An orthographic projection is a 2D representation of a 3D object created by projecting the views of the object onto imaginary planes. One method to understand the standard views is to envision placing the object in a glass box, where the outside views of each side become the orthographic projections. There are six standard views - top, front, right side, left side, back, and bottom. Measurement lines are used to transfer dimensions between views. Hidden lines, centerlines, and other guidelines help clarify the 3D shape from the 2D projections.

2. Orthographic Projection
 An orthographic projection is a 2 dimensional
representation of a 3 dimensional object.

3. Six Principle Views
 Any object can be viewed
from six perpendicular
views

4. The Glass Box
 One way to understand the standard arrangement of
views on a sheet of paper is to envision the object in a
glass box
 The outside observer would see six standard views of
the object through the sides of this imaginary glass box

5. Glass Box Method
 Glass Box Method:
 The object is placed in a glass box.
 The image of the object is projected on the sides of the
box.
 The box is unfolded.
 The sides of the box are the principle views.

6. Glass Box Method
 The object is
placed in a glass
box.
 The side of the
box represent the
6 principle
planes.

7. Six Principle Views

8. Reading Isometric Sketches

9. Reading Isometric Sketches

10. Create the orthographic projections for the
following object.
The height and depth of
is equal to 3 grid squares.

11. Create the orthographic projections for the
following object.

12. Number of Required Views
 When drawing an orthographic projection you must
include the appropriate number of views to fully
describe the true shape of the part.
 You may use a fewer number of views if you can fully
describe the part in the given views.
 How many views are required to fully describe a
rectangular box?
 How many views are required to fully describe a sphere?

13. Number of Required Views
 You may use additional views, such as the left, back,
or bottom views to describe an object if the object
cannot be fully described in the three standard views.
 additional views such as section views, detail views and
auxiliary views may also be drawn to fi.

14. Measurement Transfer Between Views
 Top and Bottom
views show LENGTH
and WIDTH.
 Left and Right views
show HEIGHT and
WIDTH
 Front and Rear views
show HEIGHT and
LENGTH.
 The line (drawn at a
45° angle) is used to
transfer depth
measurements
between the top and
right side (or left
side) views.

15. Normal Plane
 Normal Planes
will appear as an
edge in two views
and a true sized
plan in the
remaining view
when using three
views such as a
top, front and
right side.

16. Inclined Plane
 Inclined Planes
will appear as an
edge view in only
one of the three
views.
 The inclined
plane will appear
as a rectangular
surface in the
other two views.

17. Oblique Planes
 Oblique Planes will
not appear as an
edge view in any of
the six views since
they are not parallel
or perpendicular to
the projection
planes.
 They always appear
as a “plane” and have
the same number of
corners in each of
the six views.

18. Foreshortened Lines
Identify the foreshortened
lines in the orthographic
projection below.

19. Curved Surfaces
 A cylinder
will appear
as a circle in
one view
and a
rectangular
shape the
other two
views.

20. Axis and Center Lines
 The axis appears
where the cylinder
appears
rectangular.
 Center marks are
used to identify
the center of the
cylinder where it
appears circular.

21. Choosing the Front View
 Considerations when choosing the front view of an
object.
 Chose the view that shows the most features or
characteristics of the object
 Choose the view that contains the least number of
hidden lines.
 Choose the view so the part is oriented with its longest
length parallel to the bottom of the drawing.

22. First- and Third-Angle Projection
 There are two main systems used for projecting and
unfolding the views:
 Third-angle projection which is used in the United
States, Canada and some other countries
 First-angle projection which is primarily used in Europe
and Asia
 You should understand both methods

23. Third-angle Projection

24. First-angle Projection

25. Hidden Lines
 An advantage of orthographic views is that each view
shows the object all the way through as if it were
transparent
 Thick dark lines represent visible features
 Dashed lines represent features that would be hidden
behind other surfaces
 When possible, choose views that show features with
visible lines

26.  Rules for drawing hidden lines.

27. Centerlines
 The centerline is used to:
 Show the axis of symmetry of a feature or part
 Indicate a path of motion
 Show the location for bolt circles or other circular
patterns
 The centerline pattern is composed of three dashes,
one long dash on each end with a short dash in the
middle

28. Centerlines

29. Precedence of Lines
 When lines coincide on a drawing the rules of
precedence are:
 Visible lines always take precedence over hidden or
centerlines
 Hidden lines take precedence over centerlines

30. Precedence of Lines

31. Putting it all together…
 Choose the front view.
 Determine the number of required views.
 Identify the scale.
 Draw visible lines for the front view.
 Project the feature to draw the top view.
 Draw the hidden lines.
 Draw the center lines and center marks.