CNC Machining Quote Checklist: What Engineers Should Prepare Before RFQ

CNC Machining Quote Checklist: What Engineers Should Prepare Before RFQ

A fast CNC machining quote does not start with the supplier. It starts with the quality of the RFQ package. When a buyer sends only a screenshot, an incomplete STEP file, or a drawing without material and tolerance notes, the supplier has to ask basic questions before estimating machining time, tooling, inspection effort, finishing risk, and delivery feasibility. That delay can turn a same-day technical review into a week of back-and-forth emails.

This checklist explains what engineers and procurement teams should prepare before requesting a CNC machining quote. It is designed for custom machined metal parts, prototype-to-low-volume projects, and engineering teams that want fewer quotation surprises.

Key Takeaways

• Send both 3D CAD data and a 2D PDF drawing when possible. STEP or STP files define geometry, while PDF drawings clarify tolerances, threads, finishes, inspection points and notes.
• Material grade, quantity, tolerance class, surface finish and QA document requirements are the five inputs that most often change CNC price.
• If the drawing is confidential, confirm NDA handling before upload and avoid sending uncontrolled revisions through multiple channels.
• A complete RFQ package helps the supplier perform DFM review before quoting, which reduces late design changes and hidden manufacturing costs.

1. Required CAD Files: STEP, STP, IGES or Native CAD

For CNC machining RFQs, a 3D CAD file is usually the primary source for geometry. STEP and STP are the most common neutral formats because they preserve solid geometry and are widely supported by CAM software. IGES or IGS can also be useful, especially for surface-heavy files, but STEP is generally preferred for machined parts.

If you only send a 2D PDF drawing, the supplier may still quote simple parts, but complex pockets, contoured surfaces, intersecting holes, and multi-face features are difficult to evaluate accurately. Without 3D geometry, it is harder to estimate setup count, tool access, stock size, and cycle time.

Recommended file package:

2. PDF Drawing Notes: What CAD Alone Does Not Explain

A STEP file tells the supplier what the part looks like, but it often does not fully explain how the part should be controlled. The PDF drawing should clarify:

• Critical dimensions and tolerances
• Thread standards and thread depth
• Surface roughness requirements
• Deburring and edge break notes
• Datum structure and inspection references
• Coating or surface treatment notes
• Material specification and heat treatment
• Revision number and drawing release status

If a dimension is function-critical, do not rely on the general tolerance block alone. Mark it clearly. A supplier can machine every dimension tightly, but that increases cost. Good drawings tell the supplier which features actually matter.

3. Material Grade and Condition

Material is one of the first RFQ inputs because it affects cutting speed, tool wear, stock availability, inspection method, finishing compatibility and lead time. Saying “aluminum” is not enough. 6061-T6, 7075-T6, 2024-T351 and MIC-6 behave differently in machining and finishing.

For steel, specify the exact grade and condition. For example, 4140 pre-hard, 304 stainless, 316L stainless, 17-4PH H900, S45C and 440C all have different tooling and heat-treatment implications.

Include:

• Material grade
• Temper or hardness condition
• Required standard, if any
• Substitute material allowed or not
• Material certificate / MTR requirement

If substitutions are acceptable, say so. If they are not acceptable, make that explicit.

4. Quantity, Batch Size and Forecast

Quantity changes CNC pricing because setup time is distributed across the batch. A one-piece prototype and a 500-piece production batch can use different process decisions.

Provide:

• Quote quantity
• Expected annual usage, if known
• Prototype quantity vs production quantity
• Whether split delivery is acceptable
• Whether future repeat orders are expected

For example, “quote 20 pcs now, possible 300 pcs annual repeat” is more useful than simply “20 pcs.” The supplier can decide whether to optimize only for first delivery or also consider repeatable fixture strategy.

5. Tolerance Requirements

Tolerance is one of the most common reasons CNC quotes differ dramatically between suppliers. A general tolerance such as ISO 2768-mK is often appropriate for non-critical features. But if every dimension is marked ±0.01 mm, the supplier must assume high inspection and process-control effort.

Before RFQ, separate features into groups:

• Functional critical dimensions
• Cosmetic or non-critical dimensions
• Fit and assembly interfaces
• Threaded or bearing features
• Datum-related inspection dimensions

If the part does not need tight tolerance everywhere, do not specify it everywhere. Ask for DFM review if you are unsure which tolerances drive cost.

6. Surface Finish and Post-Processing

Surface finish can affect dimensions, cost and lead time. Anodizing, plating, black oxide, passivation, bead blasting, polishing and hardening all have different process risks. Coating thickness can change fits, especially on holes, threads, slots and mating surfaces.

Include:

• Finish type
• Color, if relevant
• Masking requirements
• Cosmetic surface requirements
• Coating thickness or standard
• Areas that must remain uncoated

If the part has tight fits after coating, call out whether dimensions apply before or after finish.

7. QA Documents and Inspection Requirements

Quality documentation should be requested during RFQ, not after production starts. Inspection requirements affect cost because they determine measurement time, report format and traceability.

Common options:

• CMM dimensional report
• First Article Inspection Report (FAIR)
• Material Test Report (MTR)
• Certificate of Conformance (COC)
• Surface finish report
• Hardness report
• Coating thickness report

If only a few dimensions are critical, identify them. A project-reviewed CMM report for every dimension may be unnecessary for simple parts, but it may be essential for regulated, regulated, automation, fixture or assembly-critical components.

8. Confidentiality and NDA Requirements

Many CNC RFQs involve unreleased products, proprietary fixtures, robotics parts, regulated devices or internal R&D components. If the drawing is confidential, clarify NDA requirements before sending files.

A good RFQ process should define:

• Who can access uploaded drawings
• Whether files can be shared with finishing partners
• Whether the supplier may use anonymized geometry for training or examples
• How long files are retained
• Whether an NDA is required before review

Andas Precision treats uploaded drawings and RFQ data as private project material. Public pages, llms.txt and robots.txt are separated from uploads, leads and internal data.

9. Revision Control

Revision confusion causes expensive mistakes. Before sending an RFQ, confirm that the STEP file and PDF drawing represent the same revision. If the 3D model says Rev B and the PDF says Rev C, the supplier has to stop and ask which file controls.

Include a short note:

• Current drawing revision
• What changed from the previous revision
• Whether old quotes should be invalidated
• Whether supplier feedback should be applied before final release

For complex projects, send a simple revision summary with the RFQ email.

10. Practical CNC RFQ Checklist

Use this checklist before sending files:

How Andas Uses This Information

When you upload a STEP, IGES or PDF drawing to Andas Precision, the RFQ package can be reviewed for manufacturability risks before formal quotation. engineering-assisted DFM review helps identify thin walls, internal sharp corners, deep pockets, tolerance conflicts, coating risks and missing drawing information. An engineer can then review the project requirements, QA expectations and quotation inputs.

For the fastest review, send the CAD file, PDF drawing, material, quantity, tolerance expectations, finish and QA requirements together.

FAQ

Can I request a CNC quote with only a STEP file?

Yes, but a STEP file alone may not include all tolerance, thread, finish and inspection requirements. A PDF drawing is strongly recommended for accurate quoting.

Is STP the same as STEP?

For most CNC RFQ workflows, STP and STEP refer to the same neutral CAD exchange format. Both are commonly accepted.

What information most affects CNC quote price?

Material, quantity, tolerance, surface finish, part complexity and QA document requirements usually have the largest impact on CNC quote price.

Should I request CMM reports for every CNC part?

Not always. CMM reports are valuable for critical dimensions, assembly interfaces and regulated projects, but they add inspection effort. Request them when dimensional evidence is important.

Can Andas review my drawing before formal quotation?

Yes. Andas Precision provides engineering-assisted DFM review and engineer follow-up for STEP, IGES and PDF drawings before formal CNC quotation.