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Stop Mixing Dimensions
(In accordance with Y14.5M-1994 standard)

PDF of this Tip

A recurring problem occurs when position tolerancing is used but the dimensions locating the features are not all basic. Below is a redraw of a print I recently received. The 20 and 80mm dimensions are not basic. In addition, this appears to be a symmetric part. The part could be set up two different ways (if datum feature A is not identified in some way, there are 4 possible ways to align the part). All dimensions locating position tolerance zones must be basic.

The drawing below solves both problems. Datums B and C are now center planes. The dimensioning is implied to be symmetric. The dimensions needed to locate the position tolerances are basic.

Back to Tips Tip added May 2002