ENGINEERS AND machinists have developed a common language for engineering drawings in order to communicate design ideas effectively and efficiently. This language is detailed in the ASME Y14.5M-1994 standard and is referred to as geometric dimensioning and tolerancing (GD&T). As preface to a full discussion of GD&T, we will first review best practices of dimensioning.


In order to understand the geometric dimensioning and tolerancing system, we must first understand the appropriate method for dimensioning or putting dimensions on a drawing. Dimension placement, symbols, and conventions are all important to the common language for engineers and machinists. The following concepts are essential for understanding dimensioning of technical drawings.

B.1.1 Orthographic Views

Most technical drawings show orthographic views of the object being represented. Orthographic or principal views are drawings based on the projection of the object onto a plane. The best way to visualize an orthographic drawing is to imagine a “glass box” around the object, with a projection of the object onto each surface of the box. The box is then unfolded to give rise to the six primary views of the orthographic drawing: top, front, and bottom views; and right-side, left-side, and rear views (Figure B.1). It should be noted that this particular ...

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