Machining allowance is the extra material left on a casting so critical surfaces can be CNC machined to final size. If it is not reviewed early, the final part may fail even when the raw casting looks acceptable.
Buyer takeaway: the best answer depends on the drawing, quantity, material, machined areas, and inspection requirement. Use the checklist below before comparing quotes.
Where Machining Allowance Matters Most
- Bearing seats, bores, and round fit areas on housings.
- Sealing faces on pump bodies, valve bodies, covers, and fluid components.
- Mounting faces, datum surfaces, and flat assembly areas.
- Threaded holes, bolt patterns, ports, slots, and machined edges.
What Buyers Should Mark on the Drawing
- Which surfaces are final machined surfaces and which remain as-cast.
- Tolerance, roughness, flatness, concentricity, or position requirements.
- Datum surfaces used for machining and inspection.
- Areas where extra allowance may create weight, cost, or clamping problems.
Questions to Ask Before Quotation
- Is the supplier quoting raw casting only or machined casting?
- How will the part be located during CNC machining?
- Will the allowance clean up after casting deformation or shrinkage?
- What inspection method will confirm the final machined features?
Related Pages
FAQ
Is more machining allowance always better?
No. Too much allowance can increase machining time, stress release, distortion risk, and cost. The allowance should match the casting process and final tolerance.
Can machining allowance be decided after casting?
It is risky. Allowance should be reviewed before tooling or sampling because it affects the casting shape, datum plan, and inspection route.
Send the drawing, material, quantity, machined areas, tolerance notes, inspection requirements, and delivery expectations. We will review the practical casting and machining route before quotation.
