Virtual Condition & Functional Gaging Explained

Virtual condition is a calculated worst-case boundary created by combining a feature’s material limit with an applicable geometric tolerance at MMC. It is useful because it represents whether an assembly can still fit at the most demanding condition.

Why the boundary matters

A mating pin must be able to enter a hole even when the pin is large and the hole is small. Virtual condition combines the size and geometric limits into one functional boundary that represents that assembly risk.

What a functional gage does

A functional gage is built to simulate the relevant datum features and virtual-condition boundary. A GO-style gage can check the combined requirement efficiently, but it does not replace a measurement plan when individual values or root-cause information are needed.

Use the right verification method

CMM inspection, fixed gaging, and direct measurement each answer different questions. The drawing, the tolerance level, and the production need should determine the plan—not simply whichever method is easiest to use.

Example: a position-controlled hole

⌖⌀0.20MABC

A functional gage can use datum simulators plus fixed pins sized to the hole’s virtual condition to confirm that the worst-case assembly relationship is acceptable.

Common mix-up

Virtual condition is not simply the measured diameter of a feature. It is a boundary derived from the size and geometric requirements together.

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