Basic Dimensioning

Basic Dimensioning

How to annotate simple drawings for use in constructing an object

2

Learning Objectives Be able to understand the basic rules of

dimensioning Apply dimensions to objects in accordance

with engineering standards Define the following items: Dimension line,

Extension line, Reference dimension, and Leader

3

Basic Dimensioning Dimensions allow a part to be manufactured Dimensions are ALWAYS in real world units Dimensions should be applied in a concise,

coherent manner

4

Dimension Terminology:

1.201.00

LEADER

EXTENSION LINE

1.80

1.00

.90

DIMENSION LINE

EXTENSION LINE: EXTENSION

GAP

2.00

.80

ARROWHEAD3.00

5

Extension lines Extension lines should be offset from the part by one half the text height and should extend one text height beyond the dimension line

6

Dimension Spacing

The first row of dimensions must be a minimum of 3 text heights away from the part.Any dimensions beyond it must be a minimum of 2 text heights apart

7

Arrowheads: Should be 3 times longer than they are wide.

8

Dimensioning Rules Avoid placing any dimensions

on the part (inside the view) unless there is no other option.

Always place the dimension where the characteristic shape is shown in the most descriptive view. (This means don’t place a dimension on object lines making a “T joint”.)

Always dimension holes in their circular view by stating the diameter of drilled holes. Specify the hole depth of special features such as countersinking with a note following the dimension.

Dimension cylindrical objects as diameters in their rectangular view.

Keep dimensions between the views whenever possible

Extension lines may cross each other and over other lines on the part, but dimension lines should never be crossed.

See Essentials of Engineering Design Graphics Chapter 4

9

Do not duplicate dimensions and avoid using unnecessary or superfluous dimensions

For metric drawings, omit the use of the millimeter (mm) notation following the numeral, as millimeters are the default units.

Dimension rounded corners and arc features as radii where they appear in their rounded views.

Avoid dimensioning to hidden features.

Extend leaders from the first of last word in a note. Point them toward the center of circular features that they are specifying.

Place dimensions among the various views to avoid crowding. Stagger horizontal dimensions to avoid contact or crowding of values.

The overall dimension should always be given. It should be placed outside of smaller dimensions and be the furthest dimension from the part.

Dimensioning Rules

See Essentials of Engineering Design Graphics Chapter 4

10

1. Avoid placing dimensions on the part (inside of the view).

See Essentials of Engineering Design Graphics Chapter 4

11

2. Avoid dimensioning to hidden features

There is one exception:……When the hidden line is a finished (√) surface

See Essentials of Engineering Design Graphics Chapter 4

12

3. Always place dimensions where the characteristic shape is shown in the most descriptive view

See Essentials of Engineering Design Graphics Chapter 4

13

4. Always dimension holes in their circular view with the Ø. Specify special features (hole types) with a note.

Also:Also: Remember to locate hole position with ordinate dimensions to hole centers

See Essentials of Engineering Design Graphics Chapter 4

14

5. Dimension rounded corners and arc features as radii where they appear in their rounded view.

See Essentials of Engineering Design Graphics Chapter 4

15

6. If the same value is repeated many times, then use a general note for the feature. (ALL FILLETS AND ROUNDS ARE .125R)

See Essentials of Engineering Design Graphics Chapter 4

16

7. Dimension cylinders in their rectangular view with a diameter symbol….Ø.

See Essentials of Engineering Design Graphics Chapter 4

17

8. Place the first row of dimensions 3 text heights (3/8 ”or 10 mm) away from the edge of the part.

Additional stacks of dimensions can be a minimum of two text heights (1/4 ”or 6 mm) away from each other See Essentials of Engineering Design Graphics

Chapter 4

18

9. Keep dimensions between views whenever possible .

See Essentials of Engineering Design Graphics Chapter 4

19

10. Extension lines may cross each other and over other lines on the part, but dimension lines should never be crossed. (Hint no “arrow-headed” lines can cross “arrow-headed” lines)

See Essentials of Engineering Design Graphics Chapter 4

20

11. The overall dimension should always be given. It should be placed outside of smaller dimensions and be the farthest from the part.

See Essentials of Engineering Design Graphics Chapter 4

21

12. Do not duplicate dimensions and avoid using unnecessary or superfluous dimensions

See Essentials of Engineering Design Graphics Chapter 4

22

15. For metric dimensions less than 1 mm DO place a zero in front of the decimal point.

See Essentials of Engineering Design Graphics Chapter 4

23

16. For metric drawings, omit the use of the millimeter (mm) notation following the numeral, as millimeters are the default units.

See Essentials of Engineering Design Graphics Chapter 4

24

18. Conserve space and time by using abbreviations and standardized symbols whenever possible.

See Essentials of Engineering Design Graphics Chapter 4

25

20. Extend leaders from the first or last word in a note. Point them toward (but not touch) the center of the circular features that they are specifying.

See Essentials of Engineering Design Graphics Chapter 4

26

21. Place dimensions among the various views to avoid crowding. Stagger horizontal dimensions to avoid contact or crowding of the values

See Essentials of Engineering Design Graphics Chapter 4

27

Angular features:Dimension angular features with either:

X,Y coordinate location or Vertex location & degrees

See Essentials of Engineering Design Graphics Chapter 4

28

Dimension StylesUnidirectional dimensions are read from the lower left corner of the sheet

Aligned dimensions align with individual dimension lines.

See Essentials of Engineering Design Graphics Chapter 4

29

A short review on Dimension “elements”•What is…

•an Extension line ?•an Extension line gap ?•an Extension line extension ?•a Dimension line ?•a Dimension numeral ?•a leader ?

•When are…

•Decimals used ? Not used ?•Unit designators (in. or mm) listed on dimension lines ?

•What size…

•Is an Arrowhead ?