What Is Gage R&R (Measurement System Analysis)?
Also known as: Gauge R&R, GR&R, MSA, measurement system analysis, repeatability and reproducibility
Definition
Gage R&R is a measurement system analysis study that splits observed variation into repeatability (same operator, same gage), reproducibility (different operators) and true part variation, showing whether the gage is good enough to judge the product.
Gage R&R (Measurement System Analysis) Explained
Every measurement includes error. If the gage contributes a large share of the spread you observe, you cannot tell good parts from bad, and SPC charts and capability numbers such as Cpk become misleading. A crossed Gage R&R study typically uses 10 parts spanning the process range, 3 operators and 2 or 3 repeat trials each, then analyses the results with ANOVA or the average and range method.
The usual AIAG MSA guidance reads the result as percent of study variation or percent of tolerance: under 10 percent is generally acceptable, 10 to 30 percent may be acceptable depending on the application and cost, over 30 percent needs improvement. Number of distinct categories (ndc) should be at least 5. Attribute gages, such as go/no-go gauges, use an attribute agreement analysis with kappa statistics instead.
MSA belongs with the PPAP package under IATF 16949 and is expected by many AS9100 customers on key characteristics. The study also covers bias, linearity and stability, which relate to calibration. Calibration says the gage reads the standard correctly, Gage R&R says the gage and the people using it can discriminate part to part differences in practice. A calibrated gage can still fail an R&R.
ERPs hold the gage as an asset with calibration due dates (SyteLine and LN calibration or equipment records, or a dedicated tool such as a gage management system) and the inspection plan references which gage a characteristic uses. The R&R result itself usually lives in the quality system or a statistics tool such as Minitab, linked to the part and characteristic.
Why It Matters
- Without a capable measurement system, scrap decisions and Cpk numbers are partly noise, which can mean rejecting good parts or shipping bad ones.
- Customers under IATF 16949 expect MSA results on special characteristics inside the PPAP submission.
- A failed R&R points to cheap fixes such as better fixturing, operator training or a gage with finer resolution, before buying new equipment.
- SPC control limits built on a poor gage trigger false alarms or miss real shifts.
In Practice
A bore with a tolerance of 0.05 mm is measured with a dial bore gage with 0.01 mm graduations. A study with 10 parts, 3 operators and 3 trials shows gage R&R at 38 percent of tolerance, mostly reproducibility. Adding a setting master and a fixture so every operator seats the gage the same way drops it to 14 percent. The characteristic can now go on an SPC chart with trustworthy readings.
Frequently Asked Questions
What is an acceptable Gage R&R percentage?
Under 10 percent of study variation or tolerance is generally acceptable, 10 to 30 percent may be accepted depending on the application, and over 30 percent is considered unacceptable and needs improvement.
What is the difference between repeatability and reproducibility?
Repeatability is variation when one operator measures the same part repeatedly with the same gage. Reproducibility is the variation between different operators measuring the same parts.
Is Gage R&R the same as calibration?
No. Calibration checks a gage against a known standard. Gage R&R checks how much variation the gage and operators add when measuring real parts.
How many parts and operators do I need?
The common crossed study uses 10 parts covering the process spread, 2 or 3 operators and 2 or 3 trials each. Destructive tests need a different nested design.
Related Terms
SPC (Statistical Process Control)
SPC (Statistical Process Control) is the use of control charts and statistical rules to monitor a process in real time, distinguishing normal common-cause variation from special-cause variation that signals a genuine change requiring action.
Cp and Cpk
Cp and Cpk are process capability indices. Cp compares the specification width to the process spread, assuming perfect centering, while Cpk also accounts for how far the process mean has drifted from the center of the tolerance.
PPAP (Production Part Approval Process)
PPAP (Production Part Approval Process) is a standardized supplier approval package, originating in the automotive industry, that demonstrates a supplier's production process can consistently produce conforming parts at the quoted rate before shipments are authorized.
Control Plan
A control plan is a document listing, for each process step, the characteristics to control, the specification, how it is measured, sample size and frequency, the control method and the reaction plan when results go out of limits.
IATF 16949
IATF 16949 is the automotive industry quality management system standard, published by the International Automotive Task Force, that supplements ISO 9001 with automotive-specific requirements and must be implemented together with ISO 9001 rather than on its own.
Go Deeper
SyteLine Statistical Process Control (SPC)
Implement statistical process control in SyteLine for manufacturing quality. Configure control charts, Cpk calculations, and process monitoring in CloudSuite Industrial.
How to Set Up Calibration Management in SyteLine
Guide to configuring calibration management in Infor SyteLine. Set up gauge tracking, calibration schedules, out-of-tolerance handling, and traceability to NIST standards for ISO 10012 compliance.
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