Profile of datum planes - Profile callout back to datum A (itself)

CycleMike · Jun 3, 2009

I have a part with two surfaces that make up datum A. These surfaces also have a profile callout back to datum A (itself). Does this make sense?

I'm using a Zeiss CMM with Calypso and it will not give me results using only datum A. If I add B and C I'll get results. With Calypso, this usually means that the DRF on the print is not following ASME Y14.5M-1994. The notes on the print say it was drawn to that standard.

Your thoughts?

Miner · Jun 3, 2009

This is called "Qualifying" the datum. The datum must fall within the profile zone to make an acceptable datum. If this were a continuous plane surface, it would typically use a flatness call out. Since it is broken up into two non contiguous surfaces, they used profile to control flatness and coplanarity, but the intent is the same.

Try measuring flatness across both surfaces with your CMM.

I do not have a copy of Y14.5 handy to verify whether this is drawn to the standard, but the intent is clear.

Stijloor · Jun 3, 2009

Miner said:
This is called "Qualifying" the datum. The datum must fall within the profile zone to make an acceptable datum. If this were a continuous plane surface, it would typically use a flatness call out. Since it is broken up into two non contiguous surfaces, they used profile to control flatness and coplanarity, but the intent is the same.

Try measuring flatness across both surfaces with your CMM.

I do not have a copy of Y14.5 handy to verify whether this is drawn to the standard, but the intent is clear.

The intent is clear. The feature control frame contains a datum reference "A", which is incorrect. For coplanarity, a datum (in this case) is not necessary. Once the coplanarity (flatness for an interrupted surface) is verified, it can then become datum feature "A".

Stijloor.

Miner · Jun 3, 2009

Stijloor said:
The intent is clear. The feature control frame contains a datum reference "A", which is incorrect. For coplanarity, a datum (in this case) is not necessary. Once the coplanarity (flatness for an interrupted surface) is verified, it can then become datum feature "A".

Stijloor.

Found an online resource. Profile of a surface may be used with or without a datum.

Profile with a datum controls form, location and orientation
Profile without a datum controls form only

As Stijloor stated, in this application (qualifying the datum) there should not be a datum in the feature control frame. The interpretation of the call out is the same as flatness extended to both surfaces simultaneously.

CycleMike · Jun 4, 2009

Miner said:
As Stijloor stated, in this application (qualifying the datum) there should not be a datum in the feature control frame. The interpretation of the call out is the same as flatness extended to both surfaces simultaneously.

Thanks!

That's what I thought. That the datum in the FCF is incorrect. I'll measure flatness instead.

Profile of datum planes - Profile callout back to datum A (itself)

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