Before requesting a CNC machining quote, run these ten design-for-manufacturing (DFM) checks. They help a supplier understand the geometry, functional requirements and inspection scope without guessing. The right answer is part-specific: a feature that is easy in one material or setup may need a different process in another.
1. Send a usable 3D model and a controlled drawing
Export the final solid model as STEP when possible, and pair it with a PDF drawing. Check that units, part number and revision match. The model communicates shape; the drawing communicates tolerances, threads, finishes and inspection notes. See our CAD file and RFQ checklist for accepted formats.
2. Identify the dimensions that actually control function
Mark mating features, bearing seats, sealing faces and alignment holes explicitly. Put tight tolerances only where the assembly needs them. For other dimensions, state the general tolerance standard and its edition on the drawing rather than assuming that every shop uses the same default. A quotation should distinguish routine dimensions from features that need special setups or measurement.
3. Give internal corners a machinable radius
A rotating end mill cannot cut a perfectly sharp internal corner. If a pocket must accept a square mating part, consider a corner relief, a larger radius on the mating part, or another approved design change. Ask the supplier to review the chosen radius against the pocket depth and available tool access before freezing the drawing.
4. Review deep pockets and narrow slots together
Long, slender tools can deflect and chatter, especially in a deep narrow cavity. Widen a slot, reduce depth, open one side or split an assembly when the function allows it. If the geometry is fixed, identify the critical surfaces so the manufacturing team can plan reach, support and inspection.
5. Check wall thickness against workholding and material
Thin walls can move during clamping, cutting or finishing. The risk depends on material, wall height, unsupported length and the stock-removal sequence; there is no universal safe minimum. Note which wall dimensions matter after the part is unclamped, and ask for a DFM review where distortion could affect fit.
6. Design for realistic tool access and setup count
Look at every face, side hole and undercut from the tool direction. A simple orientation change may be enough; more complex geometry may require multiple setups or 5-axis CNC machining. Choose a process based on geometry and tolerance relationships, not the axis count alone. Multiple setups can add alignment and inspection work.
7. Specify holes and threads completely
Call out the thread standard, nominal size, pitch or threads per inch, class if required, usable thread depth and whether the hole is blind or through. For blind holes, leave room for drill point and tapping or thread-milling clearance. A simple note such as “M6” does not tell the supplier enough to plan a controlled feature. See our metric, UNC and UNF thread callout guide for drawing examples.
8. Name the material grade and condition
State the alloy or polymer grade, temper or heat-treatment condition, and any certification requirement. “Aluminum” or “stainless steel” alone leaves room for substitutions with different strength, corrosion resistance, machinability and cost. If an alternative material is acceptable, describe the required properties rather than asking the supplier to guess.
9. Define finishing and when dimensions are measured
Anodizing, plating, coating and heat treatment can affect final dimensions or surface condition. Mark masking areas, cosmetic faces and dimensions that must be inspected after finishing. If color or appearance matters, provide an approved sample or a clear acceptance criterion; a vague “nice finish” is difficult to quote and inspect.
10. Make the RFQ commercially complete
Include prototype and expected production quantities, target delivery location, drawing revision, required inspection records and any assembly or packaging needs. If a first-article inspection is required, say so before quoting. This lets suppliers separate one-time setup and inspection effort from recurring unit cost.
Pre-quote checklist
| Send | Why it matters |
|---|---|
| STEP model and dimensioned PDF | Geometry and manufacturing requirements can be reviewed together. |
| Material grade, quantity and revision | Prevents pricing against the wrong stock or design version. |
| Critical tolerances, datums and thread callouts | Supports process and inspection planning. |
| Finish, certification and delivery requirements | Shows the complete quoted scope. |
Need a manufacturing review of your part? Explore our CNC machining services, then upload your drawing for a quote. Include the requirements above so our team can flag open questions before pricing.
