communicating the motion of the treadle to the crank, and sometimes with the ordinary connecting-rod. They are seldom driven by other than foot power; and as the work performed is as a rule very light, the working parts are made no stronger than is necessary to resist vibration.

The driving pulleys are usually two, of different sizes, placed on the crank-shaft, and grooved for gut bands. The gut used seldom exceeds three-sixteenths inch in diameter, whilst one-eighth inch gut is sufficient for the overhead motion. These gut bands are either nicely spliced, or jointed by hooks made specially for the purpose. The former plan is considered the neatest, but the latter is most convenient, as the gut can be unhooked readily; also, as the guts require to be of different lengths for the overhead apparatus, a short length can be hooked on, or taken off, as required.

The larger cone-pulley is used to drive the lathespindle; the smaller cone is generally employed to drive the various cutting instruments through the overhead motion. Sometimes the lathe only requires to be driven, sometimes the cutting instruments only, and occasionally both are set in motion at the same time.

The screw headstock is very similar to the one already described, only of a much lighter construction ; it is sometimes fitted with a hand-wheel, and sometimes with a hole and pin. It can be moved along the bed and fastened at any place required by turning the hand-screw underneath the bed.

The cone headstock is of somewhat peculiar con struction. The spindle has on it the usual cone pulley

and this cone has its front edge divided into several lines of divisions; at each of these divisions there is a small hole drilled, and the pointer a carries a small pin to fit into these holes. The index-pointer is so made that it may, when not in use, be shifted out of the way without the trouble of removing it altogether; and it also has the power of adjustment for height by means of the screw and nut shown. The division plate is usually divided into circles of 960, 360, 200, 180, 144, 136, 120, 112 and 96 divisions.

These lathes are seldom fitted with double gearing, as the nature of the work is not such as to require great power. Slow motion is, however, frequently necessary, and is obtained by means of the tangent screwb working into corresponding teeth cut on the edge of the wheel c. This wheel is termed the segment divider, and has another use assigned to it. It is perforated with seventy-two holes at the side, and into these holes are sometimes fitted two pins in such positions that the lathe in rotating will cause them to come in contact with the segment stop d, and so prevent the lathespindle making more than a certain portion of a revolution.

The segment stop d also has a power of adjustment by means of the screws shown, so that should a movement be required to commence or end at a point on the work represented by a space on the segment wheel between two divisions, these screws can be so moved up or down as to meet the segment pin and terminate or commence the motion at the required point.

The segment stop and this power of adjustment are both very useful, and are frequently required. It is a

distinct apparatus from the division plate of the lathe, and is used for a different purpose.

The lathe-spindle has also another appliance, which gives it a very useful motion, usually called a traversing or pumping motion; and lathe-spindles so constructed are termed traversing mandrils. The spindle itself is made of hard steel, and is for some length, in addition to the part that runs in the bearings, turned perfectly cylindrical and parallel. Any part of this parallel portion will therefore pass into the hardened steel bearings of the spindle, and will fit the bearings equally well. At the back, the spindle, a short distance after it has passed through the second bearing, is turned down rather smaller to receive certain sockets, which sockets have on their outside surface spiral grooves, or grooves of wavy curves. Just below the spindle is a small arbor or stud for carrying a piece of steel peculiarly shaped. Its edge is formed of the concave halves of circles, and each of these curved parts is fitted with a screw-thread of an inclination. corresponding to the spiral cut on the various sockets fitting on the end of the lathe-spindle. The arbor carrying this set of nuts or half-circles of screw-threads is made to have a certain amount of vertical motion, to bring the corresponding threads of the socket and half nuts either into contact or out of reach of each other.

These two screwed parts being brought into contact, it will be readily seen that they will act precisely as an ordinary screw and nut. The nut being held stationary, any rotation of the lathe-spindle causing the screw socket to rotate, will cause the spindle to

traverse forwards or backwards longitudinally in its bearings, according to the direction of rotation and inclination of the thread. Thus, supposing the screwthread to be right-handed, a forward rotary motion will cause the spindle to traverse outwards towards the other headstock.

It is of course necessary, when the lathe is working in this manner, that the motion should be slow; indeed, it is generally pulled round by hand, and when the spindle has traversed, either as far as required or so far as the length of the screw-threads will allow, it is caused to move backwards by reversing the direction of rotation, and moving it round by hand in the contrary direction.

It is also necessary, when the spindle has this movement, that all obstructions to its motion should be removed. The index-pointer must be turned downwards, and the tangent screw must be lowered out of gear with the worm-wheel. When this motion is not in use it is evidently necessary to have some means of holding the spindle steady, and of preventing longitudinal motion of any sort. This is effected by removing the screw guide from the lathe-spindle and substituting a plain socket larger than the hole of the spindle bearing, which therefore acts as a collar, and prevents the spindle moving endways.

The slide-rest can be moved from the bed and the hand-rest put in its place. The hand-tool rest and holder are very much the same as the ones already described. They do not, therefore, require further illustration or description.

The slide-rest, in its essential particulars and move

ments, is also the same as those already described; but it possesses many little points which the others

have not.

In the first place, the slide-rest fits into a separate slide, which is fitted to slide along the bed lengthways between the longitudinal bars forming the bed. This slide allows the corresponding part of the slide-rest to be placed into it and the whole rest moved as near to or as far from the line of centres as the nature of the work makes convenient. And, however placed, it always retains its parallelism with the face-plate of the lathe. The rest is fastened down to the bed by a hand-screw underneath the bed, the same as the shifting headstock.

The two slides of the rest are permanently fixed at right angles to each other, and cannot be altered. The bottom slide, it will be seen, is by far the longer, and this is fitted with a screw for causing the top slide to traverse along it. This screw has a pitch of ten threads to the inch, so that one turn of it will cause the slide to be moved exactly one-tenth of an inch; it also has a small division-index at one end for smaller or convenient measurements. The index-plate is divided into twenty divisions, but marked at every other division, so there are only ten marked divisions. The screw being moved the distance shown by one marked division, the slide will be moved only the one-tenth of the space which it would have been moved by a complete turn, or the Too of an inch, and if moved only one division the slide will only traverse the of an inch. The screw may also be fitted with tangent screw and pulley for driving from overhead.

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