Dimension edge from a radius 1

[njm789]

Is it correct to dimension an edge from a radius with a position tolerance on it? I want to control this edge as it sandwiches a cylindrical part. See attached photo. Thanks.

 

[Burunduk]

Assuming the drawing is per ASME Y14.5, the two arcs dimensioned by diameters 10.3 and 21.15 are not Features of Size. They are less than 180° and don't contain opposed points, which means they can't contain an Unrelated Actual Mating Envelope, which is needed to derive the axis to be controlled by the positional tolerances. Profile of a surface should be used instead. Also, it seems that the |A|B| Datum Reference Frame doesn't constrain all the degrees of freedom you may want to arrest for the location of the 10.3 diameter feature.

 

[looslib]

I do see that your dimensions are not following ASME Y14.5 standards for inch dimensions.
Inch dimensions do NOT use a leading zero when less than 1" is the dimension value.
See ASME Y14.5-2018 section 4.3.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[njm789]

Thanks for the replies! The profile tolerance makes sense. The location and orientation of the smaller radius is important to A and B and the larger radius should be located and oriented to C. How best would I control the top surface (how deep the radius is)… a profile on the top surface? Or would it be better to make the top surface datum A and control the smaller radius' location to that and then use a profile tolerance to control the bottom surface (current datum A) to the top surface? Basically the part bolts to a plate and another part similar to this clamps on top and sandwiches a cylinder. The height from datum A is also important as the other end of the cylinder interfaces with another bracket (just a note).

 

[TheTick]

Non-helpful editorial comment...

What a nightmare! Even if you do everything right, nearly everyone will probably read it wrong. It would be helpful to exaggerate the non-concentricy of the arcs as much as possible.

 

[Burunduk]

For the smaller radius feature designated as datum feature C, I understand from you that both location+orientation relative to A and B and the depth relative to the top face is important. Then, you could designate the top face as datum feature D and add a separate requirement, in addition to the Composite Profile you already specified, that the feature needs to be within some Profile of a Surface tolerance with reference to D. The top face itself would be controlled by Profile of a Surface relative to datum A for its height  from and orientation relative to the plane representing the plate at the bottom. Or you could skip the Profile of the smaller radius with reference to D but then the relationship between the top face and the smaller radius would be subject to tolerance accumulation but under control as  both would be controlled with reference to A as the Primary Datum Feature. You could also add the B reference for the control of the top face to create an official Simultaneous Requirement, but it wouldn't change much. Also, the top face as datum feature D could serve as the primary reference for the threaded holes' location in case they serve to locate and orient the bolts that clamp the top component that sandwiches the cylindrical part that fits in the radius (this is just a guess). Another minor issue is that the Datum Feature Symbol for C should be placed on the Profile Feature Control Frame and not on the basic radius dimension.