Precision Dimensioning
Engineering II
Dimensioning Rectangular Prisms
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.
Dimensioning Cones
Dimensioning Spheres
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
Coordinate Dimensioning with
Dimension Lines
Coordinate Dimensioning without
Dimension Lines
(Baseline Dimensioning)
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.
Tabular Dimensioning
Dual Dimensioning – Position Method
• Millimeter value is placed above (or
below) the inch value or separated by a
dash.
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.
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
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
Specification of Tolerances
Limit Dimension
Unilateral
Bilateral-Equal
Bilateral-Unequal
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.
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.
Maximum Material Condition
• For the part shown here the MMC is
1.4996 since that size would yield the
most material.
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
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.
Clearance Fit
• Space is always left between parts.
• What is the allowance in this case?
• 1.5000 – 1.4988 = .0012
Interference Fit
• Always an interference of material.
• What is the allowance in this case?
• 1.5000 – 1.5013 = -.0013 or just .0013
Transition Fit
• Fit might result in clearance or interference.
Line Fit
• Clearance or surface contact may result at
assembly.
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).
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.
Specifying a Fit - Inches
Class RC 1
Standard
Limits
Nominal
Size Range
Inches
Limits
of
Clear.
Over
Hole
H5
Shaft
g4
To
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.
Specifying a Fit - Inches
Class RC 1
Standard
Limits
Nominal
Size Range
Inches
Limits
of
Clear.
Over
Hole
H5
Shaft
g4
To
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
Specifying a Fit - Inches
Class RC 1
Standard
Limits
Nominal
Size Range
Inches
Limits
of
Clear.
Over
Hole
H5
Shaft
g4
To
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
Specifying Fits - Metric
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
Specifying Fits - Metric
• Loose Running Fit
• Basic size of 25
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