GD&T Bonus Tolerance OOS

Schkund

Involved In Discussions
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.
 

Matt's Quality Handle

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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.
 
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