1. Engineering
Drawing and Design
Chapter 10
Basic Dimensioning

2. Basic Dimensioning
Dimensions are given on drawings by extension lines, dimension lines, leaders, arrowheads, figures, notes and symbols
Length
Diameter
Angle
Location
NOT duplicated
Dimension lines are used to determine the extent and direction of dimensions
Terminated by uniform arrows
Arrows: 3:1 length/width recommended
Center lines never used for dimension lines
Avoid dimensioning to hidden lines
Avoid crossing dimension lines
Place dimension lines outside extension lines when space is tight (fig.8.3)

3. Definitions continued…
Extension lines are used to indicate the point or line on the drawing to which the dimension applies (fig.8-5)
Gap between extension line and visible object line
Perpendicular to dimension lines
Center lines may be used as extension lines
Leaders are used to direct notes, dimensions, symbols, item numbers, or part numbers to features on a drawing (fig.8-6)
Arrowheads terminate on a line; dots within the outline of the object
Leaders do not cross eachother
Leaders are pointed to the center of circles or arcs
Notes are used to simplify or complement dimensioning by giving information on a drawing in condensed and systematic manner
General notes placed in a central portion below the view which they apply
Local notes are connected by a leader to the point to which they apply

4. Basic Dimensioning Overview:
Dimensions and notes define the size, finish, and other requirements to fully define what you want manufactured.
Drawings for products must be dimensioned so that production personnel all over the world can make mating parts that will fit properly when assembled or when used to replace parts.

5. Good Dimensioning 3 Aspects of Good Dimensioning Tolerance Technique:
Good appearance of lines, spacing and arrows to allow others to read the drawing.
Placement:
Logical placement according to standard practices, so they are legible and east to find.
Choice:
Dimension for function and best manufacturing practices.
Tolerance
The total amount that the feature on the actual part can vary from the drawing or model.

6. Definitions continued…
Extension lines are used to indicate the point or line on the drawing to which the dimension applies Gap between extension line and visible object line
Perpendicular to dimension lines
Center lines may be used as extension lines
Centerlines are used to locate holes or other symmetrical features. Thin, dark lines alternating long and short dashes
Can cross other lines with out requiring gaps
Leaders are used to direct notes, dimensions, symbols, item numbers, or part numbers to features on a drawing Arrowheads terminate on a line; dots within the outline of the object
Leaders do not cross each other
Leaders are pointed to the center of circles or arcs
Notes are used to simplify or complement dimensioning by giving information on a drawing in condensed and systematic manner
General notes placed in a central portion below the view which they apply
Local notes are connected by a leader to the point to which they apply

7. BASIC DIMENSIONING
DIMENSION AND EXTENSION LINES

8. BASIC DIMENSIONING

9. PLACEMENT OF DIMENSIONS
INCORRECT

10. PLACEMENT OF DIMENSIONS
INCORRECT

11. PLACEMENT OF DIMENSIONS
INCORRECT

12. PLACEMENT OF DIMENSIONS
CORRECT

13. Units of measurement
Decimal-Inch parts are designed in basic decimal increments, preferably .02 in, and expressed with a minimum of two figures to the right of the decimal point (fig.8-7)
Whole dimensions: NOT 24
Decimal dimensions: .44 NOT 0.44 (no zero before the decimal point)
Fractional-Inch is not ANSI recommended. 1/64 inch. “ not used
Foot-and-Inch All dimensions 12 inches and greater are specified in feet and inches
24 inches 2’-0 (inch marks “ not shown)
27 inches 2’-3
SI Metric Units mm or m (micrometer)
Whole numbers 2 NOT 02 or 2.0 (numbers 1-9 shown without zero to left of decimal)
Decimal 0.2 NOT .2 or .20 (numbers <1 shown with a zero)
Large numbers (no comma or spaces to separate digits)
General note like: unless otherwise specified dimensions are in millimeters

14. DIMENSIONING UNITS
DECIMAL INCH

15. DIMENSIONING UNITS
FEET AND INCHES

16. DIMENSIONING UNITS
MILLIMETERS

17. Worth mentioning
Dual Dimensioning specify both English/SI units but not generally used anymore
Angular Units decimal degree is preferred over degrees, minutes, seconds
60.5° instead of 60°30’

18. DUAL DIMENSIONING and COMBINATION UNITS
Dual dimensioning is used to show metric and decimal-inch dimensions on the same drawing. Two methods of displaying the dual dimensions are:
Position Method
Bracket Method
DIMENSIONS IN () ARE MILLIMETERS

19. Unidirectional dimensioning: read from the bottom of the drawing
Rules for Basic Dimensioning
Symmetrical Outlines
Reference dimensions placed in parentheses
Not to scale underlined with a straight thick line
Abbreviations: Table 4 Appendix A-4

20. Form and Proportion of Dimensioning Symbols.
DIMENSION SYMBOLS
Dimensioning symbols are used to replace traditional terms or abbreviations.
Form and Proportion of Dimensioning Symbols.
(Reprinted from ASME Y14.5M-1994 (R2004),by permission of The American Society of Mechanical Engineers. All rights reserved.)

21. NECESSARY VIEWS What are the absolute minimum views
required to completely define an object?
One-View Drawing
Two-View Drawing
Three-View Drawing

22. BASIC RULES FOR DIMENSIONING
UNIDIRECTIONAL
USED ON ENGINEERING DRAWINGS

23. BASIC RULES FOR DIMENSIONING
ALIGNED
USED ON ARCHITECTURAL AND STRUCTURAL DRAWINGS

24. BASIC RULES FOR DIMENSIONING
PLACE DIMENSIONS BETWEEN VIEWS

25. BASIC RULES FOR DIMENSIONING
PLACE SMALLEST DIMENSIONS NEAREST
THE VIEW BEING DIMENSIONED

26. 8-2 Dimensioning Circular Features
Diameters
One view drawing-longitudinal view
End view drawing
Radii-circular arc
Passes through radius center and terminates with arrow touching arc
R precedes the numerical value
Cross at center of radius
Simple fillets and rounds dimensioned with a general note
Rounded ends
Cylindrical Holes-leader usually used
Multiple Holes – example 4 X ф8.4
Slotted Holes-

27. Countersink, Counterbore, Spotface
Countersink is an angular-sided recess that accommodates the head of flathead screws, rivets, and similar items [ф.40ф.80x82°]
Counterbore is a flat-bottomed, cylindrical recess that permits the head of a fastening device, such as a bolt, to lie recessed into the part[ф.38v ф .75x.25]
Spotface is an area in which the surface is machined just enough to provide smooth, level seating for a bolt head, nut, or washer [ф.38 v ф.75]

28. 8-3 Dimensioning common features
Repetitive features and dimensions use an X in conjunction with the numeral to indicate the “number of times”
Chamfering is the process of cutting away the inside or outside piece (fig.8-29)
Dimensioned normally by their angle and linear length
Example: 45°X.10
Slopes and tapers
Slope is the slant of a line
A taper is the ratio of the difference in the diameters of two sections (fig.8-31)
Knurls is specified in terms of type, pitch, diameter before and after knurling (fig. 8-32) Types include: Straight, Diagonal, Spiral, Convex, Raised Diamond
Undercutting or necking is the operation of cutting a recess in a diameter that is done to permit two parts to come together (fig.8-34a)