EGR 277 Digital Logic

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Lecture 5 EGR 110 Engineering Graphics
Reading Assignment Ch. L in Engineering
Graphics Workbook, Series 1.2 or Series
2 Sketching Assignment Sketching Assignment 4

• Chapter L Dimensioning
• Key topics in dimensioning
• Technique in dimensioning line types, spacing,
  arrowheads, leaders, radius or diameter, etc.
• Placement of dimensions in which view should a
  dimension be placed?
• Choice of dimensions which dimensions should be
  used? Baseline or continued dimensions?
  Avoiding redundant dimensions.

• Key types of dimensions
• Distances
• Angles
• Notes

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Lecture 5 EGR 110 Engineering Graphics

• Lines used in dimensioning
• Dimension lines
• Thin, dark, solid lines used to show distances
  and used for leaders
• Terminated with arrowheads
• Often break in the middle for dimension values
• Spacing should be uniform for multiple dimensions
• Extension lines
• Thin, dark, solid lines extending from object
  features to the dimension lines
• Gaps are generally needed between points on the
  object and extension lines, except when
  connecting to center lines

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Lecture 5 EGR 110 Engineering Graphics
Common rules for placement of dimensions
1) Avoid dimension lines inside objects if
possible.
Good Example
Poor Example
2) Shorter dimensions are generally placed closer
to the object. 3) Dimension lines should
generally not cross extension lines.
Good Example
Poor Example
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Lecture 5 EGR 110 Engineering Graphics
Common rules for placement of dimensions 4)
Dimension lines should not coincide with or
continue a line in a drawing.
Good Example
Poor Example
5) Spacing between dimension lines should be
uniform for multiple dimensions. 6) Dimensions
should be lined up or grouped neatly as much as
possible.
Good Example
Poor Example
7) Dimensions lines are generally perpendicular
to extension lines.
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Lecture 5 EGR 110 Engineering Graphics
Arrowheads Although styles sometimes vary,
arrowheads most commonly use a lengthwidth ratio
of 31 (this is the default in AutoCAD).

• Leaders
• Leaders are thin, solid lines used with a note or
  a dimension
• Several styles of leaders and arrows are used in
  dimensioning circles or arcs
• The leader for a circle or arc should always
  point toward the center
• A large dot is often used on the end of a leader
  for polished surfaces.

Examples
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Lecture 5 EGR 110 Engineering Graphics

• Section lines
• Section lines are thin, dark lines used to shade
  or hatch an area

Section Lines

• In general, it is best to avoid using inside
  dimensions, but if you must then the section
  lines should be interrupted (show example).

Good Example
Poor Example
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Lecture 5 EGR 110 Engineering Graphics

• Direction of figures
• There are two primary systems (show examples)
• Unidirectional dimensions (ANSI preferred) - all
  dimension texts are horizontal from the bottom
• Aligned dimensions - all dimension texts are
  aligned with the dimension lines

Unidirectional dimensions
Aligned dimensions
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Lecture 5 EGR 110 Engineering Graphics

• Dimensioning angles
• There are several styles for the text, including
  decimal degrees (default in AutoCAD) degrees,
  minutes, and seconds and radians
• Dimension lines should form an arc (either inside
  or outside the angle)

Examples
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Lecture 5 EGR 110 Engineering Graphics

• Dimensioning Arcs
• Use R with the dimension text
• Various arrow positions can be used
• The dimension may or may not include a center mark

Examples
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Lecture 5 EGR 110 Engineering Graphics

• Dimensioning Holes
• Might include center lines, center marks, or none
• Several possibilities for leader and arrow
  positions
• Use the symbol ? generally (or sometimes DIA)

Examples
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Lecture 5 EGR 110 Engineering Graphics

• Dimensioning Holes (continued)
• Dimensions for holes commonly include notes, such
  as
• ?4, 2 HOLES
• 2 x ?2.5
• 0.125 DIA DRILL
• 6 x ?2.5 EQUALLY SPACED ON ?9.5
• ?2.5 THRU
• ?2.5 BORE
• ?2.5 REAM

Example
Example Add a bolt circle and the required
dimensions
Example
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Lecture 5 EGR 110 Engineering Graphics

• Fillets and Rounds
• Fillet - a rounded inner corner Round
  - a rounded outer corner
• Use a note rather than dimensioning each one.
  Examples
• 6 x R1.25
• R0.20 TYP
• ALL FILLETS R6 AND ROUNDS R4
• ALL F R R0.25 UON

Examples
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Lecture 5 EGR 110 Engineering Graphics

• Systems of Units
• 1) Decimal inch
• Units are generally omitted. A dimension of 1.25
  means 1.25".
• 2) Metric (SI System)
• Default unit is mm
• If units other than mm are used, include a note
  (such as ALL DIM IN CM)
• Include a symbol to indicate that metric units
  are being used. Examples
• 3) Fractional inch
• Used in architectural drawings, but too
  inaccurate for machine work
• Units are typically used for inches, but not for
  feet. Examples
• 2-3¼"
• 1-0"
• 0-5¾"

METRIC
SI
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Lecture 5 EGR 110 Engineering Graphics
Example Add a dimension for the counterbored
hole below.
Example Add a dimension for the countersunk
hole below.
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Lecture 5 EGR 110 Engineering Graphics

• Dimensioning Styles
• Continued dimensioning
• Baseline dimensioning (datum line) the use of a
  baseline helps to reduce the errors that compound
  with continued dimensions
• Miscellaneous notes
• Avoid superfluous dimensions
• Generally include an overall dimension and omit
  one continued dimension

Example - Continued dimensions
Example - Baseline dimensions
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Lecture 5 EGR 110 Engineering Graphics
Size and Location A good way to check a drawing
is to review each feature in the drawing to see
if the dimensions clearly show its size and
location.
Example The example below includes size and
location information for the hole. Add size and
location information for the slot.
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Lecture 5 EGR 110 Engineering Graphics
Placement of dimensions - In which view should a
dimension be placed? General Rule Place a
dimension in the view where the feature can be
most clearly seen.
Example - Add decimal inch dimensions to the
drawing shown below. When you are done, check
each feature to see if its size and location can
be determined.