useful for tilting the hoard up at a convenient angle for work.
The T Square Figs. 8 and q, is used chiefly for drawing horizontal lines. It should be of the same length as the board used, and those with tapering blades are to be preferred. The stock should be rebated and chamfered as shown in the enlarged detail, Fig. 10, so that if the paper overhangs the board it will not throw the square out of place. The chamfering prevents the set square catching upon the edge, should the stock lie out of level. The blade should be screwed to the stock, and in the larger sizes dowelled also, as shown in Fig. 10, but not glued, as it is necessary to take it off for re-shooting at times. The fop edge should be chamfered down to T*r in. thick, so that lines may be seen easier, also to reduce the risk of irregular lines through alteration of the angle at which the pencil is held. Many draughtsmen use a square which has a strip of celluloid sunk in the working edge (see Fig. 11). as lines can be seen through it; it is chiefly of service when inking-in large drawings.
Set Squares, Figs. 12 and 13, are triangles used in conjunction with the T-square for drawing vertical, perpendicular and parallel lines at any angle. They are made of various shapes, materials and sizes. Themost useful sizes and shapes are those known as 450 and fio°, and from 4 in. to 8 in. in height. The 450 square, Fig. 12, is the triangular half of a true geometrical " square" ; one angle is a right angle, the other two contain 45 degrees each, between the adjacent edges. The 60°, Fig. 13, has angles of qo°, 30° and 6oc respectively, and it might as rightly be termed " 30°,'' but is generally described as above. They are made in hnrd-woods, vulcanite and celluloid. Wood is not to be recommended ; it alters in shape and has to be too thick to be manageable : exception may be made to this general statement in the case of " framed " or open squares made of hard-wood with the edges chamfered upon one side. These are expensive. Celluloid is the most useful, as it can be seen through, a great advantage in elaborate drawings, but it has a serious draw-
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