Understanding Dimensions on Machine Part Drawings
Dimensions are numbers placed on technical drawings to show the size of different parts. In addition to measurements, dimensioning also includes details like accuracy, surface finish, materials, and the number of parts needed. To properly add dimensions to a drawing, it’s important to consider how the parts will be manufactured, assembled, and put together.
Dimensioning Notation
Dimensioning notation refers to the lines and symbols used on a drawing to show measurements and provide notes about the size of a part or machine.
Before adding dimensions, the drawing must be fully completed, including all necessary views. Once the shape is fully described, extension and dimension lines are added to show where the measurements go. Finally, arrowheads, numbers, and notes are included.
A dimension line represents a measured distance. The exact measurement is written in the space left within the line, making it clear how big each part should be.
Six Cases of Dimensioning
The following six examples cover the basic dimensioning techniques that apply to most objects:
- Prisms and Modified Prisms
For prisms, you need to specify the length, width, and thickness. Two of these dimensions are shown on one view, while the third is placed on a different view. Typically, dimensions are placed between views rather than off to the side. - Cylinders
Cylinders are dimensioned by showing the diameter and length, both provided on the same view. - Cones and Similar Shapes
For cones and similar shapes, all dimensions are given in a single view. - Square Pyramids and Similar Shapes
Square pyramids and similar shapes are also fully dimensioned using one view. - Pyramids of Any Type
For more complex pyramids, dimensions often require two views to be shown clearly. - Rounded-End Parts
For parts with rounded ends, dimensions focus on the distances between centers.