Circular Runout, use of two Datum

huangyhg

I would like to reproduce the example as in figure R2.GIF.
Using the program 43_RUNOUT.PRG (1.GIF) I have tried to calculate the runout of the Circle CIR1 and the two cylinders.
In any way I succeed in inserting the two DATUM as cylinders. Instead I succeed in calculating the runout with two DATUM, of which one is a plane (4.GIF).
But in this case I can assign the primary DATUM to the plane and not to the cylinder (as in figure R1.GIF). Are there limitations in this type of calculation?


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There are two datum reference frames in question:
1. For Plane and Cylinder, the Plane should be the primary datum and the cylinder should be the secondary datum.  The primary plane will control orientation and the secondary cylinder will control the location of the datum axis.  If you specify the datums in the reverse order, the primary cylinder datum will control both orientation and location of the datum axis, so no secondary datum can be used.  For this reason, I believe the drawing has the datums in the wrong order.
2. Compound datum C-D.  You can use a compound datum in PC-DMIS but you must type the datum combination C-D in the datum control since the pulldown list has only individual datum letters.  With your program, the datum nominals are not exact since they are learned features (Measure features) and therefore PC-DMIS will not recognize these datums as coaxial.  You must fix the NOM XYZ and IJK for the datums (as well as the considered feature) so they are exact.  Then specifying C-D in PC-DMIS will work.  Datums are assumed to be theoretically exact features so their NOMs (as well as the NOMs of the considered features) must be exact to get correct GD&T results.

huangyhg

This is a good example for "Cutomized DRF" application.