1. ENS 207 engineering graphics
Lecture 4: Orthographic projections, Multiview drawing

2. PROJECTION THEORY
The projection theory is used to graphically represent
3-D objects on 2-D media (paper, computer screen).
The projection theory is based on two variables:
1) Line of sight
2) Plane of projection (image plane or picture plane)

3. MEANING Orthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane

4. Line of sight is an imaginary ray of light between an
observer’s eye and an object.
There are 2 types of LOS :
parallel
and
converge
Parallel projection
Perspective projection
Line of sight
Line of sight

5. Which Views to Present? General Guidelines
Pick a Front View that is most descriptive of object
Normally the longest dimension is chosen as the width (or depth)
Most common combination of views is to use: Front, Top, and Side View
Views other than the Principal Views are called Auxiliary Views
Pick the views which will help in describing the object with highest clarity.
Explain what is an auxiliary view. Explain that they are drawn to show specific features that are not clear in the Principal views.

8. AU 2005 The Idea is to have them take an object from the table.
Declare front. FRONT View is the MOST DESCRIPTIVE VIEW OF THE OBJECT. The view that gives MORE INFORMATION ABOUT THE OBJECT.
Rotate 90 degrees “up” to get top view.
Rotate Back.
Rotate 90 degrees clockwise to get right side.
This give three principal views commonly used.
AU 2005

9. Methods of Drawing Orthographic Projections
First Angle Projections Method
Here views are drawn
by placing object
in 1st Quadrant
( Fv above X-y, Tv below X-y )
Third Angle Projections Method
Here views are drawn
by placing object
in 3rd Quadrant.
( Tv above X-y, Fv below X-y ) FV TV X Y X Y G L TV FV

13. Conventional Orthographic Views
Height
Depth
Width
Front View
Top View
Right Side View
Note that the views are placed and aligned in the manner shown in the diagram. Remind the students that they have to follow the above convention for all their home work problems and exam problems.
It is very important to maintain the alignment and correct placement relative to each other.
Means line for top (and bottom) is straight across for both front view and right side view for example.
Same thing between front and top for sides.
Note : The following can be seen from the slide:
Top View and front view have the same width
Front View and Right / Left side view have the same height.
The depth of Top view is same as the width of right/ left side view.
AU 2005

14. Step 1 – Lightly Block Three Views
Use very light lines for drawing in the construction lines
Instructor:
Construction lines are to be drawn lightly, gray vs. black, so that they will not reproduce on a Xerox machine and therefore do not have to be erased.
AU 2005

15. S.V. F.V. ORTHOGRAPHIC PROJECTIONS x y PICTORIAL PRESENTATION IS GIVEN
FOR T.V.
S.V.
F.V.
ORTHOGRAPHIC PROJECTIONS
FRONT VIEW
L.H.SIDE VIEW
FOR F.V.
FOR S.V. x y
PICTORIAL PRESENTATION IS GIVEN
DRAW THREE VIEWS OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD
TOP VIEW

16. S.V. F.V. FOR T.V. ORTHOGRAPHIC PROJECTIONS X Y FOR F.V. FOR S.V.
FRONT VIEW
L.H.SIDE VIEW X Y
FOR F.V.
FOR S.V.
TOP VIEW
PICTORIAL PRESENTATION IS GIVEN
DRAW THREE VIEWS OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD

17. S.V. F.V. FOR T.V. ORTHOGRAPHIC PROJECTIONS X Y FOR S.V. FOR F.V.
FRONT VIEW
L.H.SIDE VIEW X Y
FOR S.V.
FOR F.V.
TOP VIEW
PICTORIAL PRESENTATION IS GIVEN
DRAW THREE VIEWS OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD

18. ORTHOGRAPHIC PROJECTIONS
FOR T.V.
ORTHOGRAPHIC PROJECTIONS
FRONT VIEW
L.H.SIDE VIEW X Y
FOR F.V.
FOR S.V.
TOP VIEW
PICTORIAL PRESENTATION IS GIVEN
DRAW THREE VIEWS OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD

19. ORTHOGRAPHIC PROJECTIONS
FOR T.V.
ORTHOGRAPHIC PROJECTIONS O
450 X FV Y 30 40 TV
30 D 40 15
FOR F.V.
PICTORIAL PRESENTATION IS GIVEN
DRAW FV AND TV OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD

20. PICTORIAL PRESENTATION IS GIVEN DRAW FV AND TV OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD
ORTHOGRAPHIC PROJECTIONS 10 30 50 35 FV X Y
RECT.
SLOT
FOR T.V. O
20 D
30 D
60 D TV
FOR F.V.
TOP VIEW

21. HIDDEN LINES
Hidden lines are used to represent surfaces that are not directly visible in an orthographic view.

22. SLANTED SURFACES
Slanted surfaces are surfaces that are not parallel to either the horizontal or vertical axis.

23. PROJECTION BETWEEN VIEWS

24. COMPOUND LINES A compound line is formed when two slanted surfaces
intersect. The true length of a compound line is not shown in the front, top, or side views.

25. OBLIQUE SURFACES
Oblique surfaces are surfaces that do not appear correctly shaped in the front, top, or side views

26. ROUNDED SURFACES
Rounded surfaces are surfaces that have constant radii,
such as arcs or circles. Surfaces that do not have constant
radii are classified as irregular surfaces