WEEK 6 ISOMETRIC DRAWING LATEST-converted (1)

DRAUGHTSMANSHIP

DDWQ1123

Isometric Projections

What is ISOMETRIC?

• 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



Axonometric Projections

• Observer at infinity
• Projectors parallel to each other and perpendicular to

projection plane
• Object is inclined with respect to projection plane

Types of Axonometric Projections

Isometric Projection
Dimetric Projection

Trimetric Projection

Isometric Projections

• All angles between axonometric axes are
equal

• The three coordinate axes of the object
appear equally foreshortened (about 3/4th
of true length)

• The angles between any two of the
three coordinate axes is 120°

Isometric Terminology

• The three coordinate axes are called isometric
axes

• Any line parallel to isometric axes is called
isometric line

• A non-isometric line is a line not
parallel to any one of the three isometric axis

• In isometric projection of cube, the faces of the
cube and any plane parallel to them is called
isometric planes

Isometric Drawing

Isometric Projection:
Drawing prepared
with isometric scale on
isometric axes

Isometric Drawing:
Drawing prepared
with ordinary scale
on isometric axes

Steps:

Step 1
Isometric sketches begin with defining
isometric axes, three lines, one vertical
and two drawn at 30° from the horizontal.

Steps:

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

Steps:

Step 3
Draw the font face of the isometric block.

Steps:

Step 4
Draw the rest of the isometric block.

Steps:

Step 5
Add details to the block starting from the
front face. Then add details to the other
faces.

Steps:

Step 6
Darken all visible lines to complete the
isometric sketch. (make sure that
construction lines are light)

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

• The isometric lines are only drawn to scale. Objects
composed entirely of isometric lines can be drawn by taking
all measurements parallel to main edges of the enclosing
box.

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

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

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

Objects with Normal Surfaces

Make an Isometric Drawing with corner A
at the bottom

Objects with Normal Surfaces

Objects with Oblique Surfaces

• Make an Isometric Drawing with corner A
at the bottom

NON-ISOMETRIC LINE

Objects with Oblique Surfaces

Objects with Non-isometric Lines

• Make an Isometric Drawing with apex A
facing front

Objects with Non-isometric Lines

Non-isometric lines are drawn with box construction and offset
measurements
Non-isometric lines are not drawn in true length in isometric
drawing (BA is shorter than CA in this drawing)

Irregular Objects

• Make an Isometric Drawing of the following
irregular object (pyramid)

Irregular Objects

• OA and OB offsets help to locate apex O

• Complete box construction may not be needed in
each case

Objects with Circular Geometry

A circle in a orthographic projection will appear as an ellipse
in an isometric drawing.
Instead of actual ellipses often approximate ellipses are
drawn for isometric drawing.
Four-centre ellipses are used to approximate ellipses on
isometric planes.

How to draw four-centre ellipse???

Approximate Ellipse

•Draw the isometric centre lines of the circle.
Using the centre lines, draw an isometric square with sides equal to the
diameter of the circle.
•From the near corners of the box, draw two large arcs with radius R,
using the two red points as centres.
•Draw the two smaller arcs with radius r, using two green points as centres.







Cylinder

Objects with Circular Geometry

Objects with Non-Circular Curved
Surfaces

• Make an Isometric Drawing of the following
curved object

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 in an isometric drawing.
•Curves may be drawn using a series of points by measuring along the
normal lines in the orthographic view (offset measurements)
and transferring these points on isometric drawing. Accuracy increases
with number of points.