaces | Finished versus unfinished dimensions are unclear |
| Acceptance | Critical features and required records | No agreed criterion for a functional feature |
File dates and names such as “final” are weak substitutes for an approved revision. Preserve the package actually quoted and record any later change against it. ASME’s Y14 standards collection includes practices addressing drawing and data-set revisions; select the applicable company or customer procedure rather than inventing a revision convention during the order.
Check the exported model, not only the native CAD file
Open the exact exported file that will be sent. Confirm that it contains the intended solid bodies, orientation and units. Compare a few easily recognized dimensions with the drawing, then inspect critical interfaces. A misplaced hole, missing pocket or suppressed component can survive a quick visual glance at the overall shape.
The NIST STEP File Analyzer and Viewer can inspect STEP information, display geometry and report certain file and product-information issues. NIST distinguishes graphical annotations from machine-interpretable semantic information. Therefore, visible annotations alone do not establish that downstream software can interpret every requirement.
Ask the receiving supplier to confirm import success and flag unsupported annotations. For an ordinary drawing-led order, a readable controlled drawing remains useful alongside the exchange model. For a model-based order, agree how required annotations and acceptance data will be accessed. A screenshot is helpful for discussion, but should not replace a controlled manufacturing definition.
Resolve contradictions by feature and consequence
Create a discrepancy list with one issue per row. Record the feature, the conflicting values or instructions, the likely manufacturing consequence and the person authorized to decide. Attach a marked view if it helps identify the location, while retaining the unmodified released files.
For example, consider an illustrative bracket whose drawing specifies a different hole spacing from the supplied model. Do not average the values or quietly edit the quotation model. The engineering owner should identify the required spacing, issue aligned files, and confirm whether the change affects mating components. Purchasing can then ask each supplier to quote the same corrected package.
Distinguish a clarification from a design change. Explaining where an existing note applies may be a clarification; moving a hole or changing a fit changes the manufactured part. Record both, but route changes through the release process. Questions about functional limits should connect to a proper CNC tolerance review, rather than becoming informal email tolerances.
Separate nominal geometry from acceptance requirements
A model can communicate a nominal bore diameter without defining its allowable variation, surface condition or relationship to another feature. A drawing may provide these requirements through dimensions, geometric controls and notes. Review how the part fits and functions before deciding which features need explicit inspection evidence.
NIST’s CAD and PMI testing project illustrates why exchanged product information warrants verification; its published results concern specific historical software versions, not a guarantee for a current file. For an international supply chain, identify the standards and editions required by the released package. Avoid mixing conventions casually or assuming that a supplier will infer the intended rules from the destination country.
Material is another source of hidden disagreement. A CAD material assignment may be present for visualization or mass estimates, while the drawing calls for a specific grade and condition. Confirm the purchasing requirement explicitly. Use the machining material selection guide to frame engineering discussions, then place the approved choice in the controlled package.
State what the quotation must include
Ask suppliers to identify their quoted revision, material, finish, quantities and inspection deliverables. Require exclusions and assumptions to be stated clearly. A lower price is difficult to evaluate if one quotation excludes finishing or treats a critical inspection record as optional.
Separate prototype needs from production needs. You may request different quantity breaks, packaging arrangements or reporting levels, but each option must still identify the same part definition. If a supplier proposes a manufacturability change, request a marked proposal and its implications. Do not treat an alternative quotation as approval to alter the design.
Before purchase-order release, cross-check the quotation against the approved discrepancy log. Transfer accepted answers into the controlled documents or formally referenced approval record. The first delivered parts should be checked against that same baseline; the first article inspection checklist helps structure the manufacturing follow-through.
A short release checklist
- All manufacturing files refer to the intended part and approved revision.
- The exported model opens correctly and has been compared with the drawing.
- Units, material, finish and critical acceptance requirements are consistent.
- Each discrepancy has an engineering decision and a traceable disposition.
- The quotation states its assumptions, exclusions and inspection scope.
- The purchase order references the approved package, including accepted changes.
When the package is ready, send FUMING a quotation request with the controlled files, quantities and open technical questions. Identify unresolved points as questions rather than concealing them in an attachment. Project-specific capability, inspection scope and delivery expectations should be agreed during review.
Frequently asked questions
Does a STEP model always override a PDF drawing?
No universal precedence should be assumed. Follow the released product-definition rules for the project. If the package does not say how conflicts are resolved, ask the design authority before manufacture.
Is opening the model enough to validate it?
No. Check geometry, units, revision and required annotations after export. NIST’s analyzer user guide describes file analysis capabilities, but software checks do not replace engineering approval of the design.
Can an RFQ contain an unresolved design question?
Yes, if it is clearly identified and the quotation states the assumption being evaluated. Resolve it before authorizing the affected production work. Otherwise the apparent price comparison may cover different parts.
Should every feature receive the tightest available tolerance?
No. Define acceptance according to function and the approved design. Unnecessary restrictions can increase manufacturing and inspection work without improving the assembly. Resolve the functional requirement first, then discuss a suitable process with the supplier.
