Short answer: Gage correlation helps buyers and stamping suppliers confirm that both sides measure the same feature the same way before accepting capability data, sorting results, or reject decisions. The RFQ should define datums, restraint, fixture method, sample set, operator rule, report format, tolerance risk, and what action follows when measurements do not agree.
A stamped part can pass at the supplier and fail at receiving without the process being out of control. The difference may come from datum choice, clamping force, free-state versus restrained measurement, probe location, gage wear, operator technique, or a part that is flexible enough to move during inspection.
Use this page with the datum and functional gage guide, Gage R&R and MSA guide, inspection equipment guide, and critical dimensions inspection plan.
Gage correlation details before quoting
| Correlation item | Why it matters | RFQ evidence |
|---|---|---|
| Datum setup | Different locating points can change a hole or bend result. | Drawing datum, fixture points, clamp rule, and photos. |
| Part restraint | Thin stamped parts can flex under measurement force. | Free-state, restrained, bolted, nested, or functional gage condition. |
| Sample set | Best-piece samples hide real measurement disagreement. | Low, middle, high, suspect, and retained samples with IDs. |
| Decision rule | Teams need a plan when results disagree. | Correlation limit, escalation path, and temporary acceptance rule. |
Correlate before the dispute becomes a shipment problem
Gage correlation is most useful before production release, after a tooling change, during supplier transfer, or when receiving inspection rejects parts that the supplier measured as acceptable. It should use the same drawing revision and a sample set that represents real part variation, not only perfect samples. If the dispute started at receiving, pair the review with the incoming inspection checklist so the receiving method is written down.
For flexible brackets, shields, clips, and assemblies, the measurement condition must be defined. A part may fail flatness on a table and pass in a bolted fixture, or it may pass free-state and fail in the final product. Correlation should follow the function of the feature. For coplanarity and flatness questions, use the coplanarity guide together with the fixture plan.
Do not use sorting data until the method is trusted
If buyer and supplier do not correlate, a sorting action can create false confidence. Inspectors may accept bad parts, reject good parts, or spend hours measuring noise instead of real variation. The first step is to compare the same numbered samples, in the same order, with the same datum notes and a clear pass or fail rule.
Gage correlation is not the same as a full Gage R&R study, but the two are connected. Correlation asks whether two methods agree enough for the current decision. Gage R&R asks whether a method is repeatable and reproducible enough for ongoing control. For receiving disputes, both may be needed before a lot is rejected or released.
RFQ details to include
- Drawing, revision, CTQ feature list, tolerance limits, datum scheme, material, thickness, finish, and functional assembly condition.
- Measurement method: CMM, height gage, optical comparator, pin gage, go/no-go fixture, force gage, microscope, or custom fixture.
- Part restraint rule, clamp points, measurement force, probe location, orientation, temperature if relevant, and calibration status.
- Correlation sample set, sample IDs, number of operators, number of repeats, report format, and acceptable difference limit.
- Action rule when results disagree: retest, joint review, master sample, buyer method prevails, supplier method prevails, or temporary deviation.
- Production volume, lot size, receiving inspection plan, and whether records are required with each shipment.
How to compare supplier answers
A useful answer asks how the buyer measures the same feature. It should request photos, fixture details, and a numbered sample exchange before arguing about capability. A weak answer only repeats that the supplier inspection report is correct.
Ask whether the quote includes fixture build, fixture calibration, sample exchange, and correlation reporting. These tasks cost less than repeated sorting, returns, or blocked shipments when a measurement method is not agreed.
Send drawings, receiving reject data, photos of the measurement setup, and sample IDs through the contact page. Use the RFQ form to request a gage correlation plan when supplier and buyer results do not match.
FAQ
What is gage correlation for stamped parts?
It is a comparison of buyer and supplier measurement methods using the same samples to see whether results agree enough for approval or rejection decisions.
When should gage correlation be done?
Use it before production release, during supplier transfer, after tooling changes, or when receiving inspection and supplier inspection disagree.
Is gage correlation the same as Gage R&R?
No. Correlation compares methods or locations. Gage R&R studies repeatability and reproducibility of a measurement system.
What should be sent for gage correlation?
Send drawings, CTQ list, measurement setup photos, datum rules, sample IDs, fixture details, reject data, tolerance limits, and required report format.