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Section Views

Contents

Introduction

Basic components

Kind of sections

Dimensioning

Introduction

Given

Necessity of a section view

Finish

No

Internal features

make a view

difficult to read or dimension?

Orthographic

projection

principle

Yes

Section

technique

Orthographic

projection

principle

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Purposes

Clarify an internal feature.

Facilitate dimensioning.

Example

Regular view

Section view

Basic components

Cutting plane Cutting 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.

Cutting plane

Example

Section view

Basic Components

Cutting Plane Lines

a) Composed of equal dashes each about 6mm plus the arrow and

space between dashes is 1.5mm

b) Composed of alternate long dashes and (approx 30-40mm) pair

of short dashes (approx 3mm) plus the arrow and space between

dashes is 1.5mm

(Both line thickness same as visible line)

Figure 8: Cutting plane lines.

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Cutting plane line In 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

Section view

CPL

CPL

Section view

Section view

Figure 9: Cutting planes and sections.

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 view without section lines

Section view with 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

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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 practices Examples

Section lining : Special case

When the sectioned area is large, an outline sectioning

may be used to save time.

Example

Basic Components

Class activity

Which one is a good practice in section lining?

1 2

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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 lines are omitted.

Hidden lines present.

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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 of

the cutting plane are 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

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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 unsectioned

portions are separated by

a break line.

Cutting plane line is not

necessary.

Break line is freehand drawn

as 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.

Superimposed Break

2. Break from orthographic view.

Revolved section : Placement of a cross-section view

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Revolved section : Additional example

Kinds of sections

6. Removed section

Removed section is created with the same concept

as a revolved section. But, the cross-section view

is 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

Revolved section

Removed section

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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 sections A

A

B

B

Summary

Drafter 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

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Dimensioning of the section views follows the typical rules

of dimensioning.

Dimension techniques

f 50

10

For a half-section view, use dimension line with only one arrowhead

that points to the position inside the sectioned portion.

f 50

Dimension techniques Avoid placing dimensions or notes within the section lined

area.

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

the note.

Conventional Practice

in Section View

TOPICS

Section view representation

of rib, web, spoke and lug.

Aligned section

Conventional break

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Section view

representation of

rib, web, spoke and lug

TERMINOLOGY

Rib and Web are thin, flat feature of an object that

acts as a structural support.

Rib Rib Web

Rim

Spoke is the rod radiating from the hub to the rim

of a wheel.

Spoke

Spoke

Rim

Hub

TERMINOLOGY

Hub

Lug is an ear which is built as portion of an object

for attachment.

TERMINOLOGY

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Lug is an ear which is built as portion of an object

for attachment.

TERMINOLOGY CONVENTIONAL PRACTICE

Omit the section lines on the section view of

Rib, Web and Lug, if the cutting plane is

passed flatwise through.

Spoke, if the cutting plane is passed longwise

through.

EXAMPLE : RIB

Normal multiview drawing

Normal section view

Section view drawing with

convention

EXAMPLE : WEB : flatwise cut

Normal multiview drawing

Normal section view

Section view drawing with

convention

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EXAMPLE : WEB : crosswise cut EXAMPLE : WEB : multiple section view

EXAMPLE : SPOKE

Misleading impression

EXAMPLE : LUG

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Aligned Section

DEFINITION

Aligned section is a section view that is drawn

by imaginary rotating the object’s features

appeared in a principal view about symmetry

axis

Example : Hole

Gives the impression that this holes

are at unsymmetrical position.

Example : Hole

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Example : Rib Example : Ribs & Holes

Example : Aligned section of keyway Example : Spoke & Keyway Example : Lug

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Conventional Break

CONVENTIONAL PRACTICE

For long objects that have to draw in a small

scale to fit them on the paper, it is recommended

to remove its long portion (which contains no

important information) and draw the break lines

at the broken ends.

SCALE 1:1

Example Example

SCALE 2:1

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STANDARD BREAK LINES

Rectangular

cross section

Wood

Metal

Cylindrical

cross section

Tubular

cross section

TO DRAW CYLINDRICAL BREAK

R

R/3 R/3

30o

30o

800

TO DIMENSION A BROKEN PART

Typical

dimensioning

method

f16

not to scale dimensions

f16

800