While i agree with you how do you hold the part? if you hold the part on the OD thats the datum. if you hold on the ID thats that datums. If i snap a line down the center axis of the part and call that my datum it will give me different measurements then if I only use the OD as the datum.
oh i realized that you said OD. Well in this case the ID and center axis are the datum. Because the diameter dimension is drawn to the inside of the cylinder.
cheesie in this case the drawing has the Datum is an OD but its actually a groove OD not the OD of the whole
part.
I agree the ID and the center are the Datum however they want me to use the OD as that is how they see the drawing. it is also how they are machining it. My question is how does ASME define it?
OK
browningdmis i stand corrected. I assumed since the leader lines were inward then it would refer to the ID. But one of the 16 fundamental rules of dimensioning (rule g) states "Dimensions should be arranged for optimum readability. Dimensions should be shown in true profile views and refer to visible outlines."
So with that being said since the ID is not visible in this view then it cannot be referred to as Datum A.
The bottom of the groove itself is the datum. If it is a primary datum, it is a pretty lousy one at that.
Constraining 4 degrees of freedom to the bottom of a narrow groove -
