1. Unit 3 (Sectioning) tghhhhhhhhhhhhhhhhhhh

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1. Unit 4 Sectioning

2. In engineering practice it is often required to
make drawing showing the interior details of
the object which are not visible to observer
from outside. these interior details are
shown on the drawing using hidden or
dotted lines. Therefore, to understand the
details of the complex object, sectional
orthographic Projections are used.
Further If object is made of two or more
materials, then it can be understood clearly
by sectional orthographic projections.

3. In front view there are large number of hidden lines
thus one cannot interpret the interior details in
front view. To overcome the problem complicated
objects are assumed to be cut by imaginary plane

4. After sectioning
Before sectioning

5. .
The view obtained after cutting the object in
order to reveal inner details by imaginary cutting
plane is called sectional view. CP is assumed to
be parallel to the plane on which the view is
projected

6. SECTIONING:-
The process in which object is cut by an imaginary cutting plane
passing through center line in order to show the inner detail of the
object is known as SECTIONING.
 
PURPOSE OF SECTIONING:-
To clarify the view and to show inner detail clearly by eliminating the
hidden lines.
To show the cross sectional shape.
SECTION LINES:-
These lines are used to represent the area of the object cut by the
cutting plane in a sectioned view. These are also called as hatching.
These lines are parallel to each other, equidistant & inclined at 45 deg
to horizontal.

7. TYPES OF SECTIONAL VIEWS :-
Full Sectional View
Half Sectional View
Offset Sectional View
 
Full Sectioning:-
The Process in which the object is cut by one imaginary cutting plane
passing through the center line and removing the one half portion of
the object is known as Full Sectioning. And the view so obtained is
known as Full Sectional View.
Half Sectioning:-
The Process in which the object is cut by the two imaginary cutting
planes which are at 90 deg to each other & passes through the two
center lines and removing the one fourth portion of the object is known
as half Sectioning. And the view so obtained is known as half Sectional
View.
Offset Sectioning:-
The process of cutting an object by an offset section plane (i.e.
combination of more than two cutting planes) in order to show the
maximum inner detail of the object is known as offset sectioning. The
view so obtained is known as offset sectional view.

8. Detail

9. EXAMPLE : Advantage of using a section view.

10. Terminology and
common practices

11. Cutting
plane
CUTTING PLANE
Cutting plane line
Cutting plane is a plane that imaginarily cuts
the object to reveal the internal features.
Section lines

12. Cutting plane line is an edge view of the cutting
plane used to indicate where imaginary cutting of
object has taken place
CUTTING PLANE LINE
Indicate the path
of cutting plane.

13. SECTION LINING
Section lines or cross-hatch lines are used to
indicate the surfaces that are cut by the cutting
plane.
Section
lines
Drawn with thin lines.

14. Various cutting planes or section planes
??????.
???????????? ?????? Cutting plane Parallel to profile plane.

15. Cutting plane Parallel to Principal vertical
plane

16. Cutting plane Parallel to Principal
vertical plane
When an object is cut by a plane
parallel to
Principal vertical plane then:
??????The real or true shape of the section is
observed
in F.V.
????????????Section plane will be seen as a
cutting plane line
in T.V

17. Cutting plane Parallel to Principal horizontal
plane.

18. Cutting plane Parallel to Principal horizontal plane
When an object is cut by a plane parallel to
Principal
horizontal plane then:
??????The real or true shape of the section is observed
in T.V.
??????Section plane will be seen as a cutting plane line
in F.V.

19. Thin line
CUTTING PLANE LINESTYLES
Viewing
direction
Cutting plane lines are thick
(0.7 mm) dashed lines, that
extend past the edge of the
object 6 mm and have line
segments at each end drawn
at 90 degrees and
terminated with arrows.

20. Line B-B is composed of alternating long and two short dashes,
which is one of the two standard methods.
The length of the long dashes varies according to the size of the
drawing, and is approximately 20 to 40 mm.
For a very large section view drawing, the long dashes are made
very long to save drawing time. The short dashes are
approximately 3 mm long. The open space between
the lines is approximately 1.5 mm. Capital letters are placed at
each end of the cutting plane line, for clarity or when more than
one cutting plane is used on a drawing.

21. The method used for cutting plane
lines is shown by line C-C, which is
composed of equal-length dashed lines.
Each dash is approximately 6 mm long,
with a 1.5 mm space
between.

22. SECTION LINES SYMBOLS
The section lines are different for each of
material’s type.
Cast iron,
Malleable iron
Steel Concrete Sand Wood
For practical purpose, the cast iron symbol is
used most often for any materials.

23. SECTION LINING PRACTICE
The spaces between lines may vary from 1.5 mm
for small sections to 3 mm for large sections. As a general rule, use
3mm spacing. Section lines are drawn using thin lines with h or 2h
COMMON MISTAKE

24. SECTION LINES SYMBOLS
Materials – Common
materials
The symbol for cast
iron can be used for
most section views.
Refer to any common
drafting text for
additional symbols

25. SECTION LINING
45 degree angle lines should be used.
1/8” between lines.
All lines should be uniformly spaced

26. Section Lining – Line Placement
Lines should never be parallel or
perpendicular to the object lines.
If the outline of the object has 45 degree
lines, 30 or 60 degree lines should be
used.
Assemblies with several parts should be
lined with varying angle section lines.

27. Section Lining – Line
Placement Assemblies with several parts should
be lined with varying angle section
lines.
If the outline of the object has 45 degree
lines, 30 or 60 degree lines should be
used
Lines should never be parallel or
perpendicular to the object lines

28. Hatching lines on a second part, adjacent to the first are at an angle
of 45° but in the opposite direction. Hatching lines on a third part
adjacent to first two are drawn at an angle of 30° or 60°. Sometimes
spacing or pitch of the hatching lines is varied to separate it from
the adjacent parts.

29. SECTION LINING PRACTICE
It should not be drawn parallel or perpendicular
to contour of the view.
COMMON MISTAKE

30. Sectioning rule for machine elements like :
Ribs, rivets, webs, shafts, pins, nuts, bolts,
washers, keys and cotter.
Whenever, the cutting plane is passing through
above machine elements and if cutting plane
contains the axis of above machine elements,
then they are not sectioned.

31. TREATMENT OF HIDDEN LINES
Hidden lines are normally omitted from section
views.

32. Kinds of Sections

33. KIND OF SECTIONS
1. Full section
2. Offset section
3. Half section

34. FULL SECTION VIEW
The view is made by passing the straight cutting
plane completely through the part.

35. OFFSET SECTION VIEW
The cutting plane is off-set to
include features that are not in a
straight line.
It is possible for the cutting
plane to change directions, to
minimise on the number of
sectional views required to
capture the necessary details.

36. OFFSET SECTION VIEW
The view is made by passing the bended cutting
plane completely through the part.
Do not show the edge views
of the cutting plane.

37. OFFSET SECTION VIEW

38. HALF SECTION VIEW
The view is made by passing the cutting plane halfway
through an object and remove a quarter of it.

39. HALF SECTION VIEW
A center line is used to separate the sectioned half
from the unsectioned half of the view.
Hidden line is omitted in unsection half of the view.

42. HALF SECTION VIEW
A half-section is a view of an object showing
one-half of the view in section.
Symmetrical parts can be shown in half sections.
Half section without
hidden lines

43. HALF SECTION VIEW
Half sections are commonly used to show both
the internal and outside view of symmetrical
objects.

44. EXAMPLE : Comparison among several section techniques