![]() The assumption made to trig out a coordinate system from the 0.625 DIA hole would not be correct, as it would then be creating a coordinate system that isn't supported by the given datums. But since the callout is controlling perpendicularity to -A-, the diameter symbol seems to make since in this instance. The fact that the diameter symbol is still shown can be confusing and is shown in some examples in the standard. With the position callout you are questioning, the only control the datum reference frame can control is the perpendicularity of the feature's centerline to -A-, and since -B- is only an axis, it can only control a radial distance away from -B. ![]() If you only have 1 element in the datum reference frame, such as -A- in your drawing, the only thing that position can control is perpendicularity to -A. Position callouts with 1 and or 2 elements in the datum reference frames are allowed by the standard. Since I don't have a '82 standard anymore I can only go off the '94 standards and assume the drafter just hasn't converted their symbology over to the newer style. The symbology shown in your drawing for denoting Datums is not supported in ASME Y14.5M 1994, but that from the ANSI Y14.5M 1982 standard. Thought I might add my $0.02 on this subject, since I have an abnormal interest in GD&T. Long time lurker, but I haven't posted very much. While moderately effective, it still irritates me that I am partially checking the position of the feature to itself. 350 basic distance, thereby losing any variability the positional tolerance might allow along that axis. In other words, establish a three axis coordinate system to the three Datums shown in the drawing, and then rotate 2.2 degrees to create the. My gut feeling (beyond this being a poor way to dimension this part form an inspection point of view) is that the best one can do is trig out the angle between the virtual "Y" axis (the 9.17 dimension) and the direct feature-to-feature line between the two radii and then rotate my part coordinate system accordingly (in this case 2.2 degrees.) Given that the two radii are only connected through two Basic dimensions intersecting at a virtual point, how does one go about establishing a proper rotation in order to evaluate the positional callout? 010 positional callout back to datums A and B. ![]() In the attached pic is a part with Datum A being the material surface, Datum B being an outside radius, and a third feature (a similar outside radius) having a. My task is to layout pieces using CMM, Comparitor and basic hand instruments. I know I've seen this before, but I'm drawing a blank. ![]()
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