Isometric Drawing Single View projection Prof. M. S. Dasgupta, BITS Pilani, Pilani campus

Learning Objectives

2. Know the guidelines to draw isometric drawing

3. Practice various objects and generate

an imagination skill to draw a 3-D object

1. Know the concepts of isometric projection

Single View or Pictorial Projection

Pictorial projection is classified in the following three general divisions • Axonometric projection • Oblique projection • Perspective projection

Axonometric Projection

Axonometric projection is classified in the following three general divisions

• Trimetric projection • Dimetric projection • Isometric projection

Trimetric Dimetric Isometric

Cursor Mode for Isometric Drawing

•The isometric curser has three orientations: left curser mode, right curser mode and top curser mode to work on respective plane and along the normal to that plane.

•This curser mode can be changed by pressing Ctrl and E keys at once.

For AutoCad drawing set SNAP Style to ‘iso’ & GRIDMODE to ‘1’

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

Theory of Isometric Projection

Isometric Projection & Isometric Drawing

The angle <psr is equal to <pqr and equal to 60o. The same figure shows true view of top face PQRS as PqRs. The intersection of two face diagonals PR and sq is marked as x. The sP is a true length whereas sp is an isometric length.

In triangle psx, sxsp 30cos

In triangle Psx, sxsP 45cos

45cos30cos sPsp

Therefore, 815.030cos

45cos

sP

sp

Therefore,

The true length is reduced to 81.5% in an isometric projection. Therefore while drawing an isometric projection, it is necessary to convert true lengths into isometric lengths for measuring and marking the sizes.

Isometric Projection & Isometric Drawing

Orthographic views Isometric projection Isometric drawing

But for Engineering application all foreshortening is ignored, and actual

true lengths are drawn along isometric axes and isometric lines. To avoid

confusion and to set this method apart from true isometric projection, it is

called isometric drawing.

Because of inclination with all planes, the true length is reduced by 81.5% in an isometric projection.

Isometric / Non-isometric Lines

• The lines which are parallel to the isometric axes (X, Y and Z) are called as isometric lines. Isometric lines that are parallel to the isometric axes can be directly measured.

• Lines that are inclined and are not parallel to the isometric axes are called non-isometric lines. A line of this type cannot be measured directly. Its position and projected length must be established by locating its end points. • In an isometric drawing, an angle never appears in its true size.

‘Starting Point’ Concept The starting point (S) is important and to generate an isometric drawing. There are three visible faces (Left, Top and Right) of a block. If RSV is given then the Right face is constructed with H x D dimensions and Left face is constructed with L x H dimensions. Similarly if LSV is given then the Left face is constructed with H x D dimensions and Right face is constructed with L x H dimensions.

Block Method

Block Method

Continued

Continued

Rounded surface in isometric drawing

A circle in isometric view appears as an ellipse, which is called as an isocircle. AutoCAD provides a special command for drawing an isocircles. Command: ELLIPSE [Enter] Arc/Center/Isocircle/<Axis endpoint 1>: I (for Isocircle) [Enter] Select appropriate alignment with Ctrl E

Creation of rounded object

Model Example

Stepwise Solution to Model Example

Stepwise Solution to Model Example