Fig. 2565.
The most accurate method of testing the adjustment of the ways is as follows: [Fig. 2565] represents a plan view of the frame; n represents a straight-edge applied to the surfaces of the jaws a b. The method of applying this straight-edge is to place one end across a jaw, as a, while the other end is elevated above b; then, while pressing the end firmly against a, lower the other end to the face of b; if its edge at that end falls fair with b, so as just to touch it, the process may be reversed—one end being pressed to b, and the other lowered upon a. By this means, it will not only be discovered whether the jaws a and b stand square across the frame, but also whether the frame on either side is sprung. A square c may also be rested against n, and its blade d tested with the side face of the way, as shown. The same process of testing should be applied to the other jaw faces e, f.
Suppose, however, that the width between the jaws a, f was less than that between e, b, then the straight-edge, when pressed to a, would show a space between its edge and b; and also a space between its edge and e, when its other end was pressed to f; and, when these spaces were equal in amount, the frames would be set true in one direction. To test the truth in the other direction, the straight-edge should be applied after the same manner to the bottom surfaces g, h.
It will not answer to rest the straight-edge against the two surfaces and observe their coincidence with its edge, because any error cannot be sufficiently, readily, or accurately tested by this means. Nor will it answer to test by the bearing marks of a straight-edge applied with marking, unless the coat of marking be very fine and the straight-edge be moved without any vertical pressure on it; because, under such pressure, the straight-edge will bend.
The ways for all the bearings should be tested in this manner; so that, if from any error in the machine work, some of them will not come fair, the frames may be set to align those that it is of most importance to align truly; or if there is no choice in this respect, then those carrying the largest bearing should be set true; because, if it be decided to correct the error on the other bearing or bearings, there will be less area to file or operate upon. The setting being complete the holes may be reamed and the remaining bolts put in, the testing being repeated after the frame is finally bolted together. If this final test shows that bolting the frame up has altered the alignment by springing the frame, the bolts in one foot, as say i, [Fig. 2564], may be slackened and the test repeated; and, if the frame is then found true, it is the bolting at i that causes the spring, on account of the bedding surfaces not fitting properly. If i is not found to be at fault, it may be bolted up again and j tested by loosening its bolts, and so on, until the location of the error is detected. Furthermore, when the frame is bolted up, the width of the bearings, as from a to b, should be tested; for in a job of this kind, it will pay to have the framework so true to the drawing that, if the other parts, as the shafts, bearing parts, &c., be also made to the drawings, the parts will go together, thus avoiding the necessity of varying all the other parts from the drawing to accommodate errors in the framework.
Fig. 2566.