Today, Chapter 8 Sections 8.1-8.3: Dynamics in Two Dimensions
8.1-8.3 Basic Dimension Ing
Transcript of 8.1-8.3 Basic Dimension Ing
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Chapter 8Chapter 8
EngineeringDrawing and Design
EngineeringDrawing and Design
Seventh EditionSeventh Edition
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Chapter 8.1: Basic DimensioningChapter 8.1: Basic Dimensioningy Dimensions are given on drawings by extension lines, dimension lines, leaders,
arrowheads, figures, notes and symbols
Length
Diameter
Angle
Location NOT duplicated
y 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)
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Definitions continuedDefinitions continued
y Extension lines are used to indicate the point or line on thedrawing 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
y Leaders are used to direct notes, dimensions, symbols, itemnumbers, 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
y
Notes are used to simplify or complement dimensioning by givinginformation 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
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BASIC DIMENSIONING
DIMENSION ANDEXTENSION LINES
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BASIC DIMENSIONING
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PLACEMENT OF DIMENSIONS
INCORRECT
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PLACEMENT OF DIMENSIONS
INCORRECT
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PLACEMENT OF DIMENSIONS
INCORRECT
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PLACEMENT OF DIMENSIONS
CORRECT
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Units of measurementUnits of measurementy Decimal-Inch parts are designed in basic decimal increments,
preferably .02 in, and expressed with a minimum of two figures tothe right of the decimal point (fig.8-7)
Whole dimensions: 24.00 NOT 24
Decimal dimensions: .44 NOT 0.44 (no zero before the decimal point)
y
Fractional-Inch is not ANSI recommended. 1/64 inch. not usedy Foot-and-InchAll dimensions 12 inches and greater are specified in
feet and inches
24 inches 2-0 (inch marks not shown)
27 inches 2-3
y SI Metric Units mm or m (micrometer)
Whole numbers 2 NOT 02 or 2.0 (numbers 1-9 shown without zero to left ofdecimal)
Decimal 0.2 NOT .2 or .20 (numbers
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DIMENSIONING UNITS
DECIMAL INCH
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DIMENSIONING UNITS
FEET AND INCHES
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DIMENSIONING UNITS
MILLIMETERS
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Worth mentioningWorth mentioning
y Dual Dimensioning specify both English/SI
units but not generally used anymore
y Angular Units decimal degree is preferredover degrees, minutes, seconds
60.5 instead of 6030
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Unidirectional dimensioning: readUnidirectional dimensioning: read
from the bottom of the drawingfrom the bottom of the drawingy Rules for Basic Dimensioning (p.183)y Symmetrical Outlines (fig.8.13)
y Reference dimensions (fig.8.14) placed in
parentheses
y Not to scale (fig.8.15) underlined with a
straight thick line
y Abbreviations: Table 4 Appendix A-4
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BASIC RULES FOR DIMENSIONING
UNIDIRECTIONALUSED ON ENGINEERINGDRAWINGS
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BASIC RULES FOR DIMENSIONING
ALIGNEDUSED ON ARCHITECTURALAND STRUCTURAL DRAWINGS
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BASIC RULES FOR DIMENSIONING
PLACE DIMENSIONS BETWEEN VIEWS
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BASIC RULES FOR DIMENSIONING
PLACE SMALLEST DIMENSIONS NEAREST
THE VIEW BEING DIMENSIONED
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88--2 Dimensioning Circular Features2 Dimensioning Circular Features
y Diameters
One view drawing-longitudinal view(fig.8-16)
End view drawing (fig.8-16c)
y Radii-circular arc
Passes through radius center and terminates with arrow touchingarc (fig.8-18)
R precedes the numerical value
Cross at center of radius (fig.8-18b)
Simple fillets and rounds dimensioned with a general note
y
Rounded ends (fig.8-20)y Cylindrical Holes-leader usually used (fig.8-22,8-23)
y Multiple Holes example 4 X 8.4 (fig.8-25)
y Slotted Holes-(fig.8-26)
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Countersink,Countersink, CounterboreCounterbore,, SpotfaceSpotface
(fig. 8(fig. 8--26 & 826 & 8--27)27)y Countersinkis an angular-sided recess that
accommodates the head of flathead screws,rivets, and similar items [.40.80x82]
y
Counterbore is a flat-bottomed, cylindricalrecess that permits the head of a fasteningdevice, such as a bolt, to lie recessed into thepart[.38v .75x.25]
y
Spotface is an area in which the surface ismachined just enough to provide smooth,level seating for a bolt head, nut, or washer[.38 v .75]
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88--3 Dimensioning common features3 Dimensioning common features
y Repetitive features and dimensions use an X in conjunctionwith the numeral to indicate the number of times
y Chamfering is the process of cutting away the inside oroutside piece (fig.8-29) Dimensioned normally by their angle and linear length
Example: 45X.10y Slopes and tapers
Slope is the slant of a line
A taper is the ratio of the difference in the diameters of twosections (fig.8-31)
y Knurls is specified in terms of type, pitch, diameter before
and after knurling (fig. 8-32) Types include: Straight, Diagonal,Spiral, Convex, Raised Diamond
y Undercutting or necking is the operation of cutting a recessin a diameter that is done to permit two parts to cometogether (fig.8-34a)