Section Views

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Section Views

• Engineering Graphics
• Stephen W. Crown Ph.D.

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Objective

• To demonstrate the proper use of section views
  which show internal features of objects that are
  not easily understood in standard multiview
  drawings
• To demonstrate the use of CAD tools in generating
  section views

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Outline

• Cutting Plane
• Section Lines
• Several Types of Section Drawings
• Examples of Homework Problems

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Sectioned Drawings

• Definition A multiview technical drawing that
  reveals details about internal features by
  displaying the part as if cut by an imaginary
  cutting plane
• Objective To make the drawing more
  understandable, especially the internal details
  of the part
• Since the sectioned drawing shows internal
  features there is generally no need to show
  hidden lines
• Especially helpful for assembly drawings

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The Cutting Plane

• An imaginary plane that defines where the object
  is cut
• Shown in drawing adjacent to the sectioned
  drawing
• Drawn with the PHANTOM line type
• Arrows at the end of the cutting plane line
  indicate the direction of view for the sectioned
  drawing.

• The arrows point toward the part of the object
  that is visible in the sectioned drawing.
• A sectioned drawing follows the general rules of
  any view in a multiview drawing

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The Cutting Plane

• Cutting planes may be labeled at their endpoints
  if multiple cutting plane lines are used
• When using multiple cutting planes each sectioned
  drawing is drawn as if the other cutting plane
  lines do not exist

• The cutting plane line takes precedence over
  center lines
• Occasionally cutting plane lines are not shown
  when their location is obvious

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Section Lines

• Section lines are drawn where the object passes
  through the cutting plane
• If a saw was used to cut the part then section
  lines represent the cutting marks left by the saw
  blade
• Different materials may be represented by the use
  of different section line types
• The general section line type which may be used
  for any material is the line type for iron

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Section Lines

• Section lines should not be parallel or
  perpendicular to object lines
• Section lines are generally drawn at 45 degrees
  unless this conflicts with other rules
• Section lines should be oriented at different
  angles for separate parts
• Occasionally section lines are only drawn on the
  perimeter of large areas
• Section lines are not used for thin parts rather
  they are filled in solid (Do not use closely
  spaced section lines)

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Section Drawing Types

• Full Section
• Half Section
• Assembly Section
• Offset Section
• Broken-Out Section
• Revolved Section
• Removed Section
• Special Section Conventions

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Full Section

• The cutting plane passes completely through the
  part as a single flat plane

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Half Section

• The cutting plane only passes half way through
  the part
• The other half is drawn as usual
• Hidden lines are not shown on either half of the
  part
• A center line is used to separate the two halves
• Mostly used on cylindrical parts

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Assembly Section

• Shows how parts fit together
• Different parts have different section line
  orientation
• Different materials use different section line
  types
• Standard parts (shafts, pins, dowels, rivets,
  screws, washers, gears, etc.) are not sectioned

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Assembly Section

• Cut each part of the assembly and section each
  part with the appropriate section line type
• Put the parts together in their assembled position

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Assembly Section

• The shaft is not sectioned because it is a
  standard part and section lines would provide no
  additional information
• The other two part are made from the same
  material
• The orientation of section lines clearly shows
  the location of the different parts

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Assembly Section

• The top and bottom mating part are made from
  different materials in the part shown below
• A center line is added to the shaft to show that
  it is a circular feature

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Offset Section

• The internal features of many part can not be
  shown using a single straight cut to create the
  sectioned drawing
• An offset section is used for such parts

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Offset Section

• The multiview drawing is often difficult to
  interpret when there are several hidden features
  on the object
• Look at the figure in your text and try to
  picture the part in your mind
• A sectioned view makes the object much easier to
  understand
• Use either drawing for your homework

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Offset Section

• An offset section allows the cutting plane to
  pass through all of the internal features
• There may be several bends in the cutting plane

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Offset Section

• The actual part would show a new visible line at
  the bend in the cutting plane
• Since the cutting plane bend is arbitrary, do not
  show the line representing this bend in the
  sectioned drawing

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Offset Section

• The sectioned view does not show the bend in the
  cutting plane
• Hidden lines are not shown
• Be sure to include object lines that are behind
  the cutting plane

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Broken-Out Section

• Only a portion of the view is sectioned
• A jagged break line is used to divide the
  sectioned and unsectioned portion of the drawing

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Revolved Section

• A cross section of the part is revolved 90
  degrees and superimposed on the drawing
• A jagged break line may be used to divide the
  revolved section from the rest of the drawing

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Removed Section

• Similar to the revolved section except that the
  sectioned drawing is not superimposed on the
  drawing but placed adjacent to it
• The view and the cutting plane are labeled
  (Section A-A)
• The removed section may be drawn at a different
  scale

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Special Section Conventions

• There are special rules (conventions) that are
  followed to make some parts more understandable
• Some features are rotated to their true radial
  position in sectioned views

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Special Section Conventions

• The object is difficult to understand using
  standard multiview drawings where hidden lines
  are used to represent internal features

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Special Section Conventions

• If the part is sectioned as it would actually
  appear if cut the details of the ribs and holes
  would not be clear
• Since the objective is to make the drawing easy
  to interpret the drawing is modified following
  standard conventions

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Special Section Conventions

• The cutting plane shows that the features are
  revolved to their true radial position
• Hidden features are not shown
• The sectioned drawing produced is a distorted but
  clearer picture of the object
• The section drawing appear as a full section
• The arrows show the direction of the view

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Special Section Conventions

• Ribs are not sectioned when the cutting plane
  passes through them lengthwise
• Ribs are sectioned if the cutting plane passes
  through them at other orientations

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Special Section Conventions

• The front view is replaced by a full section view
• The cutting plane shown in the top view shows the
  direction of the line of sight
• The holes and ribs have been revolved to their
  true radial position
• The ribs are not sectioned in this orientation
• The section lines are all drawn at the same angle
  since the object is one solid part

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Sectioning With Solid Models

• Slice
• cuts the solid object at the specified cutting
  plane using the current color
• breaks the objects into two parts
• one part may be deleted or moved
• Section
• creates a 2-D drawing of the section
• only draws the portion of the object that is cut
  (i.e. the portion of the object that has section
  lines)

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Sectioning With Solid Models

• SLICE command

• SECTION command

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Sectioning With AutoCAD

• Use BHATCH
• Use the correct scale
• Default line orientation is 45 degrees
• The general line type is ANSI31
• Use different line types for different materials
• Use PICK POINTS to select an internal point in
  the sectioned portion of the drawing

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Example