Dimensioning Rules
The ASME Y14.5M – 2009 standard specifies 16 fundamental rules. The rules that are relevant to interpreting basic to intermediate engineering drawing dimensions are explained.
Spacing and Readability
Rule 1) Dimensions should be arranged for maximum readability.
- The spacing between dimension lines should be uniform throughout the drawing.
- Do not dimension inside an object or have the dimension line touch the object unless clearness is gained.
- Dimension text should be horizontal which means that it is read from the bottom of the drawing.
- Dimension text should not cross dimension, extension or visible lines.
- Dimension lines should not cross extension lines or other dimension lines. However, extension lines can cross other extension lines or visible lines.
- Extension lines and centerlines should not connect between views.
- Leader lines should be straight, not curved, and point to the center of the arc or circle at an angle between 30° – 60°.
Dimensions should be placed in such a way as to enhance the communication of your design.
- Dimensions should be grouped whenever possible.
- Dimensions should be placed between views, unless clearness is promoted by placing some outside.
- Dimensions should be attached to the view where the shape is shown best.
- Do not dimension hidden lines.