Part 10

The outside must be turned in a similar manner, and a hole drilled to receive a pointed bar or wrench, for the purpose of unscrewing it when screwed up tightly. To turn up a face plate of iron or brass proceed in a similar way, but commence from the centre with a point tool. This tool is the best for taking off the rough outside of hard wood, instead of the gouge, as well as for removing the roughness of a fresh casting. It is absolutely necessary that the faces of these flat chucks, or surface chucks, be truly at right angles with the mandrel; hence it is very difficult to turn and finish them by hand. We may here also state the necessity of knowing when the slides of the rest are at right angles to each other, without which no work can be turned correctly. It is necessary to ascertain this by help of a small steel square. Once fixed truly, it is only necessary to make a mark on the quadrant (which should be marked in true degrees), by which the same position can be found again at any time. We have spoken here of the quadrant--we mean the arc, or arcs with slot--allowing the circular movement of the compound slide rest. The chief use of these is to enable the workman to turn true cones instead of cylinders, which latter will only be produced when one slide is parallel to the lathe bed. Such is the common use of the slide rest; and it will be evident from these few remarks that there is an infinity of work, not only produced with ease by its aid, but which cannot, even with expenditure of time and labour, be produced without it; hence we advise this to be the chief ambition of the tyro after he has mastered the difficulties of ordinary hand turning (and not before). The cost of a fair one for 5-in. lathe will be £5, or thereabout. At Munro's, £7 or £8; at Holtzapffel's, £10 or £12. Both the latter are of course perfect.

We have directed to tap the chuck where it is to be screwed to the mandrel with a set of three taps, or to cut it with stock and dies if an outside thread is required. In both cases more true and satisfactory work may be produced by the chasing tool. We speak of the latter as used by hand; an account of cutting the threads by help of the slide rest we reserve for the present. Mount the work in any convenient way, either driving it into a wooden chuck, or by clamping it to the face plate if you have one. Now in this way you have advantages. In the first place you need not have a drill the exact size, though it is convenient to have such a one, and also a cylinder bit. You can drill and enlarge the hole by the slide rest tools, and you can also with the slide rest ensure the perpendicular position of the hole with respect to the end. Thus it is sure to fit up close and snug to the shoulder of the mandrel. When bored thus it will be in position for chasing. It is not difficult to chase a thread in brass, as it does not chip away like wood, but cuts clean and sharp. Follow the directions already given and you will succeed in a few turns in getting the tool to run. Then let it have its own way; hold it lightly, but steadily, and do not force it either to cut too deeply, or to advance too quickly; it will run along of itself after the faintest thread is cut or scratched, and the lathe can be worked by means of the treadle all the time as soon as you have attained the knack of dropping the chaser into its place at the commencement of its cut, and suddenly withdrawing it when it has reached the bottom of the hole. A chuck thus turned and screwed entirely in the lathe is sure to prove a good fit, and there can be no better practice than to cut screws in all your brass and boxwood chucks in this way. A very good chuck to hold flat plates of brass was invented by a Mr. Wilcox, of Bishop's Stortford, some years ago--an amateur of rare ingenuity and mechanical knowledge, and who made all his own apparatus for plain and eccentric turning. The chuck, Fig. 143, as described by him in some unpublished manuscript, is made of boxwood, or may be of metal. It is a plain disc or surface chuck with three slots A B C. and a steel centre. This last must penetrate rather deeply into the wood of the chuck, but is only kept up so as to project from the surface by a spiral spring below it. Hence, when pressure is made upon its point by the application of the object to be turned, the pin recedes into the body of the chuck, suffering the work to lie flat on its surface. In the three slots are three screws, with nuts at the back of the chuck the screws pass through two pieces of brass, forming a pair of jaws, one of which is shown separately.

Fig. 143 shows the chuck complete. Suppose we have to face up a round disc in its central part, or to perform any surface work in which the jaws will not be in the way of the tool, the centre of the plate is marked at the back of it, and this mark laid on the central pin. The work can be clamped down by the three jaws, and the necessary work may be done. Now so far the chuck is but a simple affair, and the receding pin does not show itself to such great advantage; we will therefore suppose a plate is to be drilled at several spots; let these be marked at the back by a centre punch. It is now only necessary to bring these marks in turn upon the central point, and clamp the plate in position. Bring the point of the drill against the work and keep it up to cut by the back poppet screw. In the same way eccentric work or any operation may be done to such a plate, with the certainty that the point to be thus worked upon is precisely central with the axis of the pulley, or mandrel. Many similar applications of this chuck will present themselves to the reader upon due consideration. We present the chuck in this place because we have had occasion to speak of drilling as connected with the slide rest, and there are many pieces of work that could not otherwise be conveniently held in the desired position.[10]

[10] The MS. book containing the above was kindly lent to the author of the present work by Mr. Hoblyn, of Bishop's Stortford, who is the inventor of a new form of slide rest, which will be introduced in a later page. The chuck in question is, however, commonly attached to the watchmakers' lathes of the present day, and therefore may not, as the writer supposed, be actually the invention of the late Mr. Wilcox.

OVERHEAD APPARATUS.

It now becomes necessary to speak of another addition to the lathe, by means of which the use of the slide rest is considerably extended. We mean the overhead motion. Of this there are several patterns, and we have sketched three of these. As to their respective merits we can hardly venture to speak. They all answer equally well the purpose for which they have been designed, and the turner must select according to his fancy, or, if he please, design a better for himself. A, Fig. 144, represents the lathe bed. From the left-hand standard rises a round iron rod, not less than one inch in diameter. This is not generally fixed, but is attached to the standard by two staples, _a, b_, which hold it securely in an upright position, but allow it to turn with its projecting bar F, F, after the manner of a crane. It may thus be turned back, out of the way, or brought into any desired position. The part F, F is made to slide up and down on the part B, and is fixed by a clamping screw D. Thus, if the cord should break and require to be shortened, the arm can be brought nearer to the bed of the lathe. Upon F, F slide two rings, or rather short pieces of tube, from which depend two India rubber springs (door springs), E, E, now procurable at any ironmonger's at one shilling each. From these hang double pulleys, or better still two single ones. These pulleys, with their attachments, are adjustable at any position on the arm F, F, which may be round or square. If considered desirable, a second standard can be added, so as to uphold both ends of this bar; but it is hardly necessary, as the latter is seldom required of greater length than half that of this lathe-bed. It is evident that the above addition to the lathe can be made complete for a few shillings. The following are more expensive, but more general, the writer having devised the above to suit his own fancy, and for his own use. In Fig. 145 A represents the standard as before, the top of which is forked, as shown at E, and sustains the ring, free to revolve in its arms, as seen in the sketch. Through this passes a bar, B, B, with a heavy ball C cast on its end to act as a counterbalance to the longer arm and its connections, and to keep the cord stretched. By sliding this bar either way through the ring which supports it, the tension of the cord can be increased or lessened.[11] When in position it must be very securely fixed by the screw T, which should not simply press against it, but enter one of a row of depressions made for the purpose. The pulleys C, D are double, as in the previous plan of overhead, and are likewise adjustable at any position on the bar B, B. The only drawback to this pattern is the danger of the heavy ball slipping out and falling. We prefer to hang a weight from the end of the lever, as shown by the dotted line. This may be within a few inches of the floor, and if it should fall no harm can ensue. The third pattern, Fig. 146, is the most expensive, but although it is of a more finished appearance, and wears an aspect more stiff and stable, it is not practically any better than the last. From a standard A, with overhanging bar F, F, is suspended a frame H, by means of two coiled springs in brass boxes B, B, which keeps up the necessary tension on the cord, or rather cords, for in this case two are needed--one from the flywheel to the small pulley, and a second from the roller to the slide rest.

[11] Sometimes the bar is merely hung on pivots, and the weight is made to slide upon it.

This roller, which may be grooved or plain, may be replaced by a second small pulley, which is capable of being slid along the round bar which forms its axle and turns with it between the centre screws. In this case the bar is made with a groove or channel along its length, Fig. 147, and a pin projecting from the central hole in the pulley enters this groove. Thus the two will turn together, and at the same time the position of the pulley is adjustable at pleasure. The tension of the springs B, B, is increased or lessened by a turn or two of the nuts C, C, just in the same manner as the spring of the safety valve is adjusted on the boiler of a locomotive.[12] The application of the overhead motion is plainly shown in Figs. 143 and 144. The work is fixed in the lathe, and the mandrel kept stationary. The cord passes to the overhead directly from the fly wheel, and thence to a pulley on the screw of the slide rest, as in 143, to a drill, as in 144, or to any other apparatus at pleasure. To fit the work in the lathe in such a manner as to enable any point in the face or side to be operated upon, a division plate and index are required. The first is a round plate of brass or gun metal, 1-16th of an inch thick, drilled with holes in concentric circles. The index is a steel spring with a projecting point, which, entering any one of the holes, retains the plate, and with it the pulley, on the face of which it is fixed immovable. There are generally four circles of holes, the number in each selected with reference to its divisibility by the greatest possible number of divisions--thus 360, which is usually on the outside or largest circle, can be divided without a remainder by 2, 3, 4, 5, 6, 8, or 9--144 is a good number for the second circle, being divisible by 2, 3, 4, 6, 8, 9. The other two may be 112 and 96. The uses of the division plate are many. Eccentric cutting and drilling could not be done without its aid, and wheel cutting for clocks, or for making cycloidal and other chucks, is entirely dependent on this contrivance.

[12] The frontispiece shows another superior form of overhead, with balance-weights hanging close to the ground behind the lathe.

The division plate and index are shown in Figs. 147, A, B, C. The part B is a knob with a round hole through it, to take the tail of the spring C. This is shown again at C on a larger scale, to bring to view a slot which allows of some slight adjustment of the point, to suit the different-sized circles. The milled-headed screw clamps the point at any desired part of this slot. When not in use, the spring is drawn back so as to release it from the division plate, and turned down in the position shown by the dotted line.

The overhead apparatus is applicable not only to revolving cutters in the slide rest, but to other contrivances available where the latter is not possessed. There are many cases in which the back poppet may be brought into use to hold revolving drills, or stationary tools, if the resistance to their action is not too great. The only damage that can well happen in this method is to the pin working in the slot on the outside of the spindle. If this is of steel and tolerably stout and strong (being very short it cannot be subject to any very injurious strain), no harm is likely to result. With this it is possible to drill very neatly, and also to do a little eccentric cutter work, under certain conditions to be described. Screwing, or rather chasing, may likewise be done very passably. We do not, of course, advise this course when the more perfect slide rest is at hand, but there are many who are obliged to put up with all sorts of homemade contrivances, and to press into service for divers operations apparatus and tools not precisely meant to be thus used, and it is as well to learn how to act under an emergency, even if the practice is not intended to be carried out generally. The drill stock is shown in Fig. 148, in which the screw A fits into the spindle of the back poppet. If the hole in the latter is conical instead of cut with a screw thread, the drill must be made accordingly.

The pulley of brass has a hole drilled through it, and the screw is also drilled, the hole in the latter being rather larger than that in the pulley (which is tapped). The steel pin H, shown white in the sectional drawing, passes truly through the centre of the screw in which it revolves, and is screwed into the pulley. The socket of steel to hold the drill is then screwed or soldered into the opposite face of the pulley. The black part shows a flange on the screw which abuts against the cylinder of the poppet into which it is screwed. Thus the pulley, being attached to the cord from the overhead apparatus, is free to revolve upon the steel pin with great rapidity, and will carry round any drills or cutters placed in the socket B. The simple straight drill being thus worked and advanced by the leading screw of the poppet, will suffice for holes in any work held on the mandrel. On page 335, vol. ii., of the _English Mechanic_, this method is mentioned, and also a similar pattern of slide tool to be used for boring, being, in fact, the head and spindle of the back poppet, but instead of the standard and sole, a pin, like that of a =T=, to fit the socket of the rest. This has the advantage of the back poppet, but must be made on purpose, and if any special slide tool is added, a proper slide rest is by far the best. Our present purpose is to describe the use of the back poppet as a substitute for a better tool.

With the following modification of the eccentric cutter, a fair amount of good ornamental work may be done. Fig. 149 represents the back poppet with the apparatus in position. The various parts are shown separately in A, B, C, D. A is a small frame, two or three inches long, and 3/4 to 1 inch wide, cast in iron, with a circular piece at the back, 1-1/2 or 2 inches diameter. This circular piece is to be accurately divided on the edge with any even number, which is divisible as above explained. This is turned and drilled through the centre. B is a flange-shaped piece to screw to the poppet as before, and this is also accurately drilled, and the two are attached by a central steel pin, so that the two flanges can turn face to face, the outer one with frame revolving against the other. The pin must be put in its place in B, and turned at the same time as the face of B, that it may be truly central. The divisions on the edge of the outer flange are to be drilled like the division plate of the lathe, or cut into cogs, and in either case can be held at any point by a spring detent or index attached. C shows the front of the frame, with a screw down its centre and traversing slide _f_. The head of this screw is divided, and a small brass index marks its position; one side of the frame may likewise be divided. The small brass pulley and drill socket are fixed to revolve in the traversing nut or slide _f_, as shown in a side view at D. Drills of all shapes, as E 1, 2, 3, 4, may be fixed in the socket at pleasure.

It is evident that the cutter frame last described having a division plate of its own dispenses with the necessity of one on the pulley of the mandrel. Indeed it was the impossibility of supplying the latter on the face of the cogwheel of the author's back-geared lathe that necessitated the substitution of that alluded to. The latter may consequently be omitted if applied to a lathe already fitted with division plate and index. With crank-form drills the cutting edges of which may be as E 1, 2, 3, 4, or other form, such patterns can be cut, as shown in Figs. 149, 150, 151, 152, which are merely samples of the simplest combinations of circles intersecting in straight, spiral, or other lines. Although not now treating of eccentric work, we may state in passing that to produce the pattern round the edge of 150 the division plate of the instrument only is required. Select a crank-form drill which by its revolution will produce the required size of circle. Turn the divided screw head until you find upon trial that the circle will come at the required distance from the edge, and putting the lathe in motion cut the first circle. The work on the mandrel is understood to be stationary, the mandrel being fixed so as not to turn. The cutter frame is now turned on its axis, one, two, or more of its divisions, and fixed by its detent, and a second circle cut intersecting the first. This is repeated till the whole circle is completed. The straight line of circles in Fig. 151 is cut as follows:--The first circle is made as before, but the cutter-frame should be placed so as to stand either horizontally or vertically. Between each cut the divided screw-head is moved so many points according to the proposed fineness of the pattern, and no movement of the cutter frame on its axis is to be made. The spiral, 152, is simply the result of a combination of the two movements. Start from the centre by turning the screw head until the shank of the crank-form drill is coincident with the axis of the mandrel. Cut the central circle. Thence for each successive circle turn the screw head and the frame an equal number of points, and the pattern will be formed. If the divided screw head is made to take off and a handle substituted, stars formed of channelled lines, or radial flutes can be made as Fig 153, but in this case the crank form drill is replaced by a plain straight tool with a rounded end like 149 E 4. Set the tool as for pattern 150 straight across the face of the work, put the drill in rapid motion, let it be advanced by the leading screw of the poppet so as to penetrate slightly, and with the handle that has been attached to the screw of the cutter frame cause it to traverse the face of the work as it revolves. When one flute is thus cut, turn the frame on its axis as many points as required, and proceed with number two, and so on to the completion of the star. It is not necessary at present to describe other patterns. Fig. 153 is therefore merely given without special details of the method of producing it.