[Fig. 691] represents Brown and Sharpe’s Number 1 screw machine, which is designed for the rapid production of small work.
Three separate tool-holding devices may be employed: first, cutting tools may be placed in the holes shown to pierce (horizontally) the circular head f; second, tools may be fixed in the tool posts shown in the double slide rest, which has two slides (one in the front and one at the back of the line of centres); and third, tools may be placed in what may be termed the screw-cutting slide-rest j.
f is a head pierced horizontally with seven holes, and is capable of rotation upon l; when certain mechanism is operated l slides on d and the mechanism of these three parts is arranged to operate as follows. The lever arms k traverse l in d. When k is operated from right to left, l advances towards the live spindle until arrested at some particular point by a suitable stop motion, this stop motion being capable of adjustment so as to allow f to approach the live spindle a distance suitable for the work in hand.
When, however, k is operated from left to right l moves back, and when it has traversed a certain distance, the head f rotates 1⁄7 of a rotation, and becomes again locked so far as rotation is concerned. Now the relation between the seven holes in f is such that when f has rotated its 1⁄7 rotation, one of the seven holes is in line with the live spindle. Suppose then seven cutting tools to be secured in the holes in f, then k may be operated from right to left, traversing l and f forward, and one of the cutting tools will operate upon the work until l meets the stop; k may then be moved from left to right, l and f will traverse back, then f will rotate 1⁄7 rotation and l and f may be traversed by k, and a second tool will operate upon the work, and so on.
The diameter of the work is determined by the distance of the cutting edge of the tool from the line of centres, when such tool is in line with the work, or, in other words, is in position to operate upon the work. The end measurements of the work are secured by placing the cutting edges of the tools the requisite distance out from f, when l is moved forward as far as the stop motion will permit. But it is evident that the length of cut taken along the work, would under these simple conditions vary with the distance of the end of the work from the face of the chuck driving it, but this is obviated as follows:—
The live spindle is made hollow so that the rod of metal, of which the work is to be made, may pass through that spindle. A chuck on the spindle holds the work or releases it in the usual manner. Suppose then the chuck to be open and the bar free to be moved, then there is placed in the hole in f, that is in line with the work, a stop instead of a cutting tool. The end of the work may then, for the first piece turned, be squared up by a tool placed in the slide rest and then released from the chuck and pushed through the live spindle until it abuts against the stop so adjusted and affixed in the hole in f; k may then be operated to act on the work. The first tool may reduce the work to its largest required diameter, the second turn down a plain shoulder, the third may be a die cutting a thread a certain distance up the work, the fourth may be a tool turning a plain part at the beginning of the thread, the fifth may round off the end of the work, and the sixth may be a drill to pierce a hole a certain distance up the end of the work.
Now suppose the work to require its edge at the other end to be chamfered, then there may be placed in the slide rest tool posts a tool to sever the work from the bar out of which it has been made, while the other may be used to chamfer the required edge, or to round it if needs be to any required form.
Work held in the chuck but not formed from a rod may be, of course, operated upon in a similar manner.
In the case, however, of work of large diameter requiring to be threaded, the threading tool may be held and operated differently and more rigidly as follows. i is a lever carrying under its bend and over the projecting end of the live spindle, a segment of a nut whose thread must equal in pitch the pitch of thread to be given to the work. A collar or ring, oftentimes called the leader, having a thread of the same pitch, is then secured upon the live spindle, so as to rotate with it, and have no end motion; when therefore i is depressed, the nut will come into work with the collar or ring, and i will be traversed at a speed proportioned to the pitch of the threads on the collar and nut.