class 9 - sectional views

Engineering Graphics, Class 9Sectional Views

Mohammad I. KilaniMechanical Engineering Department

University of Jordan

Sectional Views

By means of a limited number of carefully

selected views, the external features of

most designs can be fully described.

However, We are frequently encountered

with the necessity of showing interiors of

parts that can not be shown clearly by

means of hidden lines.

The interior of complex parts may be

shown by imagining that the part is sliced

by one or more cutting plane. A cutaway

view is then drawn. It is called a sectional

view, a cross section, or simply a section.

Sectional views

To obtain a sectional view, a cutting plane is assumed to be passed through the part (a). This cuts the part into two halves

The cutting plane is then removed, and the two halves are drawn apart, exposing the interior construction. In (b), the direction of sight is towards the left half. The section view will be in the position of a right side view.

Full sections

The sectional view obtained by passing the cutting plane fully through the object is called a full section.

Compared to the left-side view, the sectional view gives a clearer description of the objects details, and the left-side view would naturally be omitted.

In the front view, the cutting plane appears as a line, called the cutting-plane line. The arrows at the end of the cutting-plane line indicate the direction of sight for the sectional view.

Full sections

Note that in order to obtain a sectional view, the right half is only imagined to be removed, and not actually shown removed anywhere except in the sectional view itself.

The section-lined areas in the sectional view are those portions that came in actual contact with the cutting plane. Those areas are cross-hatched with thin parallel section lines. The visible parts behind the cutting plane are shown, but not hatched.

Frequently, the location of the cutting plane is obvious from the section itself, and therefore the section line is omitted.

Lines in sectioning

All visible edges and contours behind the cutting plane should be shown. Otherwise, the section would appear to be made of disconnected and unrelated parts.

Sections are used primarily to replace hidden-line representation. Hence, hidden lines are usually be omitted in sectional views.

Lines in sectioning

A section line is always completely bounded by a visible outline never by a hidden line as in (e), since in every case the cut surface and its boundary lines will be visible. Also, a visible line can never cross a section-lined area.

In a sectional view of a part, the section lines in all sectioned areas must be parallel. The use of section lining in opposite direction is an indication of different parts, as when two or more parts are adjacent in an assembly drawing.

Hidden lines in sectioning

Sometimes, hidden lines are necessary for clearness, and should be used in such cases.

The use of hidden lines in a section may sometime allow omitting a view.

Cutting plane line

The cutting plane line is a thick dark line which uses one of the special patterns shown.

The cutting plane line can be left out when it is obvious where it must lie from the appearance of the section itself

Section lining (hatch patterns)

In the past, different section lining symbols (hatch patterns) have been used to indicate the material of the object.

Now, there are so many different material types and each general type has many subtypes. Therefore, the practice now is to use the cast iron symbol for all materials and then to detail the specification of the material in letters in the form of a note or in the title strip.

Section-lining rules

The correct method of drawing section lines is shown in part (a). Draw section lines with a sharp medium-grade pencil (H or 2H).

Always draw lines at 45 with the horizontal unless there is an advantage of using a different angles.

Space the section lines as uniformly spaced as possible by eye. Section lines should be uniformly thin, and not varying in thickness.

Avoid running the section lines beyond the visible outline, or stopping the line too short.

Section-lining rules

If section lines drawn at 45 with horizontal would be parallel or perpendicular (or nearly so) to a prominent visible outline, the angle should be changed to 39 or some odd angle.

Cutting plane in sectional 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 the cutting plane line.


The arrows at the ends of the cutting-plane lines point in the direction of sight for the sectional view.


The figure to the right shows two cutting planes. Each resulting section is completely independent of the other, and drawn as if the other were not present.

Correct and incorrect placements of sectional views and sectioning line

Visualizing a Section

An object with a drilled and counterbored hole is to be sectioned. The cutting plane is assumed along the horizontal centerline in the top view, and the front half of the object is imagined to be removed.

The two cut surfaces produced by the cutting planes are 1-2-5-6-10-9 and 3-4-12-11-7-8. The section at (c) us incomplete because certain visible lines are missing.

Visualizing a Section

If the section is viewed in the direction of sight as shown at (b), arcs A, B, C, and D will be visible. As shown at (d) these arcs will appear as straight lines 2-3, 6-7, 5-8, and 10-11.

The top and bottom surfaces of the object appear in the section as lines 1-4 and 9-12. The bottom surface of the counterbore appears as line 5-8.

Dimension values and hatching

Sectional views are used to show interior features clearly. If a dimension is necessary, and the dimension values or extension lines cross hatched areas, you should break the hatching behind the dimension.

The best practice is to place dimensions outside the object outline

Half Sections

If the cutting plane passes halfway through the object, the result is a half section.

A half section has the advantage of exposing the interior of one half of the object and retaining the exterior of the other half. Its usefulness is however largely limited to axially symmetrical objects.

Half sectioning is not used widely in detail drawings because of the difficulties in dimensioning internal shapes that are shown in part only.

Broken out sections

It often happens that only a partial section of a view is needed to expose the interior shapes. Such a section, limited by a break line is called a broken-out section.

A small broken out section is sometimes sufficient to explain the construction. In the figure to the bottom, a half section would have caused the removal of half the keyway. The keyway is preserved by breaking out around it. Note that in this case the section is limited partly by

Revolved sections

The shape of the cross section of a bar, arm, spoke, or other elongated 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 bar, then revolving the plane through 90 about the center axis.

Revolved sections examples

The superimposition of the revolved section requires the removal of all original lines covered by it (a), (b), (c) and (d).

In the incorrect method, the original lines are not removed.


The visible lines adjacent to a revolved section may be broken out if desired, as shown in (g).


When symmetric, symmetry axes are shown on the section.

Partial revolved sections may be used when clarity is improved


The true shape of the section should be retained after the revolution of the cutting plane, regardless of the direction of the lines in the view.

Removed Sections

A removed section is one not in direct projection from the view containing the cutting plane. This should be made without turning the section from its normal orientation.

Removed Sections

Removed sections should be labeled with letters that correspond to the letters at the ends of the cutting plane line, and should be arranged in alphabetical order from left to right on the sheet.

Removed Sections

Whenever possible, removed sections should be on the same sheet with the regular views. If a section must be placed on a different sheet, cross reference should be given on the related sheet. A note should be given below the section title such as:SECTION B-B ON SHEET 4A similar note should be placed on the sheet on which the cutting plane is shown, with a leader pointing to the cutting plane and referring to the sheet on which the section will be found.

Sometimes it is convenient to place removed sections on center lines extended from the section cuts.

Offset Sections

In sectioning through irregular objects, it is often desirable to show several features that do not lie in a straight line, by offsetting or bending the cutting plane. Such a section is called an offset section.

Multiple Offset Sections

Multiple offset sections may also be used to illustrate complex parts as shown below. Notice the ends of the cutting plane labeled with letters and the sections views neatly arranged and labeled to match.

Ribs in Sections

When the cutting plane passes through a thin feature, such as rib or a web, hatching would give a false impression of solidity.

If the cutting plane passes crosswise through a rib or the thin member, the member should be section-lined in the usual manner.

Revolution Convection in Sections

To include certain angled elements in a section, the cutting plane may be bent so its passes through those features that are to be included.

The plane and the feature are imagined to be revolved into the original plane. In the example shown, the cutting plane was bent to pass through angled arm, and then revolved to a vertical position, from where it was projected across to the sectional view.

Revolution Convection in Sections

In the example shown, the cutting plane is bent so as to include one of the drilled holes and counterboredholes in the sectional view. The conventional view at (b) gives a clearer and more complete description than does the one at (c), which is the true projection.

Revolved Symmetrical Features

In the view shown, the cutting plane is offset in circular-arc bends to include two holes, two ribs, and the keyway. These features are then imagined to be revolved until they line up vertically, and then projected from that position to obtain the section at (b). Note that the ribs are not hatched.

If a regular full section were drawn, the resulting section would be incomplete and confusing, in addition, would take more time to draw.

Conventional Breaks

In order to shorten a view of an elongated object, conventional breaks are recommended.

The breaks used on cylindrical metal shafts or tubes are referred to as S-breaksand are usually drawn entirely freehand or with the aid of a compass and an irregular curve. Excellent S-breaks are also obtained with an S-break template.

Breaks for rectangular metals and wood sections are drawn freehand.

class 9 - sectional views

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