Tips Towards Drawing Better Diagrams Michael N. Quigley Chevron Science Center, University of Pittsburgh, Pittsburgh, PA 15260 It is often necessary to iUustrate reports or published articles with figures, or diagrams of apparatus. Most journals impose strict rules for the format of graphs, and labeling of figures i n general, but little can be done to st&dard&e drawing ability. Even in this age of computeraided desim, skillfully hand-drawn diagrams are taken notice of, and those that are poorly drawn detract from what might be an otherwise flawless piece of work. The author is the fint to admit that his skills as a draughtsman leave a lot to be desired, but certain rules have aided in his ability to produce fairly respectable diagrams. Projection Three different projections should be considered: oblique, axonometric, and isometric, as shown in Figure 1. Most people believe that the latter produces the most realistic image, but there are instances in which the alternative projections are preferred.
Perspective This is especially useful when spatial detail needs to he emphasized. Drawing in true perspective, results in diagrams that are technically perfect, but for the nonexpert the time expended might be considered unjustified. It is possible to draw acceptable perspective projections, however, by again remembering a few simple rules. With reference to Figure 2, a line that establishes the "eye-level" first needs to be drawn. This takes account of the usual tendency to look down at an object. A series of "vanishing points" should be placed along the eye-level line. These may then be used to draw in the horizontal surfaces of the obiect. Drawine a sinele vertical at the forward facing corner of the o b j e c t ~ u t ~ m ~ t i csets a l lthe ~ length of all other vertical lines associated with it. In this wax ".the diagram can be made to have "depth". One ~roblemcommon to ~roiectionand oers~ectiveis how to'draw appropriately modified circles.BorAinstance, how can a circle be even a sense of deoth? The easiest wav t o take account oftl& is to make use dfcommercially avaiiable templates containing various sizes of ellipse.
(a) Oblique
Eye Level
(b) Axonornetric
(c) Isometric
Fioure 1. Proiections of a rectanoular orism. Dimensions A. B. and C a 6 the same'for all projections, except for dimension Bin the bblique projection (1128 is recommended).
Figure 2. Perspective of a rectangular prism. VP1 and VP2 refer to vanishing points.
Volume 69 Number 11 November 1992
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