engineering Drawing

1. Conventional practices for orthographic and sectional views
 Convention is a commonly accepted practices which disregard some strict rules of orthographic projection.

2. PURPOSES
 To improve the clarity of a drawing.
 To facilitate the dimensioning.
 To reduce the drafting effort.
 To save or efficiently use a drawing space.
CONVENTION PRACTICE FOR ORTHOGRAPHIC VIEWS
1. Incompleted views
• Incompleted side view
• Partial view
• Half view
• Local view
Incompleted side views are side views that are eliminated a feature
that can not clearly seen from a selected viewing direction.

3. Principal view
Difficult to read and to dimension.
Left-side view Right-side view
Details are interfered by those
on the opposite view.
Example : Strictly orthographic projection.

4. Example : Incompleted side views
Incompleted
left-side view
Incompleted
right-side view
Principal view
Better describe an object and
facilitate dimensioning.

5. Partial view is a view that represents portions of the part that
have a features need to clarify.
Half view is a partial view that is illustrated only half of the part.
Local view is a view that shows only features need to clarify.

6. Clearly seen
a shape.
Example : Partial view

7. Symmetry symbol
Left half Right half
Thin line
(4H)
Center line acts as a
line of symmetry.
No continuous line !
Example : Half view

8. Half view can be made by drawing the views
slightly beyond the line of symmetry.
No symmetry
symbol.
It is allow for writing
a break line.
In this course, we
omit the break line.
Example : Half view : alternative representation
Thin line
(4H)

9. Example : Half view : two symmetry axes

10. Example : Local view
Shape of the
slot is completely
shown.
R6
7
Easy for
dimensioning

11. 2. Align view
Align view is a view that is drawn by
imaginarily rotating the object’s features,
appeared in a principle view about
symmetry axis.

12. Example : Necessity of align view
Waste of time
Confuse
Apply
convention
Clear
Strictly Projection

13. CONVENTION PRACTICE
For an object that has symmetrical positioned
features, it is advisable to show them on adjacent
view in true size at true radial distance from the
symmetry axis.

14. Example : Align view of holes
Gives the impression that there
is a hole at the center of the plate.
Given
Apply
aligned
convention

15. Example : Align view of holes
Given
Gives the impression that holes
are at unsymmetrical position.
Apply
aligned
convention

16. Example : Align view of holes
Apply
aligned
convention

17. TERMINOLOGY
Rib and Web are thin, flat feature of an object that acts
as a structural support.
Rib Rib
Web

18. Rim
Spoke is the rod radiating from the hub to the rim of a
wheel.
Spoke
Spoke
Rim
Hub
TERMINOLOGY
Hub

19. Lug is an ear which is built as portion of an object for
attachment.
TERMINOLOGY

20. Lug is an ear which is built as portion of an object for
attachment.
TERMINOLOGY

21. Example :
Example : Align view of ribs
Apply
aligned
convention

22. Example : Align view of ribs & holes
Apply
aligned
convention

23. Example : Align view of ribs & holes & keyway
Make Orthographic Projection
Apply Convention

24. 3. NON-EXISTING LINE OF INTERSECTION
Non-existing line of intersection is the line of intersecting surfaces that are eliminated
by fillets and rounds.
Example of a non-filleted pole (left) and a filleted pole (right)
Conventional practice
When true projection mislead the representation of an
object, it is necessary to show the additional lines that
are projected from the actual intersection of the
surfaces as if the fillets and rounds were not present.

25. Example : Non-existing line of intersection
Object does not has
rounds and fillets
Edges of the surfaces
are shown as lines in
the top view.

26. Example : Non-existing line of intersection
The view looks like a plate
with a hole !!
Object has
rounds and fillets
No edge !
(No intersection between surfaces)
Convention practice required !
Construct a non-existing line of
intersection.

27. Example : Non-existing line of intersection

28. 4. INTERSECTION BETWEEN
FILLET AND ROUND
Runout

29. Tangent point
TO DRAW A RUNOUT
about 1/8 of circle
R
R/3
R = radius of fillet or round
R

30. HOLE IN CYLINDER
Large hole : True projection

31. HOLE IN CYLINDER
Large hole : True projection Small hole : Convention

32. Auxiliary view
Auxiliary view is needed when it is desirable to show the
true size and shape of a surface that is not parallel to
anyone of the principal planes of projection.
True size can not be observed
from these principal views.

33. Use of auxiliary view
In practice, an auxiliary view is usually a partial view
showing only the desired information.
Example
d
d
d
d
Complete view Partial view

34. Types of an auxiliary view
Primary auxiliary views may be classified into 3 types
by their relative to the principal views.
1. Adjacent to front view
2. Adjacent to top view
3. Adjacent to side view

35. Width & Height
&
True length
of edge view
Width
&
Depth
Height
&
Depth
Auxiliary view adjacent to front view
Glass box and revolution View arrangement
True size
of an inclined plane

36. Example 1
Do you remember?
Depth dimension of the auxiliary view
can be read from top view or side view.
Auxiliary
plane

37. Hidden lines of the holes
are omitted for clarity.
Start
Reference
line
A
C
D B
Prefer
distance
A
B
C
D
Example 2

38. Width
&
Height
Height
&
Depth
Auxiliary view adjacent to top view
Glass box and revolution
Width & Depth
&
True length
of edge view
True size
of an inclined plane
View arrangement

39. Width
&
Height
Auxiliary view adjacent to side view
Glass box and revolution
Width
&
Depth
True size
of an
inclined plane
View arrangement
Height & Depth
&
True length
of edge view

40. Example 4
Reference
line
Start
Prefer
distance
A
B
C
A
B
C

41. CONVENTIONAL PRACTICES IN SECTIONAL VIEWS
Omit the section lines on the section view of
 Rib, Web and Lug, if the cutting plane is
passed flatwise through.
 Spoke, if the cutting plane is passed longwise
through.

42. EXAMPLE : RIB
Normal multiview drawing
Normal section view
Section view drawing with
convention

43. EXAMPLE : WEB : flatwise cut
Normal multiview drawing
Normal section view
Section view drawing with
convention

44. EXAMPLE : WEB : crosswise cut

45. EXAMPLE : WEB : multiple section view

46. EXAMPLE : SPOKE
Misleading impression

47. EXAMPLE : LUG

48. Aligned Section

49. DEFINITION
Aligned section is a section view that is drawn
by imaginary rotating the object’s features
appeared in a principal view about symmetry
axis

50. Example : Hole
Gives the impression that this holes
are at unsymmetrical position.

51. Example : Hole

52. Example : Rib

53. Example : Ribs & Holes

54. Example : Aligned section of keyway
Example : Spoke & Keyway

55. Example : Lug

56. Conventional Break

57. CONVENTIONAL PRACTICE
For long objects that have to draw in a small scale to
fit them on the paper, it is recommended to remove
its long portion (which contains no important
information) and draw the break lines at the broken
ends.

58. SCALE 1:1
Example

59. Example
SCALE 2:1

60. STANDARD BREAK LINES
Rectangular
cross section
Wood
Metal
Cylindrical
cross section
Tubular
cross section

61. TO DRAW CYLINDRICAL BREAK
R
R/3 R/3
30o
30o

62. 800
TO DIMENSION A BROKEN PART
Typical
dimensioning
method
f16
not to scale dimensions
f16
800

63. Broken Section
 In some objects when some important interior detail must be shown, but due to the important exterior features, that
has to be shown, a full or half section is not feasible, showing a broken section is used as an alternative
 The view is made by passing the cutting plane normal to the viewing direction and removing the portion of an object
in front of it.

71. OFFSET SECTIONS
In sectioning complex objects, it is often desirable to show features that do not lie in a
straight line by “offsetting” or bending the cutting plane. These are called offset sections.
Note the offset cutting plane line

72. ALIGNED SECTIONS
When parts with angled elements are sectioned, the cutting plane may be
bent to pass through those features. The plane and features are then
imagined to be revolved into the original plane.
Aligned Section
The angle of revolution should
always be less than 90° for
an aligned section.

73. ASSEMBLY SECTIONS
Section views are often used to create assembly drawings.
Notice that the hatching on different parts has different
hatch patterns or hatch at different angles. When used on
the same part, the hatching is always at the same angle
to help you recognize the parts easily.
 The purpose of an assembly section is to reveal the interior of a machine or structure so that the
separate parts can be clearly shown and identified. However, the separate parts do not need to be
completely described.