Have a question for folks - given a single surface on a part, I'm attempting to define two datums. One at one end of the part, and one at the other. Normally in a scenario like this, I would define a datum on one side of the part (or the whole part) and provide a straightness call for the rest of the part.
The reason I have two datums (one on each end) is that each end has a feature that needs to be located relative to the surface; and the surface within that region must be of a tighter tolerance for mating. I'm fine with the surface in question here varying in straightness by a significant amount - but the feature on each end MUST be located centrally to the end on which it sits, and that surface must be controlled more tightly.
See the image I'm attaching. You'll see the intent here, I hope. This is a dramatically simplified example for the true part in question here (which is proprietary), but it is of the same principle.
I'm not as concerned about the method I'm using to do this (which is a conventional datum indicator combined with a basic dim and some notes), as I could also use datum target regions to do this - I'm also not as concerned about the method used to control the straightness of this part (I'm using coaxial between the two datums). What I'm wondering about - can I put two datums on the same feature per the 2009 standard? There's no examples in the standard like this, but it seems like a perfectly functional and applicable way to do this. The second question - what truly defines a feature? Is the outside surface I'm using here a single feature, or is it broken into 3 features due to the different tolerancing scheme?
All of this would be a moot point if I put a step (change in diameter) between the two ends - but I'm curious about the scenario shown in the image - is it per standard?
The reason I have two datums (one on each end) is that each end has a feature that needs to be located relative to the surface; and the surface within that region must be of a tighter tolerance for mating. I'm fine with the surface in question here varying in straightness by a significant amount - but the feature on each end MUST be located centrally to the end on which it sits, and that surface must be controlled more tightly.
See the image I'm attaching. You'll see the intent here, I hope. This is a dramatically simplified example for the true part in question here (which is proprietary), but it is of the same principle.
I'm not as concerned about the method I'm using to do this (which is a conventional datum indicator combined with a basic dim and some notes), as I could also use datum target regions to do this - I'm also not as concerned about the method used to control the straightness of this part (I'm using coaxial between the two datums). What I'm wondering about - can I put two datums on the same feature per the 2009 standard? There's no examples in the standard like this, but it seems like a perfectly functional and applicable way to do this. The second question - what truly defines a feature? Is the outside surface I'm using here a single feature, or is it broken into 3 features due to the different tolerancing scheme?
All of this would be a moot point if I put a step (change in diameter) between the two ends - but I'm curious about the scenario shown in the image - is it per standard?
