Orthographic Projection

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Orthographic Projection
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The Stereoscopic Effect(Understanding
Perspective Illusion)
(Understanding Orthographics)
Angle approaches 0 at Infinity
Distance Infinity
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Orthographic Projection

• a system of drawing views of an object using
  perpendicular projectors from the object to a
  plane of projection

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Projection of an Object
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Third Angle Projection

• Imagine that the walls of the box are hinged and
  unfold the views outward around the front view.
• This will give you the standard arrangement of
  views for 3rd Angle Projection which is used in
  the US, Canada, and some other countries.

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Unfolding the Glass Boxwith Third Angle
Projection
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First Angle Projection

• Imagine that the walls of the box are hinged and
  unfold the views outward around the back view.
• This will give you the standard arrangement of
  views for 1st Angle Projection which is used in
  Europe, Asia, and Africa.

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Unfolding the Glass Boxwith First Angle
Projection
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The Six Basic Views
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Position of Side Views
An alternative position for the side view
is rotated and aligned with the top view.
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Necessary Views
A sketch or drawing should only contain the views
needed to clearly and completely describe the
object. Choose the views that show the shape most
clearly, have the fewest hidden lines, and show
the object in a usual, stable, or operating
position.
One view drawing of a shim
One view drawing of a connecting rod
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Eliminating Unnecessary Views

• Show only the views needed drawing to fully
  define the shape of the object.
• Choose the views which show the shapes of the
  features clearly.
• The right side view is preferred to the left side
  view if they show the object equally well the
  top view is preferred to the bottom view if they
  show the object equally well.
• Showing only the necessary views saves time,
  makes the drawing less cluttered, and makes it
  easier to interpret.

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Partial Views
When the entire view is not necessary to show the
object clearly you can use a partial view. Use a
break line to limit the partial view as shown in
(a) below. For symmetrical parts, you can draw a
half-view on one side of the centerline as shown
in (c).
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Terminology Surface Types
Normal Surface. A surface that is parallel to
one of the principal planes of reference and
perpendicular to the other two.
Inclined or Auxiliary Surface. A surface that
skews two of the principal planes of reference
and is perpendicular to the other one.
Oblique Surface. A surface that skews all three
principal planes of reference.
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Terminology
True Surface or Edge. An edge or surface that
projects onto a principal reference plane with no
difference between its actual length or area
with its projected length or area.
Foreshortened Surface or Edge. An edge or
surface that projects onto a principal reference
plane smaller than its projected length or area.
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Terminology
Auxiliary View. A supplemental view which which
may or may not be parallel to a principal plane
of reference. The view is positioned outside of
the object looking on it.
Sectional View. A supplemental view which which
may or may not be parallel to a principal plane
of reference. The view is positioned inside of
the object looking out from it.
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Line Typesand Weights
Visible Line Hidden Line Section Line Center
Line Dimension Line, Extension Lines Cutting
Lines or Viewing Lines Short Break Lines Long
Break Lines Phantom Lines Stitch Lines Chain
Line

• Line patterns communicate what the line
  represents in the drawing
• Line patterns tell you information such as
  whether the line is hidden, visible, or a
  centerline

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The Point Projection Method
1. Visualize a glass box that surrounds the
object to be drawn and orient it to the desired
axis of reference. 2. Project implicit and
virtual points from one view of the object
perpendicularly into the corresponding
glass surface (picture plane).
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3. Assuming that the intersection line of two
adjacent surfaces of the glass box operates like
a hinge, visualize unfolding it and placing the
views on paper.
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4. Align and orient the views that are adjacent
to the front view you have chosen an equal
distance from the hinge axis. The hinge axis
is the imaginary line of intersection between the
adjacent projection plane surfaces. They are
called Folding Lines.
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In-Class Example
1. Which scale should be used to draw projection
views on engineering graph paper. Each square
unit on the graph paper should represent how many
inches? 2. Which plane projection should be
chosen as the front view of the orthographic
drawing? 3. How many inclined surfaces are
seen on the object? Oblique surfaces? 4. Which
surfaces will appear foreshortened in any one of
the projected views? 5. Using engineering graph
paper, scales, and appropriate drawing utensils,
sketch the three principle orthographic views
using third angle projection techniques. Some
unseen dimensions may be derived through
trigonometry.
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• Step 1.
• Divide paper into quarter sections by
• separating each quadrant with a phantom
• (fold) line.

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• Step 2.
• Determine which projection plane is to be used
• as the front view and sketch all projected normal
  surfaces
• first. Trigonometry may be needed to calculate
  the
• edge lengths for all inclined and oblique
  surfaces.

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• Step 3.
• From each vertex established in the front view,
  very
• lightly sketch perpendicular construction lines
  into
• each adjacent quadrant.

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• Step 4.
• Box in adjacent view parameters by using a
  compass
• or divider to transfer depth measurements. To
  transfer
• depth measurements between diagonal views, a
  miter
• line is drawn from the intersection of the fold
  lines.
• Construction lines are then routed from those
  depth
• points skewing the miter line at an angle of 45
  and
• again into the diagonal view.

B
A
A
B
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• Step 5.
• Transfer all depth measurements and identify all
• vertices in each view.

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• Step 6.
• Erase all construction, miter, and fold lines.

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Orthographic Projection 3rd View Derivation
Create the right side view off of the front of
the object below
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1. Analyze Surface Types to ascertain how they
will appear in the view to be derived. Surface
s A, B, and C Type-Normal, Parallel to XY
plane, Will appear as edges in top and
right-side view. Surfaces D, E, and F
Type-Normal, Parallel to XZ plane, Will appear
as edges in front and right side-view. Surface
G Type-Inclined, Skews the YZ and XZ planes
and is perpendicular to the XY plane, Will
appear as foreshortened surface in right side
view.
D
G
E
F
A
B
C
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2. Draw fold lines and miter line
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3. Draw construction lines from the vertices in
each view into the view to be derived.
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4. While keeping track of all visible surfaces
and edges, begin labeling each visible vertex
one at a time. Follow the construction line from
each into the view to be derived. The point of
intersection of the construction lines locates
that vertex in the derived view.
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5. Continue labeling all vertices to include
both visible and hidden corners. Follow
the construction lines to locate each in the view
to be derived.
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6. The labeled points dictate the limits to
which a specified edge is perceived in
the derived view. Having identified all the
surface types, sketch between the points
to depict the bounds of all edges and surfaces.
Knowing the definitions of each surface type
helps here.
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7. Erase all labels, fold lines, construction
lines, and notes to show the complete orthographic
drawing.
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Example (Fig 5.66, Problem 11, pg 149)
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Example (cont)
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Example (cont)
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Example (cont)
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Projecting Holes on Inclined Surfaces
Example
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Projecting Holes on Inclined Surfaces
Example (cont)
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Projecting Holes on Inclined Surfaces
Example (cont)
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