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Can I attach my datum to a dimension as per ASME Y14.5?

Matt_FarrowMatt_Farrow Member Posts: 4
It is standard practice in ASME Y14.5 to attach datums to dimensions. This communicates that the location of the datum is at the centerline/axis of the dimension. See here for a snapshot from the standard, which communicates that Datum A is an axis down the center of the cylindrical feature. This is something I have done countless times in SW, a very standard and integrated feature.

I have been unable to perform this action in a drawing in Onshape. It seems I am forced to position the datum and the dimension separately which can make the communication less clear and the drawing more cluttered.

Am I missing something? Or is it simply not possible?


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    NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,452
    Huh? Just add the datum to the dimension extension line. Yes, you have to position it by eye to be inline with the dimension leader line, but that's ok?
    Senior Director, Technical Services, EMEAI
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    Matt_FarrowMatt_Farrow Member Posts: 4
    @NeilCooke Thanks for the reply.

    I since found this post which more accurately describes what I was attempting to do. I can attach to a feature control frame, but not a dimension on it's own.


    In the example I gave, you correctly point out I can align by eye, but a "snap" to the correct location would be faster and smoother, and guarantee the datum is communicated correctly. Technically if the datum isn't bang in-line with the dimension then it is now positioned on the edge of the part and communication is lost. Because the datum and dimension are just freely positioned and not locked together this is not robust and is a potential source of error in my opinion. It feels weird not to be able to click the actual thing I was the datum to be attached to.

    Additionally, or the axial view of any cylindrical feature, it does become quite tricky to precisely line up the datum with the dimension.
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