DATUM TARGET PLACEMENT 1

[learningchecker]

ASME Y14.5-2009. I am checking a small casting, product design drawing. The part is about 6 x .75 x 2.5 inches. The tooling/manufacturing engineer wants datum A's three target areas to be on 3 different surfaces of the casted part. Datum B's two targets are on one surface and C is perpendicular to DATUM B. There are GD&T FCF referencing holes relative to A,B,&C.

The design engineer shows DATUM A as a vertical plane in the side view. There are offset BSC dims locating the other two datum A target areas. In all the views, DATUM A plane shows perpendicular to DATUM B AND C.

My query is since DATUM A's target areas create an angled plane in relation to B & C, how does that work pictorially? Do I show it angled or perpendicular like the engineer has on his product design drawing?

Thanks for your help, I'm hoping to receive.

 

[fsincox]

Offset established datums have been part of the standards for years, see ASME Y14.5M-1994, fig 4.38,pg 78.
Frank

 

[learningchecker]

"Offset established datums", yes, not my question. I don't have a 1994 standard, only 2009.

 

[ewh]

The target areas do not define the datum until you apply the offset dimension, which defines the plane. Is this plane at an angle (other than 90º) relative to your other datums?

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[learningchecker]

yes, it is not 90 degrees to B & C

 

[Belanger]

My query is since DATUM A's target areas create an angled plane in relation to B & C, how does that work pictorially?

No -- since you state that there are basic dimensions showing an offset between the different A targets, then the true datum A will not be angled.

If you're able to include a sketch, that will help. But since you have the 2009 standard, look at Figure 4-47. Notice that the targets for datum A appear to create an angled plane if you connect them all. But that's not the real datum; the true datum A is a plane that is horizontal. This is because of the 20 mm basic dimension showing their offset. (Without that basic dim, datum A would be angled.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[learningchecker]

Belanger, thank you so much. You explained it perfectly.

Also, thanks to all of you for the help.