Sectional Views - Mechanical Engineering · © 2011 Pearson Higher Education, 2 Upper Saddle River,...

transcript

C H A P T E R 62

Sectional Views

Engineering Graphics with AutoCAD 2011, 1/e James Bethune

Sectional views Sectional views are used in technical drawing to expose internal

surfaces. They serve to present additional orthographic views of surfaces

that appear as hidden lines in the standard front, top, and side

orthographic views.

Hatch lines

Hatch lines are drawn on the surfaces that represent where the cutting

plane passed through solid material. Also shown are the front and right-

side orthographic views and a sectional view.

CUTTING PLANE LINES

Cutting plane lines are used to define the location for the sectional

view’s cutting plane. An object is “cut” along a cutting plane line.

SECTION LINES

Section lines are used to define areas that represent where solid

material has been cut in a sectional view. Section lines are evenly

spaced at any inclined angle that is not parallel to any existing edge line

and should be visually distinct from the continuous lines that define the

boundary of the sectional view.

If two or more parts are included within the

same sectional view, each part must have

visually different section lines.

Section lines are drawn in AutoCAD using the Hatch tool, located on the

Draw panel under the Home tab. The Hatch tool offers many different

hatch patterns and spacings. The general pattern of evenly spaced lines at

45° is defined as pattern ANSI31 and is the default setting for the Hatch tool.

STYLES OF SECTION LINES

AutoCAD has more than 50 different hatch patterns. The

different patterns can be previewed in the Swatch option in the

Hatch Creation panels.

SECTIONAL VIEW LOCATION Sectional views should be located on a drawing behind the

arrows. The arrows represent the viewing direction for the

sectional view

HOLES IN SECTIONS

As with orthographic views, a conical point must be included on holes

that do not completely penetrate the object.

A common mistake is to omit the back edge

of a hole when drawing a sectional view.

GRADIENTS

In AutoCAD a gradient is shading that varies in intensity.

OFFSET SECTIONS

Cutting plane lines need not be drawn as straight lines across the

surface of an object. They may be stepped so more features can be

included in the sectional view.

MULTIPLE SECTIONS

More than one sectional view may be taken off the same

orthographic view.

ALIGNED SECTIONS

Cutting plane lines taken at angles on circular shapes

may be aligned.

Aligning the sectional views prevents the foreshortening that would result if

the view were projected from the original cutting plane line location. A

foreshortened view would not present an accurate picture of the object’s

surfaces.

DRAWING CONVENTIONS IN

SECTIONS Slots and small holes that penetrate cylindrical surfaces may be drawn as

straight lines, as shown below. Larger holes, that is, holes whose

diameters are greater than the radii of their cylinders, should be drawn

showing an elliptical curvature.

HALF, PARTIAL,AND

BROKEN-OUT SECTIONAL VIEWS

Half and partial sectional views allow a designer to show an

object using an orthographic view and a sectional view within one

view..

REMOVED SECTIONAL VIEWS Removed sectional views are used to show how an object’s shape

changes over its length. Removed sectional views are most often used

with long objects whose shape changes continuously over its length.

BREAKS It is often convenient to break long continuous shapes so that they

take up less drawing space. There are two drawing conventions used

to show breaks: freehand lines used for rectangular shapes, and S-

breaks used for cylindrical shapes.

SECTIONAL VIEWS

OF CASTINGS Cast objects are usually designed to include a feature called a rib.

Ribs add strength and rigidity to an object. Sectional views of ribs

do not include complete section lines because this is considered

misleading to the reader.

Work on your projects as indicated by your teacher

Sectional Views - Mechanical Engineering · © 2011 Pearson Higher Education, 2 Upper Saddle River,...

Documents