mallikarjun_questionI want to show the dimension to the hole from Datum A. Where the Datum A surface and hole center are in line means the zero dimension. Kindly suggest how to represent the dimension.

Please see the attached drawing.

Note: I cannot shift the Datum A since it is a functioning surface.

ASME Y14.5 permits a few dimensions to be omitted from the drawing because their indication would not clarify the reading of the drawing. Those dimensions are the 90 degree angle, basic 90 degree angle, zero degree angle, and linear dimensions of zero.

Per the drawing you provided, the use of 4X and the composite position tolerance would require the drawing reader to interpret that there are 4 coaxial diameters, even without seeing another drawing view.

The reference to datum A as a primary datum reference requires the reader to interpret that the 4 diameters are to be parallel to datum A, as well as located to datum A within the diameter 0.010 at MMC allowance.

The datum reference to datum B as a secondary datum requires the reader to interpret that the 4 diameters are located 2.675 from datum B within the diameter 0.10 at MMC allowance.

Not being able to see datum feature C in this drawing, I cannot elaborate on the requirement to datum C.

If the rules of ASME Y 14.5 are understood, the reader will understand the relationship to datum A that you were concerned about. This is partly why it is important to evaluate your supplier’s understanding of GD&T.

ETI has some interesting dialogue on this subject on our Linked-in group. Click here to connect with Alex and join the group.

Michael Adcock
ASME GDTP Senior Certified
Dimensional Engineering Mentor