Scales. The scales used for obtaining measurements on drawings are made in several forms, the most convenient being the flat, with beveled edges, and the triangular. The scale is usually graduated for a distance of 12 inches. The triangular scale, Fig. 30, has six surface's for different graduations, and the scales are arranged so that the drawings may be made in any proportion to the actual size. For mechanical work, the common divisions arc multiples of two; thus drawings are made full size, V size, 1/4,1/8,1/16,1/32,1/64 etc. If a drawing is 1/4 size, 3 inches equals 1 foot, hence 3 inches is divided into 12 equal parts and each division represents one inch. If the smallest division on a scale represents 1/16 inch, the scale is said to read to 1/16 inch.

Fig. 30. Triangular Scale

Fig. 30. Triangular Scale.

Scales are often divided into 1/10,1/20,1/30,1/40, etc for architects and civil engineers, and for measuring indicator cards.

The scale should never be used as a substitute for the triangle or T-square in drawing lines.

Protractor. The protractor, an instrument used for laying off and measuring angles, is made of steel, brass, horn, or paper. When made of metal the central portion is cut out, Fig. 31, so that the draftsman may see the drawing. The outer edge is divided into degrees and tenths of degrees. To lay off the required angle - use a very sharp, hard pencil in order that the measurements may be accurate - place the protractor so that the two zero marks are on the given line, produced if necessary, and the center of the circle is at the point through which the desired line is to be drawn.

Fig. 31. Protractor

Fig. 31. Protractor.

Irregular Curve. One of the conveniences of a draftsman's outfit is the French or irregular curve, which is used for drawing curves other than arcs of circles, with either pencil or line pen. This instrument, which is made of wood, hard rubber, or celluloid - celluloid being the best - is made in various shapes, three of the most common being shown in Fig. 32.

To draw a curve through a series of located points find that position of the irregular curve that passes through several points and draw the line through them. Now shift the curve so as to include a few more points and so on until the curve is completed. It frequently facilitates the work and improves its appearance to draw a free hand pencil curve through the points and then use the irregular curve, taking care that it always fits at least three points. In inking the curve, the blades of the pen must be kept tangent to the curve.

Fig. 32. Irregular Curves

Fig. 32. Irregular Curves.

Beam Compasses. The ordinary compasses are suitable for drawing circles up to 8 or 10 inches diameter. For larger circles beam compasses, Fig. 33, are provided. The two parts called channels which carry the pen or pencil and the needle point are clamped to a wooden beam at a distance equal to the radius of the circle. The chumb nut underneath one of the channel pieces makes accurate adjustment possible.



W. Carbys Zimmerman, Architect, Chicago, 111. For First and Second Story Plans, See Page 42; for Elevations, See Page 58.

Fig. 33. Channels of a Beam Compass

Fig. 33. Channels of a Beam Compass.