Engineering Design Graphics: Sketching, Modeling, and Visualization, 2nd Edition

CHAPTER 6

DIMENSIONING AND TOLERANCING

DIMENSIONING

Introduction

An engineering drawing, once submitted to production for manufacture or construction, must include all of the information needed to build the part, assembly, or system. To this end, technical drawings include dimensions and general notes describing the size and location of part features, as well as details related to the construction or manufacture of the part.

A dimension is a numerical value used to define the size, location, geometric characteristic, or surface texture of a part or feature. The main goals of dimensioning (as laid out in ANSI/ASME Y14.5M, “Dimensioning and Tolerancing for Engineering Drawings”), are the following:

1. Use only the dimensions needed to completely define the part, nothing more.
2. Select and arrange dimensions to support the function and mating relationship of the part. It is important that the dimensioned part not be subject to differing interpretations.
3. In general, do not specify the manufacturing methods to be used in building the part. This is done both to leave options open to manufacturing and to avoid potential legal problems.
4. Arrange the dimensions for optimum readability. Dimensions should appear in true profile views and refer to visible object edges.
5. Unless otherwise stated, assume angles to be 90 degrees.

Units of Measurement

Drawings are typically dimensioned using either millimeters ...