[Figs. 671], [672], and [673], represent a lathe having a special feed motion designed and patented by Mr. Horace Lord, of Hartford, Connecticut. Its object is to give to a cutting tool a uniform rate of cutting speed (when used upon either flat or spherical surfaces), by causing the rotations of the work to be retarded as the cutting tool traverses from the centre to the perimeter of the work, or to increase as the tool traverses from a larger to a smaller diameter. If work of small diameter be turned at too slow a rate of cutting speed, it is difficult to obtain a true and smooth surface; hence, as the tool approaches the centre, it is necessary to increase the speed of rotation. As lathes are at present constructed, it is necessary to pass the belt from one step to another of the driving cone, to increase the speed. In this two disadvantages are met with. First, that the increase of speed occurs suddenly and does not meet the requirements with uniformity. Second, that the strain upon the cutting tool varies with the alteration of cutting speed. As a result, the spring of the parts of the lathe, as well as of the cutting tool, varies, so that the cut shows plainly where the sudden increase or decrease (as the case may be) of cutting speed has occurred. The greatest attainable degree of trueness is secured when the cutting speed and the strain due to the cut are maintained constant, notwithstanding variations of the diameter.
This, Mr. Lord accomplishes by the following mechanism: Instead of driving the lathe from an ordinary countershaft, he introduces a pair of cones which will vary the speed of the lathe as shown in [Fig. 672] as applied to ball turning. l is a belt cone upon the counter-shaft driven from the line shaft. l drives h, which may be termed the lathe countershaft, and from the stepped cone k the belt is connected to the lathe in the usual manner. p is a shipper bar to move the belt n upon and along the belt cones, and thus vary the speed. r is a vertical shaft extending up at the end of the lathe and carrying a segment. This segment is connected to the belt shipper bar p by two cords, one passing from r1 around half the segment to r2, and the other passing from r3 to r4, so that if the segment be rotated, say to the right, it and the bar will move as denoted by the dotted lines, or if moved in an opposite direction, the bar motion will correspond and move the belt n along the cones respectively left or right.
At the back of the lathe is a horizontal shaft s, similar to an ordinary feed spindle, and connected to the segment shaft by a pair of bevel gears s2. Between the two ears e e, at the rear of the lathe carriage, is a pinion t, which drives the splined shaft s, which works in a rack t′. The tool rest is pivoted directly beneath the ball, to be turned after the usual manner of spherical slide rests, and carries a gear a2, which, as the rest turns, rotates a gear a3. Upon the face of the latter is a pin a4 working in a slot a5 at the end of the rack t′; hence as the tool rest feeds, motion is transmitted from a2 through a3, a4, a, t′, t, and s s2 to r, which operates the belt shipper p. As it is the rate of tool feed that governs the speed of these motions, the effect is not influenced by irregularity in feeding; hence the speed of the work will be equalized with the tool feed under all conditions. The direction of motion of all the parts will correspond to that of the tool feed from which their motion is directed, and therefore the work speed will augment or diminish automatically to meet the requirements.
Fig. 674.
[Fig. 673] illustrates the action of the mechanism when used for surfaces, like a lathe face plate. In this case the two gears and the rack t′ simply traverse with the cross-feed slider, and the mechanism is actuated as before. In [Fig. 674] a different method of actuating the belt shipper is illustrated. A pulley is attached to the intermediate stud of the change gears, being connected by belt to the shipper, which is threaded as shown at d, the belt guiding forks, as p2, being carried on a nut actuated by the screw d.
Cutting-off Machine.—The cutting-off machine is employed to cut up into the requisite lengths pieces of iron from the bar. As the cutting is done by a tool, the end of the work is left true and square and a great saving of time is effected over the process of heating and cutting off the pieces in the blacksmith’s forge, in which case the pieces must be cut off too long and the ends left rough.
