About MMC True Position Functional Gaging
MMC true position is used when a feature has its most restrictive material size. For a hole, MMC is the smallest allowed diameter. For a pin or boss, MMC is the largest allowed diameter. The position tolerance at MMC creates a fixed virtual boundary. A functional gage checks that boundary in a simple pass or fail way.
Why The Calculator Helps
Manual gage sizing can become confusing. Size limits, actual size, positional error, bonus tolerance, datum shift, and gage maker allowance all affect the result. This calculator keeps those values together. It shows the virtual condition, the bonus tolerance, the total allowed position, and the practical gage size. It also shows the remaining margin. That margin helps teams judge process risk.
How Results Should Be Read
True position is diametric. It equals twice the distance between the measured point and the basic location. Bonus tolerance is added when the feature departs from MMC. Datum shift can also add usable tolerance when the datum feature allows movement. The part passes the mathematical check when actual true position is not greater than the total available tolerance.
Functional Gage Meaning
For an internal feature, the gage is usually a fixed pin. The pin is based on the virtual condition. It is normally made slightly smaller for gage tolerance and wear. For an external feature, the gage is usually a receiving hole. That hole is normally made slightly larger. These allowances protect the product boundary.
Best Practice
Use verified units. Keep all inputs in the same unit system. Confirm whether the feature is internal or external before entering values. Do not mix radius position with diametric position. Review drawings for datum modifiers. Check gage design against company standards and customer rules. Use the output as a planning aid. Final acceptance should follow the approved drawing and inspection plan.
Statistical Use
The margin value can support trend review. A stable process should keep margin positive and consistent. When margin shrinks, tooling, fixturing, or measurement setup may need review. Repeating the calculation for sample parts helps compare shifts, lots, and operators. It also creates a clean record for quality discussions, corrective actions, and future capability studies across similar inspected features.