Fig. 734.
In the [figure] a roll is shown in position in the lathe. The journals of the rolls are first turned in a separate lathe, and form the guide by which the body of the roll is turned in the lathe shown in the figure. The lathe consists of a bed plate p, at one end of which is mounted the driving head. Upon this bed plate are also mounted three standards or vertical frames, to the two end ones of which are pivoted the binder arms shown. These frames hold the bushes at l and n, in which the journals of the roll revolve. They also carry the bar g, secured to the arm w of the frame by clamps a, a, a. Upon the bar g are two slide rests, consisting of a tool rest e, a tool clamp a, and a feed yoke b, which is screwed up by a wrench applied to the nuts as shown on the right-hand tool rest in the figure. The binder arm is adjusted to hold the bushings l n (which are varied to suit the size of the roll journal) a fair working fit upon the roll journals, the bolts s holding the binder arms firmly against the enormous pressure due to the cut. It is obvious that the frames w may be adjusted anywhere along the bed plate p to suit the length of roll to be turned, and that the slide rests may be moved to any required position along the bar g. Further details of the construction are as follows. [Fig. 731] is an end, and [Fig. 732] is a top view of the tool rest; a is the tool clamp securing the tool to the rest e, r representing a section of the roll, b is the feed yoke, which to put on a cut is screwed inwards by operating the nuts d. The pins c are fast in b, and their ends abut against the tool, which is fed in under the full pressure of the clamp a. The tool is shown at f in figure, and also at f in [Fig. 733], which is a view of the rest with the clamp a removed. The form of tool employed is shown in [Fig. 734], its length varying from five to six inches. As the tool feeds in and does not traverse along the roll it is obvious that it cuts along its entire length, the cuttings coming off like a bundle of fine ragged needles.
When the tool has been fed in cutting the roll to the required diameter the rest is moved along the bar g, a distance equal to the length of the tool, and the operation is repeated until the full length of the roll has been turned. It is obvious that to feed the tool in parallel, both nuts d of the tool rest are operated. The tool is held as close in to the rest as the depth of cut to be taken will permit, and is used at a cutting speed varying from about 21⁄3 feet to 5 feet per minute according to the hardness of the roll. The tool has four cutting edges, and each cutting edge will carry in at least one cut, and may sometimes be used for a second one. The tools are used dry and the amount of clearance is just sufficient to clear the roll and no more.
The rolls are driven by a socket bolted to the lathe face plate, and containing a square hole, in which fits loosely the square end of the roll. The object of this arrangement is to permit the roll to be guided entirely by the bearings in which it rotates, uninfluenced by the guiding effect that accompanies the use of centres in the ordinary method of turning.
Fig. 735.
[Fig. 735] represents a lathe designed and constructed by the American Tool and Machine Company, of Boston, Mass. This class of lathe is strictly of American origin, and has become the most important tool in the brass finishing shop.