Define Precision by Function, Not by a Label
China CNC precision machining is not a single tolerance level that applies to every part. Precision requirements should follow what the component must do: mate with another part, align to a datum, seal a joint, move through a guide, or hold a specified surface. A clear drawing helps a supplier review those requirements instead of guessing from the word âprecision.â
Choose Which Features Need Tight Control
Start with the assembly or interface. Identify the dimensions that affect fit or function, then define datums and tolerances for those features. Keep general dimensions under the drawingâs stated default tolerance where appropriate. Over-tolerancing unrelated features can add machining and inspection effort without improving the part.
Make the Model and Drawing Agree
- Use a consistent part number and revision on the drawing, model, and RFQ.
- Show the controlling dimensions and datum references on the drawing.
- Call out material, finish, threads, and any edge or burr requirements.
- Flag dimensions that need measurement records or special acceptance criteria.
- Resolve conflicting notes before the quote is approved.
For a supplier-focused checklist on measurement evidence, see precision factory inspection requirements. For the general process scope, review opzioni di servizio di lavorazione CNC.
Discuss Inspection Before Production
Tell the supplier which dimensions are critical and what evidence is needed for acceptance. Agree whether measurements apply to a sample, first article, or production lot, and state the report format if one is required. Ask the supplier to raise any measurement-access or drawing concerns before production, and record the agreed resolution against the current revision.
Domande frequenti
Does precision CNC machining mean every feature has a tight tolerance?
No. Apply tighter requirements to dimensions that affect function or assembly and use a suitable general tolerance for other features.
How do I know which dimensions are critical?
Review how the part fits, moves, seals, or aligns with adjacent components. Mark the dimensions and surfaces that control those functions on the drawing.
Should the 3D model define the tolerance?
Use the controlled drawing to state dimensions, datums, tolerances, and acceptance notes. The model can support the drawing by clarifying geometry.
When should inspection requirements be agreed?
Set them in the RFQ and confirm them in the accepted quote, before production begins.
What should happen if the drawing has conflicting requirements?
Pause quote approval and resolve the conflict in writing. Issue a corrected revision if needed so the supplier and buyer work from the same definition.