Besides scales of the kind just described, which are termed plain divided scales, there are in common use what are known as diagonal scales, an illustration of one of which is shown in Fig. 118. The scale represented is that of 1 1/2 inches to the foot. The left-hand unit of division has been divided by means of the vertical lines into 12 equal parts, representing inches. In width the scale is divided into 8 equal parts by means of the parallel lines running its entire length. Next the diagonal lines are drawn, as shown.
Fig. 117. - Plain Scale (1 inch to the Foot)
By a moment's inspection it. will be seen that, by means of these diagonal lines, one-eighth of an inch and multiples thereof are shown on the several horizontal lines. A distance equal to the space from A to B, as marked on the scale, is read (first at the right for feet) 2 feet (then to the left for inches by means of the vertical lines figured both at top and bottom) 6 inches (and last, by means of the diagonal line, figured at the end of the scale, for fractions) and three-eighths. The top and bottom lines of the scale measure feet and inches only. The other horizontal lines measure feet, inches and fractions of an inch, each horizontal line having its own particular fraction, as shown. Such scales are frequently quite useful, as greater accuracy is obtained and, as the reader will sec, may be constructed by any one to any unit of measurement, and divided by the number of horizontal lines into any desired fractions.
Fig. 118. - Diagonal Scale (1 1/2 inches to the foot).
A scale in common use, and known as the triangular scale, is shown in Fig. 110. The shape of this scale, which is indicated by the name, and which is also shown in the cut, presents three sides for division. 13y dividing each of these through the center lengthways by a groove, as shown, six spaces for divisions are obtained, and by running the scales in pairs - that is, taking two scales, one of which is twice the size of the other, and commencing with the unit at opposite ends - the number of scales which may be put upon one of these instruments is increased to twelve. This article, which may be had in either boxwood, ivory or plated metal, and of 6, 12, 18 or 24 inches in length, is probably the most desirable for general use of any sold.
Fig. 119 - Triangular Boxwood Scale.
A flat scale is also manufactured in both boxwood and ivory. Fewer scales or divisions can be put upon it than upon the triangular scale, yet for certain purposes it is to be preferred to the latter. There are less divisions to perplex the eye in hunting out just what is required, and accordingly, there is less liability to error in its use. However, the limited number of scales which it contains greatly restricts its usefulness.
Fig. 120 shows another form of the flat scale, in quite common use in the past, but now virtually discarded in favor of more convenient dimensions and shapes. This scale combines with the various divisions of an inch the divisions of the protractor, as shown around the margin. The fact that the divisions of an inch for purposes of a scale are located in the middle of the instrument, away from the edge, which makes it necessary to take off all measurement with the dividers, renders the article awkward for use, and the arrangement of the divisions of the circle, on the margins, is less satisfactory for use than the circular protractor.
Fig. 120. - Flat Scale with Divisions of the Protractor on the Margins.
Lead Pencils. - Various qualities of pencils arc sold, some at much lower prices than others, but, all things considered, in this as in other cases, the best are the cheapest. The leading brands are made in two grades or qualities. The ordinary grades employ numbers, 1, 2, 3, etc., to indicate hardness of lead, No. 1 being the softest, and No. 5 being the hardest in common use. A finer grade of pencils, known as poligrades, is marked by letters, commencing at the softest with B B, and ending at the hardest with H H H H H H, while other makes of pencils are marked by systems peculiar to their manufacturer. The draftsman has the choice of round or hexagon shape in all except the finest grades, the latter being made exclusively hexagon. Whatever kind of pencil the draftsman or mechanic uses, he will require different numbers for different purposes. For working drawings, full-sized details, etc., on manila paper, a No. 3 (or F) is quite satisfactory. Some like a little harder lead, and therefore prefer a No. 4 (or H). For lettering and writing in connection with drawings upon manila or ordinary detail paper, a No. 2 (H B) is usually chosen. For fine lines, as in developing a miter, in which the greatest possible accuracy is required, a No. 5 is very generally used, although many pattern cutters prefer the liner grade for this purpose and use a H H H H H.
The quality and accuracy of drawings depend, in a considerable measure, upon the manner in which pencils are sharpened. A pencil used for making line straight lines, as, for instance, in the various operations of pattern cutting, should be sharpened to a chisel point, as illustrated in Fig. 121. Pencils for general work away from the edges of the T-square, triangle, etc., should be sharpened to a round point, as shown in Fig. 122. It facilitates work and it is quite economical to have several pencils at command, sharpened in different ways for different purposes. Where for any reason only one pencil of a kind can be had, both ends may be sharpened, one to a chisel point and the other to a round point.