JSS 3.TOPIC 6: ISOMETRIC DRAWING

Definition: Isometric drawing is defined as a 3-dimensional drawing of an object. It is a pictorial method of drawing. What you see is what you draw to the given scale. The three dimensions are the length, width and height.

Isometric Axis: The term isometric axis means the lines formed by the 30⁰ set square and the vertical line of any given plane or block to be drawn. The lines that slant at 30⁰ are called the receeding lines. The vertical line is also drawn using the side of the 30⁰/60⁰ set square.(your teacher will show you how).
The lines drawn are often referred to as projection lines. Apart from the vertical lines, all other lines are inclined at 30⁰ slant. It is always better to complete the drawing in construction line (faint lines) first, check that everything is correct before outlining the block given.

Steps Involved in Isometric Drawing: Drawing isometric views goes through four main stages. They are:
(i). Drawing of the isometric axis
(ii).Drawing of the given isometric box
(iii).Shaping of the box through outlining of the edges (i.e. making the box drawn thicker).
(iv).Dimensioning.

1. Drawing the Isometric Axis: After setting your paper on your board and drawing border lines and title block, follow the steps below:
i.   On the lower section of your drawing paper mark a small cross(+).
ii.  Using the 30⁰-60⁰ set-square, supported by the T-square, draw the first vertical axis from the intersection of the +.
iii.  Turn the set square to the 30⁰ slant with the edge intersecting at the + either to the right or left and draw the first receeding axis.
iv.  Rotate the set-square until another edge rest as base on the T-square on the same intersection and draw the second receeding axis.(your teacher will demonstrate).

                                                         Drawing Isometric Boxes

To draw the block given in isometric drawing, you can follow the steps below:
i.   Starting on the marked point(+), locate the length, breadth and height with the aid of a pair of compasses and mark these on the already drawn axis.
ii.   With the aid of the 30⁰ slant, starting from the marks made on the axis, draw parallel lines to the previous ones including the vertical axis.
iii.  Draw all parallels to complete any given block. (teacher will demonstrates)
NOTE: Please, note that all the steps explained above must be done in construction (faint) lines using the 2H pencil.

2. Outlining the Edges: Finally, using the HB pencil with moderate pressure, thicken the outline of the given block. You may erase the extra projected lines on your work since they may not be required as part of the given block.

3. Dimensioning: This is the technique of adding the actual size (length, breadth and height) of any block given. The following steps explains how:
(i). With the aid of the set-square and a little distance from the block drawn, draw faint projections (the projection lines should not touch the block) as the block.
(ii). Rotating the set square appropriately, draw arrowhead lines to indicate demarcations on the given block.

Practice Exercises:
1. Using the block sown on page 157 (fig. 7), draw the block in Isometric projection as shown.
2. Draw the block shown on page 158 (fig.11) in isometric projection.
(The teacher demonstrates)

                                                                   ASSIGNMENT

Draw the Isometric blocks shown on pages 156 – 165 of your J.N. Green Technical Drawing Text Book.
(i).Figure 10
(ii).Figure 9
(iii).Figure 8.

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