Lect 16 P. 1

1
Dimensioning

• Lecture 16

2
Dimensioning

• Goals
• Understand the principles of good dimensioning
  practice
• Apply the standard dimensioning practices for
  engineering drawings
• Reference
• BTG Chapter 7 Dimensions and Tolerances

3
Geometrics

• The science of specifying and tolerancing shapes
  and locations of features of on objects

4
Geometrics

• It is important that all persons reading a
  drawing interpret it exactly the same way.
• Parts are dimensioned based on two criteria
• Basic size and locations of the features
• Details of construction for manufacturing
• Standards from ANSI (American National Standards
  Institute)

5
Scaling vs. Dimensioning

• Drawings can be a different scales, but
  dimensions are ALWAYS at full scale.

6
Units of Measure
Angle Dimensions

• Length
• English - Inches, unless otherwise stated
• Up to 72 inches feet and inches over
• SI millimeter, mm
• Angle
• degrees, minutes, seconds

7
Dimensioning Terminology
8
Dimensioning Standards
(.25 in)
(.375 in)
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Dimensioning Basic Shapes -Assumptions

• Perpendicularity
• Assume lines that appear perpendicular to be 90
  unless otherwise noted
• Symmetry
• If a part appears symmetrical it is(unless it
  is dimensioned otherwise)
• Holes in the center of a cylindrical object are
  automatically located

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Dimensioning Basic Shapes

• Rectangular Prism

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Dimensioning Basic Shapes

• Cylinders
• Positive
• Negative

12
Dimensioning Basic Shapes

• Cone Frustum

13
Dimensioning Basic Shapes

• Circle Pattern Center Lines

14
Dimensioning Shows

• Size Location
  Orientation

15
Example Problem

• What dimensions (size location) are needed?
• Where should they be placed?

Think Individually, then share with the person
next to you. - Compare with the other pair at
your table
16
Grouping Dimensions

• Dimensions should always be placed outside the
  part

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Staggering Dimensions

• Put the lesser dimensions closer to the part.
• Try to reference dimensions from one surface
• This will depend on the part and how the
  tolerances are based.

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Extension Line Practices
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Repetitive Features
Use the Symbol x to Dimension Repetitive
Features
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Symbols for Drilling Operations
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Example Problem

• What dimensions (size location) are needed?
• Where should they be placed?

Think Individually, then share with the person
next to you. - Compare with the other pair at
your table
22
Assignments

• Dwg 31 DIM-1
• Fully dimension the objects shown using correct
  dimensioning practices.(part is fully
  dimensioned if it is possible to machine it from
  the dimensions provided)
• Use Inch Dimensions to the second place (x.xx)
• Dwg 32 DIM-2
• Fully dimension the objects shown using correct
  dimensioning practices.
• Use one-place metric dimensions (x.x)
• Bring your AutoCAD 2D Book Tomorrow