Primary Datum Plane?

[NBO CMM]

Is there anything written in a standard that specifies how parallel surfaces need to be to each other to make a single datum plane? For instance; I have 4 separate surfaces that make up [A],
I know they can be at different heights and still create a Datum plane but per a STANDARD do they also have to be parallel or is there a max degree one or more of the surfaces can be out from the others
before it is considered technically unusable?Capture.PNGCaptionhttps://www.pcdmisforum.com/image/gif;base64,R0lGODlhAQABAPABAP///wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==

[Mike Ruff]

The callout is not telling you to measure 4 planes to construct datum A. It is telling you to take 1 hit in each of the areas and construct the datum from those 4 hits. In your picture, it is telling you that the first hit of datum A (A1) needs to be taken somewhere within the specified Ø27 area. You should have similar callouts for the rest of the datum hits as well (A2, A3, etc.). Take ONLY 1 hit in each area for all of your datum A targets and construct a plane from those points for datum A.

If you want more info on this, look up "Datum Targets". If you have a copy of ASME Y14.5-2009, it is in Section 3.3.3

[Darius11]

Hi, 
as per Mike Ruff comment " The callout is not telling you to measure 4 planes to construct datum A. It is telling you to take 1 hit in each of the areas and construct the datum from those 4 hits. In your picture, it is telling you that the first hit of datum A (A1) needs to be taken somewhere within the specified Ø27 area. You should have similar callouts for the rest of the datum hits as well (A2, A3, etc.). Take ONLY 1 hit in each area"

I think this is right to point of construction of plane, you don't need construct plane. Datum like this can bee seen on automotive sheet metal parts. What you need to do is to measure 6 points (one point on one are) then use "INTERACTIVE ALIGNMENT".

[kingsld1]

The callout is not telling you to measure 4 planes to construct datum A. It is telling you to take 1 hit in each of the areas and construct the datum from those 4 hits. In your picture, it is telling you that the first hit of datum A (A1) needs to be taken somewhere within the specified Ø27 area. You should have similar callouts for the rest of the datum hits as well (A2, A3, etc.). Take ONLY 1 hit in each area for all of your datum A targets and construct a plane from those points for datum A.

If you want more info on this, look up "Datum Targets". If you have a copy of ASME Y14.5-2009, it is in Section 3.3.3

Don't think that's not quite right. It means that the HIGHEST point in each area needs to be found. Need to think in terms of a hard have she. Datum targets are involved.

[RanDawgg]

This. I normally measure each datum target a a plane and pull the highest point from each, then construct a plane out of those highest points.