GD&T Bonus Tolerance OOS

[Schkund]

I am wondering how it is handled when the dimension used to calculate a bonus tolerance falls outside of specifications. For example, say there is a circular hole and there is a GD&T callout for the true position with an MMC based on the diameter of the hole. Now say the hole diameter itself falls outside of specifications; let's say the hole is too small. Obviously the part itself fails, but if I still want to do some analysis of the true position regardless, how exactly should I handle it? A hole that is too small will have a negative MMC bonus tolerance.

Statistical analysis of a GD&T feature with bonus features tends to get a bit hairy in and of itself and with an OOS bonus tolerance, I think I'm getting a bit out of my depth.

 

[Jim Wynne]

If the whole is too small, MMC is irrelevant because you've already used up the allowance. If you just want to know about the hole location, disregard MMC and measure as if it weren't called out.

 

[Matt's Quality Handle]

A hole that is too small will have a negative MMC bonus tolerance.

Functionally, that is what happens. Your location must be even more precise for a proper assembly. But as you pointed out, it's a moot point if the hole is OOS small.

As for analysis, I've found it more helpful to analyze the X and Y coordinates (using same coordinate system as the machining process) independently. To demonstrate TP to the customer, I calculate % of total tolerance used.