SECTIONALSECTIONAL

ORTHOGRAPHIC

PROJECTIONSPROJECTIONS

Why sectional Orthographic projections are used?

I. To understand inner details of complex object:When the object is complex from inside thereWhen the object is complex from inside, therewill be many hidden lines in the projections and it will be difficult to understand the orthographicwill be difficult to understand the orthographicprojections. Therefore, to understand the details of the complex object sectionaldetails of the complex object, sectional orthographic Projections are used.

II To understand the materials of object :II. To understand the materials of object : If object is made of two or more materials, then it can be understood clearly by sectionalcan be understood clearly by sectional orthographic projections.

Orthographic projections of complex Orthographic projections of complex objects are drawn after imagining it as an

object cut by an imaginary cutting plane/planes

parallel to principal planes passing through the

details of the objectdetails of the object.

An imaginary plane by which the object is cutis known as cutting plane or section plane.

P ti f th bj t b t tti l Portion of the object between cutting plane and observer is imagined to be removed and g

then the object is viewed by the observer and

projection is drawn.

P j ti f t bj t i k Projection of cut object is known as sectional view or sectional projection.p j

Generally hidden lines are not drawn insectional view.

In sectional views, the Shape of the section,visible edges and contours of object behindvisible edges and contours of object behind

the section plane are drawn.

When one view is drawn sectional, other viewsare drawn as if the object is not cut and the

object exists as a wholeobject exists as a whole.

It means other views are not affected by taking section in one view, but Cutting plane

line is shown in non sectioned view to locate theline is shown in non sectioned view to locate the

section plane and arrows are drawn to show the

direction of sight.

Cutting plane line

Cutting plane line is also known as line of

section or trace of the cutting plane.

The portion of the object cut by cutting plane andtouching the cutting plane is shown by

drawing hatching or section lines in them.

Hatching or section lines are drawn thinner than Hatching or section lines are drawn thinner than object lines.

Normally hatching or section lines are drawn at 45.

Hatching lines are evenly spaced at about Hatching lines are evenly spaced at about 2 to 3 mm apart.

H t hiobserver

Cutting plane or section planeParallel to H.P

Hatching

Parallel to H.P.

Sectional T VSectional T.V.

X

Portion between observer and plane (Upper half portion)i i i d t b d

F.V.

is imagined to be removed.

Sectioned portion will be as shown in fig.Back True shape of sectioned portion will be

seen in T.V

Various cutting planes or section planes

Cutting plane Parallel to Principal verticalplane.

C tti l P ll l t P i i l h i t l Cutting plane Parallel to Principal horizontalplane.plane.

Cutting plane Parallel to profile plane.

Cutting plane Parallel to Principal vertical planeCutting plane Parallel to Principal vertical plane

Wh bj t i t b l ll l tWhen an object is cut by a plane parallel to

Principal vertical plane then:p p

The real or true shape of the section is observedin F.V.

Section plane ill be seen as a c tting plane lineSection plane will be seen as a cutting plane linein T.V.

Cutting plane line

T.V.

Sectional F.V.

Object

observerback

Sectioned object

Vertical cuttingplane

Sectional F.V.

ObserverT.V.

observer

Sectioned object

observerBack

C tti l P ll l t P i i l h i t l lCutting plane Parallel to Principal horizontal plane

When an object is cut by a plane parallel to Principal j y p p p

horizontal plane then:

The real or true shape of the section is observedi T Vin T.V.

Section plane will be seen as a cutting plane linep g pin F.V.

observer Cutting planeline

Horizontal cuttingplane

F.V.F.V.

Sectional T.V.

Sectioned object

C tti l P ll l t fil lCutting plane Parallel to profile plane

When an object is cut by a plane parallel to profilej y p p p

plane then:

The real or true shape of the section is observed i id iin side view.

Section plane will be seen as a cutting plane linep g pin T.V.

AA Sectioned object

X

Cutting plane line

Sectional R.H.S.V F.V.

A

T.V.X ASectioned object

Sectioning rule for machine elements like :Sectioning rule for machine elements like :

Ribs rivets webs shafts pins nuts boltsRibs, rivets, webs, shafts, pins, nuts, bolts, washers, keys and cotter.

Whenever, the cutting plane is passing through

above machine elements and if cutting plane

contains the axis of above machine elements,

then they are not sectioned.then they are not sectioned.

However, when the cutting plane is cutting,

Elements perpendicular to the axis of the

Above Machine elements, section is taken

and in the projection hatching lines are drawn.

If tti l d t i l d i thIf cutting plane does not include axis then

These elements are hatchedThese elements are hatched.

Sectioning of Rivets

CORRECT WRONG

30 DEEP

F.V.

X

T.V.T.V.

30 DEEP

Sectional F.V.X

T.V.

F.V.

AC

R=MOTC

C CM

OR

CM

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A

F.V.

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Sectional T.V.

OR=MO

C CM

O

R

Rib MRib

F.V.Sectional L.H.S.V.A

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C

XA

RULES OF HATCHING:

1) A f t l t i l t b ti1) Area of a metal or a material, cut by a section

plane is shown by hatching lines in projection.plane is shown by hatching lines in projection.

It is executed by thin lines normally at an angle of

45 to the axis or to the main outlines of the

ti lsectional area.

(2) If the axis of the boundary of section is at 45then(2) If the axis of the boundary of section is at 45 then the vertical or horizontal hatching lines are drawn.

Axis at 45

Axis at 45

(3) Separate area of a section of a single(3) Separate area of a section of a single component are hatched in the same mannermanner. CLICK FOR EXAMPLE

(4) Hatching lines on a second part, adjacent to the first are at an angle of 45adjacent to the first are at an angle of 45 but in the opposite direction. Hatching li thi d t dj t t fi t tlines on a third part adjacent to first two are drawn at an angle of 30 or 60. Sometimes spacing or pitch of the hatching lines is varied to separate it from g pthe adjacent parts.

Hatching more than two adjacent components g j p

C

hatched45at 60B

45

A hatched

(2) D45at 30on D(2) D45 on D

(5) If hatching is required on a large section(5) If hatching is required on a large section

area, it is avoided. It is limited to a zone

following the contour of the sectioned area

required to be hatched.

Large area

(6) If hatching is required on a very thin section(6) If hatching is required on a very thin section

area, it is avoided. Complete section is shown

entirely black. Thin space is left between

adjacent section of the same type.

(7) As far as possible avoid dimensioning inside ( ) p g

hatched area, but, if not possible, hatching

lines may be interrupted for the dimensioning.

(8) Hatched area can never have dashed or

dotted boundary.dotted boundary.

Figure shows isometric view of agmachine component. Draw its

(1)Front view, Top view & L.H.S

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5

(1)Front view, Top view & L.H.SView, using 3rd angle methodof projections.

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(2) Sectional Front view, Topview & L.H.S.V., using 3rd

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, gangle method of projections.

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R i d li f h

It will be nearer to V.P.in 1st angle method &against the vertical

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Retained split of the machine parts

plane in 3rd anglemethod.

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Sectional Front View -ABL.H.S. ViewB

Figure shows the pictorialview of a machine component.D i f ll i i

AADraw its following views asper First angle method ofprojections

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projections(1) Front view from X direction.(2) Sectional top view-AA

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(2) Sectional top view-AA(3) L.H.S. View

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Sketch shows the assumed cut model (retained part ofthe machine component / split against the observer) dueto horizontal section plane passing through AB.

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Sectional T.V.Sectional T.V.--AAAA

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Figure shows the pictorial viewof a machine components.Draw its following views,using 3rd angle method ofprojectionsprojections.

(1) Front view from arrow X

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(2) Top View

(3) Sectional R H S V - AB(3) Sectional R.H.S.V - AB2

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Retained split, will benearer to VP in 1st

Bnearer to V.P. in 1stangle method &against the verticalgplane in 3rd anglemethod.

No hatching inthis area as notcontained in thecontained in thesection plane

R i d li f h

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Retained split of the machine parts

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Full SEC.R.H.S.V

PROBLEM

Sketch, shows isometric view of a machine part.Draw itsDraw its (1) Full Sectional F.V. (sectional F.V.)

(2) T.V.

(3) R.H.S.V.U thi d l th d f th hiUse third angle method of orthographicprojection. Dimension the view as per thep j palign system.

R30AGiven Given

IsometricIsometric R30Isometric Isometric viewview

R20

BL=100, D=100 & H= 100L=100, D=100 & H= 100

AR20

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SEC. FRONT VIEWSEC. FRONT VIEW

PROBLEM - 1

The following figure shows theisometric view of a machine componentisometric view of a machine componentDraw its1)F ll ti l F t i1)Full sectional Front view (sectional F.V.)2)Top view3)L.H.S view

Use First angle method of projections anddi i i i li d t ldimensioning using aligned system only

R 25R 25

25 ,10 deep

R 2510 25105

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L.H.S. VIEW -AB

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AimAim::--SketchSketch--11,, showsshows IsometricIsometric ViewView ofof aamachinemachine partpart.. DrawDraw itsits followingfollowingorthographicorthographic viewsviews usingusing thirdthird angleangle

SOLUTION`SOLUTION`

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SketchSketch--11

SOLUTION`SOLUTION`Aim:Aim:--SketchSketch--1, shows Isometric View of a 1, shows Isometric View of a machine part. Draw its following machine part. Draw its following

th hi i i thi d lth hi i i thi d lorthographic views using third angle orthographic views using third angle method of projections, giving dimensions.method of projections, giving dimensions.(1) Sectional F.V.(1) Sectional F.V.--AAAA(2) T.V.(2) T.V.

SCALE:SCALE:-- 1:11:1

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Types of sectional view

(1) Full sectional View ( )

(2) Half sectional View .

(1) Full section:

The sectional view obtained after removing oneThe sectional view obtained after removing one half portion of the object through its centre line p j g

by an imaginary cutting plane is known as full

sectional view.

If it happens to be elevation (front view),If it happens to be elevation (front view),it is known as Full sectional elevation or

Full sectional front view. Normally the word

f ll i itt dfull is omitted.

If it happens to be plan (top view), it is knownIf it happens to be plan (top view), it is knownas full Sectional plan or full sectional top view.

Similarly there can be full sectional side view.

N ll th d f ll i itt dNormally the word full is omitted.

Important points:

hidden lines should not be drawn in sectional viewview

Visible lines behind the cutting plane should be Visible lines behind the cutting plane should beshown.

The portions which are actually cut by cutting l h ld b h t h dplane should be hatched.

The position of the cutting plane should be shown by using cutting plane line.

SPECIALSECTIONSSECTIONS

HALF SECTIONHALF SECTION

HALF SECTIONAL F.V.-AB HALF SECTIONALLEFT S V BCLEFT S.V.-BC

BB

A

CTOP VIEW

(2) Half sectional view:(2) Half sectional view:

When the object is symmetrical about its centrej yline, from outside as well as from inside, half

sectional view is preferred.

The main usefulness of the half section is in assembly drawing where it is often required toassembly drawing where it is often required to

show both internal and external construction of

the object on the same view.

i) Half sectional front view :

The sectional view obtained after removing th f t t ti f th bj t b tthe front quarter portion of the object by two

imaginary cutting planes at right angles to g y g p g g

each other is known as half sectional

elevation or half sectional front view.

The half sectional front view may be left or right depending upon the left or right frontright depending upon the left or right front

quarter portion of the object is removed.

ii) Half sectional top view:

sectional top view. The sectional view bt i d ft i th t t tiobtained after removing the top quarter portion

of the object by two imaginary cutting planes atof the object by two imaginary cutting planes at

right angles to each other is known as half

sectional plan or half

Th h lf ti l t i b l ft i htThe half sectional top view may be left or right depending upon the left or right top quarterdepending upon the left or right top quarter

portion of the object is removed.

Similarly there can be half sectional side view.

OFFSETOFFSET S C OSECTION

OFFSET SECTION: The path of the cutting planeis bent to pass through features not located in ais bent to pass through features not located in astraight line, i.e. it is offset to pass through bothprinciple features of the object Example is shownprinciple features of the object. Example is shownbelow.

Section lines are to be staggered Rto be staggered as shown at R

R

B

B

SPECIAL SECTIONSSPECIAL SECTIONS

REMOVED &REVOLVED SECTIONS

REVOLVEDSECTIONSECTION

REMOVED SECTION

REVOLVED REVOLVEDREVOLVEDSECTION

REVOLVEDSECTION

REMOVEDSECTION

REVOLVED SECTION

REMOVED SECTION

REMOVED SECTIONS

Partial (broken localPartial (broken, local or Zonal) Sectionor Zonal) Section.

Partial (broken, local or Zonal) Section.

This is used to show only a desired features of thebj t N tti l li dobject . No cutting plane lines are necessary, and

it shown by wavy line

Tap- bolt fastenerPartial (broken, local or Zonal)

pulleylocal or Zonal)

Section.

shaft

Shaft and pulley partly broken out to show internal fasteningg

SPECIAL SECTION

Cross hatching of adjacent parts

Part 1

Part 2Part 3

SPECIAL SECTION

Hatching more than two adjacent components at (2)

Part C

P B(hatched45Part B(at 60 )

45

Part A hatched

Part D45at 30on DPart D45 o

A B

F.V.

SEC.T.V.Two vertical plates ,fastened by a horizontalrivet is shown in its F.V. & T.V., cut by horizontalsection plane. Note: the rivet is shown in section inT.V.

AimAim::--SketchSketch--11,, showsshows IsometricIsometric ViewView ofof aamachinemachine partpart.. DrawDraw itsits followingfollowingorthographicorthographic viewsviews usingusing thirdthird angleangle

SOLUTION`SOLUTION`

g pg p gg ggmethodmethod ofof projections,projections, givinggiving dimensionsdimensions..(1) Sectional F.V.(1) Sectional F.V.--AAAA(2) T V(2) T V(2) T.V.(2) T.V.(3) L.H.S.V(3) L.H.S.V

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SketchSketch--11

SOLUTION`SOLUTION`Aim:Aim:--SketchSketch--1, shows Isometric View of a 1, shows Isometric View of a machine part. Draw its following machine part. Draw its following

th hi i i thi d lth hi i i thi d lorthographic views using third angle orthographic views using third angle method of projections, giving dimensions.method of projections, giving dimensions.(1) Sectional F.V.(1) Sectional F.V.--AAAA(2) T.V.(2) T.V.

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AimAim::--SketchSketch--11,, showsshows IsometricIsometric ViewView ofof aamachinemachine partpart.. DrawDraw itsits followingfollowingorthographicorthographic viewsviews usingusing thirdthird angleangle

SOLUTION`SOLUTION`

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SketchSketch--11