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
Bilateral-EqualLimit Dimension
Bilateral-UnequalUnilateral
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
NominalSize Range
Inches
Over To
Class RC 1
Limitsof
Clear.
StandardLimits
HoleH5
Shaftg4
0-0.120.10.45
+0.2–0
–0.1–0.25
0.12-0.240.150.5
+0.2–0
–0.15–0.3
0.24-0.400.20.6
+0.25–0
–0.2–0.35
0.40-0.710.250.75
+0.3–0
–0.25–0.45
0.71-1.190.30.95
+0.4–0
–0.3–0.55
1.19-1.970.41.1
+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
NominalSize Range
Inches
Over To
Class RC 1
Limitsof
Clear.
StandardLimits
HoleH5
Shaftg4
0-0.120.10.45
+0.2–0
–0.1–0.25
0.12-0.240.150.5
+0.2–0
–0.15–0.3
0.24-0.400.20.6
+0.25–0
–0.2–0.35
0.40-0.710.250.75
+0.3–0
–0.25–0.45
0.71-1.190.30.95
+0.4–0
–0.3–0.55
1.19-1.970.41.1
+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
NominalSize Range
Inches
Over To
Class RC 1
Limitsof
Clear.
StandardLimits
HoleH5
Shaftg4
0-0.120.10.45
+0.2–0
–0.1–0.25
0.12-0.240.150.5
+0.2–0
–0.15–0.3
0.24-0.400.20.6
+0.25–0
–0.2–0.35
0.40-0.710.250.75
+0.3–0
–0.25–0.45
0.71-1.190.30.95
+0.4–0
–0.3–0.55
1.19-1.970.41.1
+0.4–0
–0.4–0.7
Specifying Fits - Metric
BasicSize
Loose Running
HoleH11
Shaftc11
Fit
1 Max Min
1.0601.060
0.9400.880
0.1800.060
20 Max Min
20.13020.000
19.89019.760
0.3700.110
25 Max Min
25.13025.000
24.89024.760
0.3700.110
• 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
BasicSize
Loose Running
HoleH11
Shaftc11
Fit
1 Max Min
1.0601.060
0.9400.880
0.1800.060
20 Max Min
20.13020.000
19.89019.760
0.3700.110
25 Max Min
25.13025.000
24.89024.760
0.3700.110
• Loose Running Fit• Basic size of 25
Top Related