This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The next part of the apparatus to which attention is called is the rest, upon which the operator supports the turning tool. There are 2 kinds, the common rest and the slide-rest; the former is that represented in the figure. M L is a short hollow column, provided with a foot sufficiently long to reach across the lathe-bed; in the bottom of the foot is planed a dovetailed groove N, which retains the head of a clamping screw O, but at the same time allows of a sliding motion when not clamped. From this it is evident that the rest can be placed and fixed in any position.
"Within the hollow column is a cylindrical rod, which carries a straight strip of metal, the whole being raised or lowered by sliding the rod vertically in the column; when the proper elevation has been attained, the rest is fixed by a screw working in a thread cut in the thickness of the column.
The lathe-bed is supported on standards or frames P P, which also serve to carry the crank-shaft R by means of 2 conical-pointed screws Q Q, which enter countersunk recesses in the ends of the shaft. The shaft is made with one or two cranks, or throws, according to its length. This shaft is also fitted with grooved driving pulleys S, made of various diameters, in order to obtain any speed which may be required. The pressure imparted to the treadle T is communicated to the crank by a link with a hook at each end, or by a chain; some turners preferring the former, and others the latter.
The next consideration is the means by which the work is held in the lathe and caused to rotate with the mandrel.
Fig. 1178 represents the fork, prong, or strut-chuck, so called from the steel fork or prong a, which is fitted into the square socket of the chuck; this chuck is used for long pieces, the point supporting one end of the work, the other being supported by the back centre. The chisel edges on each side of the point take hold of the work and ensure its rotation. The fork being fitted into a square recess in the chuck may be replaced by drills, etc, or small pieces of wood or ivory to be turned. It is usually made of metal, and attached to the mandrel by an internal screw corresponding to that on the nose of the mandrel.
Fig. 1179 illustrates the hollow or cup-chuck; it is used for holding short pieces, or pieces that are to be turned out hollow. Its inside is turned slightly conical so that the work may be driven tightly into it. This chuck is usually made of boxwood, sometimes strengthened by a metal ring round the mouth of it; but this is scarcely necessary, as a very slight blow is sufficient to fix the work if it has previously been reduced to a form nearly approaching the circular by the chisel, paring knife, or other hand tools.
Fig. 1180 shows the face-plate or facing chuck; it may be made of iron or other suitable material. This chuck is turned flat and perfectly true, and is fitted at its centre with a conical screw to hold objects to be turned on the face. It can only be used when the hole made in the work is not objectionable, or can be plugged up. The screw should only be very slightly taper, otherwise the work will not hold when reversed.
Fig. 1181 is a chuck for flat work, where a hole in the centre would be detrimental. It is a face-plate with 3 or more small spikes projecting from its surface to penetrate the material to be wrought, which is held against it by the back centre. A plane face-plate is used where the work cannot be conveniently fixed to either of the 2 foregoing, as in the case of thin pieces of horn, tortoise shell, and so on. The work is attached by means of glue, or of jewellers' or turners' cement.
Fig. 1182 represents the arbor-chuck, usually made of brass. It is used for holding small hollow works or rings.
For very small work, Fig. 1178 is useful for holding the arbors in the place of a strut a.
Fig. 1183 shows a spring-chuck which is used for holding very slight work that requires to be hollowed out. It is turned conical externally, the apex of the cone being to the left. A few holes a are drilled through the chuck near its base and at equal distances from each other. From these holes saw kerfs or slits are cut longitudinally to the front of the chuck, which allow the chuck to expand slightly to take a firm hold of the work, and when the work has been forced into the chuck, the grip is rendered still more firm by drawing a strong ring towards the front of the chuck. These chucks are sometimes made of wood, but those of metal are much neater and more convenient; they may be made of a piece of brass tube firmly driven on a wooden block.
A similar chuck is used for holding hollow work, but instead of being provided with an external ring, it is fitted with a short solid plug, which is forced forwards after the chuck has been inserted into the work. When long and slender pieces have to be turned, an extra poppet or a support is required to keep the work from shaking, or chattering, as it is termed. It is generally made of wood, and is formed similar to Fig. 1184. It consists of ahead, in which is bored a hole c of the proper diameter, and a tail-piece fitted to the lathe-bed and sufficiently long to receive an aperture b, through which a wedge may be passed to hold it down firmly upon the lathe-bed.
Another and more convenient form of support is shown at Fig. 1185: a is a cast-iron frame, having a foot fitted to the lathe-bed and furnished with a bolt and nut by which it is firmly bolted down to the lathe-bed; b is a block of wood fitted into the frame, where it is secured by the cross-bar c. An aperture of the required diameter is now bored in the block; it is then taken out of the frame and sawed in half, so as to form a top and bottom bearing; d shows a section of the frame; any other form of groove may be used, but the V has been selected on account of the ease with which the blocks may be fitted to them. One great advantage of the latter apparatus is, that the 2 bearings may be brought together when the hole is worn. When a slide-rest is used, this additional support should be attached to it; it will then keep close to that part of the work on which the tool is acting, by which a more satisfactory piece of work is turned out, and the trouble of shifting the poppet avoided. The application of a little grease to these bearings will sometimes be found beneficial.