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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
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10
For a half-section view, use dimension line with only one arrowhead
that points to the position inside the sectioned portion.
f 50
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.