1. What are Dimensions?
Dimensions are the text that is provided with a drawing that describe the exact size and location for the features shown.
Also known as size descriptions.
Why use Dimensions?
To ensure that the part made is the part you asked for.

2. Elements of Dimensioning
ARROWHEADS
Copyright © 2003 Glencoe/McGraw-Hill

3. Dimension Lines
Thin lines that show where a measurement begins and where it ends and the size of an angle.
Broken for text.
3/8” (10 mm) away from the object.
1/4” (6 mm) away from other dimension lines.

4. Extension Lines
Thin lines that extend the lines or edges of the object.
Used to located center points and to provide space for dimension lines.
DO NOT touch the object – start 1/16” (1.5 mm) away from the object.
Extend past the dimension line 1/8” (3 mm)

5. Arrowheads
Used at the ends of dimension lines and leaders to show where a dimension begins and ends.
Can be open or solid.
Must be uniform through out drawing.
Length = 2 ½ x Height
Usually 1/8” (3mm) long

6. Other Arrowheads

7. Leaders
Thin lines drawn from a note or a dimension to the place where it applies.
Drawn with one small straight line 1/8” (3 mm) long then a long line at an angle of 60, 45 or 30 degrees.
Ends with an arrowhead.

8. Dimension Text and Notes
Height = 1/8” (3 mm)
Linear dimension text is centered on dimension line.
General notes apply to entire drawing.
Local notes apply only to object pointing to.

9. Tolerances
The amount by which a machined part is allowed to vary from absolute measurements and still function as intended.
Shown within dimension line or in title block to cover entire drawing.

10. Placing Dimensions for Reading
Two methods:
Aligned
Unidirectional

11. Aligned System
Dimension text is placed in line with the dimension lines.

12. Unidirectional System
Dimension text reads parallel to the bottom of the sheet, no matter what.

13. Basic Rules
Only dimension a feature once.
Correct Incorrect

14. Basic Rules Do not place dimensions on objects.
If possible, place dimensions between views.
Place large dimension on the outside and small dimensions on the inside so not to cross dimension lines with extension lines.
Correct Incorrect

15. Basic Rules Dimension a feature in the most descriptive view.
Group associated dimensions.

16. Basic Rules
Do not dimension to hidden lines or centerline of hidden features.
Correct
Incorrect

17. Basic Rules
Circles require a diameters () and location (X & Y) dimensions.
Arcs are dimensioned with radius (R) and location (X & Y) dimensions.
Circles and arcs should be dimensioned using Leaders. Arrowheads should point to the centermark.

18. Basic Rules
Circular features should be located by dimensioning the centerlines.
Rounded objects will not have an overall dimension.

19. Basic Rules
Use appropriate symbols for describing common features.

20. Fillets, Rounds, and Radii
Radius Dimension
Round Dimension
Fillet Dimension
Copyright © 2003 Glencoe/McGraw-Hill