Two CNC machining quotes can differ substantially even when both suppliers read the same drawing. The difference often comes from assumptions about material, setup, tolerance and inspection.
1. Material form and allowance
Bar, plate, casting and forging create different stock costs and machining routes. Confirm grade, condition, certification and whether excess material has been included.
2. Datum and setup strategy
A part requiring several orientations needs more handling and may accumulate positional error. Critical relationships should be clear so the supplier can design a stable sequence.
3. Tolerance where it matters
Applying a tight general tolerance to every feature increases machining and inspection effort. Functional fits and critical surfaces should be identified separately from non-critical geometry.
4. Finish before and after machining
Heat treatment, plating, anodizing or coating may change dimensions. The route should state which features are completed or protected at each stage.
5. Inspection evidence
A basic dimensional check, full report and formal first-article package are different scopes. Define sampling, equipment and report expectations before comparing prices.