Referring to Fig. 29, it will be seen that the jaw is open two-tenths and three-quarters, which is equal to two hundred and seventy-five thousandths (0°275). Now suppose the vernier was moved to the right so that the tenth division should coincide with the next one on the scale, which will make ten-thousandths (o'o10) more to be added to BEVEL SQUARE о DETAILS FIG. 31A. In making inside measurements with the 6-in. vernier and the pocket vernier calipers, two and one-half tenths or two hundred and fifty thousandths (0.250) of an inch, and with the 12-in. and 24-in. verniers, three-tenths or three-hundred thousandths (0*300) of an inch should be added to the apparent reading on the vernier side for the space occupied by the caliper points. When the other side of the instrument is used, no deduction is necessary, as there are two lines, one indicating inside and the other outside measurements. Universal Bevel Protractor.-Protractors are instruments by which angles are set out in degrees. Fig. 30 is the Brown and Sharpe Universal Bevel Protractor, and is adapted for those classes of work in which angles are to be laid out or established. The circular dial is graduated in degrees round the entire circle, and is recessed below the face to protect it as the bevel is used. This combination of "bevel" and protractor render it indispensable for setting THE LS STARRETT CO.ATHOL, MASS.U.S.A. FIG. 33.-Spirit level for testing shafting. out and gauging work in the tool-room. The blade can be moved either way its full length, and clamped independently of the dial. The THE LS STARRETTICO ATHOL MASS US A FIG. 34. Electrician's non-magnetic spirit level. many uses to which the instrument can be put cannot all be cited here, but further comment is unnecessary after looking at some of its applications in Fig. 31. A fitter's bevel square is shown in Fig. 31A. Thickness Gauge, or "Feeler."-Thickness gauges (Fig. 32) are used either singly or in combination, to ascertain the width of gap between two surfaces, also to test the thickness of sheet material. FIG. 35.-Pocket level. The leaves vary in thickness by 1000 in., running from 0'004 to 0'025. Spirit-levels. -Spiritlevels are used to test the alignment of shafts, tables, beds, and other fitting parts of machinery. The under surface of a level is scraped to a true plane, so that it will lie even. Fig. 33 shows THE L.S.STARRETT.CO. FIG. 36.-Depth gauge. one of these instruments made with a concave groove running the length of its base, which renders it useful when testing the evenness of shafts. In addition to the longitudinal glass, the base is fitted with a cross-level which removes the necessity of changing the position L.S.STARRETT. THE LSSTARRETT CO. ATHOL MASS. U.S.A. FIG. 37.-Depth gauge. FIG. 38.-Depth gauge. of the instrument so frequently. Fig. 34 is a non-magnetic level, being designed for use in electrical work. Fig. 35 shows a pocket level made of steel and plated; the length is 2 in. Depth Gauges.-Depth gauges are used to measure the depths of grooves in milled and planed work, also in lathe face plate work, when one surface has to be turned to a definite distance from another surface. The gauge can be set to the depth required, and secured by the setscrew. Fig. 36 shows a gauge in which the wire is held by a friction spring inside the nut. Fig. 37 is a similar gauge, except that a marked scale is substituted for the wire rod. The gauge shown in Fig. 38 admits of a more accurate setting; it has a micrometer screw reading to 10 in. Standard collars are passed on the spindle when the depth of the recess to be measured is considerable. A lock nut at the top of the spindle prevents any changing after the gauge has been set. CHAPTER II. "MARKING" OR "LINING-OUT” WHEN castings and forgings are delivered into the machine shop, they are first placed on a marking-off table, and “set out" for machining. It is the practice for templates to be made to dimensions on drawing for each type of engine or machine, a practice which greatly facilitates the marking, and whereby the templates serve as guides, and sometimes as gauges, for the machine operatives. The above system can be generally applied to duplicate work. When, however, it is not practised, drawings fully dimensioned are supplied. Whichever system is adopted, a careful and reliable workman is sought for the post of marking off. He is obviously required to thoroughly understand all kinds of drawing details, and be able to trace them out, frequently from complicated elevations, end views, or plans, and is responsible for each part being correctly tooled and fitted to the lines scribed. Marking tables" vary in dimensions from 4 ft. to 12 ft. long. The upper surface is truly planed, as are also the edges which are truly at right angles to the face and to each other. The under side of the table is strengthened with ribs, similar to a surface plate, to keep it true under varying conditions. The table should be set by the aid of a spirit-level to lie even in all directions, and supported in such a manner as to remain firm under any load. Such a table is shown in Fig. 39, provided with a complete set of tools, as follows: Nos. 1 and 2, large and small squares; Nos. 3, 4, and 5, scribing blocks; No. 6, parallel blocks; Nos. 7, and 8, vee blocks; No. 9, compasses; No. 12, large straight-edge. Tools not numbered.-Accurate steel rule, marked in terms of British and decimal measures. A plumb-bob and spirit-level, pair of inside and outside calipers, also odd-leg calipers, trammels and scriber, centre and prick punch. EXAMPLE. The engine connecting-rod, No. 10, is mounted on parallel and vee blocks after machining, while the centre and other dotted lines are tested with the scribing block (a temporary pin being inserted in the fork end). The example, No. 11, represents a rough, forged fork end, marked off for machining; the centre line shown would be marked similarly on the opposite side of fork. The inner circle |