Bonus Tolerance Calculation - GD&T

When geometric tolerance is applied to a feature of size and it contain a MMC modifier in the tolerance portion of the feature control frame, a bonus tolerance is possible. Note that bonus tolerance is only available when there is a MMC modifier in the feature control frame.

When actual size of the feature varies from MMC then we will have bonus tolerance.

Let us consider an example for bonus tolerance, take a steel rod with diameter 25.3 – 25.0 and having a straightness tolerance at MMC as 0.2

Then at MMC (25.3) we have zero bonus tolerance,

at 25.2 –> bonus tolerance 0.1

at 25.1 –> bonus tolerance 0.2

at 25.0 (LMC) –> bonus tolerance 0.3 (maximum tolerance)

In other words bonus tolerance can be simply defined as extra tolerance available due the feature size variation from MMC.

Now let us discuss the importance of virtual condition in GD&T on next chapter

Labels: ASME, Engineering Standards and Codes, feature, GDT, Machine Design, Training