CNC Machining Quote Checklist: Models, Threads and Tolerances

Prepare a CNC machining RFQ with consistent CAD files, critical dimensions, complete thread instructions and clearly scoped finishing and inspection requirements.

Keep the solid model and drawing consistent

Release one intended part revision. Reopen the exported model, check its overall size and compare it with the drawing. Remove superseded exports from the manufacturing package so that the quotation does not depend on guessing which file is current.

The DIYIPCB CNC enquiry accepts STEP/STP, IGES/IGS and ZIP packages, together with reference attachments. Use a solid model to communicate the shape and a dimensioned PDF to communicate the requirements that are not fully defined by that shape.

If an early request is only for budget review, label it accordingly and identify the missing information. A preliminary model should not silently become the approved manufacturing release.

Identify the dimensions that control the assembly

Start with mating faces, hole patterns, locating features and the outside envelope. Explain how they relate to the assembled product and identify the reference surfaces used for measurement. Include the relevant interface of a mating component when it clarifies the requirement.

Separate critical dimensions from reference information. Applying one demanding tolerance everywhere may add review and manufacturing work without improving the function that matters. Ask for feasibility feedback on the actual interfaces and agree the accepted requirements.

State whether inspection applies before or after finishing where that distinction affects the fit. Keep the drawing, finish specification and acceptance plan consistent rather than leaving their relationship implicit.

Complete the thread and hole instructions

A modeled hole does not automatically communicate thread size, pitch, class, handedness or depth. Add the details needed for the specific design and distinguish threaded features from clearance holes, locating holes and other bores.

For a blind feature, distinguish the required usable thread from the overall hole geometry. Ask the reviewer to confirm feasibility where access or available depth is uncertain. Use a section view if the relationship is difficult to read in a top view.

Keep threaded hardware and mating parts identified in the assembly documentation. If a feature is intended for an insert or another secondary operation, specify that requirement rather than allowing it to be interpreted as a standard tapped hole.

Review tool access and internal geometry

Identify deep pockets, narrow features, enclosed areas and faces that may need access from another direction. Ask which parts of the geometry need a manufacturing change and what that change would do to the assembly.

For conventionally milled pockets, internal corners need consideration because the cutter geometry affects the result. Manufacturer CNC design guidance also recommends drawings for threads, tolerances and other machining notes.

Do not prescribe a generic corner radius or depth ratio without reviewing the actual tool approach and part requirements. A useful response identifies the affected feature, proposed geometry and functional consequence, then updates the released files if accepted.

Scope material, finish and inspection by feature

Record the material grade, any required documentation and the permitted approval route for alternatives. For finishes, identify the process, color or appearance reference and the surfaces that need masking or additional review.

Specify surface roughness on the faces where it is functionally necessary. If an inspection report is required, identify which dimensions or features it must cover. A general request for “full inspection” can mean different things unless its scope is defined.

For a project with several parts, keep these requirements with each item. A finish suitable for one material or component should not be assumed to apply to the rest of the assembly.

Send a controlled RFQ summary

Part/revision: [reference]. Model and drawing: [files]. Units: [value]. Quantity and alternatives: [details]. Material/grade: [specification]. Critical dimensions: [callouts]. Threads: [drawing references]. Finish and masking: [scope]. Inspection documents: [requirements]. Delivery target: [date and destination].

Review the resulting quotation against that summary. Record excluded operations and proposed alternatives before approval. Keep subsequent changes in one controlled revision, and identify whether a later request is an unchanged repeat order or a new design requiring review.