ity of the shadows of the T-square blade or triangle being cast on the lines to be drawn.

Sharpening a Ruling Pen. The blades of the pen should be curved at the points, and elliptical in shape. To sharpen the pen, screw the blades together and then move the pen back and forth upon a fine oil-stone, holding it in the position it should have when in use, but moving it so that the points are ground to the same length, and to an

ground as thin as possible without giving them a cutting edge. To do this, the pen should be moved back and forth and slightly revolved at the same time. Both blades must be made of equal thickness. If either blade is ground too thin, it will cut the paper as would a knife, and the process must be repeated from the beginning. In order to see the condition of the blades, they should be slightly separated while being brought to the proper thickness.

Drafting Instruments. A leather-covered case

Fig. 11-Complete Set of Instruments in Case. elliptical form. When this form has been secured, draw a folded piece of the finest emery paper two or three times between the blades, which are pressed together by the screw. This will remove any roughness from the inner surfaces of the blades, these surfaces should not be ground upon the oil-stone.

When the blades are ground to the proper shape, they must be placed flat upon the stone and

Fig. 12-Slanting Blade T-Square.

with a complete set of instruments in a velvet lined tray is shown in Fig. 11. This outfit is sufficient to fulfill the requirements of any ordinary draftsman in the way of instruments.

T-Square. The length of a T-square is always measured by the length of the blade outside of the head. The T-square should always be as long as the drawing board, and if possible a little longer. For the general run of work the head of the Tsquare should be of a single and fixed piece, that

is, fastened permanently to the blade. The head should have its upper inside corner rabbeted, so that the guiding edge of the head may be trued up when occasion demands it. A very convenient

AA

Fig. 13-60 and 45 Degree Triangles.

form of T-square is shown in Fig. 12, which has a slanting blade, the working edge of which is lined with ebony.

clamped in any desired position by means of a thumb-screw.

Triangles or Set-Squares. Triangles are made of wood, hard rubber or transparent celluloid. The principal forms of triangles are shown in

Fig. 15-Flat Beveled-edge Scale.

Figs. 13 and 14, which are 60°, 45° and 15° respectively. The two triangles generally used by draftsmen are the 60° and 45°. The former has angles of 30°, 60° and 90°. The latter two 45° and a 90° angle.

Testing Triangles. Place the triangle on the Tsquare with the vertical edge at the right, draw a

60

Fig. 14-15 Degree Triangle.

More elaborate forms of T-squares are sometimes used, in which the head is double and one side swivels in order to draw parallel lines other than horizontal. The adjustable or swivel head is

Fig. 16-Triangular Scale.

fine line in contact with this edge, then reverse the triangle and move the vertical edge towards the line. If the vertical edge of the triangle and the line coincide the angle is 90°. If they do not coincide, and the vertex of the angle formed by

the line and the vertical edge of the triangle is at the top, the angle is greater than 90° by half the angle indicated. If the, vertex of the angle is below, the angle is less than 90° by half the amount indicated.

&a

Fig. 17-French Curves.

Scales. The best and most convenient form of scale for general use is that shown in Fig. 15. Another form of scale which is very commonly used is shown in Fig. 16. The ordinary length of a

scale is 12 inches, not counting the small portion at each end, which is undivided, and whose use is to protect the end graduations from injury. A scale should be used for dimensioning drawings only, and not used as a ruler or straight-edge. The measurements should be taken directly from the scale by laying it on the drawing, and not by transferring the distances from the scale to the drawing by means of a pair of dividers.

Curves. For inking in lines which are neither straight lines nor arcs of circles, it is necessary to

26

Fig. 18-Useful Form of Curve.

use curves. They are made in a great variety of forms as illustrated in Fig. 17, but the form similar to that illustrated in Fig. 18 will be found the most useful. They are made of wood, hard rubber and celluloid. Many curved lines can be inked in by means of a compass, but when the radius is too great, a curve should be used.

Paper. The paper must be tough and should

14

have a surface which is not easily roughened by erasing lines drawn upon it. This is important when drawings are to be inked. For all mechanical work, the paper should be hard and strong.

For pencil drawings a paper which is not smoothly calendered is best, because the pencil marks more readily upon an unpolished paper, and because its surface will not show erasures as quickly as that of a smooth paper. For sketching, several kinds of paper, which are good enough for the work, may be obtained both in sheets, in block form, and also made up in blank books.

Whatman's paper is the best for drawings which are to be inked. There are two grades, hot and cold pressed, suitable for this use, the coldpressed having the rougher surface. If the paper is not to be stretched, the cold-pressed is preferable, as its surface shows erasures less than that of the hot-pressed. The side from which the water-marked name is read is the right side, but there is little difference between the two sides of hot and cold pressed papers. Stretching the paper is unnecessary except when colors are to be applied by the brush, or when the most perfect inked drawing is desired.

Pencils. Lead pencils for drafting use are made of different degrees of hardness and each kind of pencil has its grade indicated by letters stamped on it at one end. The grade of pencil mostly used by draftsmen is 4 H; a 6 H pencil is

too hard and unless used with great care will indent the paper so that the pencil marks cannot be erased. A 4 H pencil requires greater care and more frequent sharpening, but the draftsman will in this manner acquire a lighter touch, which is of much value. Drafting pencils should always be sharpened to a chisel or wedge-shaped point, as shown in Fig. 19, the finishing of the point should always be completed with a fine file or a sand paper pencil sharpener, but never with a knife. In drawing the pencil should be held ver

Fig. 19-Correct Manner of Sharpening a Pencil. tical, or nearly so, the arm free from the body, and the flat side of the chisel-point lightly touching the edge of the blade of the T-square. Always draw from left to right, or from the bottom to the top of the board.

Pencil Sharpeners. Pencil sharpeners or pointers are of many different kinds, from a piece of fine sand paper or a file to quite complicated machines. For ordinary use a sand paper block from which the sheets can be removed as soon as worn out will be found the most convenient, as shown in Fig. 20. In sharpening a drafting pencil remove