DRAFTING PENCILS

Engineering Aid 3 - Beginning Structural engineering guide book
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DRAFTING PENCILS Two types of pencils are used in drafting: wooden and mechanical. The latter is actually a lead holder and may be used with leads of different hardness or softness. Drafting pencils are graded according to the relative hardness of their graphite lead. A pencil that is considered soft is designated by the letter B. On the other hand, a hard pencil is designated by the letter H. Figure 2-1 shows 17 common grades of drafting pencils from 6B (the softest and the one that produces the thickest line) to 9H (the hardest and one that produces a thin, gray line). You will notice that the diameters of the lead vary. This feature adds strength to the softer grades. As a result, softer grades are thicker and produce broader lines, while harder grades are smaller and produce thinner lines. Unfortunately, manufacturers of pencils have not established uniformity in grades. Hence, a 3H may vary in hardness from company to company. With experience and preference, you may select the trade name and grade of pencil that suits your needs. Selection of drafting pencils will be covered in chapter 3. 45.672X Figure 2-2.-Types of erasers. ERASERS AND ERASING ACCESSORIES You must be very careful in selecting an eraser that will remove pencil or ink lines without damaging the surface of the drawing sheet. A vinyl eraser (fig. 2-2, view A) is ideal for erasing lines drawn on tracing cloth and films. An ordinary double-beveled pencil eraser generally comes in red or in pink color (sometimes called a PINK PEARL). A harder eraser (sometimes called a RUBY RED) (fig. 2-2, view B) is designed for erasing lines in ink. The ART GUM eraser (fig. 2-2, view C), made of soft pliable gum, will not mar or scratch. It is ideally suited for removing pencil or finger marks and smudges. You can also use a kneaded eraser—the type used by artists. It is a rubber dough, kneadable in your hand, and has the advantage of leaving very little refuse on the drawing sheet. The so-called STEEL ERASER, shown in figure 2-3, is, of course, actually a scraper. It is used principally for scraping off erroneous ink lines, especially from tracing cloth. The figure shows a short-bladed steel eraser; long-bladed steel erasers are also available. A steel eraser is not generally recommended for use by beginners because it has a tendency to damage the surface of the drawing sheet. Figure 2-4 shows an ELECTRIC ERASER. The control switch is directly under the fingertip; 45.673 Figure 2-3.-Steel eraser. 45.674 Figure 2-4.-Electric eraser. 2-5

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