Chapter X: Part 10

One of the most useful tools for ornamentation, especially of plain surfaces, such as the top of a box cover, is the eccentric cutter, Fig. 283. The shank, A, lies in the receptacle holder of the slide rest, and is drilled throughout to receive a steel spindle, carrying at one end a double pulley, B, to receive the cord from the overhead motion, and at the other frame, E, with its leading screw, of which the movable milled and graduated head is seen at H. This frame has one surface, level with the centre of the main spindle, which is cut away as shown, and, consequently, as the point of the tool is on its flat side, which latter rests upon the frame (the bevel being below), this point can, by the tangent screw, be brought into a line with the centre of the main spindle, so that when the cord from the overhead is passed round B, the spindle revolves with great rapidity, and the point of the tool, K, in the position described, makes a simple dot. By turning round the milled screw head, H, either by the thumb and finger or by a small winch handle, fitted on the square part beyond the head of the screw, the tool holder, D (which is in one piece with the nut of the leading screw), is made to traverse the frame, and the tool will cut a circle small or large according to the eccentricity thus given to it. In Fig. 285 D, is the tool holder on the front of the frame; C, the end of the spindle; L, a bell-shaped washer, which is acted on by the small square-headed screw, drawing D towards the frame and clamping the tool. The whole is in the figure of full size. The tool holder is in one piece with the nut, through which passes the leading screw, and which is continued as a screw for the action of the bell-shaped washer and tightening nut; hence it is necessary to allow a degree of play between the nut and leading screw, to prevent bending the latter when clamping the tool. This is effected by filing off the threads in the nut at the top and bottom, to render the whole slightly oval. The remaining threads suffice for the action of the leading screw: a very slight degree of play in the required direction will be found sufficient. The powers of the eccentric cutter frame will be found sufficiently extensive to make it a most serviceable, perhaps necessary, piece of lathe apparatus. If it cannot be said absolutely to supply the place of the eccentric chuck, it has nevertheless the advantage of great lightness of construction, lowness of cost, and ease of manipulation. The weight of the eccentric chuck, whether single or double, as of all chucks in which sliding plates are used, is a sad drawback to their value--a drawback unfortunately beyond remedy, and specially felt when the slides are drawn out to a great degree of eccentricity. Combined together, these two form a _compound_ eccentric chuck, and in this way are capable of nearly everything in the way of eccentric ornamentation. Where the _chuck_ is not to be had, it is by all means advisable to procure the cutting frame, for which the writer confesses a great partiality. It appears, indeed, to him a far more rational proceeding, as it is also now of extensive application, to act upon fixed work by revolving or moving tools, instead of proceeding in the contrary way; and all these little tools used with the overhead apparatus are so lightly and elegantly constructed, and so well adapted for the parts they have to perform, that the originator of them (_native talent devised them_), deserves to be well and lastingly remembered; instead of which it is doubtful whether his name is even known. (_Sic transit_ is a quotation too stale for this work.)

To cut circles deeper in one part than another--the shell pattern, for instance--with this tool, it is not necessary to alter the level of the sole of the rest, as it is when the eccentric chuck is used with a fixed tool, as it suffices to set the rest itself at an angle, by moving it round in the socket, so that the revolving tool should touch the face of the work sooner at one point than at an opposite one. In the same way the work may be considerably undercut on one side of the circles, by giving the angular set to the rest, and placing a tool in the holder, with a point of the form shown at 285 B. There is nothing prettier than this undercut work when well and sharply done, for which purpose the tool should not only be rendered keen on the hone, but burnished and polished on the brass and iron slabs already described.

The following remarks on the work of this cutter frame on flat surfaces only, will be useful to the reader in designing and working out the various combinations of circles, intersecting or otherwise, which it is calculated to produce. On a surface represented by 286 A, the line of circles, _a, a_, is on a diameter, and, supposing them to be described by the eccentric cutter (or by a simple double-pointed drill), their centres are obtained by means of the leading screw of the slide rest, moved the requisite number of turns between each cut, while the work is retained in a fixed position on the mandrel. But if the line of circles is on such a line as _b b_, above or below the centre, and consequently not on a diameter, it is plain that no movement of the slide rest or cutter, or both, can avail to place them in position, except with great difficulty and tedious working with the division plate of the lathe and the screw of the slide rest. Hence the eccentric chuck must be brought into play, and being fixed with its slide in a vertical position, the screw is turned and the work is lowered thereby until the line _b, b_, is on a level with the point of the tool. The eccentric cutter or double drill will then suffice to work the row of circles. When the centres of the circles are themselves on parts of the circumferences of other circles, the division plate of the lathe or of the eccentric chuck will be called into requisition, according as these circles are concentric with the mandrel or otherwise. In Fig. 286B, the curved lines are parts of circles of equal size with that representing the surface of the work, and their centres lie on one and the same diameter, viz., at opposite extremities of the line, _a, b_. Being thus eccentric to the work, the division plate of the chuck is used to arrange the intersecting circles of the pattern--its slide having been first drawn down, until the centre of the arc to be worked with circles is brought opposite to the tool. The work will be in position when, on turning the mandrel slowly, the cutting point of the tool passes across its centre. The division of the original circle is in this instance into four parts, two of which are thirds, and two sixths of its circumference. The arcs of circles are also lines equal to thirds of the circumference of the work. It is well to remember this division of a circle by other equal circles described round it from points on its circumference, these circles passing through the centre. The original circle will in this way be divided, as shown at C, into six equal parts. To produce it with the aid of the eccentric cutter is easy. Set the tool of the cutter first to the centre of the work, so that on revolving it will make a simple dot. This should always be done, whatever pattern is subsequently to be cut. Fix the index of the division plate of the lathe at 360. Move the screw of the slide rest until the point of the cutter, on being advanced, rests on the circumference of the circle previously cut upon the work, or on the circumference of the work itself, if the divisions are to reach the edge. Screw back the _tool_ (not the rest) until its point reaches the centre of the work and cause it to revolve so as to cut one arc. Move the lathe pulley forward to 60° and cut a second arc, and so on, advancing 60° each time, and the figure will be cut. This division of the circle will form the groundwork of many handsome patterns. When the arcs thus formed are intended merely to be the lines of centres, and not themselves to form integral parts of the pattern, they should, nevertheless, be marked with a pencil in the tool holder, if possible, as there will be less liability to error in working the proposed pattern. In the present advanced stage of the art of turning, mere surface work done by the eccentric cutter is rather apt to be despised, owing to the extended powers of Ibbetson's or Plant's geometric chuck; but, valuable as the two latter are, they are necessarily so costly that few can obtain them, whereas the little cutter frame is comparatively cheap, and it is really capable of very exquisite work in skilful hands.

SEGMENT ENGINE. Fig. 287.

In very many cases of ornamentation it is required that the mandrel, instead of making an entire revolution, should stop at a given point in both directions, so that, for instance, the turner should be able to move it 60, 80, or 100 divisions to and fro, with the certainty of its not advancing beyond that distance. This is effected by the racked and divided brass wheel B, fixed on the mandrel against the small end of the pulley. This wheel is sufficiently thick to allow of racking part of its edge to be acted on when necessary by the tangent screw, and leaving the other part for divisions, which are generally seventy-two in number, and marked in figures at every sixth division. On the other side of the plate are a number of holes drilled through its whole thickness to receive stop pins, Fig. 289, P, which are sawn through as shown, that they may spring, and fit the holes tightly. There are seventy-two holes corresponding with the divisions. These pins are about 3/16ths of an inch diameter, generally with flattened heads, and a hole through them to receive a pin to aid in removing them. The holes are sometimes made in the edge, instead of the side of the segment plate, but the latter is the best position. At Fig. 288, T, is seen the interior part of the poppet, with a piece of brass let in, and fixed securely, in which are inserted two screws, against which the segment stops abut, and prevents further rotation of the pulley. Side by side with this latter piece is placed the frame which carries the tangent screw. It is shown at Fig. 289. This frame is not fixed to the base of the poppet, but pivotted at _e_, between two short standards screwed into the poppet for that purpose. When not in use, the whole frame, therefore, drops down towards the front, but it can be raised by the small cam, K, Fig. 289, so as to gear with the worm wheel. In many cases the latter is not used, but the pulley turned by hand. The screw, however, gives a steadier and more easily regulated movement, essential in delicate operations, and sometimes convenient, even when the stops do not require to be inserted. The use of the cam, acting on the frame which carries the tangent screw, is now generally followed in the eccentric and oval chucks, and also in the dome chuck. It enables the workman, by throwing out of gear this part, to turn the worm wheel with the fingers, to set it at the required number on the division plate, a slow process when effected by the screw.

HOLTZAPFFEL'S ROSE CUTTER FRAME.

Among the newer devices for ornamental turning, must be mentioned the rose cutter frame of Holtzapffel and Co., an ingenious adaptation of the principle of the rose engine, without the drawback of cumbersomeness and costliness. It works like the ordinary eccentric and other cutters by a cord from overhead motion. The apparatus is represented in Fig. 290, and its various parts in Fig. 291, &c.

In the first of these figures, A is the shank, fitting the receptacle of the slide rest, and drilled to receive a hardened spindle, at one end of which is a worm wheel, turned by tangent screw B C, and shown again at A, B, C, Fig. 292. By this are turned the parts beyond K, namely, the frame D, carrying the tool, as in the eccentric cutter, adjacent parts S, representing chamfered bar, P, back plate, and O, which is a round piece in one casting, with the back plate, and having a hole through it for the coiled spring seen between O and N. All these are secured to the spindle, and turn together as one piece with it. Fig. 291 is a front view of these parts. H is the back plate of brass, with steel chamfered bars on its face, E, E, as in the eccentric chuck. Between these slides the plate, D, D, to the face of which is attached the long steel frame, carrying the tool holder. Close to the letter H, it will be noticed that a slot is cut in the back plate, through which projects a hard steel pin, screwed into the back of the sliding plate. This is seen at O, Fig. 290, and is attached to one end of a coiled spring, the opposite end of which is secured to a pin fixed in the back plate of this part. The pin O, is thus kept in contact with the edge of the rosette or pattern plate, K, and, as the whole turns with the spindle while the rosette is fixed, the pin, or rubber, is compelled to follow the undulations of the pattern, the motion being, of course, communicated to the tool. An inspection of Fig. 294 will show the arrangement of the parts on which the rosettes are fixed, and which is capable of turning, but does not, unless the tangent screw and wheel, H, are brought into requisition, as will be presently explained. The end of the main shank of the instrument is round, as seen at C, the worm wheel B being screwed fast, by four small screws, to the end of the square part of the shank. Upon this rounded end fits what may be called the sleeve E, to which is fixed the tangent screw, and on which also are placed the rosettes. The latter have a large central hole, Fig. 293, A and B, and fitting closely beyond the screw F, F, of the sleeve, and, being prohibited from turning upon it by a small key or feather, are secured by a screwed ring or ferrule seen at L, Fig. 296, the edge of which is milled. At F, Fig. 291, is seen a short stop, or set screw, the head of which is divided into ten degrees. By this, the rubber is prevented from penetrating to the bottom of the undulations on the edge of the rosette, and, if it is allowed only just to touch the summits of them, the tool will cut a circle. Thus, as the screw stop can be accurately set, one rosette will produce at pleasure graduated waved lines, the waves growing less and less undulated as the centre (or circumference) of the work is approached, giving a most delicate and chaste pattern, and _chased_ it certainly is.

Another variation of the pattern producible from any rosette results from the frame of the tool holder being extended beyond the axis of the spindle in both directions. When the tool is on that side of the axis nearest to the rubber pin, the undulations of the rosettes will be so followed as to produce their exact counterpart on the work. When the tool-holder is on the other side of the axis, the undulations become reversed, the raised parts of the rosettes producing hollows and _vice versa_. It may here be mentioned that in the case of the rose cutter, eccentric, and universal cutter, and similar apparatus, the screw heads carry ten chief divisions and ten smaller divisions. The screws are cut with ten threads to the inch, so that one turn advances the slide, or the tool, or wheel as the case may be, one-tenth of an inch. One large division, therefore, produces a movement equal to one-hundredth, and one small division one two-hundredth of an inch. If the screw is small it is generally cut with a double thread equal to one-twentieth of an inch. It is evident that in addition to the movements of the various parts of the rose cutter, the turner also has in his power those of the slide rest, and of the division plate on the lathe pulley, by one or both of which further complications become possible. Six modifications of pattern produced from one rosette alone are shown in Holtzapffel and Co.'s catalogue, and these may be further multiplied according to the taste and skill of the operator.

It is not possible to apply rapid movement to this rose cutter, else the rubber would probably miss touching the rosette in places; hence the tangent or worm wheel is used to give motion to the central spindle. An end view of this is given in Fig. 292. The object of the other tangent screw is, to move the sleeve and therewith the rosette at pleasure, so that the higher parts of the undulations in the second cut may, if desired, be arranged to meet the lower parts of the same in the first cut or to fall intermediately. The effect of the gradual shifting of the rosettes in this way is perfectly marvellous, and the writer much regrets that he is unable to supply specimen plates, as he is not in possession of the rose cutter. In the end of Holtzapffel's latest edition of his catalogue are several such specimens, but without any drawing or description of the instrument, the cost of which is moreover omitted.

The centres of circles cut by this eccentric tool will be always regulated in regard to position by the slide rest, because these centres are, as explained, always in a line with the centre of the spindle. Hence, to place a circle in any desired position, it is only necessary to determine its centre, and, after drawing back the tool by means of the screw till its centre runs truly as a mere drill, turn the screw of the slide rest until the point touches the required spot.

UNIVERSAL CUTTER FRAME.

This is represented in Fig. 284, in its latest improved form. It consists of a shank, A, which fits the tool receptacle, and is bored throughout its length for the reception of a central steel spindle, to which is securely attached at one end the worm wheel, G, acting as a dividing plate, and at the other the crank-formed frame, B, C, with its small poppets, D, D. These are sawn lengthwise, and thus spring upon the centre screws, which pass through them and carry the revolving cutter spindle, K, L, M, in the centre of which is a slot to receive the tool, the latter being clamped by the tightening screw, L. There are certain points to be attended to in the construction of this instrument, which must on no account be neglected. In the first place, the screws which pass through the poppets must lie in the line which would bisect at right angles that of the main spindle in the same plane. A line, in fact (as dotted), passing from screw to screw will pass across the centre of the end of the spindle. In the next place, when the tool-holder, with its pulleys, is in place between D, D, this line must be even with the _top line_ of the central mortise, H, for the _point_ of the tool is level with its upper surface, it being bevelled below; and it is essential that this point be capable of being so placed as to form a continuation of the centre of the main spindle. At E, E, are shown two of four thin pulleys. The two front ones are removed to show the poppets. They should not be made thicker than necessary, in order to avoid their interfering with the action of the tool. Either pair will be used with either pulley, K, K, according as the right or left side of the instrument is the highest, for, as will be explained, the cutter frame is used at all angles between the horizontal and the vertical lines, the cuts being consequently inclined in either direction, left, or right, at pleasure. The centre screws and points of the tool spindle must be carefully hardened. Before commencing to use this cutter, it is necessary to test the centrality of the point of the tool. Place the latter in its holder. Let the part C of the instrument be turned till vertical; cause the tool to revolve and to cut a light line or scratch on the face of the work. By means of the tangent screw cause C to become vertical in the opposite direction, so as to bring the other pulley upwards, and with the small screws in the poppets set the revolving tool holder, till the tool falls exactly on the line first made. It is, of course, understood that the line in question passed through the _centre_ of the work. If in both positions of the tool the central point is passed through, the cutter tool is correctly placed. The poppet screws are for this purpose specially, though sometimes used to place the cutter purposely above or below the centre of the work. Compared with the old form previously given, this pattern of universal cutter is very superior.

ROSE ENGINE.

The rose engine, as hitherto constructed, has not been entirely supplanted by the neat little apparatus already described, but is still used almost universally by the watch case makers; and its construction differs little, if at all, from that described by Bergeron; although the slide rest used with it is somewhat modified and improved. There are two kinds of rose engine, in one of which the mandrel with its poppets and fittings oscillates between centres fixed beneath the lathe bed; while in the other, the frame carrying the slide rest is thus movable, the mandrel head remaining stationary as in an ordinary lathe. In both cases the mandrel is allowed a to-and-fro or pumping movement in its collars; as the rosettes used are cut upon the face as well as upon the edge; and the rounded parts of an article can be operated on as well as the plane surfaces.

The second pattern, in which the poppet remains a fixture, will be first described, because it is capable of being applied to an ordinary lathe for surface work, and if the lathe has a traversing mandrel, it can be completely fitted for rose work.

The drawings and description annexed are from Bergeron's work; but the slide rest there represented, and arrangement of screwed mandrel, are omitted as obsolete:--

A strong iron frame, A, A, Figs. 295 A, 295 B, and 296, is made with one of the ends carried up and branched, so as to embrace the mandrel and rosette; which latter is attached to the back part of the chuck which carries the work. The top of the frame is double, so as to form of itself a lathe bed of small dimensions, upon which an ordinary slide rest can be fitted. It must, however, be used with a short socket, or it will be too high; as the top of the frame alluded to stands slightly above the level of the bearers. B, is a point of hardened steel which fits into a conical hole in the bottom of the lathe poppet, or (if this is not long enough to reach a good way down between the bearers) into a piece of iron arranged for the purpose similar to that now to be described, and which is again shown in Figs. 297 and 298. This is a kind of poppet in a reversed position, the clamping nut and screw being above the bed, and the head with centre screw below. The frame lies, therefore, between the mandrel head and this reversed poppet, or between two of the latter, and oscillates upon their centres whenever the projections or depressions of the rosette compel it to assume such motion.

Fig. 299 is a section of the chuck which carries the rosette, the latter being shown in position. A, is the body of the chuck; B, the inside screw to fit the mandrel. On the outside of this part are a few turns of a somewhat finer thread, beyond which a plain part is left next to the flange, C, and on this the rosette is placed, and is clamped by the nut, cut outside into beads, or milled, or left plain and drilled for the insertion of a lever pin; this nut is marked D in the figure. It will be seen to lie within a recess formed in the face of the rosette, E. The latter is shown in Fig. 300. A, is the recess just alluded to; B, C, the pattern on the face and edge; D, the large hole in its centre, allowing it to be slipped on the back of the chuck. It is prevented from turning on the latter by a pin, which fits into the small hole, F. From the front face of the chuck rises a conical pin, G, similar to that on the eccentric chuck, over which fits the circular division plate, I, with its projecting screw, H, to hold the ordinary chucks. This plate is recessed at the back, leaving a mere ring of metal, _e, e_, which fits a corresponding circular groove, and secures the steady movement of the plate, which is fixed by a conical washer and screw, as seen in the plate. This division plate is formed with cogs, into which a stop falls, as described, when treating of the eccentric, but the divisions are differently arranged, the cogs being divided into sets of eight or ten teeth. Let the whole circumference be first divided into six equal parts, and, beginning at the first division, cut six or eight teeth, as if the whole circle were to be divided into 60. Pass to the second portion, and cut eight teeth, as if the circle were to be divided into 72. Let the third carry eight teeth, with a pitch of 80 to the circle; the fourth a similar number, with a pitch of 84; the fifth 96; the sixth 100 to the circle. These must be cut with the same cutter, so that the spring click, or stop teeth, may fit any of the six sets. There will be several undivided spaces, which are to be left plain. The several sets are to be marked in numbers, so that the pitch may be discovered at a glance, and the teeth in each being so few will hardly require separate numbering. The part of the apparatus which carries the rubber--that is to say, the heads of the branched part of the swinging frame, are made flat on the top, which projects on three sides, forming small tables on which the actual holder or clamp can be fixed by a turn of the screw, X, in the first figure. The rubbers are merely flat pieces of steel, with edges sufficiently sharp to penetrate to the lowest depths of the undulations and recesses on the rosettes, but rounded off and polished, so as not to cut and damage the softer metal against which they act; other materials have been tried, as ivory, and the harder tusk of the hippopotamus, but hard steel is most generally preferred. It is, of course, necessary that the rubber press with some force against the rosette, which force should, moreover, admit of being regulated at pleasure. This is effected by a spring of steel under the lathe bed, to the end of which is affixed the arm, W, which has a ring handle nearest to the operator, and is perforated with a row of holes from end to end. This arm is flat, and falls into a fork at the end of the tail piece, Y, which is seen in the second figure attached to the centre of the lower bar of the frame. A pin passes through holes in this fork, and through one of those in the arm. By this arrangement it is easy to regulate the force which the spring shall exercise, as this will be increased by moving the pin nearer to the spring, and diminished by placing it in a hole nearer to the ring handle. In forming the rosettes great care should be exercised to make the corresponding parts agree. The depth of similar hollows must be precisely equal, and elevated portions intended to match, must do so with great accuracy. Supposing, for instance, a rosette to be made with ten elevations and ten recesses, all of equal curves. If these are accidentally unequal, and it is desired to arrange a set of these waved rings one within the other, so that the depressions of the one shall be opposite to the elevations of the other, or so that this effect shall take place gradually--if the curves of the pattern are unequally cut the several portions of the device will not tally, and an irregularity will be produced of disagreeable appearance; an inspection showing at once that such irregularity is not part of the device, but unintentional and erroneous. This leads to a consideration of the division plate of this rose engine, and an explanation of the object of its peculiar construction. The pattern of the rosette is, as it were, in sections; either similar elevations and recesses are alternately repeated, or there may be a variety of such, extending over a part of the circumference, and forming a certain complete device, which may then give place to a second pattern, extending a similar distance; and these two may alternate regularly round the circumference. Each of these sections must be of precisely similar length, and the repetition of the pattern must also be precisely similar, for the reason stated above.

It is evident that all possible alternations of the device or set of devices may be obtained by means of six or eight notches of the division plate; for, by moving it forward to that extent, the whole pattern may be compassed. In treating of the second form of rose engine, and of the method of using it, this will again be adverted to, and illustrated by an example.

Hitherto we have spoken only of the use of the pattern on the edge of the rosette, but, as already stated, it is frequently repeated on the face, and by this means it becomes easier to work upon the outside of a cylindrical piece, as well as on the two ends. Patterns thus cut on the face of a rosette tend, of course, to move the mandrel to and fro in its collars, which is only possible when the lathe is made on the plan of a screw-cutting or traversing mandrel lathe. The spring which keeps the rubber in contact with the face of the rosette is shown at P.

The head on the top of the arm, which forms the clamp or holder of the rubber, must be turned round to face the rosette, or a separate rubber must be used, which passes through the clamp at right angles to that used in surface work, and the frame must be prevented from oscillating by a stop which fits between the bearers of the lathe, and embraces the upright side of the frame. The top of the slide rest must be turned round, or a side tool used. In this case, the rest and frame with its rubber become fixtures, as in ordinary turning, the mandrel and work being alone moved in correspondence with the pattern on the face of the rosette. It would indeed be much better to do away with the frame altogether, fixing the rubber to an upright pedestal mounted on the lathe bed, and using the slide rest in the usual way, were it not that in general the work is constantly being varied, the side and face being worked in turn--and the apparatus is rather cumbrous to remove and re-mount often. It is, nevertheless, easy to finish the ornamentation of plane surfaces first, and then to remove the frame altogether, and substitute a fixed rubber, as stated.

The rose engine now described has certain evident advantages over the rose cutter frame, and is capable of the most exquisite devices. It may be, perhaps, a mere question of taste, whether rose engine work finely executed is not in point of beauty, superior to any that can be done by geometric chucks, however elaborate. That it is so, is decidedly the writer's opinion, more especially when this apparatus is used in combination with the oval chuck. Moreover, there is nothing in the form of rose engine described to make it a very expensive article, or beyond the skill of an amateur; and with a set of only three rosettes, the patterns may be varied continually, and multiplied--if not _ad infinitum_--yet quite sufficiently for the display of skill and taste of the operator.

In using the rose engine, it is necessary to carry the cord to the pulley from a very small wheel on the axle. Sometimes the lowest speed pulley of the flywheel may answer, but if the recesses of the rosette are deep and sharp, or only slightly rounded, it may become necessary to mount a still smaller wheel on purpose; else the rubber will jump over and miss parts of the design, thereby spoiling the work. The watch-case turners, indeed, altogether dispense with the flywheel, and use instead a small pulley, fixed to the side of the lathe bed, and turned by hand.

These artificers always use a more elaborate form of rose engine, which will be presently described, and which is the most perfect in detail of all similar contrivances, but it is necessarily costly, and cannot be said to be well adapted for plain turning also, except in a limited degree. The work, if not of soft material, like a watch-case, should be turned first of all upon an ordinary lathe, the mandrel screw of which is a counterpart to that of the rose engine, and the latter should merely be used for the final cut, to perfect the form of the material previous to its ornamentation.

In the Appendix will be found a new method of obtaining the required oscillatory motion of the rose engine, which might apparently be applied to tool holder[22] frame here described, or to the poppet head.

[22] _I.e._, the main frame carrying the slide rest.

The rose engine proper is arranged with an oscillating poppet head carrying the mandrel and its rosettes, the tool being stationary. The following account of this machine, and the drawings, are copied almost exactly from Bergeron. The modern rose engine is not indeed made with the projecting lugs referred to as intended for the application of the guide ring in oval turning, as this guide is now altered to fit a poppet head of ordinary form, as already detailed. The pulley and division plate are also of obsolete form, but as the main arrangement of parts described are sufficiently similar to that now followed, Bergeron's drawing and description have been retained. Fig. 302 is a longitudinal view, and Fig. 303 a transverse view of the working parts of this lathe. A, A are the poppets, which are in one casting, with the connecting piece shown by the dotted lines, which latter has a tail piece firmly attached to its centre, to which a spring is affixed as in the lathe previously described. In the drawing the cylindrical collars carrying the mandrel are split, so that in case of wear they can be tightened in the usual manner by a screw at the top of the poppet marked B, 303. The lugs, _f, f_, with square holes _e, e_, are for the application of the guide for oval turning, the latter being originally a ring with slotted arms on either side. The points of oscillation are precisely similar to those of the rose engine first described, two short poppets C, Figs. 302 and 303, having centre screws, whose points fall into conical holes made in opposite faces of the poppet, a little below the level of the lathe bed. These are formed with a slit to receive the stop _h_, which is hinged at the point _o_, and which, when raised by a wedge, catches into a small projection _p_, thereby fixing the poppet in a perpendicular position and preventing its oscillation. The rose engine can then be used as an ordinary lathe, to finish the preparation of the work to be operated on, which should, if possible, be commenced and mainly formed on an ordinary lathe, the mandrel of which is a counterpart of that of the rose engine. The tail piece, E, does not require a separate description, being precisely similar to that already described. The to-and-fro movement of the mandrel caused by the action of the rubbers on the face of rosette, is also arranged in a manner similar to the last. F is the spring, turning in the middle of its length on a pin in a piece of iron fixed on the bed, so that if both ends wore free it could swing backwards and forwards between the cheeks of the lathe on this pin as a centre. The upper end of this spring is branched in a semicircular form to embrace the mandrel, this fork falling into a groove formed to receive it. It can thus be brought to bear against either of the shoulders visible at this part. The lower end of the spring fits into a notch, or rather a slot in the arm H of the second figure; the handle of this arm being L in both figs. This piece is pivotted at K, and at its other end falls into one of the notches in the retaining plate, G, of the first figure. By this plan the tension of the spring, can be brought against the mandrel in either direction at pleasure, for if the lever is placed in one of the left hand notches, the tendency of the spring will be to move the mandrel towards the right, and _vice versa_. The tension of the spring can also be regulated by the use of the groove B or X at pleasure. In the second figure of Bergeron's the piece which at first sight appears to be a continuation of the holding down bolt of the short poppet carrying the centre screw, is the tail piece or lower end of the long spring just described, and its reduced extremity is visible passing through a short slot in the lever H, near the handle of which appears the _edge_ of the notched piece G of the other figure. All the above parts are commonly of iron, the following are in brass or gun metal.

On the bed and parallel to it, two pieces of brass, or standards, rise, similar to H in the first figure, the two being opposite to each other, one on each side of the mandrel, as shown in the second figure. Both these are firmly secured to the bed by long bolts and nuts, it being of the utmost importance that they should not move or vibrate in the least. They are in addition united to each other by two horizontal braces, one of which is seen at N in the second figure. At _l, l_ are seen two rectangular notches, which are the ends of grooves made in the upper part of the head piece, H, and which traverse its whole length. They receive the crooked part, _a_, of the rubber holder, Fig. 304, so that the latter can be slid along this bar, and brought opposite to any one of the rosettes, after which it can be secured in position by the screw, _b_, Fig. 304. The mandrel is thus arranged. It is cylindrical, with a shoulder against which the chucks can rest, as in an ordinary traversing mandrel, and a similar but reversed shoulder at _g_, Fig. 302. Against the latter abuts the end of an accurately turned sleeve of brass, which fits over the mandrel with slight friction, so as to have no shake or play upon it. Upon this sleeve the rosettes are placed. They fit accurately over it, and are prevented from turning round upon it by a feather extending the length of the sleeve, which fits into a corresponding notch cut on the inside of the rosettes. These are arranged in pairs back to back, and each couple is separated from the next by a short sleeve or ferrule, which Bergeron recommends to be of wood, as tending to hold the rosettes more securely than metal when pressed together by the nut at the end of the set. The fibres of the wood are to be placed parallel with the mandrel, because there is no shrinkage of this substance as regards its length. The pulley is fixed beyond the rosettes on a part of the mandrel filed into six faces for that purpose, and lastly comes the nut, which secures all the parts to their several positions, but which nevertheless does not so jam them together but that the mandrel can be turned within the sleeve when the positions of the rosettes are to be changed in the course of working a pattern. The division plate is not attached to the pulley, though lying close upon its surface. It slips on to the sleeve on which the rosettes fit, and its spring-catch only on the face of the pulley. Thus the latter is held to the sleeve and its fittings when the catch is down, so that all turn together, but, when the catch is raised, the division plate, carrying with it the rosettes, can be turned round upon the mandrel as may be required. It is not necessary to repeat what has been said respecting the manner of graduating the division plate, as that used with the lathe already described is in that respect a counterpart of what is used with the rose engine now treated of.

The following description of the method pursued in turning a pattern shown in Fig. 307 will suffice to show the working of the rose engine:--First, says Bergeron:--It is not enough to know the general construction of the rose engine, it is necessary to know thoroughly the particular one in use, _i. e._, as regards the details of its construction, the slight defects or imperfections it may chance to have, and the means whereby they may be lessened or corrected. It is necessary, in addition, to know well, and to have always at hand, the numbers of each rosette, or any rate to have a table of them which can be readily referred to. It is equally necessary to recognise at a glance the various sets of divisions on the division plate, for which purpose, and that no mistake may be made, such numbers ought to be engraved upon each. The same holds good with regard to the slide rest, and, in addition, practice should be frequent upon box or other inexpensive material by which the turner may have made himself perfect in the several combinations possible, and the various effects producible by the rosettes and different shaped tools over which he has control. It is thus, by actual experiment only, that the turner can become acquainted with the powers of his own lathe and apparatus, and thus only, after working out the patterns already executed, will he be in a position to design new ones, and to work with ease and certainty. The rose engines are usually fitted with tools of variously shaped edges, as shown in Figs. 305 and 306, by this means a pattern of some width and great variety is of course produced at once, and by one rosette. In the following, however, a tool with single point, Fig. 308, is to be used. This simplest design is supposed to be on the cover of a box or other plane surface, and it is evident that the movement or oscillation required of the mandrel is that at right angles to the bed of the lathe. To obtain this movement, when the rubber is fixed in its clamp, on the side of the workman, as it is necessary that the rubber should press against the rosette through the medium of the spring, the handle of the lever, Fig. 302, must be drawn forward towards the operator, and kept by a pin, as described, passing through it and the tail piece of the mandrel frame. The tension must not be too great, especially if the rosette to be used is deeply indented, and care must be taken to free the frame from the action of the stop, _p_, by removing its wedge before making any attempt to try the pressure by moving the mandrel. The design under consideration is produced from rosette numbered 2 in the drawing, and in fixing the rubber care must be taken that it does not bear against the adjacent rosette. Choose a rosette of forty-eight teeth or undulations, and as the second circle of ornamentation exactly intersects the first, the raised part of the one falling under the depression of the other, and as it were _halving_ it, the set of divisions on the click plate to be used will be twice 48, or 96. Place the rest parallel to the face of the work and so that the forward motion of the tool shall be perpendicular to it. By means of the leading screw of the rest, place the tool near the edge of the work and level with the centre, and gently moving it forward and putting the lathe in motion, commence the cut. After having made a light cut, without moving the tool, stop the lathe and judge of the depth of cut, and if sufficient, screw up the stop screw of the slide rest, to insure all the following cuts penetrating to the same depth. Observe the position of the tool as marked by the graduations of the slide rest, and then withdrawing it from the cut, move the click plate one notch, which will divide exactly in half the several undulations of the rosette. By the rest screw move the tool towards the centre of the work and mark the number of divisions passed over, so that the circles of undulations may be equidistant, and cut a second. Now for the third, _go back or advance_ on the click plate one division, for the position of the undulations in the third is precisely that of the first circle. It is indeed immaterial whether an advance or retreat of one notch is made in this case, but now is evident the reason for not dividing the plate equally all round, five or six teeth being ample for each division. If there are eight rosettes the plate should be first divided into eight parts, and each rosette having a different number of undulations, these eight parts should be divided into degrees proportionate to the numbers on the rosette, the one being a multiple of the other. In working the _side_ of a cylinder, that of a box, for example, the longitudinal movement of the mandrel is required, the poppet being retained immovable by the wedge and stop. The tool is to be placed at right angles to the side of the work, the rubber brought to bear on the face of the rosette. The method of working will be self-evident, after the description already given. It is impossible in a brief work like the present, to go into details of other patterns referred to and illustrated by Bergeron, one or two of which are nevertheless of great beauty, and are executed with the aid of the eccentric chuck mounted on the mandrel of the rose engine. There is, however, a different class of work, to which reference will be made in our next, and we shall also give a description of a simple addition to the slide rest, used by watch case turners, which does away with the necessity of counting the number of divisions upon this instrument when used as above.

The slide rest used by the watch case turners is almost identical in form with one figured and described by Bergeron. It is necessary that the tool holder should have a circular motion, somewhat similar to that of a spherical rest, in order to reach the sides and curved surfaces of the articles to be engine turned; hence the tool receptacle and its bed work upon a central pin. The pin here called "the bed" is usually a flat brass plate of a quadrant form, the central pin being at the apex, and carrying on its face the guides for the tool receptacle. The pin on which it turns is a reversed truncated cone rising from a similar flat plate, which itself forms the sole of the rest, or traverses the lower frame as usual; when the tool is beyond the central pin, it will ornament conical surfaces, and _vice versa_. On the edge of the arc is a racked part, and a tangent screw works into it. The tool is moved to and fro by a lever, as usual, the depth of cut being regulated by a stop screw. These details being already entered into, in treating of slide rests and chucks, need not be more specially explained here; but a contrivance for regulating the traverse of the upper part upon the frame underneath, is ingenious and serviceable, and will therefore be described. The end of the leading screw is fitted with a ratchet wheel of the same construction as that of the ratchet brace for drilling, patented by Fenn, of Newgate Street, to which in the same way a handle and spring are attached, as shown in the drawing, Fig. 309, A, and Fig. 310. The handle rises between two semicircular plates drilled in the face, with holes for the reception of stop pins, B, C. These regulate the traverse of the handle, and thence of the screw. If the former, therefore, is thrown over till the left stop is touched, and then pulled forward to the other stop, between each cut of the tool, the latter will leave equidistant spaces upon the work, without need of counting divisions at each cut. As a traverse of one inch or more of the lever handle at the place of the stop pins only moves the screw a very minute quantity, the holes for the pins need not be very close together even for fine work. This is a very simple contrivance, and perfect in action, enabling the operator to work with ease and certainty, and with great speed.

RECTILINEAL CHUCK.