Precision Dimensioning

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Precision Dimensioning

• Engineering II

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Dimensioning Rectangular Prisms
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Dimensioning Cylinders

• The diameter of cylinders should be dimensioned
  in the rectangular view (not the circular view).
• Cylinders without a hole passing through them
  only require one view.

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Dimensioning Cones
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Dimensioning Spheres
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Rectangular Coordinate Dimensioning

• Used when computer-controlled production machines
  are used to manufacture parts.
• The designer should consult with personnel in
  manufacturing to ensure that the origin is
  located in an appropriate position.
• Two types of rectangular coordinate dimensioning
• Coordinate Dimensioning with Dimension Lines
• Coordinate Dimensioning Without Dimension Lines

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Coordinate Dimensioning with Dimension Lines
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Coordinate Dimensioning without Dimension Lines
(Baseline Dimensioning)
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Tabular Dimensioning

• Tabular dimensioning is used when a series of
  parts consists of the same features or geometry
  but vary in dimension.
• Letters are used in place of dimension values,
  and the values are then placed in a table.
• Most standard parts are dimensioned this way in
  catalogs, the machinery handbook, and in the back
  of most textbooks.

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Tabular Dimensioning
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Dual Dimensioning Position Method

• Millimeter value is placed above (or below) the
  inch value or separated by a dash.

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Dual Dimensioning Bracket Method

• Millimeter value is enclosed in square brackets.
  A note should be placed on the drawing such as
  DIMENSIONS IN ARE MILLIMETERS.

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Tolerance Dimensioning

• Why do we need tolerance dimensioning?
• Interchangeable parts manufacturing
• Parts are manufactured at widely separate
  localities
• Effective size control
• Modern industry relies on it for subcontracting
  and replacement parts
• Accuracy is Expensive, however

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Reading Dimensions
.1 One tenth of an inch
.01 One hundredth of an inch
.001 One thousandth of an inch
.0001 One ten-thousandth of an inch
.00001 One millionth of an inch
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Specification of Tolerances
Limit Dimension
Bilateral-Equal
Unilateral
Bilateral-Unequal
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Tolerance

• Tolerance is the total amount a specific
  dimension is permitted to vary (difference
  between the maximum and minimum limits).
• The dimension below has a tolerance of .0003.

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Maximum Material Condition

• When specifying tolerance dimensions, the maximum
  material condition (MMC) means the product or
  part contains the maximum amount of material
  specified by the tolerance.
• The heaviest part.

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Maximum Material Condition

• For the part shown here the MMC is 1.4996 since
  that size would yield the most material.

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Allowance

• Allowance is the minimum clearance or maximum
  interference intended between the maximum
  material condition (MMC) of mating parts.
• The allowance for the system below is 25.000 -
  24.890 0.110

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More Terminology

• Nominal Size - General identification in
  fractions (ex. 1-1/2 for 1.500).
• Basic Size - General identification in decimal
  (ex. 1.500).
• Actual Size - Measured size.
• Limits - Maximum and minimum sizes indicated by
  the tolerance dimensions.

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Clearance Fit

• Space is always left between parts.
• What is the allowance in this case?
• 1.5000 1.4988 .0012

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Interference Fit

• Always an interference of material.
• What is the allowance in this case?
• 1.5000 1.5013 -.0013 or just .0013

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Transition Fit

• Fit might result in clearance or interference.

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Line Fit

• Clearance or surface contact may result at
  assembly.

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Basic Hole System (Hole Basis)

• The minimum size hole is taken as the basic
  size. 
• Used when standard tools are used to produce
  holes (reamers broaches).

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Basic Shaft System (Shaft Basis)

• The maximum shaft size is taken as the basic
  size. 
• When several parts having different fits, but one
  nominal size are required on a single shaft.

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Specifying a Fit - Inches
Nominal Size Range Inches Over To Class RC 1 Class RC 1 Class RC 1
Nominal Size Range Inches Over To Limits of Clear. Standard Limits Standard Limits
Nominal Size Range Inches Over To Limits of Clear. Hole H5 Shaft g4
0-0.12 0.1 0.45 0.2 0 0.1 0.25
0.12-0.24 0.15 0.5 0.2 0 0.15 0.3
0.24-0.40 0.2 0.6 0.25 0 0.2 0.35
0.40-0.71 0.25 0.75 0.3 0 0.25 0.45
0.71-1.19 0.3 0.95 0.4 0 0.3 0.55
1.19-1.97 0.4 1.1 0.4 0 0.4 0.7

• Determine type of fit and find corresponding
  table
• Determine basic size
• Find size range on table
• Determine tolerances for Hole and Shaft
• Remember values are in thousandths of an inch.

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Specifying a Fit - Inches
Nominal Size Range Inches Over To Class RC 1 Class RC 1 Class RC 1
Nominal Size Range Inches Over To Limits of Clear. Standard Limits Standard Limits
Nominal Size Range Inches Over To Limits of Clear. Hole H5 Shaft g4
0-0.12 0.1 0.45 0.2 0 0.1 0.25
0.12-0.24 0.15 0.5 0.2 0 0.15 0.3
0.24-0.40 0.2 0.6 0.25 0 0.2 0.35
0.40-0.71 0.25 0.75 0.3 0 0.25 0.45
0.71-1.19 0.3 0.95 0.4 0 0.3 0.55
1.19-1.97 0.4 1.1 0.4 0 0.4 0.7

• RC1 - Close Sliding Fit
• Basic size of 1.500
• Upper tolerance on hole is 0.4, which is really
  0.0004
• Lower tolerance on hole is -0.
• Upper tolerance on shaft is -0.0004
• Lower tolerance on shaft is -0.0007

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Specifying a Fit - Inches
Nominal Size Range Inches Over To Class RC 1 Class RC 1 Class RC 1
Nominal Size Range Inches Over To Limits of Clear. Standard Limits Standard Limits
Nominal Size Range Inches Over To Limits of Clear. Hole H5 Shaft g4
0-0.12 0.1 0.45 0.2 0 0.1 0.25
0.12-0.24 0.15 0.5 0.2 0 0.15 0.3
0.24-0.40 0.2 0.6 0.25 0 0.2 0.35
0.40-0.71 0.25 0.75 0.3 0 0.25 0.45
0.71-1.19 0.3 0.95 0.4 0 0.3 0.55
1.19-1.97 0.4 1.1 0.4 0 0.4 0.7
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Specifying Fits - Metric
Basic Size Loose Running Loose Running Loose Running
Basic Size Hole H11 Shaft c11 Fit
1 Max Min 1.060 1.060 0.940 0.880 0.180 0.060
20 Max Min 20.130 20.000 19.890 19.760 0.370 0.110
25 Max Min 25.130 25.000 24.890 24.760 0.370 0.110

• Determine type of fit and find corresponding
  table
• Determine basic size
• Find size range on table
• Determine tolerances for Hole and Shaft

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Specifying Fits - Metric
Basic Size Loose Running Loose Running Loose Running
Basic Size Hole H11 Shaft c11 Fit
1 Max Min 1.060 1.060 0.940 0.880 0.180 0.060
20 Max Min 20.130 20.000 19.890 19.760 0.370 0.110
25 Max Min 25.130 25.000 24.890 24.760 0.370 0.110

• Loose Running Fit
• Basic size of 25