Introduction to Sectional Views

ENGINEERING DRAWING-IDWG-101

Aamir Naveed

Lecture # 5

Sectioned Drawings

A multi-view technical drawing that reveals details about internal features by displaying the part as if cut by an imaginary cutting plane

To make the drawing more understandable, especially the internal details of the part

Since the sectioned drawing shows internal features there is generally no need to show hidden lines

Especially helpful for assembly drawings

The Cutting Plane

An imaginary plane that defines where the object is cut

Shown in drawing adjacent to the sectioned drawing Arrows at the end of the cutting plane line indicate

the direction of view for the sectioned drawing The arrows point toward the part of the object that is

visible in the sectioned drawing. A sectioned drawing follows the general rules of any

view in a multi-view drawing

The Cutting Plane

The Cutting Plane

Cutting planes may be labeled at their endpoints if multiple cutting plane lines are used

When using multiple cutting planes each sectioned drawing is drawn as if the other cutting plane lines do not exist

The cutting plane line takes precedence over center lines

Occasionally cutting plane lines are not shown when their location is obvious

The Cutting Plane

Section Lines

Section lines are drawn where the object passes through the cutting plane

If a saw was used to cut the part then section lines represent the cutting marks left by the saw blade

Different materials may be represented by the use of different section line types

The general section line type which may be used for any material is the line type for iron

Section Lines

Section Lines

Section lines should not be parallel or perpendicular to object lines

Section lines are generally drawn at 45 degrees unless this conflicts with other rules

Section lines should be oriented at different angles for separate parts

Occasionally section lines are only drawn on the perimeter of large areas

Section lines are not used for thin parts rather they are filled in solid (Do not use closely spaced section lines)

Section Lines

Section Drawing Types

Full Section Half Section Assembly Section Offset Section Broken-Out Section Revolved Section Removed Section Special Section Conventions

Full Section

The cutting plane passes completely through the part as a single flat plane

Half Section

The cutting plane only passes half way through the part

The other half is drawn as usual

Hidden lines are not shown on either half of the part

A center line is used to separate the two halves

Mostly used on cylindrical parts

Assembly Section

Shows how parts fit together

Different parts have different section line orientation

Different materials use different section line types

Standard parts (shafts, pins, dowels, rivets, screws, washers, gears, etc.) are not sectioned

Assembly Section

Cut each part of the assembly and section each part with the appropriate section line type

Put the parts together in their assembled position

Assembly Section

The shaft is not sectioned because it is a standard part and section lines would provide no additional information

The other two part are made from the same material

The orientation of section lines clearly shows the location of the different parts

Assembly Section

The top and bottom mating part are made from different materials in the part shown below

A center line is added to the shaft to show that it is a circular feature

Offset Section

The internal features of many part can not be shown using a single straight cut to create the sectioned drawing

An offset section is used for such parts

Offset Section

The multi-view drawing is often difficult to interpret when there are several hidden features on the object

Look at the figure in your text and try to picture the part in your mind

A sectioned view makes the object much easier to understand

Offset Section

An offset section allows the cutting plane to pass through all of the internal features

There may be several bends in the cutting plane

Offset Section

The actual part would show a new visible line at the bend in the cutting plane

Since the cutting plane bend is arbitrary, do not show the line representing this bend in the sectioned drawing

Offset Section

The sectioned view does not show the bend in the cutting plane

Hidden lines are not shown

Be sure to include object lines that are behind the cutting plane

Broken-out Section

Only a portion of the view is sectioned

A jagged break line is used to divide the sectioned and un-sectioned portion of the drawing

Revolved Section

A cross section of the part is revolved 90 degrees and superimposed on the drawing

A jagged break line may be used to divide the revolved section from the rest of the drawing

Removed Section

Similar to the revolved section except that the sectioned drawing is not superimposed on the drawing but placed adjacent to it

The view and the cutting plane are labeled (Section A-A)

The removed section may be drawn at a different scale

Special Section Conventions

There are special rules (conventions) that are followed to make some parts more understandable

Some features are rotated to their true radial position in sectioned views

Special Section Conventions

The object is difficult to understand using standard multi-view drawings where hidden lines are used to represent internal features

Special Section Conventions

If the part is sectioned as it would actually appear if cut the details of the ribs and holes would not be clear

Since the objective is to make the drawing easy to interpret the drawing is modified following standard conventions

Special Section Conventions

The cutting plane shows that the features are revolved to their true radial position

Hidden features are not shown The sectioned drawing produced

is a distorted but clearer picture of the object

The section drawing appear as a full section

The arrows show the direction of the view

Special Section Conventions

Ribs are not sectioned when the cutting plane passes through them lengthwise

Ribs are sectioned if the cutting plane passes through them at other orientations

Special Section Conventions

The front view is replaced by a full section view

The cutting plane shown in the top view shows the direction of the line of sight

The holes and ribs have been revolved to their true radial position

The ribs are not sectioned in this orientation

The section lines are all drawn at the same angle since the object is one solid part