Fig. 1441.
Another method of closing such a piece as an eye of large diameter compared to its section, is shown in [Fig. 1440]; first dipping the heated eye at a and holding it there till cold and then slowly lowering it into the water, which would close the diameter across c, and, after reheating, dipping at d till cold, and then slowly immersing, which would close the eye across e. To shrink a square ring, the whole ring would require to be heated and a side of the square dipped, as shown in [Fig. 1441], until quite cold, and then immersed slowly for about an inch, the operation being performed with a separate heating for each side. Connecting rod straps, wheel-tires, and a large variety of work may be refitted by this process, but in each case the outside diameter will be reduced.
Chapter XV.—MEASURING TOOLS.
For what may be termed the length measurements of lathe work it is obvious that caliper gauges, such as shown in [Fig. 1402], may be employed. Since, however, these length measurements rarely require to be so accurate as the diametrical measurements, the ordinary lineal rule is very commonly employed in work not done under the standard gauge system. It is obvious, however, that when a number of pieces are to be turned to corresponding lengths, a strip of sheet iron, or of iron rod made to the required length, may be employed; a piece of sheet iron filed to have the necessary steps being used where there are several steps in the work; but if the lineal measuring rule is used, and more than one measurement of length is to be taken, some one point, as one end of the work, should be taken wherefrom to measure all the other distances. Suppose, for example, that [Fig. 1442] represents a crank pin requiring to have its end collar 1⁄4 inch thick, the part a 2 inches long, part b 3 inches long, collar c 1⁄2 inch thick, and the part d 7 inches long. If the length of each piece were taken separately and independently of the others, any errors of measurement would multiply; whereas, if some one point be taken as a point wherefrom to measure all the other distances, error is less liable to occur, while at the same time an error in one measurement would not affect the correctness of the others. In the case of the crank pin shown, the collar c would be the best point wherefrom to take all the other measurements. First, it would require to be made to its proper thickness, and the lengths of b, a, and the end collar should be measured from its nearest radial face. The length of d should then be measured from the same radial face, the thickness of the collar being added to the required length of d, or d may be measured from the nearest radial face of c, providing c be of its exact proper thickness. In measuring the length of the taper part d, a correct measurement will not be obtained by laying the rule along its surface, because that surface does not lie parallel to its axis, hence it is necessary to apply the measuring rule, as shown in [Fig. 1443], in which s is a straight-edge held firmly against the radial face of the crank pin (the radial face being of course turned true), and r is the measuring rule placed true with the axial line of the crank pin. Whenever the diameters of the lengths to be measured vary, this mode of measuring must be employed. On small work, or on short distances requiring to be very exact, a gauge such as shown in [Fig. 1444] at a may be employed, which will not only give more correct results, but because it is more convenient, as it can be conveniently held or tried to the work with one hand while the other hand is applied to the feed screw handle to withdraw the cutting tool at the proper moment, and to the feed nut to unlock it and stop the feed.
Fig. 1442.