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hole pattern datum

apgar
PC-Demon 2013 MR1 SP2
I got this part...
Datum A is a straight forward plane. Datum B is a 4 hole pattern on Datum A. First time I've run into this and had to look it up in the standard (4.12.3 ASME Y14.5 2009).
In the demon how do you assign the 4 holes to be Datum B for ExactMeasure dimensioning? The demon would not let me select multiple holes when assigning a datum.

thanks
eric
  • I think you need to construct a circle using the 4 holes.
  • I forgot to mention there is a circle M on Datum B where ever items are dimensioned back to A & B. If I construct a circle and assign it as Datum B I suspect that will mess up the MMB on Datum B?
  • I forgot to mention there is a circle M on Datum B where ever items are dimensioned back to A & B. If I construct a circle and assign it as Datum B I suspect that will mess up the MMB on Datum B?

    If I were you, I would forget about MMB on those holes. Having said that, you can build a single feature from the holes. I, personally, would:

    1) construct 2 lines from hole to hole, such that they intersect in the center.
    2) construct a point at the intersection.
    3) create an array of the 4 holes to pick the hole with the smallest diameter. (This is the part that I need others to help out with, sorry)
    4) construct a generic circle.
    5) edit the XYZ to be from your intersection point in step 2, and the Diameter to be from your assigned smallest diameter.
    6) Define that generic to be Datum B.

    Viola! (Note that there might be simpler ways to accomplish this :squareSlight smile
  • The 'Similar Threads' feature actually had some useful info. I was able to create a feature set of the four holes and assign a datum to the feature set. PC-DMIS does not let me turn on MMB on this "feature set" datum, but it's a start.
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