Drawing Pins must be thin enough at the edges for the T-square to slip over them readily, and yet thick enough in the centre for the pin to be firmly attached to the brass head. If the head be of soft brass it is likely to give way when pressed home, with the result that the blunt end of the steel pin runs into the thumb of the user. The wound made is a troublesome and painful one, which can be avoided by selecting only good pins of hard brass or German silver, and these are not expensive.

The two forms which are in most general use are those lettered A and B in Fig. 6, the dome-shaped head (A) being the best for large pins, while the flat head with bevelled edge (B) is most convenient in smaller sizes. Both sorts are made in several sizes, from 1/2 to 7/8-inch diameter; but the larger pins are far the best, gripping the paper well, easy to remove, and not very easily lost.

The pin lettered D in Fig. 6 is better still. It is of gimlet form, and makes a very small hole either in paper or in board, while the head, besides having bevelled and milled edge, has four holes through it, to facilitate its being inserted or removed by a twisting action with the thumb. It is known as the "Grip."

The small pins, lettered C, are stamped out of solid nickel-plated steel, head and pin being in one piece. They are very cheap, and are useful for the temporary attachment of small tracings rather than for large work.

Set-Squares (see Fig. 7) are small triangles of which one angle is necessarily a right angle. The other angles may vary, but for most work it is sufficient to keep one having each of these 45 degrees, and another having one angle of 30 and one of 60 degrees. Those of the forms shown as A and B in Fig. 7 are generally made of pear-wood, vulcanite, or transparent celluloid. Of these, pear-wood is generally preferred, for it is clean and cheap, while vulcanite collects dust and rubs it into the paper, and celluloid buckles. The framed form, C, is generally made of mahogany, with bevelled edges, often of ebony; but it is exceedingly liable to lose its shape, and a set-square whose angles are incorrect is worthless and must be destroyed.

Drawing Instruments And Materials 7

Fig. 6.

Drawing Instruments And Materials 8

Fig. 7.

Fig. 10. Parallel Ruler.

Fig. 10. Parallel Ruler.

A set-square having a movable arm which can be adjusted to any desired angle, known as a clinograph (see Fig. 8), is also made, but as a general rule it is dispensed with, and parallel lines at unusual angles are drawn by adjusting the T-square on the board so as to use one of the ordinary set-squares, sliding it along the T-square as desired while holding it carefully in position(Fig.

Drawing Instruments And Materials 10

Fig. 8.

9).

The same result can be obtained by using a T-squ are with a revolving head to which the blade can be clamped at any desired angle, or by employing a Parallel Ruler (see Fig. 10). This, to be of any real service, should be large and heavy, with large grooved rollers projecting but slightly below the under flat surface, and with bevelled edges. None should be purchased without first testing, as any inaccurate setting of the rollers will prevent accurate rolling, and render impossible the production of parallel lines.

A few French Curves (see Fig. 11) are kept in most offices to assist the unskilled to draw subtle curves in short lengths, little by little; but a good freehand draughtsman will generally disdain their assistance. The Scales in general use for architectural work are those of 1, 2, 4, and 8 feet to an inch, known colloquially as "inch," "half-inch," "quarter," and "eighth" scales respectively. They are to be obtained 6, 12, or 24 inches long, the 12-inch scales being generally used, engine divided with extreme accuracy on either box-w o o d or ivory; and while it is best to have only one scale on each edge, and that reading only in one direction, for the avoidance of errors, yet many prefer to have the readings from both ends, and even to have several scales on the same edge (see Fig. 12). Two sections are made (see Fig. 13), of which the oval has readings on both sides, and is most convenient as a short 6-inch scale for carrying about in a rule-pocket for occasional use, as illustrated in Fig. 12, while the flat form has readings on the bevelled edges only, and is the more suitable for use on the drawing board. A 2-foot Rule should be carried by everybody engaged in building operations, from the architect downwards, and is most useful if it has a series of scales along bevelled inside edges. A special pocket has to be made for it, preferably in the coat of a draughtsman and in the trousers of a workman, this pocket measuring 6 inches deep by 1 1/2 inches wide, and being useful also for pencils and fountain pen.

Drawing Instruments And Materials 11

Fig. 9.

Drawing Instruments And Materials 12

Fig. 11.

Drawing Instruments And Materials 13oval section.

Oval section.

Fig. 13. flat section.

Fig. 13. flat section.

Indian or Chinese Ink may be rubbed up from a stick in a palette with a little water, the rubbing being continued until the liquid begins to thicken and becomes jet black, or may be purchased in bottles ready mixed. This latter form is so convenient that it is now almost entirely used, though it is slightly more expensive; and an indelible ink, which, once dry, will not " run" when washed over with ink or colour, is as easy to obtain as the ordinary kind.