7. A sketch, when possible, should have all the dimensions written upon it, but—
8. Sketches in shop practice should not take the place of working-drawings; the latter have a check upon them in being drawn to a scale—hence the figures written upon them and dimensions by scale must agree.
9. Place title and date on each sketch—no matter how seemingly unimportant—for future reference.
10. Practice sketching at every favorable opportunity. There is no necessity for detail at first—simply the outlines of the article and its parts.
11. Sketch-books, with paper bound in cloth covers, are utilized for bold, off-hand sketches by experienced draughtsmen, but a single sheet of paper, used on both sides, is not unworthy of service in an emergency—or even the blank side of a letter may be available. Sketching-blocks, or paper “pads,” 4 × 6, or more, in size, and containing 48 sheets, are sold by stationers, and are found to be most convenient to have in hand and for practical use. Portfolio-envelopes, made of extra length paper (manila) are useful in filing away sketches and drawings. The size 101⁄2 × 15 is used for United States Patent Office drawings.
The function of the pencil—in mechanical drawing—is to make a path for the pen to follow. If it were possible to make a drawing with all its lines ending at the proper place, at the first time, there would be no necessity for using the pencil. One is obliged, however, so to use the pencil that all lines pass beyond the actual ending place, thus making a distinct point for the drawing pen to stop at.
The pencil should be pressed to the paper just enough to make a clean, fine line, and no more; once over the path is sufficient, if the line is visible and true.
To sharpen drawing pencils, 1, use a fine file, after taking off enough of the wood with a knife; 2, make a conical point for the free-hand drawing pencils and a chisel point for ruling and marking distances.
Pencil compasses are instruments where one leg is provided with a pencil point. [Fig. 209] shows the mode of manipulation of those shown in [fig. 180] and [fig. 181].
The pencil compass is held by the projection above the joint between the thumb and first finger, which enables it to be rotated by a movement of the finger without causing any undue pressure on the points. Should much pressure be applied, there is a tendency to force the point or center through the paper, making an ugly center mark; at the same time the pressure tends to break off the pencil point.