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Lecture 2:2-D Transformation
and Projection
Multi-view Drawing
1PTT 105/3 Engineering Graphicss
Outline Projection Theory Multi-view Projection Principle views & View placement Projection angle Detail drawing: 1view, 2 view, 3
view drawing Creating multi-view drawing View Selection Line convention
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Projection Theory
Engineering and technical graphics are depend on projection methods.
Two methods commonly used:a) Parallel: object positioned
at infinity & viewed from multiple points on an imaginary line, parallel to the object.
b) Perspective: object positioned at finite distance & viewed from a single point. 3PTT 105/3 Engineering Graphicss
Projection theory comprises of principles used to
graphically represent 3D objects on 2D media based on 2
variables:
i. Line of Sight (LOS): an imaginary ray of light
between an observer’s eye and an object.
• Parallel- all LOS are parallel
• Perspective- all LOS start at a point.
ii. Plane of projection: an imaginary flat plane where
the image created by LOS is projected.
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Orthographic Projection
A parallel projection technique
The projection plane is placed between observer and object.
The projection plane is also perpendicular to the parallel line of sight.
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Multi-view projection
Multi-view projection is an orthographic projection for which the object is behind the plane of projection.
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Multi-view drawingsi. Employ multi-view projection techniqueii. Generally 3 views of an object are
drawniii. Each view is a 2D flat image
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Example: Multi-view Projection
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Multi-view Lines
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Multi-view: Planes
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Multi-view: Planes
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Multi-view: 6 Principle Views
The 6 principle views are the six mutually perpendicular views that are produced by six perpendicular planes of projection.
Image an object is suspended in a glass box, the 6 sides become projection plane showing the six views.
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The views are laid flat by “unfolding the glass box”
This forms the basis of two important multi-view drawing standard:a) Alignment of viewsb) Fold lines
Top and bottom views are all aligned vertically & share the same height with dim.
Rear, left, front and right side are aligned horizontally & share same height with dim.
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Fold lines are imaginary hinged edges of the glass boxi. The fold line between
the top & front views is labeled H/F
ii. The distance from a point in front view to the H/F is the same as the distance from the corresponding point in the top view to the H/F fold line.
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View Placement
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View Placement
The arrangement of views may vary as shown, where the top view is considered the central view.
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Angle Projection
There are two standard arrangement of all six views of an objecti. First-angle projectionii. Third-angle projection
Each uses different symbol The names are derived from the method
used to view the object being drawn
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In 1st angle projection, the object is placed in the first quadrant. In 3rd angle projection, the object is placed in
third quadrant.
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Rules:
Symbols
1st angle projection
3rd angle projection
View from above is placed underneath
View from above is placed above
View from below is placed above
View from below is placed below
View from left is placed on right
View from left is placed on left
View from right is placed on left
View from right is placed on right
(a) 1st angle projection (b) 3rd angle projection
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Example: 1st and 3rd angle view projection
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1, 2 and 3 view drawing
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Step in creating multi-view drawing
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Before start drawing, produce sketch on rough paperi. Decide on front view
and projection angleii. Obtain the overall
width, height and depthiii. Place the views (in
block)iv. Determine approximate
space between the views
v. Sketch the component, place dimensions
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Creating 3-view drawing
1. Draw border/frame, title block, etc.
Draw border, title block Locating the view
i. should be approx. in centre
ii. distance between view = total length available
– view length / 3
Drawing projection lines
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Creating 3-view drawing
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Creating 3-view drawing
2. Light construction of the
views
Draw light/thin horizontal & vertical lines accordingly for front view
Draw center lines and hidden lines as final
Draw top (or side) view Project top view (or side) from
front view using thin, light construction line
Draw side (or top) view Project side view (or top) from
front view and top (or side) view All arcs and circles should be
lined (final) at this stage 26PTT 105/3 Engineering Graphicss
Creating 3-view drawing
3. Lining in of the views
To darken all visible edges (lines that represent a hard edge)
Done using thick, black pencil (0.5mm, 2B)
Should be done systematically for 3 views
Start with horizontal line at the top of the top/plan view, working down the page using T-square
From left hand side, working across the page, line in all vertical lines, using T-square and set square
Projection lines may be left on the drawing if they are light
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Creating 3-view drawing
4. Write dimensioning, notes, annotation, etc.Be aware of redundant dimensioning
5. Complete drawing by writing the rest of title block, parts list & revision table, and others
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View Selection
4 basic decisions:
1. Determine the best position. The object must be positioned such a way that the surface of major features are either perpendicular or parallel to glass planes
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View Selection
2. Define the front view. Should show the object in natural state and show most
features
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View Selection
3. Determine the minimum number of views needed to completely describe the object.
4. Determine other views that fewest number of hidden lines
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Line Convention
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Line Convention
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THANK YOU…
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