Basic Dimensioning with Auto CAD How to annotate

Basic Dimensioning with Auto. CAD How to annotate simple drawings for use in constructing an object

Learning Objectives n n 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 Be able to recognize the following machined holes: Spotfaced, Counterbored, Countersunk, & Counterdrilled. 2

Basic Dimensioning n n n Dimensions allow a part to be manufactured Dimensions are ALWAYS in real world units Dimensions should be applied in a concise, coherent manner 3

Dimension Terminology: 4

Extension lines should be offset from the part by one half the text height and should extend one text height beyond the dimension line 5

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 6

Arrowheads: Should be 3 times longer than they are wide. 7

Dimensioning Rules n n n Avoid placing any dimensions on the part (inside the view) unless there is no other option. Avoid dimensioning to hidden features 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 rounded corners and arc features as radii where they appear in their rounded views. If the same value is repeated many times, then use a general note for the features. n n n Dimension cylindrical objects as diameters in their rectangular view. Always place the first row of dimensions a minimum distance of 3 text heights away from the edge of the part. Additional stacks can be a minimum of 2 text heights away from each other. 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. The overall dimension should always be given. It should be placed outside of smaller dimensions and be the furtherest dimension from the part. See Essentials of Engineering Design Graphics Chapter 4 8

Dimensioning Rules n n n Do not duplicate dimensions and avoid using unnecessary or superfluous dimensions When all of the dimensions are expressed in inches, do not use inch mark (“) or the abbreviation for inches (in. ) For drawings dimensioned in inches, values less that one inch should not be preceded with a zero. For metric drawings, omit the use of the millimeter (mm) notation following the numeral, as millimeters are the default units. The origin for baseline or ordinate dimensions used as a datum should be extended from a finished edge of the part. n n n Conserve space and time by using abbreviations and standardized symbols whenever possible. Reference dimensions should be placed in parentheses or should include the abbreviation “REF”. Basic sizes (to be toleranced) should be placed inside a rectangular box 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. See Essentials of Engineering Design Graphics Chapter 4 9

1. Avoid placing dimensions on the part (inside of the view). See Essentials of Engineering Design Graphics Chapter 4 10

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 11

3. Always place dimensions where the characteristic shape is shown in the most descriptive view See Essentials of Engineering Design Graphics Chapter 4 12

4. Always dimension holes in their circular view with the Ø. Specify special features (hole types) with a note. Also: Remember to locate hole position with ordinate dimensions to hole centers See Essentials of Engineering Design Graphics Chapter 4 13

5. Dimension rounded corners and arc features as radii where they appear in their rounded view. See Essentials of Engineering Design Graphics Chapter 4 14

6. If the same value is repeated many times, then use a general note for the feature. (ALL FILLETS AND ROUNDS ARE. 125 R) See Essentials of Engineering Design Graphics Chapter 4 15

7. Dimension cylinders in their rectangular view with a diameter symbol…. Ø. See Essentials of Engineering Design Graphics Chapter 4 16

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 17

9. Keep dimensions between views whenever possible. See Essentials of Engineering Design Graphics Chapter 4 18

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 19

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 20

12. Do not duplicate dimensions and avoid using unnecessary or superfluous dimensions See Essentials of Engineering Design Graphics Chapter 4 21

13. When all of the dimensions are expressed as inches. DO NOT use inch marks ('') or the abbreviation (. in) See Essentials of Engineering Design Graphics Chapter 4 22

14. For drawings dimensioned in inches, values less than 1 inch should not be proceeded with a zero. See Essentials of Engineering Design Graphics Chapter 4 23

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 24

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 25

17. The origin for baseline or ordinate dimensions used as a datum should be extended from a finished edge of the part. See Essentials of Engineering Design Graphics Chapter 4 26

18. Conserve space and time by using abbreviations and standardized symbols whenever possible. See Essentials of Engineering Design Graphics Chapter 4 27

19. Reference dimensions should be placed in parenthesis or should include the abbreviation “REF”. Basic sizes (to be toleranced) should be placed inside of a rectangular box See Essentials of Engineering Design Graphics Chapter 4 28

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 29

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 30

Angular features: Dimension angular features with either: X, Y coordinate location degrees or Vertex location & See Essentials of Engineering Design Graphics Chapter 4 31

Dimension Styles Unidirectional dimensions Aligned dimensions align are read from the lower left with individual dimension lines. corner of the sheet See Essentials of Engineering Design Graphics Chapter 4 32

A short review on Dimension • What is… “elements” • 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 ? 33

Dimensioning In Auto. CAD

Dimensioning in Auto. CAD n n n Auto. CAD does semi-automatic dimensioning You select the features which should be dimensioned and the location for each dimension Auto. CAD measures the distance in question and applies the appropriate dimension complete with arrowheads, extension lines, and dimension lines 35

The Dimensioning Toolbar n The dimensioning commands can be easily accessed by: q q Right Click on an existing toolbar and activate the dimensioning toolbar; Or, From the “pull down” menu n View q. Toolbars 36

Linear Dimensions n n n Linear dimensions are use to show basic dimensions of parts They can be orientated either in a horizontal or vertical (or even aligned) fashion Auto. CAD will automatically measure the length specified and insert all the parts of the dimension. 37

Leaders n n n Leaders are used to apply thread notes and other annotations Leaders begin at the arrow and continue from their elbow to their annotation The annotation can be any text string you want to type 38

Radius and Diameter n n By selecting a circular feature (arc or circle) with the Radius or Diameter option Auto. CAD will measure the size and place the dimension at a user selected point Using the Center option will place automatic centerlines on arcs or circles 39

Auto. CAD Dimension Variables: See Essentials of Auto. CAD by Whiteacre appendix 6 40

Auto. CAD Dimension Variables: Variable Default Description dimaso on All parts of the dimension are one entity. dimscale 1. 00 Changes sizes of text arrows. dimasz . 18 Sets arrowhead length. dimexe . 18 Extension beyond dimension line. dimtad off Places text above the dimension line. dimtxt . 18 Sets height of text. dimtix off Forces text inside of extension lines. dimdec ? ? Sets number of decimal places of dimension dimcen ? ? Sets center tick mark size See Essentials of Auto. CAD appendix 6 41

Special Characters in Auto. CAD: n n n %%c will show as the Diameter symbol: Ø %%d will show as the Degree symbol: %%p will show as the Plus-minus symbol: %%u will start/stop text underlined %%o will start/stop text overline 42

Spotfaced holes: No depth required. Cleans an uneven surface deep enough to allow full contact with bolt or washer. 43

Counterbore holes Require both a diameter and a depth dimension. 44

Counterdrilled holes: Require both a diameter and a depth dimension. (measured to the shoulder). 45

Countersunk holes: Used with flat head screws and bolts. They become flush when tightened. Used extensively in the aerospace industry. The 82 angle is common for cutting tools and screw threads 46

Chamfers: Break away sharp edges and help guide the part into a mating assembly. May be specified with one distance and one angle, or with two distances. 47

Necks: Necks are used for “O” ring seals, parts turned on lathes, and designed failure points 48

Knurls: Knurling is a process of rolling patterns onto cylindrical objects to make them easier to grip. 49

Dimensioning in small places 50

Repetitive features A combination of dimensioning & notes is used. A number in parenthesis indicates how many are required. The word TYPICAL (or TYP) indicates that all shown are the same. 51

SI symbol When dimensions on the drawing are all stated in millimeters, place an SI symbol near the title block. 52

SI symbol: 1 st vs 3 rd angle projection. Metric Units and 3 rd angle projection Metric Units and 1 st angle projection 53

Finish marks: Rough surfaces that need to be machined to provide a smooth, finished surface are indicated with finish marks. The vertex of the √ needs to touch the edge view of the surface. 54

Individual Assignment: n Auto. CAD q q n Plate 51………………. …all Plate 52…………C & D Plate 53 ……………. . B & D Plate 54 ………………. …. . A & D Due: Beginning of class 12. 2 Preview: n Tolerances: ………………. Plate 57 -63 q You will need your “paper copy” of the Vinson plate book for this assignment 55

Dimensioning Errors: n What is wrong with: 56

Dimensioning Errors: n What is wrong with: 57

Dimensioning Errors: n What is wrong with: 58

Dimensioning Errors: n What is wrong with: 59

Learning Objectives n n Apply dimensions to objects using Auto. CAD Be able to write correct notes for machined holes 60