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Lecture 3Saturday 10 October 2015 1

ENGINEERING GRAPHICS

1E9Lecture 3: Isometric

Projections

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What is ISOMETRIC?

It is a method of producing pictorial viewof an object showing all three faces of theobject simultaneously.

It is a type of parallel projection

It is a type of axonometric projection

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Axonometric Projections

Observer at infinity

Projectors parallel to each other and perpendicularto projection plane

Object is inclined with respect to projection plane

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Types of AxonometricProjections

Isometric Projection

Dimetric Projection

rimetric Projection

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Isometric Projections

!ll angles between axonometric axes aree"ual

he three coordinate axes of the objectappear e"ually foreshortened #about $%&thof true length'

Te !n"#es $et%een !ny t%o of tetree coor&in!te !xes is 1'()

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Isometric Termino#o"y

he three coordinate axes are called isometricaxes

!ny line parallel to isometric axesis called

isometric line

! non-isometric line is a line not parallel toany one of the three isometric axis

In isometric projection of cube( the faces of thecube and any plane parallel to them is calledisometric planes

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Isometric Sc!#e

rue lengths of the edges of the object aree"ually foreshortened

)orrect isometric projection can be drawn

using an isometric scale #always smallerthan ordinary scale'

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Isometric *r!%in"

Isometric Projection*Drawing preparedwith isometric scale onisometric axes

Isometric Drawing*Drawing prepared

with ordinary scaleon isometric axes

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Steps+

Step 1Isometric s+etches begin with definingisometric axes( three lines( one verticaland two drawn at $,- from the horiontal.

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Steps+

Step 'hree lines of the isometric axes representthe three primary dimensions of theobject* width( height( and depth

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Steps+

Step ,Draw the font face of the isometric bloc+.

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Steps+

Step -

Draw the rest of the isometric bloc+.

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Steps+

Step .

!dd details to the bloc+ starting from thefront face. hen add details to the otherfaces.

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Steps+

Step /

Dar+en all visible lines to complete theisometric s+etch. #ma+e sure thatconstruction lines are light'

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!xonometric projection shows all $ dimensions( length( widthand height.

he isometric lines are only drawn to scale. Objects

composed entirely of isometric lines can be drawn by ta+ingall measurements parallel to main edges of the enclosing box.

/on0isometric lines are drawn by transferring the ordinates#which are on isometric lines' of the end of the lines

Inclined and obli"ue surfaces are drawn using endcoordinates. 1ox construction and offset measurements arecommon methods

In an isometric drawing( an angle never appears in its truesie. !ngles( irregular curves re"uire special techni"ues

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O$jects %it Norm!# S0rf!ces

2a+e an Isometric Drawing with corner !at the bottom

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O$jects %it Norm!# S0rf!ces

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O$jects %it O$#i0e S0rf!ces

2a+e an Isometric Drawing with corner !at the bottom

NON-ISOMETRIC INE

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O$jects %it O$#i0e S0rf!ces


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O$jects %it Non2isometric3ines

2a+e an Isometric Drawing with apex !facing front


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O$jects %it Non2isometric 3ines

/on0isometric lines are drawn with box constructionand offset measurements

/on0isometric lines are not drawn in true length inisometric drawing #1! is shorter than )! in thisdrawing'


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Irre"0#!r O$jects

2a+e an Isometric Drawing of the followingirregular object #pyramid'


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Irre"0#!r O$jects

O! and O1 offsets help to locate apex O

)omplete box construction may not beneeded in each case


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O$jects %it Circ0#!r Geometry

! circle in a orthographic projection will appear asan ellipse in an isometric drawing.

Instead of actual ellipses often approximate ellipsesare drawn for isometric drawing.

3our0centre ellipses are used to approximate ellipseson isometric planes.

Ho% to &r!% fo0r2centre e##ipse???


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Approxim!te E##ipse

Draw the isometric centre lines of the circle. 4sing the

centre lines( draw an isometric s"uare with sides e"ual to thediameter of the circle.3rom the near corners of the box( draw two large arcs withradius 5( using the two red points as centres.Draw the two smaller arcs with radius r( using two green points

as centres.


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Cy#in&er


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O$jects %it Circ0#!r Geometry


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O$jects %it Non2Circ0#!r C0r4e&S0rf!ces

2a+e an Isometric Drawing of the followingcurved object


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ectu e 3 y

O$jects %it Non2Circ0#!r C0r4e& S0rf!ces

! line that appears as a noncircular curve in a normal

orthographic view of an object appears as a non0isometric linein an isometric drawing.

)urves may be drawn using a series of points by measuringalong the normal lines in the orthographic view #offsetmeasurements' and transferring these points on isometric

drawing !ccuracy increases with number of points

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