Engineering Graphic Modelling

Representing Circles

The projections: ISOMETRIC, DIMETRIC, TRIMETRIC etc, require

circles on their 'inclined' faces to be represented as ellipses. Each

ellipse must have its major axis at right angles to the normal of the

plane in which the ellipse lies. This may be illustrated by the following

reminder:

The technique of freehand sketching ellipses should be developed and

experience gained in drawing three dimensional representations. The

starting point is a sketch of a cube, with little regard being paid to

the formalised projection requirements.

THE RULE THAT THE MAJOR AXIS OF THE ELLIPSE MUST BE

AT RIGHT ANGLES TO THE NORMAL OF THE PLAN