Transcript Chapter 13

Chapter 13
Section Views
Objectives
• Use cutaway, or section, views as a
method for showing the features of a part
that are normally hidden when presented
on a multiview drawing
• Decide when a section view is necessary
Objectives (cont’d.)
• Decide what category of section view
should be used for particular
circumstances
• Create a desired section view such that it
adheres to accepted engineering drawing
practices
Introduction
• Multiview drawings may not be adequate to
define all features in many types of parts
– Some may be obscured
– Too many hidden lines cause confusion
• Section views reveal interior detail
A Look Inside
FIGURE 13.01. Two views
of an object (a coffee
mug) with interior detail.
A Look Inside (cont’d.)
FIGURE 13.03. Orthographic
views of the coffee mug fail to
define interior detail.
FIGURE 13.04. A multiview
drawing of the coffee mug
using hidden lines to show
interior detail.
A Look Inside (cont’d.)
FIGURE 13.05. Hypothetical
cutting of the object to reveal
interior detail.
FIGURE 13.06. A multiview drawing
of the coffee mug using section
views to show interior detail.
Full Sections
• Object is cut completely by cutting plane
perpendicular to a standard viewing plane
– Associated viewing direction
• Section views do not have to remain
aligned with adjacent orthogonal views
• Section view can have different
magnification than the view in which it was
created
Full Sections (cont’d.)
FIGURE 13.07. Creating a full
section. An object is projected
onto a viewing plane in (a). A
cutting plane orthogonal to the
viewing plane slices the object
in (b). The piece to be viewed
remains, while the other piece
is removed in (c). The
projection of the sliced object
is made on the cutting plane
in (d). The cutting plane and
image are rotated about the
section line in (e). The section
view is coplanar with the
viewing plane in (e).
Full Sections (cont’d.)
FIGURE 13.12. Multiple
sections with nonaligned
section views and different
scales.
What Happens to the Hidden
Lines?
FIGURE 13.14. The need
for many hidden lines in
the original drawing (a) is
reduced by the use of a
section view (b).
The Finer Points of Section Lines
FIGURE 13.15.
Examples of proper and
poor cross-hatching
techniques.
Offset Sections
• Modifications of full sections
• Allows multiple features, requiring multiple
section views, to be seen in a single view
• Cutting surface is not flat, but stepped
• Viewing direction indicated by arrows
Offset Sections (cont’d.)
FIGURE 13.17. Creating an
offset section. An object is
projected onto a viewing plane
in (a). A stepped cutting plane
orthogonal to the viewing plane
slices the object in (b). The
piece to be viewed remains,
while the other piece is removed
in (c). The projection of the sliced
part is made on the outermost
segment of the stepped cutting
plane in (d). The cutting plane
and image are rotated about the
section line in (e). The section
view is coplanar with the viewing
plane in (f ).
Half Sections
FIGURE 13.19. Creating a half
section. An object is projected
onto a viewing plane in (a). A
stepped cutting plane slices
through the object to the plane
of symmetry in (b). The piece
to be viewed remains, while the
other piece is removed in (c).
The image of the sliced object
is projected onto an orthogonal
viewing plane in (d). The viewing
plane and image are rotated
about the intersection line in (e).
The section view is coplanar
with the original viewing plane
in (f).
Procedures for the Creation of
Section Views
• Deciding when to use section views
– If the answer to any of the following questions
is yes if only hidden lines will be used:
• Are any hidden lines composed of multiple
segments?
• Do any hidden lines of a feature intrude into the
area occupied by another hidden feature?
• Do any hidden lines of a feature share or come
close to sharing any hidden lines with another
feature unless the lines are exactly common?
Creating a Full Section View
FIGURE 13.22. Construct a full
section view of this part. It is
desired to reveal the indicated
features (step 1).
FIGURE 13.23. Step 2: Draw
the cutting plane and the desired
viewing direction.
Creating a Full Section View
(cont’d.)
FIGURE 13.24.
Step 3: Outline
the sectioned
part based on the
adjacent view.
FIGURE 13.25.
Step 4: Identify the
intersection points
with the cutting plane
and see what is
happening on the
adjacent view.
Creating a Full Section View
(cont’d.)
FIGURE 13.26.
Step 5: Outline the
internal features
associated with the
intersection points
on the cutting plane.
FIGURE 13.27.
Continue and
outline the next
internal feature
associated with the
intersection points
on the cutting
plane.
Creating a Full Section View
(cont’d.)
FIGURE 13.28.
Continue and
outline the last
internal feature
associated with
the intersection
points on the
cutting plane.
FIGURE 13.29.
Step 6: Find the
boundaries of air
and solid and
cross-hatch the
solid areas.
Creating a Full Section View
(cont’d.)
FIGURE 13.30. Step 7: Add any
new edges that are revealed. Label
the view. Note that the former front
view may be removed since it adds
no additional information.
Creating a Half Section
• Identical to steps for creating full section
except only half of interior revealed
FIGURE 13.32. Presentation
as a half section view.
Multiple Section Views
• For complex objects, multiple section
views used
FIGURE 13.33. A complex object
requiring multiple sections. It is
desired to reveal the interior of
the indicated features (step 1).
Creating an Offset Section
• Step 1: Identify features to be revealed and
desired viewing direction
• Step 2: Draw stepped cutting plane line to
reveal desired features
• Step 3: Outline modified part in adjacent
orthogonal view
Creating an Offset Section (cont’d.)
• Step 4: Identify intersection points of
exterior and interior edges with each
segment of cutting plane
• Step 5: Outline internal features associated
with intersection points on cutting plane
Creating an Offset Section (cont’d.)
• Step 6: Find boundaries between solid and
empty space and fill solid areas with
section lines
• Step 7: Add or remove background edges
in space and remove edges in solid areas
Creating an Offset Section (cont’d.)
FIGURE 13.44. Step 2: Draw
the cutting plane and select
the desired viewing direction.
Creating a Sectioned Pictorial
FIGURE 13.50. To visualize the
sectioned part, remove the portion
that is not seen from the existing
orthogonal views.
FIGURE 13.51. For ease of visualization,
turn the former section view into the bottom
view by removing cross-hatching and
adding a section step line. Add a left view.
Creating a Sectioned Pictorial
(cont’d.)
FIGURE 13.52. Create the pictorial using the sectioned part
instead of the whole part.
Removed Sections
FIGURE 13.53. Creating a
removed section. An object is
projected into a viewing plane
in (a). The cutting plane slices
the object in (b). The image of
the intersection is removed from
the object in (c). The removed
image is initially perpendicular
to the viewing plane in (d) but
is then rotated to be parallel
to the viewing plane in (e).
The removed image is finally
projected onto the viewing
plane in (f).
Revolved Sections
FIGURE 13.56. Creating a
revolved section. An object
is projected onto a viewing
plane in (a). The cutting
plane slices the object in (b).
An image of the intersection
is removed in (c). The
intersection image is initially
perpendicular to the viewing
plane in (d) and then rotated
to be parallel to the viewing
plane in (e). The image is
projected onto the viewing
plane in (f ).
Broken-Out Sections
FIGURE 13.59. Creating a
broken-out section. The
object is projected onto a
viewing plane on (a). A
cutting plane slices through
the feature of interest (but not
the entire part) in (b). The
portion in front of the cutting
is broken out and removed in
(c). The interior details of the
feature are shown in (d). The
image of these features is
projected forward in (e) and
placed directly on the part
image in (f).
Sections of Assemblies
FIGURE 13.62. The method
for showing the assembly
of many parts.
A Few Shortcuts to Simplify Your
Life
• Small cutouts on curved surfaces
FIGURE 13.63. A permitted
shortcut for small holes and
slots in curved surfaces.
Threaded Parts
FIGURE 13.64.
A section of a
threaded part.
Thin Features
FIGURE 13.65. The conventional section (a) and
recommended variation for a thin feature (b).
Vanes, Fins, Spokes, and the Like
FIGURE 13.67. Two examples of the recommended presentation
of spoke, vanes, and fins.
Symmetry
FIGURE 13.68. The preferred presentation of symmetrical features.
Considerations for 3-D Modeling
• Section views can be created quickly and
accurately with software
• Selection of where to section object still up
to person making drawing
• Disadvantages
– Sometimes shortcuts not available
– May not allow adequate development of
spatial reasoning and mental imaging skills
Summary
• Discussed section views as a method of
looking at internal details of objects
• Discussed cutting planes and cutting plane
lines
• Described several types of section views
that can be used and the rules that must
be followed when making them