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LECTURE 6: SECTIONING

PREPARED BY:NOR HELYA IMAN KAMALUDIN

helya@unimap.edu.my

PTT 105: Engineering Graphics

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OUTLINE…

Cutting Plane

Section Lines

Several Types of Section Drawings

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Purpose of Sectioning

To demonstrate the proper use of section views which show internal features of objects that are not easily understood in standard multiview drawings

To demonstrate the use of CAD tools in generating section views

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Sectioned DrawingsDefinition: A multiview technical drawing that reveals details about internal features by displaying the part as if cut by an imaginary cutting plane.Objective: 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.

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The Cutting PlaneAn imaginary

plane that defines where

the object is cut

Shown in drawing

adjacent to the sectioned drawing

Drawn with the PHANTOM line

type

Arrows at the end of the

cutting plane line indicate the

direction of view for the

sectioned drawing.

Cutting Plane

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The Cutting Plane (cont’d)

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

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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.

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Section Lines (cont’d) 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)

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Section Drawing Types

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

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Full Section The cutting plane passes completely

through the part as a single flat plane.

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Half Section

The cutting plane only passes half way through the part

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

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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

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Assembly Section (cont’d)

Steps in assembly section:Cut each part of the

assembly Section each part with

the appropriate section line type

Put the parts together in their assembled position

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Assembly Section (cont’d)

Example 1: Consider the following object:The shaft is not

sectioned because it is a standard part.

The other two part are made from the same material.

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

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Assembly Section (cont’d)

Example 2: Consider the following object:

The top and bottom mating part are made from different materials

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

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Offset Section In order to create

the sectioned drawing, an offset section is used to show the internal features of many part that can not be shown using a single straight cut.

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Offset Section (cont’d) The multiview drawing is often

difficult to interpret when there are several hidden features on the object

A sectioned view makes the object much easier to understand.

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Offset Section (cont’d)

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

There may be several bends in the cutting plane

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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

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Offset Section (cont’d) 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

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Broken-Out Section Only a portion of

the view is sectioned

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

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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

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Removed Section Similar to the revolved

section except that the sectioned drawing is not superimposed on the drawing but placed next to it

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

The removed section may be drawn at a different scale

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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

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Special Section Conventions (cont’d)

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

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Special Section Conventions (Cont’d)

In order to make the drawing easy to interpret the drawing is modified following the standard conventions (rules).

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Special Section Conventions (cont’d)

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

Hidden features are not shown The sectioned drawing

produced is distorted but clearer picture of the object is obtained.

The section drawing appear as a full section

The arrows show the direction of the view.

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Special Section Conventions (cont’d)

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

Rib are not sectionedRib are sectioned

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Special Section Conventions (cont’d) 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

Full section view (top view)

Front view

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Sectioning With Solid Models

Slice› Cuts the solid object at the

specified cutting plane using the current color

› Breaks the objects into two parts

› One part may be deleted or moved

Section› Creates a 2-D drawing of the

section› Only draws the portion of the

object that is cut (i.e. the portion of the object that has section lines)

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Sectioning With Solid Models (cont’d)

SLICE command SECTION command

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Sectioning With AutoCAD

Use BHATCH Use the correct scale Default line orientation

is 45 degrees The general line type is

ANSI31 Used:

different line types for different materials

different line orientations for different parts

Use PICK POINTS to select an internal point in the sectioned portion of the drawing

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