Chapter 02 Section

8/13/2019 Chapter 02 Section

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Chapter 2

Section Views


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Introduction


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Given

Necessity of a section view

Finish

No

Internal features

make a viewdifficult to reador dimension?

Orthographic

projection

principle

Yes

Sectiontechnique

Orthographic

projectionprinciple


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Purposes

Clarify an internal feature.

Facilitate dimensioning.

Example

Regularview

Sectionview


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Basic components


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Cutting planeCutt ing planeis an imaginaryplane 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


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Viewingdirection

Cutting plane line : Line stylesThe 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 atthat 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


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Class activity

Do 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 totouch the short visible line)

Yes

No

Right!

Wrong!

(Because the cutting plane line usedin this course is a chain line )

2


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Class activity

Change the following incorrect cutting plane line style to that previously

suggested.

1 2


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Section lining : Purpose

Section l inesor cross-hatch l inesare 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.


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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


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It shou ld notrunparallel orperpendicularto contour of

the view.

Section lining : Recommended practice 2

Poor practicesExamples


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Section lining : Special case

When the sectioned area is large, an outline sectioning

may be used to save time.

Example

Basic Components


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Class activity

Freehand sketch a section lines.

1 2


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Class activity

Which one is a good practice in section lining?

1 2


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Kinds of section


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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.)


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Conventional practice : Treatment of a hidden line

Hidden lines are usually omit tedwithin the section lined area.

Example

Hidden linesare omitted.

Hidden linespresent.


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Full section : Concept & exampleA section view is made by passing the stra ightcutting

plane completely throughthe part.

Example


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Offset section : Concept & exampleA section view is made by passing the bendedcutting

plane completely throughthe part.

Example

Edge views of

the cutting planeare omitted

Kinds of sections


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Half section : Concept & exampleA section view is made by passing the cutting plane halfway

through an object and remove a quarterof it.

Example

Kinds of sections


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A section view is made by passing the cutting plane normal

to the viewing direction and removing the portion of anobject in front of it.

Broken-out section : Concept & example

Example

Kinds of sections

The sectioned and unsectioned

portions are separated bya break l ine.

Cutting plane line is not

necessary.

Break line is freehand drawn

as a thin continuous line (4H).

Conventional practices


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Revolved section : Additional example

Kinds of sections


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6. Removed section

Removed section is created with the same conceptas a revolved section. But, the cross-section view

is shown outside the view.

Removed section : Concept


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Example : Revolved vs. removed sections.

Revolved section Removed section

Removed section :Comparison with a revolved section


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

Removed section technique can improve a reading of

the orthographic view.

Example

Revolvedsection

Removed

section

R d ti


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Section AA Section BB

A single or multiple removed (cross) section view(s) can bearranged 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

S


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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 eachother, 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


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Comparison of a different section techniques


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Dimensioning

Di i t h i


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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.

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Di i t h i


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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.

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