sectional views section views
DESCRIPTION
Section Views Often there is a need to show interiors that cannot be illustrated clearly by hidden lines. Interiors are shown by slicing through the object resulting in a cutaway view of the part. Cutaway views are called sectional views, cross sections, or simply sections.TRANSCRIPT
Sectional Views Section Views Section Views Often there is a
need to show interiors that cannot be illustrated clearly by hidden
lines. Interiors are shown by slicing through the object resulting
in a cutaway view of the part. Cutaway views are called sectional
views, cross sections, or simply sections. Section Views To produce
a section view a cutting plane is passed through the part (figure
a). The cutting plane is removed and the two halves are drawn apart
(figure b) exposing the interior detail. Section Views A section
view obtained by passing the cutting plane fully through the object
is called a full section. In the front view the cutting plane
appears as a line called a cutting-plane line.The arrows at the
ends of the cutting-plane line indicate the direction of sight for
the section view. To obtain the section view the right half of the
front view is only imagined to be removed.The cross-hatched areas
of the section view are those portions that are in actual contact
with the cutting plane. Section Views A correct front view and
section view are shown in figure (a) and figure (b).All visible
edges and contours behind the cutting plane should be shown.
Section views are used primarily to replace hidden lines so as a
rule hidden lines should be omitted in section views (figure d). A
section-lined area is always completely bounded by a visible
outline, never by a hidden line as in figure (e). Section lines in
a section view must be parallel and at the same angle and direction
(figure f). Section Views Sectioning lining symbols can be used to
indicate specific materials.These symbols represent general
material types. Because there are so many different types of
materials the general purpose cast iron symbol can be used for all
materials. Section Views The correct method of drawing section
lines is shown in figure (a).Section lines are drawn thin and at an
angle of 45 degrees unless there is some advantage in using a
different angle.Section lines are spaced evenly approximately 1/16
to 1/8 or more depending on the sectioned area.As a rule, are
spaced generously as possible and yet close enough to distinguish
clearly the sectioned area. Section Views If section lines drawn at
45 degrees would result in being parallel or perpendicular to a
visible object line the angle should be changed to 30 degrees, 60
degrees, or some other angle. Section Views The cutting plane is
indicated in a view adjacent to the sectional view.In this view the
cutting plane appears edgewise as a line called a cutting-plane
line. Section Views There are two styles of cutting-plane
lines.
The cutting-plane line in figure (a) is composed of equal dashes
approximately 1/4 long with arrowheads indicating the direction of
sight.For CAD drawings use the line type HIDDEN. The cutting-plane
line in figure (b) is composed of alternate long dashes and pairs
of short dashes plus arrowheads indicating the direction of
sight.For CAD drawings use the line type PHANTOM2. Cutting-plane
lines are drawn as thick as a visible object line or thicker.For
CAD drawings set the line weight to either or Section Views Correct
and incorrect relations between cutting-plane lines and
corresponding section views. Section Views Visualizing a
Section:
Two views of an object to be sectioned are shown (figure a).It has
a drilled and counterbored hole.The cutting plane is assumed to
pass through the horizontal center line in the top view. The
corresponding section view shown in figure (c) is incomplete
because certain visible lines are missing. If the section view is
viewed in the direction of sight shown in figure (b) the arcs A,B,C
and D will be visible and appear as straight lines as shown in
figure (d). Section Views Half Sections:
If a cutting plane passes halfway through an object the result is a
half section (figure a).The half section has the advantage of
showing the interior of one half of the object and the exterior of
the other half (figure b). Note the cutting-plane line.Only one
arrowhead is used to show the direction of sight. Hidden lines
should be omitted from both halves of a half section view. A center
line is used to separate the halves of the half section view.
Section Views Broken-Out Sections:
Often only a partial section of a view is needed to expose interior
shapes.Such a section, limited by an irregular break line is called
a broken-out section. Section Views Revolved Sections:
The shape of a cross section of an object may be shown in the
longitudinal view by means of a revolved section. Revolved sections
are made by assuming a plane perpendicular to the center line or
axis of the object and then revolving the plane 90 degrees about a
center line at right angles to the axis. Section Views Removed
Sections:
A removed section is a section view that is not in direct
projection from the view containing the cutting plane. Removed
sections should be labeled Section A-Aand Section B-B,
corresponding to the letters at the ends of the cutting-plane line.
Removed sections should be arranged in alphabetical order from left
to right on the drawing sheet Section Views Offset Sections:
In sectioning through an irregular object it is often desirable to
show features that do not lie in a straight line by offsetting or
bending the cutting plane.Such a section is called an offset
section. The offsets or bends in the cutting plane are all 90
degrees and are never shown in the section view. Section Views Ribs
in Sections:
To avoid a false impression of thickness and solidity, ribs, webs,
gear teeth, and other similar flat features are not section lined
even though the cutting plane passes through the feature. In the
example the cutting plane A-A passes through the vertical rib or
web but the rib or web is not section lined (figure a). Figure (b)
is incorrect because it gives a false impression of thickness or
solidity. Section Views Aligned Sections:
To include in a section view certain angled elements, the cutting
plane may be bent to pass through those features. The plane and
features are imagined to be revolved into the original plane. In
the example the cutting plane is bent to pass through the angled
arm and then revolved to a vertical position (aligned) from where
it is projected across to the section view.