Transcript sectional views

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 0.020 or 0.030.
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-A and 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.