engn103 engineering drawing isometric … scale •true lengths of the edges of the object are...

L E C T U R E 4

ENGN103 ENGINEERING DRAWING

ISOMETRIC PROJECTIONS

WHAT IS ISOMETRIC DRAWING?

It is a method of producing pictorial

view of an object showing all three

faces of the object simultaneously.

It is a type of parallel projection.

It is a type of axonometric

projection.

ISOMETRIC PROJECTIONS

Observer is placed at infinity.

Projectors parallel to each other and perpendicular to projection plane.

Object is inclined with respect to projection plane in order to see all the three faces.

ISOMETRIC TERMINOLOGY 1. The three coordinate axes are

called isometric axes.

2. Any line parallel to isometric

axes is called isometric line.

3. A non-isometric line is a line not

parallel to any of the three

isometric axis.

4. In isometric projection of cube,

the faces of the cube and any

plane parallel to them is called

isometric planes.

ISOMETRIC SCALE

• True lengths of the edges of the object are equally

foreshortened.

• Correct isometric projection can be drawn using an

isometric scale (always smaller than ordinary scale)

Isometric Projection:

Drawing prepared

with isometric scale on

isometric axes

Isometric Drawing:

Drawing prepared

with ordinary scale

on isometric axes

MAKING ISOMETRIC PROJECTIONS: Step 1

Isometric sketches begin with defining isometric

axes, three lines, one vertical and two drawn at 30°

from the horizontal.

Step 2

Three lines of the isometric axes represent the three

primary dimensions of the object: width, height,

and depth

Step 3

Draw the front face of the isometric block.

Step 4

Draw the rest of the isometric block.

Step 5

Add details to the block starting from the front face.

Then add details to the other faces.

Step 6

Darken all visible lines to complete the isometric

sketch. (make sure that construction lines are light)

• Isometric projection shows all 3 dimensions, length, width and height.

• The isometric lines are only drawn to scale.

1. Objects composed entirely of isometric lines can be drawn by taking all measurements parallel to main edges of the enclosing box.

2. Non-isometric lines are drawn by transferring the ordinates (which are on isometric lines) of the end of the lines

3. Inclined and oblique surfaces are drawn using end coordinates. Box construction and offset measurements are common methods.

4. In an isometric drawing, an angle never appears in its true size. Angles, irregular curves require special techniques.

VIEWING DIRECTION

• The position of the eye with respect to the object is

the viewing direction.

CLASSWORK: Make Isometric Drawing for the Front view

and Top view given.

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HOMEWORK Make Isometric Drawing for the Front view

and Top view given.

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