Gage R R
Gage R&R (Gage Repeatability and Reproducibility) is a measurement system analysis that quantifies variation from the gage, operator, and method versus true part variation. It determines if an inspection method can reliably distinguish real dimensional changes from measurement noise, ensuring data integrity for process control and quality decisions.
In CNC machining, Gage R&R is essential before relying on data for process control, capability studies, first-off approvals, or accept/reject decisions on tight-tolerance features like bore diameters, slot widths, and parallelism checks. A typical study uses multiple operators, parts spanning production variation, and repeated measurements. The acceptance rule: less than 10% of total variation is good, 10–30% marginally acceptable, over 30% indicates the measurement system needs improvement. Weak Gage R&R often shows when different inspectors get different results on the same part or when repeated readings exceed the tolerance window, distorting tool-offset decisions, setup validation, or edgebanding QA. The goal is to avoid masking process drift or triggering false scrap/rework.
What does a good Gage R&R indicate?
A good Gage R&R indicates the measurement system contributes a small enough share of total variation that data can be trusted for control and acceptance decisions, typically when Gage R&R is under 10% of total variation.
Is Gage R&R the same as accuracy?
No. Gage R&R primarily evaluates precision—repeatability and reproducibility—not absolute accuracy against a certified standard. Accuracy and precision are distinct concepts in measurement system analysis.
What is the usual study structure for Gage R&R in machining?
Common practice uses 3 operators, 5–10 parts that span the process variation, and 2–3 trials per part. The exact design may vary by method or standard, but this structure is widely accepted.