A casting gives the part its shape, but many cast parts are not ready for assembly until important surfaces are machined. Buyers should think about CNC machining before tooling or production starts, not after the raw casting arrives.
This article is written for buyers preparing a casting RFQ. The best answer still depends on the drawing, material, quantity, machining areas, and inspection requirements.
Where Casting Usually Needs Machining
- Holes, threads, locating pins, slots, grooves, and bolt patterns.
- Sealing faces on pump bodies, valve bodies, manifolds, and covers.
- Bearing seats, bores, flat mounting faces, and datum surfaces on housings.
- Edges, burrs, flash areas, and surfaces that touch another assembly part.
The Buying Risk
- If machining allowance is too small, the final dimension may not clean up.
- If datums are not planned, holes and bearing seats may shift after machining.
- If the casting deforms, flatness or hole position may fail even after CNC work.
- If inspection access is not considered, the buyer may not get useful reports.
What to Confirm Before Quoting
- Which surfaces are functional and which are only cosmetic.
- Tolerance notes, roughness, thread requirements, bearing fits, and sealing faces.
- Whether CMM, thread gauge, roughness check, pressure/leakage test, or material documents are required.
- Whether the supplier is quoting raw casting only or machined casting ready for assembly.
Related Pages
CNC Machining for Cast PartsCNC-Machined Cast ComponentsQuality ControlGearbox Housing Casting and CNC Machining Case
FAQ
Can all cast parts be CNC machined?
Most cast metals can be machined, but allowance, hardness, distortion risk, clamping, and datum surfaces should be reviewed before quoting.
Should the machining drawing be sent with the casting drawing?
Yes. If the final part needs holes, threads, sealing faces, bearing seats, or flatness control, those details should be shown from the beginning.
