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