Bilateral True Position of a Slot

Bilateral True Position of a Slot

Bilateral True Position (Slot actual parallel to slot nominal)


This is how most people think of True Position.  It is simply derived from the “offset” of the actual to the nominal.

In our example here, we have a tolerance band of +/- 0.025 (TP tolerance of 0.050).  The slot is shifted 0.010 to the right.  The difference between the nominal and actual is 0.010 mm.  This is doubled for TP output, so our TP actual would be 0.020.  Well within limits.


Bilateral True Position (Slot actual not parallel to slot nominal)


Bilateral True Position also considers the tilt (and form) of the feature.

This is the same slot.  It still has the same basic 0.010 “offset” in the center, but it is also twisted somewhat (exaggerated here for clarity).  The True Position is still calculated based on the original nominal which is still parallel to the axis system!  The largest distance from nominal is used for the calculation.  In our example here, the top end of the actual slot is at about 0.030 from nominal.  Doubled, that would be 0.060 which would exceed the TP tolerance of 0.050 by 0.010.





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