Chapter 8Section Views

Contents

Introduction

Basic components

Kind of sections

Dimensioning

Introduction

Given

Necessity of a section view

Finish

No

Internal featuresmake a view

difficult to reador dimension?

Orthographic projectionprinciple

Yes

Sectiontechnique

Orthographic projectionprinciple

Purposes

Clarify an internal feature.

Facilitate dimensioning.

Example

Regularview

Sectionview

Basic components

Cutting planeCutting plane is an imaginary plane that cuts through the object.

Location and direction of a cutting plane depend on a hidden feature that is needed to be revealed.

A section view is obtained by viewing the object after removed the cover up part in the direction normal to the cutting plane.

Cuttingplane

Example

Section view

Basic Components

Cutting plane lineIn an orthographic view, a cutting plane is presented as a “cutting plane line, CPL” and is drawn in either of an adjacent view of the section view.

Given Direction 1 Direction 2 Direction 3

Sectionview

CPL

CPL

Sectionview

Sectionview

Viewingdirection

Cutting plane line : Line styles

The cutting plane line is presented by a chain line. (This course)

Begin and end the line with a short visible line.

When the line changes its direction, draw a short visible line at that corner.

Draw an arrow at about the mid-length of a short visible line, the arrow head is pointed toward to this line in a viewing direction.

Examples

1

2

3

Basic Components

Class activityDo you find something wrong in the following cutting plane lines?

3

1Yes

No

Right!

Wrong!(The arrow on the right side should be pointed downward)

Yes

No

Right!

Wrong!(The arrow head have to touch the short visible line)

Yes

No

Right!

Wrong!(Because the cutting plane line used in this course is a chain line )

2

Class activityChange the following incorrect cutting plane line style to that previously suggested.

1 2

Section lining : Purpose

Section lines or cross-hatch lines are added to a section view to indicate surface that are cut by a cutting plane.

Examples

Section viewwithout section lines

Section viewwith section lines

Visible surfaces and edges behind the cutting plane are drawn in a section view.

The section lines are different for each type of material.

Cast iron,Malleable iron

Steel Concrete

Sand Wood

Practically, the cast iron symbol is used most often for any materials.

Section lining : Symbol

Examples

The spacing between lines may vary from 1.5 mm for small sectioned areas to 3 mm for large sectioned areas.

Poor practices

Section lining : Recommended practice 1

Too dense Too coarse

Uneven spacing Uneven orientation

Examples

It should not run parallel or perpendicular to contour of the view.

Section lining : Recommended practice 2

Poor practicesExamples

Section lining : Special case

When the sectioned area is large, an outline sectioningmay be used to save time.

Example

Basic Components

Class activity

Freehand sketch a section lines.

1 2

Class activityWhich one is a good practice in section lining?

1 2

Kinds of section

Kind of sections

1. Full section

2. Offset section

3. Half section

4. Broken-out section

5. Revolved section (aligned section)

6. Removed section (detailed section)

A skill requirement

1. Ability in orthographic visualization

2. Understanding in a conventional practice for each kind of sections. (You will learn about them from now on.)

Conventional practice : Treatment of a hidden line

Hidden lines are usually omitted within the section lined area.

Example

Hidden linesare omitted.

Hidden linespresent.

Full section : Concept & example

A section view is made by passing the straight cutting plane completely through the part.

Example

A closer look

Kinds of sections

Offset section : Concept & example

A section view is made by passing the bended cutting plane completely through the part.

Example

Edge views ofthe cutting

planeare omitted

Kinds of sections

Half section : Concept & example

A section view is made by passing the cutting plane halfway through an object and remove a quarter of it.

Example

Kinds of sections

Half section : Conventional practice

A center line is used for separating the sectioned half from the unsectioned half of the view.Hidden line is omitted in unsectioned half of the view.

Kinds of sections

A section view is made by passing the cutting plane normal to the viewing direction and removing the portion of an object in front of it.

Broken-out section : Concept & example

Example

Kinds of sections

The sectioned and unsectionedportions are separated bya break line.

Cutting plane line is not necessary.

Break line is freehand drawnas a thin continuous line (4H).

Conventional practices

Revolved section : Concept & example

A section view is made by revolving the cross-section view 90o about a cutting plane line and drawn on the orthographic view.

Example

a

a

b

b

1. Superimposed to orthographic view.

SuperimposedBreak

2. Break from orthographic view.

Revolved section :Placement of a cross-section view

Revolved section : Additional example

Kinds of sections

6. Removed sectionRemoved section is created with the same concept as a revolved section. But, the cross-section viewis shown outside the view.

Removed section : Concept

Example : Revolved vs. removed sections.

Revolved section Removed section

Removed section :Comparison with a revolved section

Example : Situation that removed section is preferred.Removed section : Advantage

Removed section technique can improve a reading of the orthographic view.

Example

Revolvedsection

Removedsection

Section A–A Section B–B

A single or multiple removed (cross) section view(s) can be arranged without aligning with the cutting plane line, but it have to be labeled name of the cutting plane line.

Removed section : Alternative placement of a view

Example

Kinds of sectionsA

A

B

B

SummaryDrafter has several choices of section techniques to reveal an internal feature of an object.

Object having a symmetry, an appropriate choice is such as full section or half section.

Object having several features that do not locate in-line among each other, an offset section may be a good choice.

Broken-out section is usually used when a drafter need to reveal a local detail of each feature.

Revolved and removed section views are efficient when a drafter need to reveal only a cross section shape of an object.

Kinds of sections

Comparison of a different section techniques

Dimensioning

Dimensioning of the section views follows the typical rules of dimensioning.

Dimension techniques

50

10

For a half-section view, use dimension line with only one arrowhead that points to the position inside the sectioned portion.

50

Dimension techniquesAvoid placing dimensions or notes within the section linedarea.

If the situation is unavoidable, omit the section lines in the area of the note.