CNC Machining Tolerances: Which Features Need Tighter Control?
Tighter tolerances should follow the function of a feature, not a blanket request for maximum precision. They can affect both machining effort and inspection cost. When ordering custom CNC machined parts, identify the dimensions that control fit or alignment, explain their purpose and agree how conformity will be checked.
CNC production equipment and machined components in the workshop.
1. Explain which features control the assembly
A locating bore, mounting pattern or mating face can have a different role from a nonfunctional external surface. Identify these features on the drawing and explain the assembly relationship to the machining team. The customer defines the functional requirements; the factory reviews the machining approach and feasibility. Any proposed change to an acceptance limit needs customer approval.
2. Separate size requirements from geometric requirements
A size limit does not automatically define every requirement for the position or orientation of a feature. Use the drawing to communicate the intended controls and reference features. If a callout is ambiguous, clarify it before manufacture rather than choosing an interpretation during inspection.
3. Agree what the inspection record must contain
Inspection and a recorded dimensional report are different deliverables. State the feature list, sample quantity, drawing revision and any report format needed. Ask whether the proposed inspection method covers the requested features. Do not assume that checking a few dimensions is the same as a full first-article review.
Inspection equipment; measurement methods are selected for the part and agreed requirements.
4. Confirm the finished condition
Where finishing affects a mating feature, state whether acceptance applies before or after the agreed treatment. Keep material condition and relevant surface requirements consistent with the quoted revision. A successful measurement of an unfinished part does not by itself confirm the finished assembly fit.
5. Review the machining plan and cost drivers
Discuss with the machining team which features require additional setups, more demanding machining or further inspection. If a different approach could simplify production, have the customer's engineering team review the proposal and record any approved drawing change. Compare quotations using the same revision, quantities, finishing and documentation requirements.
Review your critical features with Kianzee
Kianzee provides custom CNC machining for parts and mechanical assemblies. Share your drawings, functional dimensions and inspection requirements so our manufacturing team can review the machining process and quotation. Achievable precision, price and inspection deliverables are confirmed for the specific part. Contact: [email protected].
