What buyers should verify first
A reliable decision starts with evidence that matches the drawing, production volume and business risk. Use the table below during RFQ review; replace assumptions with named documents, owners and acceptance criteria.
| Review area | What good control looks like | Buyer action |
|---|---|---|
| Caliper | Fast general checks | Limited for tight or complex geometry |
| Micrometer/bore gauge | Size features with higher resolution | Requires correct technique/masters |
| Height gauge/surface plate | 2D positional and height checks | Setup sensitive |
| Optical system | Small profiles and edges | Surface/lighting dependent |
| CMM | 3D geometry and datum relationships | Programming and fixturing matter |
1. Start from the drawing characteristic
Map each CTQ to instrument range, resolution, accessibility and datum simulation.
For sourcing approval, convert this point into a written requirement: identify the responsible party, evidence to retain, acceptance rule and response when the rule is not met. This keeps a sample success from being mistaken for a capable production system.
2. Review the measurement program
For CMM work, inspect alignment, probe qualification, point strategy, filtering and report definition—not only the machine brand.
For sourcing approval, convert this point into a written requirement: identify the responsible party, evidence to retain, acceptance rule and response when the rule is not met. This keeps a sample success from being mistaken for a capable production system.
3. Check calibration and environment
Verify current status, traceable standards, maintenance, temperature control and reaction to out-of-calibration findings.
For sourcing approval, convert this point into a written requirement: identify the responsible party, evidence to retain, acceptance rule and response when the rule is not met. This keeps a sample success from being mistaken for a capable production system.
4. Run a correlation study
Measure the same retained part at supplier and buyer using agreed methods. Resolve bias before production.
For sourcing approval, convert this point into a written requirement: identify the responsible party, evidence to retain, acceptance rule and response when the rule is not met. This keeps a sample success from being mistaken for a capable production system.
5. Audit operator evidence
Training, work instructions, gauge handling and repeatability are as important as equipment ownership.
For sourcing approval, convert this point into a written requirement: identify the responsible party, evidence to retain, acceptance rule and response when the rule is not met. This keeps a sample success from being mistaken for a capable production system.
Practical buyer scenario
True position of multiple bores relative to a datum structure may suit a CMM, while a production bore diameter can be monitored faster with a mastered bore gauge.
The useful output is a controlled plan, not a promise. Record the drawing revision, assumptions, open questions, required evidence and approval gate in the RFQ or purchase order. For critical applications, obtain engineering, quality and regulatory review appropriate to the product.
RFQ checklist
- Controlled 3D model and 2D drawing with matching revision
- Material grade, condition or temper, and any certificate requirement
- Quantity per release, annual demand and target delivery date
- Critical-to-quality characteristics and agreed measurement method
- Surface finish, cosmetic zones, masking and post-finish dimensions
- Packaging, labeling, Incoterm and destination
- First-article, sampling, traceability and corrective-action expectations
Frequently asked questions
Is a CMM more accurate than every hand tool?
Not automatically; accuracy depends on task, uncertainty, setup and operation.
Can calipers verify ±0.01 mm?
They are generally a poor choice for such tight acceptance; agree on a more suitable method.
What is gauge R&R?
A study of measurement variation from equipment and operators for a defined method.
Should every part receive a CMM report?
Use risk-based sampling unless contract or regulation requires otherwise.
Sources and further reading
Technical note: Examples in this guide are planning guidance, not a universal manufacturing specification. Final capability, certification, tolerances, treatment and acceptance criteria must be confirmed for the exact drawing and contract.
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