Fig. 49a. how the lines for isometric drawings are made
(2) Take a sheet of white paper exactly 5¹⁄₈ inches wide and 10 inches long and draw two diagonal lines from corner to corner so that they will cross each other, then draw a vertical line through the middle and a horizontal line near the bottom. The diagonal and horizontal lines will be 30 degrees apart.
(3) By laying a 30 degree triangle on your T square and drawing a line along the 30 degree side of it as shown in [Fig. 47]; and (4) by laying off 30 degree lines with a protractor.
To do this tack a sheet of paper on your drawing board and draw a horizontal line near the bottom of the paper with your T square; put your protractor on the horizontal line near one end, lay the edge of the rule on the center of the protractor and exactly on the 30 degree scale mark and then draw a line.
Fig. 49b. a sheet of isometric drawing paper
Slide the protractor on the opposite side of the board, draw another 30 degree diagonal line so that it will cross the first one and draw a vertical line down through the middle of the paper.
Having, now, your sheet of isometric ruled paper you are ready to do the drawing. Whatever the picture is to be, all you need to do is to follow the 30 degree lines and the vertical lines and you simply can’t help getting it in perspective.
In drawing isometric perspective circles, such as wheels, disks and the like, they are always shown as ellipses, that is, closed oblong curves. To draw an isometric ellipse,[40] make it in the proportion of ⁵⁄₈ to 1, that is, if it is ⁵⁄₈ inch wide, as we will call its minor axis, then make it 1 inch long, as we will call its major axis, as shown at [C in Fig. 49], and you will have one that is near enough the right shape for your purpose; thus if you want to show a tube or a pipe, draw it as pictured at [C]. Now with these few principles well in mind you can make a working drawing of nearly anything you please.