Fig. 2583.
Notwithstanding that every care and attention may be taken to make a lathe true in the process of manufacture, yet when the whole of the parts are assembled it is found essential to test the truth of the finished lathe, because, by the multiplication of minute errors the alignment of the lathe, as a whole, may be found to need correction. A special inspector is therefore employed to test finished machines before they leave the works, and in [Fig. 2583] is represented the device employed for testing the alignment of the line of centres of lathes.
Upon the face of the face plate and near its perimeter there are turned up two steps, as denoted by b and c. The tail-spindle is provided with a stud s, which fits in the place of the dead centre, and carries what may be termed a double socket, one-half of which (as f) envelops the stud s, while the other half (a) envelops and carries a rod r. These two halves are in reality split sleeves, with set screws to close them and adjust the fit. By means of the screws e, the sleeve f may be made a tight working fit upon s, while, by means of screws g, sleeve a may be made to firmly grip the rod r, which may thus be securely held while still capable of being swung upon stud s. Upon the outer end of the rod r is another sleeve i, which is also split and secured to the rod r by means of screws corresponding to those shown at g. It also carries a pin, upon which a disk k is pivoted, and a lug through which the adjusting screw v is threaded. Upon k is a lug which has on one side of it the end of a spring t, and it is obvious that by operating v the disk k will be rotated upon its central pin. k carries two lugs, l and m, the latter being threaded and split. These two lugs receive a sleeve n, threaded into m, and a close plain fit in l. The small end of this sleeve is split and is threaded slightly taper, and is provided with the nut p. Through this sleeve passes a needle q q, one end of which is bent as shown, and it is obvious that by screwing nut p upon n the sleeve will be closed and will tightly grip the needle q q. Now, suppose that the head of n is operated, and it will move endwise through l and m, carrying with it the needle q q, which will remain firmly clasped in the sleeve; or suppose that screw v is operated, and k will revolve, carrying with it the needle q q, which will still remain firmly gripped, and it follows that there is thus obtained a simple means of adjusting the needle without releasing it.
The application of the instrument is as follows: To test if the head and tailstocks are of equal height from the bed, the instrument is set and adjusted exactly as shown in the engraving, the needle being adjusted to just touch the diameter of the step at b. The rod r is then swung around so that the needle comes opposite to the same step b at the bottom of the face plate, and if the needle just touches there also the adjustment for tailstock height is correct. Similarly for testing if the tailstock is set true sideways the needle may be tried in the same manner and upon the same step, but upon the two opposite sides of the face plate, instead of at the top and bottom. It now remains to test if the tailstock is in line in a horizontal direction with the live spindle, and this is done by reversing the needle end for end in the sleeve n, and setting it to just touch the face c of the turned step on the face plate, and if it just touches at the top and bottom as well as at the two sides the tail-spindle is obviously in line. It may be observed, however, that if an error in any one direction is found, it is necessary to go through the whole series of tests in order to precisely locate the error. Suppose, for example, that the needle, being adjusted as in the engraving to just touch the step at b, does not touch it when tried at the bottom of the plate, then the error may be caused in three ways—thus, in the first place, the whole tailstock may be lower than the headstock; in the second place, the front end of the tailstock may be too low; or, in the third place, the back end of the tailstock may be too high. If the first was the cause, the test with the needle point tried with face c would show correct. If the second or third was the cause of the error, the needle point when tried to face c would touch when applied at the top, but would not touch when tried at the bottom of the face plate. Another case may be cited. For example, suppose the needle applied as shown touched at the bottom but not at the top of the step b, then the test with the needle reversed would show whether the whole tailstock was too high, or whether the front end only was too high, or the back end too low. There is one excellent feature in this device to which attention may be called, which is that the tests are made on as large a diameter of face plate as possible, which shows the errors magnified as much as possible.
Fig. 2584.
The same device is used to test if the cross slide of the carriage or saddle is at a right angle to the lathe shears, the method of its application being as shown in [Fig. 2584]. The split sleeve a receives in this case a rod r, which is laid in the slideway s of the carriage or saddle, and a long rod h carries the needle-holding devices. The rod r is held fair against the slideway, and the face of the sleeve a is held against the edge of the carriage or saddle. The needle q is then adjusted to just touch the edge d of the lathe bed. When this adjustment is made the rod h is swung over to the right and the coincidence of the needle point again tried with the edge of the lathe bed, the cross slideway being at a right angle when the needle point touches the edge d of the lathe bed when tried on the left hand, and also on the right hand, of the carriage. The stiffening rod u is brought under tension by a nut operated against a lug on x. To counterbalance the overhanging weight of the rod h and its attachments, a rod carrying a weight w is employed. It is obvious that the truth of the operation depends wholly upon the straightness and parallelism of the enlarged sections p of the rod r, upon keeping the end face of a in contact with the carriage at z, and upon the correct adjustment of the needle to the edge of the lathe bed.