isometric.ppt

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Lecture 3Wednesday, 18 June 2014 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

Trimetric Projection


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Isometric Projections

All angles between axonometric axes areequal

The three coordinate axes of the objectappear equally foreshortened (about 3/4thof true length)

The angles between any two of thethree coordinate axes is 120


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Isometric Terminology

The three coordinate axes are calledisometric axes

Any line parallel to isometric axesis called

isometric line

A non-isometric line is a line notparallel to any one of the three

isometric axis

In isometric projection of cube, the faces ofthe cube and any plane parallel to them is

called isometric planes


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Isometric Scale

True lengths of the edges of the object areequally foreshortened

Correct isometric projection can be drawn

using an isometric scale (always smallerthan ordinary scale)


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Isometric Drawing

Isometric Projection:Drawing preparedwith isometric scale onisometric axes

Isometric Drawing:Drawing prepared

with ordinary scaleon isometric axes


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Steps:

Step 1Isometric sketches begin with definingisometric axes, three lines, one verticaland two drawn at 30 from the horizontal.


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Steps:

Step 2Three lines of the isometric axes representthe three primary dimensions of theobject: width, height, and depth


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Steps:

Step 3Draw the font face of the isometric block.


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Steps:

Step 4

Draw the rest of the isometric block.


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Steps:

Step 5

Add details to the block starting from thefront face. Then add details to the otherfaces.

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Steps:

Step 6

Darken all visible lines to complete theisometric sketch. (make sure thatconstruction lines are light)

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Axonometric projection shows all 3 dimensions,length, width and height.

The isometric lines are only drawn to scale. Objectscomposed entirely of isometric lines can be drawnby taking all measurements parallel to main edgesof the enclosing box.

Non-isometric lines are drawn by transferring theordinates (which are on isometric lines) of the endof the lines

Inclined and oblique surfaces are drawn using end

coordinates. Box construction and offsetmeasurements are common methods

In an isometric drawing, an angle never appearsin its true size. Angles, irregular curves require

special techniques

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Objects with Normal Surfaces

Make an Isometric Drawing with corner Aat the bottom

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Objects with Normal Surfaces

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Objects with Oblique Surfaces

Make an Isometric Drawing with corner Aat the bottom

NON-ISOMETRIC LINE



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Objects with Oblique Surfaces



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Objects with Non-isometricLines

Make an Isometric Drawing with apex Afacing front



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Objects with Non-isometric Lines

Non-isometric lines are drawn with box constructionand offset measurements

Non-isometric lines are not drawn in true length inisometric drawing (BA is shorter than CA in thisdrawing)



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Irregular Objects

Make an Isometric Drawing of the followingirregular object (pyramid)



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Irregular Objects

OA and OB offsets help to locate apex O

Complete box construction may not beneeded in each case



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Objects with Circular Geometry

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

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

Four-centre ellipses are used to approximate ellipseson isometric planes.

How to draw four-centre ellipse???



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Approximate Ellipse

Draw the isometric centre lines of the circle.

Using the centre lines, draw an isometric square with sidesequal to the diameter of the circle.From the near corners of the box, draw two large arcs withradius R, 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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Cylinder

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Objects with Circular Geometry

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Lecture 3 ed esday, 8 Ju e 0 8

Objects with Non-Circular CurvedSurfaces

Make an Isometric Drawing of the followingcurved object



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y,

Objects with Non-Circular Curved Surfaces

A line that appears as a noncircular curve in a normal

orthographic view of an object appears as a non-isometric line inan isometric drawing.

Curves 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 Accuracy increases with number of points

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isometric.ppt