The Part Moves, the Gauge Doesn't: Where Go/No-Go Gauging Actually Goes Wrong

When a go/no-go result looks wrong, the gauge is the last thing to check and the first thing to blame. More often the problem sits in the way the part is held, the way the gauge is driven, or the way the operator interprets the boundary case. None of these show up on a calibration certificate, and all of them move the verdict.

Clamping force bends thin parts

A thin-walled housing pressed flat against a fixture becomes oval under the clamping force. The GO gauge that slid through on the soft-jaw setup now binds halfway. The gauge did not change; the hole did. For thin parts, gauge in the free state or in a fixture that supports the part without squeezing it.

Driving force is part of the method

The GO member should enter under its own weight or a light, steady push, never a hammer tap. The NOT GO member gets tried and refused: if it starts to enter, the hole is oversize, but if it is jammed with force it can be forced into a hole it should have rejected, and the false accept hides until assembly. Keep the boundary definition visible at the bench: GO passes freely, NOT GO must not pass, no middle ground.

Operator bias and the boundary case

Two inspectors can disagree on the same part when the hole sits right at tolerance. The one expecting good parts feels a slight binding as "acceptable drag"; the one expecting rejects calls it interference. A visible decision card at the bench, agreed wording for drag versus bind, and occasional cross-checks between operators shrink this grey zone. When the disagreement persists, a measurement with a bore gauge settles it, and the gauge set stays out of the argument.