Reading Dimensions

1
CHAPTER 8

• Reading Dimensions

2
Learning Objectives

• Identify the ASME standard for dimensioning and
  tolerancing
• Read prints displaying a variety of dimensioning
  applications
• Read and calculate dimension tolerances on a
  print
• Determine the maximum material condition of given
  features

3
Learning Objectives

• Calculate clearance and allowance between mating
  features
• Answer questions about basic fits
• Read casting and forging dimensions and related
  information
• Read the information given in surface finish
  symbols

4
Dimensions

• Required on detail drawings
• Provide shape and size description
• Size dimensions
• Location dimensions
• Notes
• Local notes (specific notes)
• General notes

5
Dimensions
6
ASME Dimensioning Standards

• ASME Y14.5, Dimensioning and Tolerancing
• General note DIMENSIONING AND TOLERANCING PER
  ASME Y14.5-2009
• Several other ASME documents with standards
  related to dimensioning and tolerancing

7
Dimensioning Definitions

• Actual size
• Allowance
• Basic dimension
• Bilateral tolerance
• Datum
• Diameter
• Feature

• Feature of size
• Geometric tolerance
• Least material condition (LMC)
• Limits of dimension

8
Dimensioning Definitions

• Maximum material condition (MMC)
• Nominal size
• Radius
• Reference dimension
• Stock size
• Specified dimension
• Tolerance
• Unilateral tolerance

9
Fundamental Dimensioning Rules

• Each dimension has a tolerance except reference,
  maximum, minimum, or stock
• Dimensioning and tolerancing must be complete
• Show each necessary dimension of an end product
  is shown
• Select and arrange dimensions to suit the
  function and mating relationship of a part

10
Fundamental Dimensioning Rules

• Dimensions must not be subject to more than one
  interpretation
• Do not specify the manufacturing processes unless
  necessary
• Identify nonmandatory dimensions with an
  appropriate note
• Arrange dimensions to provide required
  information and optimum readability
• Show dimensions in true profile views and visible
  outlines

11
Fundamental Dimensioning Rules

• Dimension diameter or thickness of materials
  manufactured to gage or code numbers
• 90angle is implied for centerlines and lines
• 90basic angle is implied for centerlines located
  by basic dimensions
• A zero basic dimension applies where axes, center
  planes, or surfaces are shown one over the other
  with established geometric controls

12
Fundamental Dimensioning Rules

• Unless otherwise specified, all
• Dimensions and tolerances are measured at 20C
  (68F)
• Dimensions and tolerances apply in a free state
  condition except for nonrigid parts
• Tolerances apply for the full depth, length, and
  width of the feature
• Dimensions and tolerances apply on the drawing
  where specified

13
Fundamental Dimensioning Rules

• Coordinate systems
• Right-handed (arranged clockwise)
• Labeled axes and positive direction shown
• 3-D model complies with ASME Y14.41, Digital
  Product Definition Data Practices

14
Dimensioning Components
15
Dimensioning Symbols
16
Unidirectional Dimensioning

• Numerals, figures, and notes lettered
  horizontally
• Read from the bottom of the drawing sheet
• Mechanical drafting for manufacturing

17
Aligned Dimensioning

• Numerals, figures, and notes aligned with the
  dimension lines
• Horizontal dimensions read from the bottom
• Vertical dimensions read from the right side
• Architectural and structural drafting

18
Rectangular Coordinate Dimensioning without
Dimension Lines

• Ordinate dimensioning
• Dimension values aligned with extension lines
• Dimension represents a measurement originating
  from datums or coordinates
• Features such as holes sized using specific notes
  or a table
• Popular for
• Precision sheet metal part drawings
• Electronics drafting

19
Rectangular Coordinate Dimensioning without
Dimension Lines
20
Tabular Dimensioning

• Form of rectangular coordinate dimensioning
  without dimension lines
• Features dimensioned in a table

21
Chart Drawings

• Used when a part or assembly has one or more
  dimensions that change depending on the specific
  application

22
Millimeter Dimensions

• Millimeters (mm)
• Common International System of Units (SI) unit of
  measure
• General note UNLESS OTHERWISE SPECIFIED, ALL
  DIMENSIONS ARE IN MILLIMETERS
• Inch dimensions followed with IN

23
Proper Use of Metric Units

• Decimal point and 0 omitted when dimension is a
  whole number
• Decimal value that is less than 1 preceded with a
  0
• When the value is greater than a whole number by
  a fraction of a mm, a 0 does not appear next to
  last digit
• Exception when displaying tolerance values

24
Proper Use of Metric Units

• Plus and minus tolerance values have same number
  of decimal places
• Limit tolerance values have same number of
  decimal points
• Unilateral tolerances use a single 0 without a
  corresponding or sign

25
Inch Dimensions

• Decimal inches (IN)
• United States (U.S.) customary unit of measure
• General note UNLESS OTHERWISE SPECIFIED, ALL
  DIMENSIONS ARE IN INCHES
• Millimeter dimensions followed with mm

26
Proper Use of Inch Units

• Value that is less than 1 inch is not preceded
  with a 0
• Specified dimension expressed to the same number
  of decimal places as its tolerance
• Fractional inches generally indicate larger
  tolerance

27
Proper Use of Inch Units

• Plus and minus tolerance values have the same
  number of decimal places
• Unilateral tolerances use the and sign
• The 0 value has the same number of decimal places
  as the value that is greater or less than 0
• Limit tolerance values have the same number of
  decimal points

28
Proper Use of Angular Units

• Use decimal or degreesminutesseconds format
• Angle and tolerance values have the same number
  of decimal places
• 0or 00? included when only minutes or seconds
  are specified, as applicable

29
Fractions on Prints

• Not as common as decimal inches or millimeters
• Architectural and structural drawings
• Generally indicate larger tolerance

30
Arrowheads

• Terminate dimension lines and leaders
• Filled in solid or open

31
Chain Dimensioning

• Creates tolerance stacking (tolerance buildup)
• One intermediate dimension or the overall
  dimension omitted

32
Baseline Dimensioning

• Size or location of features controlled from a
  common reference plane
• Reduces possibility of tolerance stacking

33
Direct Dimensioning

• Results in the least tolerance stacking

34
Symmetrical Objects on a Print
35
Cylinders on a Print
36
Square Features on a Print
37
Angles Dimensioned on a Print
38
Chamfers Dimensioned on a Print
39
Conical Shapes Dimensioned on a Print
40
Dimensioning of Hexagons and Other Polygons

• Dimension across the flats

41
Dimensioning Arc Radius
42
Dimensioning Arc Length
43
Additional Radius Dimensioning Applications

• True radius
• TRUE R followed by the actual radius
• Controlled radius
• CR followed by the radius
• Spherical radius
• SR followed by the radius

44
Dimensioning Contours Not Defined as Arcs

• Dimension coordinates or points along the contour
  from common surfaces
• Series of dimensions on the object and along the
  contour
• Tabular dimensioning

45
Locating a Point Established by Extension Lines
46
Dimensioning Holes
47
Dimensioning Hole Depth
48
Dimensioning a Counterbore
49
Dimensioning a Spotface
50
Countersink or Counterdrill
51
Dimensioning of Multiple Features

• Number of features, X, a space, feature
  specification
• Dimensioned to one of the features only
• Examples
• 4X Ø6 THRU or 4X Ø6
• 2X R.50
• 3X 8X45

52
Slots Dimensioned on a Print
53
Dimensioning Keyseats and Keyways on Prints
54
Dimensioning of Knurls
55
Dimensioning Necks and Grooves on Prints
56
Rectangular Coordinate Dimensioning
57
Polar Coordinate Dimensioning
58
Dimensioning Repetitive Features
59
Locating Multiple Tabs in a Polar Orientation
60
Locating Multiple Features of Nearly the Same Size
61
The Dimension Origin Specified on a Print

• Clearly identifies from which feature the
  dimension originates

62
Dimensions Placed on Auxiliary Views
63
Finding General Notes on a Print

• Sheet blocks
• Material
• General tolerances
• Scale
• Part name
• Sheet size
• Part number
• Number of revisions
• Projection

• Outside sheet blocks
• Machining practices
• Common dimensions
• Finish or other treatments

64
Flag Notes on a Print

• Delta note
• Specific note placed with general notes
• Keyed to the drawing
• Delta symbol (?) common
• Hexagons and circles also used

65
Tolerances

• Help ensure parts fit together and function in an
  assembly
• Apply to all dimensions on a drawing, except
• Reference
• Maximum
• Minimum
• Stock size

66
Plus-Minus Dimensioning

• Calculate the upper and lower limits from the
  specified dimension and plus-minus tolerance
• Bilateral tolerance
• Most common tolerancing method
• Equal bilateral tolerance
• Often preferred by manufactures
• Unequal bilateral tolerance

67
Unilateral Tolerance

• Used by some companies to define fits between
  mating parts
• Often avoided by CNC machine programmers

68
Limit Dimensioning

• Calculate the tolerance from the upper and lower
  limits
• Common for defining fits between mating parts
• Preferred by some companies or departments

69
Single Limits

• Can be used for common machine processes
• Follow dimension value with (MIN) or (MAX)
• Design determines unspecified limit

70
Specified and Unspecified Inch Tolerances
71
Specified and Unspecified Metric Tolerances

• ISO 2768 classes of size tolerances
• Fine (f)
• Medium (m)
• Coarse (c)
• Very coarse (v)

72
Applying Statistical Tolerancing
73
Maximum Material Condition (MMC)

• External feature is at MMC at its largest limit
• Internal feature is at MMC at its smallest limit

74
Least Material Condition (LMC)

• External feature is at LMC at its smallest limit
• Internal feature is at LMC at its largest limit

75
Clearance Fit
76
Allowance
MMC Internal Feature
MMC External Feature
Allowance
77
Interference Fit

• Force or shrink fit
• Examples
• Bushing pressed onto a housing
• Pin is pressed into a hole

78
Extreme Form Variation

• Established by limits of size
• Specified by Rule 1 in ASME Y14.5

79
Limits and Fits Between Mating Parts

• Fit determined first based on the use or service
• Limits of size established second to ensure the
  desired fit
• ANSI/ASME B4.1 Preferred Limits and Fits for
  Cylindrical Parts
• ANSI/ASME B4.2 Preferred Metric Limits and Fits
• Tables of establishing dimensions for standard
  ANSI fits

80
Running and Sliding Fits (RFC)

• RC1Close sliding fits
• RC2Sliding fits
• RC3Precision running fits
• RC4Close running fits
• RC5 and RC6Medium running fits
• RC7Free running fits
• RC8 and RC9Loose running fits

81
Locational Fits (LC, LT, LN)

• LCLocational clearance fits
• LTLocational transition fits
• LNLocational interference fits

82
Force Fits (FN)

• FN1Light drive fits
• FN2Medium drive fits
• FN3Heavy drive fits
• FN4 and FN5Force fits

83
Dimensions Applied to Platings and Coatings

• General note
• DIMENSIONAL LIMITS APPLY BEFORE (AFTER) PLATING
  (COATING)
• Specific note
• Leader with a dot pointing to the specific
  surface instead of an arrowhead

84
Casting Prints

• Depends on
• Casting process and characteristics
• Material
• Design or shape of the part
• Die or mold
• Based on ASME Y14.8, Castings and Forgings
  standard

85
Draft

• Not necessary on horizontal surfaces
• Begin at the parting line and parting plane
• Tapers away from the molding material

86
Fillets and Rounds in Casting

• Allow the pattern to eject freely from the mold
• Fillets help reduce the tendency of cracks to
  develop during shrinkage
• Radii determined by part thickness

87
Machining Allowance

• Extra material for any surface to be machined
• Examples
• Iron and steel .125 in. (3 mm)
• Brass, bronze, and aluminum .062 in. (1.5 mm)
• Greater for large castings or those with a
  tendency to warp

88
Casting Prints

• Casting print
• Machining print
• Combined casting and machining on a print
• Phantom lines show machining allowance and draft
  angles

89
Forging Prints

• Focuses on dies
• Draft
• Fillets and rounds
• Machining allowance
• Based on ASME Y14.8, Castings and Forgings
  standard

90
Forging Prints

• Stock material drawings show
• Size and shape of the stock material
• Outline of the end product using phantom lines
• Detail drawings
• Show the end product
• Usually show draft
• Phantom lines show machining allowance and draft
  angles

91
Surface Finish (Surface Texture)

• Obtained by
• Machining
• Grinding
• Honing
• Lapping
• Specified using surface finish symbol

92
Surface Finish Characteristics

• Roughness
• Waviness
• Lay
• Flaws

93
Surface Finish Symbol
94
Introduction to ISO 9000

• ISO 9000-1
• Direction and definitions that describe what each
  standard contains
• Assists companies in the selection and use of the
  appropriate ISO standard
• ISO 9001
• Model for designing, documenting, and
  implementing ISO standards
• ISO 9002
• ISO 9001 but does not contain the requirement of
  documenting the design and development process

95
Introduction to ISO 9000

• ISO 9003
• Companies or organizations that only need to
  demonstrate through inspection and testing
  methods that they are providing the desired
  product or service
• ISO 9004-1
• Set of guidelines for development and
  implementation of a quality management system

96
Glossary

• Actual size
• The measured size of a feature or part after
  manufacturing.
• Allowance
• The tightest possible fit between two mating
  parts.
• Allowance
• The tightest possible fit between two mating
  parts.

97
Glossary

• Baseline dimensioning
• A common method of dimensioning machine parts
  whereby each feature dimension originates from a
  common surface, axis, or center plane.
• Basic dimension
• A theoretically exact size, location, profile, or
  orientation of a feature or point.
• Bilateral tolerance
• A tolerance allowed to vary in two directions
  from the specified dimension.

98
Glossary

• Bilateral tolerance
• A tolerance in which variation is permitted in
  both directions from the specified dimension.
• Casting
• An object or part produced by pouring molten
  metal into a mold.

99
Glossary

• Chain dimensioning
• Also known as point-to-point dimensioning, a
  method of dimensioning from one feature to the
  next.
• Chamfer
• A slight surface angle used to relieve a sharp
  corner.
• Clearance fit
• A condition when, due to the limits of
  dimensions, there is always a clearance between
  mating parts.

100
Glossary

• Controlled radius
• The limits of the radius tolerance zone must be
  tangent to the adjacent surfaces, and there can
  be no reversals in the contour.
• Counterbore
• Often used to machine a diameter below the
  surface of a part so a bolt head or other
  fastener can be recessed.
• Counterdrill
• A combination of two drilled features.

101
Glossary

• Countersink
• A conical feature in the end of a machined hole.
• Datum
• A theoretically exact surface, plane, axis,
  center plane, or point from which dimensions for
  related features are established.
• Delta
• A triangle symbol (?) placed on the drawing for
  reference.

102
Glossary

• Diameter
• The distance across a circle measured through the
  center.
• Die
• Any device used to produce a desired shape, form
  or finish to a material.
• Dimension
• A numerical value or values, or mathematical
  expression provided in appropriate units of
  measure and used to define form, size,
  orientation or location of a feature or part.

103
Glossary

• Direct dimensioning
• Dimensioning applied to control the size or
  location of one or more specific features.
• Draft
• The taper allowance on all vertical surfaces of a
  pattern, which is necessary to facilitate the
  removal of the pattern from the mold.
• Equal bilateral tolerance
• A tolerance where the variation from the
  specified dimension is the same in both the and
  directions.

104
Glossary

• Extreme form variation
• The variation of the form of the feature between
  the upper limit and lower limit of a size
  dimension.
• Feature of size
• One cylindrical or spherical surface, a circular
  element, or a set of two opposed elements or
  opposed parallel plane surfaces, each of which is
  associated with a directly toleranced dimension.
• Feature
• The general term applied to describe a physical
  portion of a part or object, such as a surface,
  slot, tab, pin, keyseat, or hole.

105
Glossary

• Forging
• A process of shaping malleable metals by
  hammering or pressing between dies that duplicate
  the desired shape.
• Free state condition
• Distortion of the part after removal of forces
  applied during manufacturing.
• General notes
• Information that relates to the entire drawing.

106
Glossary

• General notes
• Notes placed separate from the views and relate
  to the entire drawing.
• Geometric tolerance
• The general term applied to the category of
  tolerances used to control size, form, profile,
  orientation, location, and runout.
• Interference fit
• The condition that exists when, due to the limits
  of the dimensions, mating parts must be pressed
  together.

107
Glossary

• Keyseat
• A groove or channel cut in a shaft.
• Keyway
• A shaft and key are inserted into a hub, wheel,
  or pulley where the key mates with a groove
  called a keyway.
• Kinematics
• The study of mechanisms.

108
Glossary

• Knurling
• A cold forming process used to form a cylindrical
  or flat surface uniformly with a diamond or
  straight pattern creating a knurl.
• Lay
• The direction or configuration of the predominant
  surface pattern.
• Least material condition (LMC)
• The condition where a feature contains the least
  amount of material allowed by the size limits.

109
Glossary

• Least material condition (LMC)
• The opposite of MMC, the least amount of material
  possible in the size of a feature within the
  stated limits.
• Limit dimensioning
• A system of dimensioning where the upper and
  lower limits of the tolerance are provided and
  there is no specified dimension given.
• Limits of dimension
• The largest and smallest possible boundary to
  which a feature can be made as related to the
  tolerance of the dimension.

110
Glossary

• Limits of size
• The amount of variation in size and geometric
  form of a feature control. The boundary between
  maximum material condition (MMC) and least
  material condition (LMC).
• Local notes (specific notes)
• Notes connected to specific features on the views
  of the drawing.
• Location dimensions
• Dimensions that provide the relationship of
  features of an object.

111
Glossary

• Locational fits (LC, LT, LN)
• Provide rigid or accurate location, as with
  interference fits, or provide some freedom of
  location, as with clearance fits.
• Maximum material condition (MMC)
• The condition of a part or feature when it
  contains the most amount of material within the
  stated limits.

112
Glossary

• Mold
• A form made to pour or inject material to produce
  the desired shape.
• Neck
• The result of a machining operation that
  establishes a narrow groove on a cylindrical part
  or object.
• Nominal size
• A dimension used for general identification such
  as stock size or thread diameter.

113
Glossary

• Nonrigid parts
• Parts that can have dimensional change due to
  thin wall characteristics.
• Notes
• A type of dimension that generally identify the
  size of a feature or features with written
  specifications that are more detailed than a
  numerical value.
• Parting line
• The separation between the mold or die
  components, and is a line on the drawing
  representing the mating surfaces between the mold
  or die components.

114
Glossary

• Parting plane
• The mating surfaces of a die or mold.
• Plus-minus dimensioning
• A system of dimensioning that provides a nominal
  dimension and an amount of allowable variance
  from that dimension.

115
Glossary

• Polar coordinate dimensioning
• Using angular dimensions to locate features from
  planes or centerlines.
• Radius
• The distance from the center of a circle to the
  outside.
• Rectangular coordinate dimensioning
• Using linear dimensions to locate features from
  planes or centerlines.

116
Glossary

• Reference dimension
• A dimension used for information purposes only
  and is usually without a tolerance.
• Running and sliding fits (RFC)
• Intended to provide a similar running performance
  with suitable lubrication allowance throughout
  their range of sizes.
• Single limits
• Used when the specified dimension cannot be any
  more than the maximum or less than the minimum
  given value.

117
Glossary

• Size dimensions
• Dimensions placed directly on a feature to
  identify a specific size or may be connected to a
  feature in the form of a note.
• Specifications
• Any written information or instructions included
  on the drawing or with a set of drawings, giving
  all necessary information not shown in the
  drawing field.
• Specified dimension
• The part of the dimension from which the limits
  are calculated.

118
Glossary

• Spotface
• Provides a flat bearing surface for a washer face
  or bolt head.
• Statistical tolerancing
• The assigning of tolerances to related dimensions
  in an assembly based on the requirements of
  statistical process control (SPC).
• Stock size
• A commercial or pre-manufactured size, such as a
  particular size of square, round, or hex steel
  bar.

119
Glossary

• Surface finish (surface texture)
• The roughness, waviness, lay, and flaws of a
  surface.
• Surface roughness
• Fine irregularities in the surface finish and is
  a result of the manufacturing process used.
• Surface waviness
• The often widely spaced condition of surface
  texture usually caused by such factors as machine
  chatter, vibrations, work deflection, warpage, or
  heat treatment

120
Glossary

• Tolerance stacking (tolerance buildup)
• The tolerance of each dimension builds on the
  next.
• Tolerance
• The total permissible variation in size or
  location.
• True radius
• The actual radius of an arc even though it may be
  shown not true size and shape.

121
Glossary

• Unequal bilateral tolerance
• A tolerance where the variation from the
  specified dimension is not the same in both
  directions.
• Unilateral tolerance
• A tolerance where the variation is permitted to
  increase or decrease in only one direction from
  the specified dimension.