Simplify Your GD&T - 1994 & 2009 (#8)
(In accordance with the ASME Y14.5-2018 standard)
(In accordance with the ASME Y14.5-2009 standard)
(In accordance with Y14.5M-1994 standard)
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Consider revising your general title block tolerance! You can clean up the drawing and move toward the new technology of minimally dimensioned or dimensionless drawings. As companies mature with Geometric Dimensioning and Tolerancing, more and more of the dimensions on a drawing need to be basic dimensions. Basic dimensions are used to indicate the desired location or orientation of features. These basic dimensions indicate the ideal geometry of the part and are not toleranced. The tolerance applies to the features that are located or oriented by the basic dimensions. In other words, any basic dimensions or dimensions with a tolerance specified on the drawing do not use the general title block tolerances. On this drawing, for example, none of the dimensions shown use the linear or angular general tolerances.
Another approach is shown on the revised drawing below. By stating that UNTOLERANCED DIMENSIONS ARE BASIC and specifying a general profile tolerance relative to a datum reference frame, there is no need for all of those boxes around the dimensions.
NOTE: If this approach is used, general plus/minus tolerance should NOT be shown. This could lead to confusion about whether the untoleranced dimensions are basic or controlled by the general plus/minus tolerances. In the 2009 standard, having both is explicitly prohibited [2.1.1.2(b)], but drawings in accordance with the 1994 standard should follow this recommendation as well. See Tip #8A for how the 2009 and 2018 standards address this issue.
Many companies have taken the next step which is to have dimensionless or minimally dimensioned drawings by making the CAD model BASIC with a general profile tolerance and only specifying datums, position tolerances on features of size and tighter profile tolerances where needed on the drawing or CAD file.
This tip is in accordance with ASME Y14.5M-1994 and ASME Y14.5-2009. This tip was originally released in January 1998.
