Datum definition

Sieht für mich auf den ersten Blick korrekt aus. Worum dreht es sich genau?

Thanks Frank. Please translate to English. Thanks again.

Mohamed

Looks correct to me at first glance. What exactly is it about?

I have to measure all the circles to get Datum-B- All I need is to immobilize the part. Datum-A- is Okay.  Datum-B- just give me the center os the inner circle and daum -C- one of the circles for rotation.

For reference C, two circles [C1] and [C2] must be measured. Then a constructed line is created through the two circles. This line is then reference C.

For reference C, two circles [C1] and [C2] must be measured. Then a constructed line is created through the two circles. This line is then reference C.

That is correct for rotation. That is clear. My question is for Datum-B-. Do I have to measure al the circles to get Datum-B-? Why not the OD or the ID?

hi

B is a constructed circle, it would be better if you included all the holes in the construction.

There is no rule that you have to use all the holes, but use at least 4 evenly distributed.

For Datum B you need to measure the circles and construct a BF circle in all the holes. This constructed circle will be datum B. 

The drawing is simply syntactically incorrect. You can't have a "bolt circle" diameter be a datum feature. You can use a pattern of features collectively as a single datum feature, but that is not the correct way to specify such a thing. Plus, if you did use the pattern of features as a datum feature, it would stop up to 5 degrees of freedom. As a secondary datum feature, with A as the primary datum feature, all 6 degrees of freedom would be stopped, and calling out |A|B|C| would be over-constrained.