[Fig. 494] is a sectional side elevation of the headstock; a a′ represents the headstock carrying the bearing boxes b and b′, which are capable of bore closure so as to be made to accurately fit the spindle s by the construction of the front bearing b, being more clearly shown in [Fig. 495]; b is of composition brass, its external diameter being coned to fit the taper hole in the head; it is split through longitudinally, and is threaded at each end to receive the ring nuts c and c′. If c be loosened from contact with the radial face of a, then c′ may be screwed up, drawing b through the coned hole in a, and, therefore, causing its bore to close upon s.
Fig. 496.
At the other end of s, [Fig. 496], c′′ is a ring nut for drawing the journal box b′ through a′ to adjust the bore of b′ to fit the journal of s, space to admit the passage of b′ being provided at e. d is a box nut serving to withdraw b′ or to secure it firmly in its adjusted position, and also to carry the end adjusting step e. f is a check nut to lock e in its adjusted position.
The method of preventing end motion to s is more clearly shown in [Fig. 496], in which h is a steel washer enveloping s, having contact with the radial face of b′ and secured in its adjusted position by the check nuts g, hence it prevents s from moving forward to the right. f is a disk of raw hide let into e; the latter is threaded in d and is squared at the end within f to admit of the application of a wrench, hence e may be screwed in until it causes contact between the face of f and the end of s, thus preventing its motion to the left. By this construction the whole adjustment laterally of s is made with the short length from h to f, hence any difference of expansion (under varying temperature) between the spindle and the head a a′, or between the boxes and the spindle s, has no effect towards impairing the end fit of s in its bearings.
The method of adjusting the bearings to the spindle is as follows:—c′′ and c′ are slackened back by means of a “spanner wrench” inserted in the holes provided for that purpose. c and d are then screwed up, withdrawing b and b′ respectively, and leaving the journal fit too easy. c′ is then screwed up until b is closed upon the spindle sufficiently that the belt being loose on the cone pulley, the latter moved by the hand placed upon the smallest step of the cone can just detect that there is contact between the bore of b and the spindle, then, while still moving the cone, turn c′ back very slowly and a very little, the object being to relieve the bore of b from pressure against s. c may then be screwed up, firmly locking b in its adjusted position. c′′ may then be operated to adjust b′ in a similar manner, and d screwed up to lock it in its adjusted position. Before, however, screwing up d it is better to remove f and release e from pressure against f, adjusting the end pressure of e after d has been screwed home against a′.
To prevent b and b′ from rotating in the head when the ring nuts are operated, each is provided with a pin, q, grooves c and c′ permitting of the lateral movement of b and b′ for adjustment. The boxes b, b′ admit of being rotated in their sockets in a and a′ so as to assume different positions, the pins q and q′ being removable from one to another of a series of holes in the boxes b, b′ when it is desired to partly rotate those boxes. The tops of the boxes are provided with oil holes, and the oil ways shown at r, s being the oil groove through the head and a simply a stopper to prevent the ingress of dust, &c.
The thread on s at z, [Fig. 494], is to receive and drive the face plates, chucks, &c., which are bored and threaded to fit over z. To cause the radial faces of such face plates or chucks to run true, there is provided the plain cylindrical part l, to which the bore in the hub of the face plate or chuck is an accurate fit when the radial face of that hub meets the radial face m.
Referring again to [Fig. 494], g′ is the pinion to drive the back gear while g receives motion from the back-gear pinion. The object of the back gear is to reduce the speed of rotation of s and to enable it to drive a heavier cut, which is accomplished as follows:—g′′ is secured within the end k of the cone and is free to rotate with the cone upon s; at the other end the cone is secured to m, which is free to rotate upon s so far as its bore is concerned. g is fixed upon s and hence rotates at all times with it; but g may be locked to or released from m as follows:—