This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The Pencils most used are H and F for small scale general drawings, and HB and B for details, but both harder and softer pencils are used occasionally. With regard to quality, it only need be said that a gritty pencil or one which breaks frequently is a constant source of annoyance. It is economy to pay a good price for a reliable pencil.
Drawing Pens need to be selected with the greatest care, as, after the T- and set-squares, they are the most used of all the appliances of an architectural draughtsman; and they vary much. The principal requirement is a stout lower nib, which will not yield to moderate pressure against the T- or set-square; but beyond this a good pen should be hinged to open, as shown in dotted lines in Fig. 14, so as to be easily cleaned, as it always ought to be directly after it has been used, wet ink being removed by a duster and dry ink scraped off with a knife.
If a pen becomes blunt with use, it has to be "set" or resharpened by rubbing the outside of each blade gently on an oil-stone, first when open, separately, and finally when closed together, when possibly the point may need a little rubbing vertically on the stone to bring both nibs to the same length. A little practice is necessary, and a novice is recommended to watch the process in the hands of an older man before trying it himself, else he may make matters worse instead of better, and produce a pen which will scratch or cut the paper. Generally a slightly rounded and broad point is preferred for the modern thick line on good paper, but for fine work and for clear lines on tracing cloth a sharp and narrow point is necessary.
Compasses are of several forms, including Dividers, Large Compasses, Bows, Spring Bows, Napier Compasses, Proportional Compasses, and Beam Compasses.
Of these, Dividers (see Fig. 15) are the most elementary, consisting of two similar legs ending with points as shown, or needles. They are used mostly for accurately measuring and transferring distances from one drawing to another. The screw at the top, which actuates a spring and enables very fine measurements to be made, is not always present, an instrument which possesses it being called a Hair Divider. The hinge joint can be tightened up if it works loose, by means of a key supplied with all boxes of instruments, and fitting all the compasses in the box.
Large Compasses (see Fig. 16) have either steel or needle points, needle points being shown in the illustration, so that they may be used as dividers, while one of the points may be removed from the socket at A and replaced either by the pen point, pencil point, or lengthening bar. There are knuckle joints at B, so that needles, pen, and pencil can all be brought vertically to their work, as shown in Fig. 17, in which the compass is shown with lengthening bar and pen point inserted, ready for striking a large circle. Needless to say, it requires some skill and steadiness of hand to draw such a circle accurately without slipping; and in fact it is best, when the lengthening bar is inserted, to use both hands, one holding the needle point on the centre while the other guides the pen.
Bows are small compasses (Fig. 18), made separately for pen and for pencil having a holder, A, beyond the joint to enable small circles to be struck at a single sweep. They are more used than any others, and the only respect in which they require special care is in keeping the pencil the same length as the needle point. The pencil may, if preferred, be cut to a chisel edge instead of a point. Spring B,ows (Fig. 19) are intended for the very smallest circles. They are made of fine steel, and act like a spring, tending to open out against a small screw nut, by means of which they can be adjusted to the nicest accuracy, the extent to which they are allowed to open remaining constant for any desired length of time. It is necessary that the screw bolt should pass through a slotted hole in the needle arm, else the bows will open in a jerky manner.
Napier Compasses are made to fold, so as to be carried in a pocket, and are of many different forms; but they are unfortunately liable to work loose at the joints, and so are not reliable for accurate work.
Proportional Compasses (Fig. 20) open at both ends round an adjustable centre screw hinge working in a long slot. They are made with points only, and the centre screw can be so set that the distances between the long points are equal to those between the shorter points, or two, three, four, or more times those distances, as may be required. They are consequently of great value for enlarging or reducing drawings in exact ratio - and by varying the scales engraved upon them they can be adjusted to give the proportions either of lines, areas, or solids.
Beam Compasses (Fig. 21) are quite different from the other forms, and are intended for striking very-large circles only. They consist of two separate legs, each of which can be clamped, by means of metal plates and a screw, to a long lath or the blade of a T-square. Each leg can be fitted at will with either needle point, pen, or pencil, and to one at least there is a travelling thread worked by a mill - headed screw A, to give absolutely exact adjustment of distance. In use, especially with circles of really large radius, it is necessary for one person to hold the needle on the centre, while another guides the pen or pencil.
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A Pricker is another important instrument, though it is nothing more than a needle with a handle to it, for use when transferring drawings from one sheet of paper to another, by placing the sheets over one another and pricking the principal points through from the upper to the lower sheet.
A Protractor is an instrument for measuring angles on a drawing with more or less accuracy. Most of those supplied with sets of instruments in boxes or cases are made of horn or ivory and are quite unreliable. Somewhat heavy circular protractors made of brass (see Fig. 22) are those upon which most dependence can be placed, though if very close readings are required they must be supplied with an extending revolving arm, with a vernier scale on it like that on a theodolite, with similar clamp and tangent screws for accurate adjustment.
Drawing pens, pricker, compasses, bows, spring bows, and protractor are frequently bought in cases or boxes, but there is always some risk that a set thus purchased may contain one imperfect instrument or more, and many draughtsmen prefer to purchase singly in consequence, keeping their instruments in a roll of chamois leather pockets (see Fig. 23) such as can readily be made at home.