EGR 277

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Lecture 7 EGR 110 Engineering Graphics
Reading Assignment Ch. J in Engineering
Graphics Workbook, Series 1.2 or Series
2 Sketching Assignment Sketching Assignment 6
Sectional Views   Standard Orthographic Views -
Using standard orthographic planes of projection
(top, front, side views, etc.) it is difficult to
illustrate internal features in an object and
many confusing hidden lines may be
needed.   Sectional Views (also called sections
or cross-sections) - A sectional view is a view
using a plane (called a cutting-plane) that cuts
through the object to create a view that reveals
internal features.
Full Section A full sectional view represents
what you might see if a saw was used to cut an
object in half and the front half was discarded.
Reference Engineering Graphics Workbook, Series
1, p. J-1
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Lecture 7 EGR 110 Engineering Graphics
Creating a section view 1) A cutting plane
passes through the object, cutting the object in
half (for a full section) 2) Remove the cutting
place and pull the two halves apart 3) Discard
the front half. Add section lines to indicate
where material was cut by the cutting plane.
Reference Engineering Graphics Workbook, Series
1, p. J-2
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Lecture 7 EGR 110 Engineering Graphics
Add additional visible lines as needed to
represent the back edges of the half cylinders.
Cutting-plane lines are used in a view adjacent
to the sectioned view to show the location of the
cut and includes arrow indicating the direction
of sight for the sectioned view.
Imagine where the material was cut by the cutting
plane. Sketch these areas and fill them with
section lines. Add center lines as needed.
Reference Engineering Graphics Workbook, Series
1, p. J-2
4
Lecture 7 EGR 110 Engineering Graphics
Two new types of lines are introduced with
sections Section lines Section lines are used
over the surface of all areas that are in contact
with the cutting plane. If you envision cutting
the object in half, then section lines appear
over all surfaces that were cut. Example Section
lines inside a rectangular area         Cutting
plane line A cutting plane line is used to show
the edge view (EV) of the cutting plane. It is
always shown in a view that is adjacent to the
sectioned view. Arrows are included on the ends
of the cutting plane lines to indicate the line
of sight.
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Lecture 7 EGR 110 Engineering Graphics

• 3 primary types of sectional views (briefly
  discuss each)
• full section the cutting plane passes entirely
  through the object
• half section the cutting place only passes half
  way through an object (so one half of a view will
  the sectioned and the other half will not)
• broken-out section an irregular cut is used to
  expose certain internal features

Note Hidden lines are generally omitted from
the sectioned view when using full sections.
Example Sketch a simple block of wood that has
a counterbored hole. Draw the top view and the
front view in full section. Include the
cutting-plane line.
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Lecture 7 EGR 110 Engineering Graphics
Rules for cutting-plane lines 1) Cutting-plane
lines have precedence over other line types (such
as visible, hidden, and center lines). 2) A
cutting-plane line should be used in a view that
is adjacent to the sectioned view. The
cutting-plane line represents the edge-view (EV)
of the plane that cuts the object to form the
section. 3) The arrow(s) on the cutting-plane
line represent the direction of sight.
Rules for section lines 1) Section lines are
thin, dark, parallel lines that fill an area cut
by the cutting plane. 2) Section lines should be
at the same angle for all sectioned areas made of
the same material.
Example Show correct and incorrect section
lines in the figures below.
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Lecture 7 EGR 110 Engineering Graphics
Rules for section lines (continued) 3) There are
different types of section lines for different
types of materials. If no material is specified,
ANSI-31 is often used as a default.
Example Section lines for various types of
materials are shown below.
Reference Engineering Graphics Workbook, Series
1, p. J-3
8
Lecture 7 EGR 110 Engineering Graphics
Rules for section lines (continued) 4) Different
section line angles are often used for different
materials.
Example The top area is cast iron and the
bottom area is brass. Show correct and incorrect
section lines in the figures below.
Example Section lines for various types of
materials are shown below. Note that different
angles are used since the materials are adjacent.
Reference Engineering Graphics Workbook, Series
1, p. J-3
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Lecture 7 EGR 110 Engineering Graphics
Rules for section lines (continued) 5) Avoid
section lines that are parallel or perpendicular
to visible lines in the object.
Example Show correct and incorrect section
lines in the figures below.
6) Sectioned areas are always completely bounded
by visible lines.
Example Show correct and incorrect sectioned
areas.
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Lecture 7 EGR 110 Engineering Graphics
Sectioned Pictorials Sectioned objects are
sometimes illustrated using pictorials
(isometrics, typically). Several of the homework
problems in this chapter require sectioned
isometrics.
Example
Reference Engineering Graphics Workbook, Series
1, p. J-9
11
Lecture 7 EGR 110 Engineering Graphics
Example Draw the top view and the front view in
full section. Also sketch a sectioned pictorial
(isometric) of the object.