Fig. 2579.
The method of aligning the lathe heads at the Pratt and Whitney Company’s workshops is as follows: [Fig. 2579] is a side and an end view of a part of a lathe shears a, with the tailstock b thereon. To the bore of the tailstock there is closely fitted an arbor c, accurately turned in the lathe, and having at the end d and at e two short sections of enlarged diameter. A plate f is fitted to the inside Vs of the shears (upon which Vs the tailstock sits). This plate carries a stand g, and a second gauge or stand g. Stand g fits at its foot into a V provided in f, as shown, the object of which is to so hold g to f that its (g′s) face will stand parallel to arbor c. The stand is so adjusted that a piece i may be placed between c and g and just have contact with both, and it is obvious that if this is found to be the case with the tailstock and the stand placed at any position along the bed, the arbor c, and, therefore, the bore of the tailstock, must be true, sideways, to the inside Vs of the lathe shears. The testing, however, is made at the enlarged sections d and e, g of course being firmly bolted to f. To test the height of the arbor c from the Vs, and the parallelism in that direction, stand h is provided. It carries a pointer or feeler k, whose end is adjusted to just touch the enlarged sections d and e of c, it being obvious that when the degree of contact is equal at these two sections, with the tailstock and the plate f moved to various positions along the bed, the adjustment or alignment in that direction is also correct. The adjustment and corrections may then be made with the headstock of the lathe in place of the tailstock, the arbor fitting into the bored boxes of the lathe and extending from it, and having two sections of the same diameter, as sections e in the figure. Now, suppose that in the test thus made the bar c proves to stand true in some locations, but not in others, upon the bed; then it is proof that it is the Vs that require correction, while the tailstock is in error in all cases in which the error is constant, with the tailblock moved in various positions along the shears.
In some practice the heads are bored after being fitted to the ways, and in this case the boring bar may be supported by standards fitting to the lathe bed, running in bearings, and not on centres. There should be three of these bearings, one at one end of the head, and as close to it as convenient, another at the other end, as close as will permit the insertion of the cutters, and the third as far from the second as will permit the insertion on the bar and between them of a pulley to drive the bar, which must be splined to receive a feather in the pulley, so that the bar may be fed through its bearings and through the pulley to the cut. After the live head has been bored the tailstock or back-head may be bored from the other end of the bar, so that the standards will not require to be moved on the bed until the boring is completed. The bar may be fed by hand, or an automatic feed motion may be affixed to one of the standards. The heads being secured to the bed while being bored, there is no liability of error in their alignment, because, even if the holding bolts spring the heads in clamping them to the bed, the holes will be true when the heads are firmly home upon the bed, as they will be when in use, whereas under this condition such will not be the case if the holes for the spindles are bored before the seats are planed and fitted.
The feed screw must be placed quite parallel to the Vs or guides of the bed, or otherwise the pitches of threads cut in the lathe will be finer than they should be, and the screw will bind in the feed nut, causing undue wear to both.
The method employed to test the truth of lathe shears and heads in the David W. Pond Works, at Worcester, Massachusetts, is as follows:—
Fig. 2580.
The planing, both of the lathe shears and of the heads, being done as accurately as possible, the heads are provided with a mandrel or arbor, to the end of which is secured the device shown in [Fig. 2580], in which a is a hollow cylindrical piece having a threaded and split end, so that by means of a nut the bore may be closed to tightly fit the arbor referred to; b, b are two arms, a sliding fit in a, to enable their adjustment for the width of lathe Vs, and having a flat place on one side, as at c c, to receive the pressure of a locking device d, by means of which b, b may be fastened in their adjusted positions; e, e are cylindrical arms, a sliding fit in b, b, also having flat sides, and capable of being secured in their adjusted positions by means of locking devices f, f.