Dewey Wu General Manager & senior mechanical engineer at EPOC CRAFTER, 15 years in design engineering, quality, and metallurgy. Hands-on across CNC machining, metalwork, sheet metal, and prototyping (subtractive + 3D printing).
A CNC machining quote is comparable only when every bidder receives the same released geometry, drawing revision, material definition, tolerance scope, inspection requirements, quantity, and delivery basis. For a first RFQ to a China CNC machining supplier, send the 3D CAD model with a controlled 2D manufacturing drawing whenever the model does not carry every requirement needed for manufacturing and acceptance. State material grade and material condition, critical tolerances, CNC machining surface finish, quantity, CNC machining lead time, inspection documentation, and commercial delivery scope before pricing starts.
Quote, quotation, and RFQ have different meanings inside different companies. In this guide, the manufacturing RFQ is the controlled input package and the CNC machining quotation is the supplier response. A quote comparison is useful only after the bidders have priced the same technical and commercial scope.
1. Build One RFQ Package for Every Supplier
Use the same RFQ package for every bidder. A machined parts quote can look cheaper because it excludes finishing, inspection records, packaging, certified material, or delivery responsibility. The engineering scope can drift too. One shop may price the specified material condition while another prices an available substitute. One may inspect every CTQ feature while another assumes normal shop inspection.
The table below turns the RFQ package into a scope control. Each row tells the buyer what to send and what decision must be fixed before the supplier prices the job.
| Part identity and revision | Part number, released part revision, matching 3D model and 2D drawing | An obsolete geometry or mixed revision can be priced | Confirm the released revision for quotation |
| 3D geometry | STEP or another agreed solid CAD file for CNC machining | CAM review, stock planning, and setup strategy depend on the released geometry | Send the same geometry file to every bidder |
| 2D manufacturing drawing | Dimensions, CNC machining GD&T, threads, critical features, finish callouts, and notes | The supplier may fill missing acceptance requirements with its own assumptions | State which requirements govern manufacturing and acceptance |
| Material | Material grade, material condition or temper, governing specification when required, and substitution rule | Different conditions or substitute grades create different purchasing scopes | Allow, prohibit, or require approval for an equivalent |
| Quantity and timing | Current quantity, credible follow-on or annual volume, required date | Setup, purchasing, scheduling, and inspection planning change with volume and timing | Give every bidder the same quantity and timing basis |
| Quality scope | Inspection level and required quality documents for CNC machining | Inspection labor and documentation may be included by one supplier and excluded by another | Request only the records the program needs, before quotation |
| Delivery scope | Delivery destination, packaging requirement, trade term when used, and commercial inclusions | Freight, export handling, packaging, and exclusions can distort the headline unit price | Define what the quoted price must include |
A simple noncritical spacer does not need the same documentation as a drawing controlled aerospace or automotive part. The RFQ should match the program risk and acceptance requirements. For a China CNC machining supplier, extra paperwork has no value unless it closes a real technical, quality, or commercial gap.
2. Send the STEP File and a Controlled 2D Manufacturing Drawing
A STEP file for CNC machining gives the supplier nominal 3D geometry for CAM review. A technical drawing for CNC machining carries acceptance information that may not be embedded in the model. For a drawing controlled job, send both files and make the file precedence explicit.
2.1 Use the 2D Drawing for Controlled Requirements
The technical drawing package should carry the requirements the supplier must price and inspect: critical dimensions, datums, GD&T for CNC machining, thread callouts, surface requirements, material notes, and inspection notes. A bearing bore, press fit, sealing face, or controlled hole pattern cannot be priced responsibly from nominal geometry alone.
A model based definition workflow is a valid exception. When the 3D model contains validated PMI and the buyer designates that model as the authority, the separate drawing may carry less information. The RFQ still needs to state that authority and confirm the supplier can consume the PMI correctly.
EPOC CRAFTER keeps the deeper tolerance discussion in its CNC drawing tolerance guide, so this article stays focused on the information needed before pricing.
2.2 Drawing Revision Control and File Precedence
Drawing revision control should be obvious from the file set. Put the released part number and revision on the CNC engineering drawing, and name the matching model so the revision can be identified without relying on email timestamps or filenames such as final2.step.
State which document controls when the model, drawing, purchase order, and referenced specification disagree. A practical drawing controlled rule is: the 3D model defines nominal geometry; the released 2D drawing defines tolerances, GD&T, threads, surface finish, inspection requirements, and controlled notes. Any conflict goes back to the buyer for clarification before quotation or manufacture. Companies using authoritative MBD can define a different hierarchy.
3. Specify Material Grade, Material Condition, and Approved Equivalents
A material specification for CNC machining needs more than the alloy family. Write the exact material grade and condition or temper, then add the governing product specification and raw material form when the purchase requirement depends on them. An aluminum CNC machining quote should not start from aluminum alone; 6061-T6 is a usable grade and condition callout. The same rule applies to a stainless steel CNC machining quote, alloy steel, copper alloys, and engineering plastics.
Product form can change the governing specification. ASTM A276/A276M-25, for example, covers stainless steel bars and shapes. A 316L callout still needs the right product specification when the RFQ controls certification or purchasing basis. EPOC CRAFTER provides broader selection context in its CNC machining materials guide.
3.1 Approved Material Equivalents Need Buyer Control
Do not approve a substitute from a material grade equivalent chart alone. An ASTM to GB equivalent or SAE to GB equivalent must be checked against the part requirement, including composition, material condition, product form, heat treatment, mechanical requirements, corrosion requirement, certification, and customer restrictions. GB material standards define their own purchasing requirements; similarity in grade names does not create automatic interchangeability.
Use one of three RFQ positions: no substitution, a listed approved material equivalent, or a proposed alternative that requires buyer approval. When approval is required, ask for the exact designation, governing standard, condition, and product form before the supplier purchases stock.
3.2 Material Certificates and Traceability
State certificate requirements at quotation stage. A CNC machining material certificate, mill test report, certificate of conformity, or heat and lot traceability adds work only when the program requires that evidence. Material traceability for CNC machining can extend from the raw stock heat or lot through the machined batch and finished part identification. Define the required chain instead of writing only “material cert required.”
4. Define CNC Machining Tolerances, GD&T, and Surface Finish
CNC machining tolerances should follow function. Mark the features that control fit, sealing, location, motion, alignment, or interchangeability. Leave noncritical dimensions under the validated general tolerance system on the drawing. This tells the supplier where machining and inspection effort belongs.
4.1 Use GD&T for Functional Relationships
ISO 1101:2017 remains the current published ISO foundation for geometrical tolerancing. For ASME drawings, ASME Y14.5-2018 (R2024) remains in effect. The RFQ should state the governing drawing convention when the distinction affects interpretation.
Use CNC machining GD&T where a feature relationship needs datum based control. Position for a hole pattern, flatness on a sealing face, or perpendicularity between a shaft axis and mounting face communicates more than an isolated plus or minus size. CTQ labels can help process planning, but they do not replace the tolerance or feature control frame.
4.2 Keep Fits and Threads Functional
ISO 286-1:2010 remains current after its 2026 review, and ISO 286-2:2010 remains the published edition for tolerance classes and limit deviations. A fit such as H7/g6 should stay tied to its nominal size and the ISO 286 system. Do not round it into a convenient bilateral tolerance without checking the applicable limits.
Use the ISO 286 fit callouts guide when the design needs a defined clearance, transition, or interference relationship. Threads need the same discipline: specify thread designation, pitch, class or tolerance, and any inspection requirement that affects acceptance.
4.3 Specify Surface Texture and Secondary Finish Separately
ISO 21920-1:2021 is still the published edition for indicating profile surface texture, with a revision under development as of September 2026. ISO 21920-2:2021 defines the related terms and profile parameters. Where function needs a controlled surface, state the parameter and value, for example Ra 1.6 µm when that is the validated design requirement.
CNC machining surface finish also includes secondary treatment. State anodizing, plating, passivation, bead blasting, powder coating, painting, polishing, or the required process. Identify masking, cosmetic zones, and dimensions that must be accepted after finishing when those controls affect the part. The CNC surface finishing capabilities page gives process specific context without turning this RFQ article into a finishing guide.
5. State Quantity, CNC Machining Lead Time, and Delivery Scope
Quantity and timing belong in the same RFQ as the drawing. A prototype CNC quote, low volume CNC quote, and production CNC quote can use different setup, stock purchasing, fixturing, inspection, and scheduling assumptions even for the same geometry.
5.1 Current Quantity and Annual Volume
State the current production quantity first. Add credible follow-on demand or annual volume when it can change the sourcing plan. A one-off prototype order should not be priced against an annual commitment that does not exist.
For early builds, the CNC machining for prototyping guide covers file and validation needs around prototype CNC work. For recurring batches, low volume production planning covers the handoff from prototype quantities into repeat production.
5.2 Lead Time, Destination, Packaging, and Trade Terms
Write the milestone behind the requested date: factory completion, shipment, or arrival. Add the delivery destination and any packaging requirement that changes handling. Cosmetic surfaces, precision edges, capped threads, corrosion sensitive parts, and separated assemblies may need packaging beyond bulk bags or cartons.
When the purchase uses Incoterms, write the rule, named place, and version. ICC Incoterms 2020 remains the most recent edition and allocates delivery related tasks, costs, and risks. Payment terms, currency, tooling ownership, inspection charges, and other commercial exclusions still need separate agreement when they affect the quote.
6. Set Inspection Level and Quality Documentation Before Quoting
Inspection requirements change the quoted work. Define the inspection level and the inspection documentation the buyer expects to receive. A simple commercial part may need normal supplier inspection with no separate report. A customer controlled program may require recorded CTQs, material traceability, FAI, PPAP, ISIR, or other approval evidence.
| Dimensional report | Recorded evidence is required for selected or all drawing characteristics | Every dimension needs a CMM |
| FAI | The program requires a documented first article or first production verification | Every FAI means AS9102C |
| AS9102C FAI | The aerospace contract or customer invokes AS9102C | It is a generic CNC inspection format |
| MTR or material certificate | Material identity, condition, chemistry, mechanical data, or traceability must be documented | Every stock purchase includes the same certificate content |
| CoC | The contract requires supplier conformity documentation | A CoC replaces material or dimensional evidence that is separately required |
| PPAP or ISIR | The customer or production approval workflow invokes it | Every prototype or short run needs it |
| CMM report | CMM is the appropriate method and recorded output is required | CMM is the correct instrument for every characteristic |
EPOC CRAFTER lists material certificates, inspection reports, first article documentation, PPAP, and ISIR among the records available by project requirement. The CNC quality and certification controls page gives the broader QMS context.
6.1 Match the Inspection Report to the Characteristic
A CNC machining inspection report can contain caliper, micrometer, bore gauge, thread gauge, height gauge, profilometer, fixture, or CMM results. A CNC machining CMM report is appropriate when the specified geometry and reporting requirement justify CMM measurement. Do not use “CMM report” as a generic name for every dimensional record.
For aerospace programs that invoke first article inspection, SAE AS9102C is the current revision, dated June 28, 2023. A supplier first piece check, a CNC machining dimensional report, and an AS9102C FAI are different deliverables. State the required format in the RFQ.
6.2 Use PPAP and ISIR Only When the Program Requires Them
AIAG PPAP 4th Edition, 2nd Printing remains the listed PPAP manual as of September 2026. PPAP for CNC machining belongs in the quote when the customer or production program invokes it. ISIR for CNC machining also needs the customer or OEM format and approval path. Neither term should be added as a generic quality badge.
7. Close China Sourcing Gaps Before Quote Comparison
When sourcing China CNC machining services, the recurring RFQ gaps sit at the interfaces between drawing rules, material standards, inspection scope, and commercial terms. These gaps can appear with any overseas supplier. Cross border sourcing makes them easier to miss because the buyer and supplier may use different standards, unit conventions, and logistics assumptions.
Apply the same scope controls to a China CNC machining manufacturer, China CNC machine shop, sourcing platform, or direct factory. Custom CNC machining in China and precision CNC machining in China still need one released definition of the part.
7.1 Do Not Let an Equivalence Table Approve the Material
A proposed substitute should identify the exact grade, standard, condition, and product form. The buyer approves the change before stock purchase or production. This rule is especially useful for prototype parts sourcing in China, where a fast material substitution can otherwise turn into a drawing or certification mismatch later.
7.2 A DFM Review Does Not Release a Design Change
A DFM review can flag an internal radius, tolerance, thread depth, stock size, or other feature that affects machining. The supplier may quote the released design and propose an alternate. The released drawing stays unchanged until the buyer approves the revision. EPOC CRAFTER keeps that approval logic separate from its CNC DFM review guidelines.
7.3 Compare Inclusions Before Unit Price
Check part revision, material, quantity, secondary finish, inspection documentation, packaging, delivery basis, and exclusions before comparing prices. One supplier may include a finish and dimensional report while another prices machining only. Those offers are different scopes even when the part number is identical.
The same check helps avoid hidden costs in CNC machining quotes. Tooling or fixture charges, inspection records, special packaging, freight, taxes, and commercial exclusions should be visible before award.
8. CNC Machining RFQ Checklist Before You Send
Use this RFQ checklist before sending the package. Remove requirements that do not apply; do not leave them ambiguous.
- ☐ Part number and released revision are identified.
- ☐ The STEP model matches the released drawing revision.
- ☐ The 2D manufacturing drawing carries tolerances, GD&T, threads, finish requirements, and inspection notes that are not controlled by the model.
- ☐ The RFQ states which document governs when files conflict.
- ☐ Units and the applicable drawing convention are clear.
- ☐ Material grade, material condition, and governing specification are defined where required.
- ☐ Material substitution is prohibited, preapproved, or subject to buyer approval.
- ☐ Critical tolerances and CTQ features are separated from general tolerances.
- ☐ Fits, threads, datums, and GD&T are fully called out where function requires them.
- ☐ Surface texture and secondary finish requirements identify the controlled surfaces and post finish acceptance condition.
- ☐ Current quantity, credible follow-on quantity, and annual volume are stated as applicable.
- ☐ Required completion, shipment, or delivery date is defined.
- ☐ Delivery destination and packaging requirements are stated.
- ☐ Incoterms rule, named place, and version are stated when Incoterms govern delivery.
- ☐ Inspection level and required dimensional reporting are defined.
- ☐ FAI, CMM output, MTR, CoC, PPAP, ISIR, and traceability are requested only when the program needs them.
- ☐ DFM changes follow an explicit approval path.
- ☐ Every bidder receives the same RFQ package and revision.
- ☐ Quote comparison checks inclusions and exclusions before unit price.
The same control logic applies to a CNC milling quote and a CNC turning quote. Geometry, material, acceptance criteria, quantity, and delivery scope still have to match across bidders.
9. What Buyers Ask Before Sending a CNC RFQ
9.1 What Files Are Needed for a CNC Machining Quote?
For a drawing controlled part, send the released 3D CAD file, controlled 2D drawing, material requirement, quantity, surface finish, inspection scope, and delivery requirement. This also answers what information a machine shop needs for a quote: enough controlled information to price manufacturing, inspection, finishing, and delivery without filling gaps with assumptions.
9.2 Is a STEP File Enough for CNC Machining?
A STEP file can be enough when the model is the agreed authoritative product definition and carries every requirement needed for manufacturing and acceptance. For a conventional drawing controlled RFQ, pair the STEP file with the controlled 2D drawing. This is also the practical answer to “do I need a 2D drawing for CNC machining?”
9.3 What Tolerances Should I Specify for CNC Machining?
Specify the tolerances that protect fit, sealing, location, motion, alignment, or interchangeability. Keep noncritical dimensions under the validated general tolerance system. The drawing should show the CNC machining GD&T, fits, and critical tolerances that the supplier must price and inspect.
9.4 How Should I Specify Material for CNC Machining?
State material grade and condition or temper. Add the governing specification, product form, certificate requirement, and substitution rule when they affect purchasing or acceptance. An approved equivalent needs an approval path, especially when an ASTM, SAE, or GB designation is involved.
9.5 What Quality Documents Should I Request from a CNC Supplier?
Request the evidence needed to accept the part or satisfy the customer program. That can range from no separate report to a dimensional report, material certificate, FAI, CMM output, PPAP, or ISIR. The document list should follow the drawing, contract, and quality plan.
9.6 How Do I Compare CNC Machining Quotes from China Suppliers?
Normalize the scope first. Check revision, material, quantity, finish, inspection documentation, packaging, delivery terms, and exclusions, then compare price and lead time. The same method applies when you source CNC machining from China through a direct supplier, manufacturer, or sourcing platform.
A first CNC machining RFQ does not need maximum paperwork. It needs enough controlled information for every bidder to price the same part and the same acceptance scope. Send the released files, material definition, critical requirements, quantity, quality records, and delivery basis together.
For a CNC milling quote or CNC turning quote, EPOC CRAFTER can review the released drawing package through its CNC machining capabilities page. Send the STEP model, controlled drawing, material requirement, quantity, finish, and inspection scope with the request.
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