Datum Strategy
How to Select Datums for CNC Machined Parts
Select datums from stable, accessible features that reproduce how the part is located in assembly and inspection. The primary datum establishes the main plane, the secondary controls the next degrees of freedom, and the tertiary completes location. Do not choose datums only because they are easy to dimension.
Recommended Engineering Method
- Identify the surfaces or axes that locate the part in use.
- Choose a stable primary feature with sufficient contact.
- Select secondary and tertiary features that establish functional direction and position.
- Verify the features can be manufactured, fixtured and measured.
- Use the same functional logic across mating-part drawings.
Common Specification and Inspection Errors
- A small flexible surface used as primary datum
- A datum hidden after finishing or assembly
- Datum targets omitted where full-surface contact is unrealistic
- Machining and inspection using unrelated origins
Questions the Buyer and Supplier Must Resolve
- How is the part constrained in assembly?
- Is the datum accessible after finish?
- Can the fixture simulate it repeatably?
- Does the datum sequence overconstrain the part?
Required Evidence
Use the controlled drawing, actual-value results, stated equipment/method, datum or support setup, inspection condition and approval record. The appropriate method and achievable uncertainty remain feature- and project-specific.
Acceptance Boundary
Formexi can review manufacturability and inspection feasibility, but the buyer retains design authority for functional requirements and deviations. Any GD&T interpretation must follow the standard edition stated on the drawing.
From How to Select Datums for CNC Machined Parts Requirements to a Controlled Manufacturing Plan
A useful supplier solution for How to Select Datums for CNC Machined Parts starts when ambiguous datums or blanket tight tolerances make machining and inspection plans disagree. Because the buyer can pay for unnecessary precision yet still receive results that do not predict fit, seal or motion, our project review maps each critical characteristic to a manufacturable datum scheme, process stage and accessible measurement method with suitable uncertainty. That approach helps the buyer avoid paying for the wrong process and lowers the chance of discovering a critical issue after machining or finishing.
For the How to Select Datums for CNC Machined Parts buying decision, our review needs the controlled 2D drawing, datum sequence, functional interfaces, tolerance standard, measurement condition and required report. We record assumptions, approval points and evidence requirements before the quotation becomes the production baseline.
Apply Select Datums for CNC Machined Parts to the Buyer Decision
For Select Datums for CNC Machined Parts, use the controlling 2D drawing and 3D model to define part number and revision, material and condition, quantity and annual demand, critical tolerances and GD&T, roughness, heat treatment, surface finish, inspection documents, packaging, delivery address and target date. Identify confidentiality restrictions and which DFM changes may be considered for this part.
Price and lead time can be confirmed only after geometry, material availability, programming, workholding, external processes, inspection effort, first-article approval and logistics are reviewed together.
Check the complete RFQ inputs before supplier comparison.