Isometric Projection (v) Isometric Drawing

From the previous page you should now appreciate when drawing an isometric projection of an object scales need to be constructed. These scales are used to measure off lines parallel to the isometric axes. Thus, a line drawn in isometric is smaller than its actual size (approximately 80% full size). What would happen if we drew an object in isometric but drew the edges full length? The object would simply look bigger than an isometric projection of the same object i.e. about 20% to 25% larger. Visually an isometric drawing (i.e. using an ordinary scale) of an object is just as satisfactory as an isometric projection (i.e. using an isometric scale) of it. Generally, isometric drawings are preferred to isometric projections as no time is wasted in setting up and using scales.

Making an Isometric Drawing

Q. Draw an isometric drawing of an object from its orthographic views?

It is advisable to draw a quick sketch of the object in isometric before you start the isometric drawing. The first step in any axonometric drawing is to draw the projection of the axes. As this is an isometric drawing the angles between the axes are all equal i.e. 120º. It is very important that all measurements are made parallel to these axes i.e.isometric axes.

It is always important to position the isometric axes so that the view taken best describes the object. After drawing the axes draw a box that will completely enclose the object you wish to draw. This is known as Box Construction. The height, width and breadth (length) for this box are obtained from the orthographic views, height = 50mm, width = 88mm, breath = 50mm. This box should be drawn in lightly so that it can be easily removed when the drawing is finished. As in most drawing topics the key to simplifying the answer lies in good indexing techniques i.e. lettering points. Good indexing practices simplify problems and reduce the time spent answering questions. Remember, all measurements are marked off parallel to the isometric axes. The same procedure is used to generate an isometric projection except an isometric scale is needed. In this example all the objects edges are parallel to the isometric axes. There are no non-isometric lines in this drawing.

Inclined Surfaces in Isometric Projection

Inclined surfaces are drawn in isometric projection by the Offset Measurements method, sometimes referred to as Offset Location Measurements in some textbooks. For example, lets make an isometric drawing of an object given its plan and elevation.

Again, from its orthographic views, make a rough sketch of what you think the object will look like in isometric. Draw the rectangular box into which the object will fit. In this example I have only indexed the points which concern us the most i.e 'A', 'B', 'C' and 'D'.
To find point 'A' simply measure along the top edge a distance 20mm. To find 'B' measure in a distance 30mm and up a distance of 20mm. Remember, to always measure along the isometric axes or on isometric lines. We now have the start and end points for line 'AB' so we simply join 'A' to 'B'. The same procedure follows for line 'CD' (like 'AB' this is a non-isometric line). Locating points relative to other points in this way is known as the Offset Location Measurements method. Lines 'AB' and 'CD' are non-isometric lines. Non isometric lines are obtained by measuring on isometric axes or on lines parallel to the axes. See if you can follow all the construction.

Q. Try drawing this regular tetrahedron, of side edge 80mm, in isometric.