Dimensioning a surface from 4 inline holes. 1

[chevy1000]

I do drafting checking. We basically need a small flat surface dimensioned from 4 inline holes (it is a very complex part). A +/- .0100 dimension will suffice. A couple of the old timers say you cannot dimension from a hole unless you use a basic dimension. I am guessing they mean to put a profile on the surface. Is this really necessary or will the +/- dimension be ok.

 

[ctopher]

You really should have a copy of ASME-Y14.5M 1994, it is explained there. Add a feature position frame for the holes, then basic dim to the surface.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[ewh]

If you make the dimension basic and add a profile control of .0100 to the surface, you don't get anything more than the way you already have it. The oldtimers may be concerned because you are measuring from a common axis of 4 holes, and they have a point, but your tolerance is large enough that this may not need to be of concern.
If you don't need to control the flatness and orientation (or profile) better than +/- .01, then you should be able to use a toleranced dimension, depending on how tightly the holes are held relative to each other. You may want to subtract that hole positional tolerance from your +/-.0100 just to be safe.