Rectilineal Chuck.

Figs. 295B, 297, 298, 300.

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. Thespring 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 notad 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 alimited 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. 302is a longitudinal view, andFig. 303a 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 holese, 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.302and303, 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 stoph, which is hinged at the pointo, and which, when raised by a wedge, catches into a small projectionp, 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 therubbers 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 ona 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 forkfalling 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, andvice 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 theedgeof the notched piece G of the other figure. All the above parts are commonly of iron, the following are in brass or gun metal.

Fig. 303.

Figs. 302, 304, 305, 306, 308.

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. Atl, lare 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 atg,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 pairsback 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.

Fig. 307.

The following description of the method pursued in turning a pattern shown inFig. 307will 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 werehalvingit, 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 ofthe 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 advanceon 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 thesideof 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, andvice versa. On the edge of thearc 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, andFig. 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.

Figs. 309, 310.

Fig. 311represents a modification of the eccentric chuck, when the latter is used as a fixture, to present to revolving cutters and drills the different parts of the work which is to be operated on. The eccentric chuck is commonly made to slide in one direction only, and the traverse is limited. In the present case there is ample traverse in both directions, the slide being arranged to descend to the lathe bed, and upwards to an equal degree. A is a cross section of this chuck, the length of which is 7½ inches. It is very strongly made in brass, and is altogether much more substantial than the eccentric chuck. B and C are the guide bars, between which worksthe sliding part. The nut of the leading screw is below this as usual. The tangent wheel has 120 teeth, and is thus divided: 0—12—24, &c. The tangent screw head is divided thus: 0—1—2—3—4—5, with half divisions, marked but not numbered. This rectilineal chuck is most commonly used in a vertical position, but may be otherwise placed. In using it for any work likely to bring a strain upon it, the ordinary spring index attached to the lathe for use with the face plate, should not be entirely relied on to keep it in position. It is safer to make use in addition of the segment engine stops or other available contrivance. The special function of the chuck is the production of straight lines on the face of work forming stars or radial flutes, which can be worked with a drill. Fluting is also readily done by its aid, with the addition of the vertical eccentric, or dome chuck, already described. Its use is, however, by no means confined to ornamental work—small tenons, mortises, and even dovetails are producible by it; and in fitting together the various parts of temples, shrines, and similar complicated specimens, its uses will beinnumerable; and here may be noted the extension of the lathe and its apparatus to work apparently in no way suited to it. It has now become more of a universal shaping machine than it used to be, owing to the great accuracy of the work done by it, and the variety of fittings that can be added to it. In a later page will be found a drawing and description of a new device of the kind—a planing machine, devised by an ingenious and first-class maker, Munro, of Lambeth, and patented by him. Mention is made of it in this place, because the rectilineal chuck is in some degree capable of similar work. The slide moved up and down by a screw the handle of which is of extra length to allow the vertical traverse, is also capable of being moved by a cam-eccentric chain or rack and cogged wheel, so that by pulling down a handle the slide may be made to slide up and down more rapidly than by the screw motion; any piece of wood of rectangular or other figure may thus be planed on the face, by being fixed on the rectilineal chuck, and acted upon by a fixed tool in the slide rest, the latter affording the horizontal traverse of the tool across the face of the work, the former the perpendicular movement of the material. If a slide rest is thus arranged in combination with the chuck in question, and the lathe bed is imagined to be set up on end with the chuck downwards and horizontal, the whole will become, in fact, a precise counterpart of those planing machines, the bed of which traverses to and fro, with the work under a fixed tool. Munro's arrangement is, of course, of far more extended application, and more suited for metal work; but for lighter and more delicate operations of a similar kind the rectilinear chuck and slide rest will be found very serviceable. It is with such an adaptation of this chuck as has been alluded to, namely, a quick speed movement of the slide by a lever handle, that the rays are drawn so exquisitelyfine and close upon the faces of many gold dial plates of watches, the handle being arrested by a stop at any given point, so that these rays shall not transgress their appointed limits. It will be hardly necessary to allude to those other applications of this apparatus, or other particulars in which it is identical with the eccentric chuck, as the description already given of the latter applies to both alike, the extra traverse of the present in both directions being its chief distinguishing feature.

Fig. 311.

Fig. 312.

This chuck has been in use for many years, and has in consequence been of late rather neglected. It is, nevertheless, the parent of those more elaborate contrivances included under the general title of Geometric Chucks, of which Ibbetson's stands first in order of date, and possibly of merit, though this last qualification may admit of question. The epicycloid, defined mathematically, is a curve described by the revolution of a point in the circumference of a circle, when the latter is made to roll upon the concave or convex side of another circle. A pin in the rim of a wheel revolving round and in contact with another wheel, therefore, describes this curve, which constitutes two or more loops, as will be seen by the annexed illustrations. The number of these loops is variable, and the chuck will produce almost any number by changing the pinions, and thus altering the relative velocities of the revolving parts. The following description will make the action of this chuck clear, and enable any good mechanic to construct one for himself. In the first place, the above remarks show a necessity for a fixed wheel, round which another may revolve.Fig. 313represents this attached to a plateof brass, which can be fixed to the lathe head, the mandrel passing through its centre. This is the original pattern of plate, and need not, of course, be adhered to, as the form can be modified to suit the lathe to which it is to be applied. It is merely necessary to affix such a wheel to the face of the poppet, so as to be concentric with the mandrel [a plan done away with, however, or rather reversed, in Plant's geometric chuck]. The epicycloidal chuck, which screws to the mandrel as usual, consists of a foundation plate of brass, A,Fig. 314, behind which is mounted the cogwheel, B. The axis of this wheel passes through the plate, and is carried by another plate,e, which is curved and adjustable upon the former. The axis of this wheel carries a small pinion, D, so that the whole turn together. This pinion being one of a set of change wheels, necessitates the possibility of adjusting the plate which carries its axis, as all the several change wheels must gear with E, which always retains its position on the chuck. The sliding plate in question being put in place, is clamped by the screw F. A plate of iron, G, of the form shown, and of sufficient thickness for the secure attachment of the wheel and of the screw which carries the ordinary chucks, is fitted to turn on the axis of the wheel E. Its larger end traverses within the arc H, which is graduated. The arc is bevelled underneath, serving to hold down securely to the foundation plate the piece of iron which is chamfered to fit it. At the left side of the back plate is seen a stop, L, which is placed in such a position, that when the iron plate rests against it, the screw M is concentric with the mandrel, andwork may be turned as upon an ordinary chuck. To throw the iron plate, and consequently the nose of the chuck, on one side, or in other words to place the work eccentrically, the screws which retain the arc are loosened and the adjustment made by hand. The eccentricity is marked by an index on the iron plate, which points to the graduations seen upon the face of the arc. The eccentricity being determined, the arc is again screwed down to retain the movable plate in its new position. [Although this is Bergeron's method, it appears vastly inferior to the plan of racking the edge of the iron plate, and moving it to any required degree of eccentricity by the aid of a tangent screw.] When made as above, the chuck will produce loops varying in number according to the relative dimensions of the pinion (or change wheels gearing with E) and the central wheel, M. If the latter has 120 teeth, and the change wheel 60, two loops will result. If the pinion has ten teeth, the number of loops will be 12, and so forth. The practicallimitto the number depends on the possibility of diminishing the pinion in size and number of cogs, and still keeping the latter of such size and pitch as to gear with E. If, therefore, a larger number of loops is required than can be obtained thus, it becomes necessary so to modify the form of chuck as to permit of intermediate change wheels, and when the modification is carried out, we have the geometric chuck, the most perfect, but the most complicated and expensive of all. To understand the nature of the work, the following is given in clear language by Bergeron, and will sufficiently explain and simplify matters.

Fig. 313.

Fig. 314.

Fig. 315.

If one considers the movement of the piece (of work) when the wheel M is concentric with the mandrel, it will be perceived that although it makes two revolutions upon its axis, yet inasmuch as it has no eccentricity it will describe no particular curve or figure; but if an eccentricity of three divisions is given to it, two buckles or loops will result as inFig. 315. Before cutting the material, however, approach the tool as near the work as possible, and putting the lathe in motion, observe whether the buckle[23]passes too near the centre or too far from it, and also how near it goes to the circumference. If another change wheel with forty teeth instead of sixty is substituted, the slide C, being adjusted accordingly, three loops will be described (forty being one-third of one hundred and twenty), but it is always necessary before actually cutting the material, to try whether the buckles will pass near to the centre without going beyond it. The result of the latter movement will be shown presently, as it entirely alters the appearance of the pattern. The divisions commence on the arc at the left hand, the index resting at 0° when the plate is against the stop L, and the screw of the chuck concentric with the mandrel. The preceding figure of three loops will become similar toFig. 317, retaining the same wheels and some degree of eccentricity, but by means of the slide rest moving the tool towards the circumference, so that the buckles overlap the centre. The effect thus produced is, that of a set of three curvilineal triangles of which the apex of one falls upon the base of the next. The use of this chuck is stated to require upon the part of the operator more care than any other, as regards the derangement of work or tool in the least during the operation, as, if either is once moved in the least out of position, it will be found next to impossible to strike the line again, owing to the peculiar nature of the curve, for although the tool may be replaced upon any one part of the line already cut with the intention of deepening—it is by no means certain that it will trace the same curve again. This curve, says Bergeron does not produce an agreeable effect on the cover of a box,unless it is very finely cut, the tool, therefore, should be very sharp in the angle and very keen. Bergeron specially mentions this in reference to filling the cuts with thin strips of horn or shell, a method of inlaid ornamentation not much known or admired in the present day, but to which allusion may probably be made again in this series. To form the second set of loops, which are parallel with the first in these designs, it is only necessary to use the leading screw of the slide rest, to move the tool nearer to or further from the centre, while the eccentricity and the arrangement of change wheels remain as before. It is scarcely necessary to detail the formation of the larger series of four loops and upwards, as these are simply the result of different sized change wheels: the following principles, however, by which the buckling of the several loops is controlled or prevented, may perhaps be serviceable. "When, for example an eccentricity of sixteen divisions is used—if the tool is placed at a distance of two such divisions from the centre of the piece, a line only will be produced of as manycurvesas the wheel or pinion D would producebuckles. If the tool is moved further from the centre by a quarter division, the angles (connecting the curves) will be more defined, but still no buckles will be made. A little further movement of the tool will produce very small buckles which will thus gradually increase as the tool is set further and farther from the centre—until at last when the curves pass beyond the centre, the result is arrived at already shown inFig. 317. Another formof this chuck is shown in318, in which, instead of the iron plate being pivotted for the purpose of eccentricity upon the axis of the wheel E, a parallel slide motion is given to the main wheel by guide bars, as in the eccentric and oval chucks. This form is figured in "Lardner's Cabinet Cyclopædia." The large front wheel carrying the screw for chucks is pivotted to the slide C, and protected by a plate D which nearly covers it. The wheel L, is arranged to follow this slide, so as to remain in gear with the large wheel without leaving the fixed wheel or ring on the face of the poppet. In both patterns of this chuck the front wheel is used as a division plate, being moved in either direction as many cogs as desired to produce interlacing of the looped designs. It is better, however, to add a racked division plate and tangent screw, as in the eccentric chuck to act as one piece with the chuck screw, and with the latter turning on a conical pin in the centre of the large wheel underneath. The above apparatus requires to be used with a slow motion owing to the complication of parts, and the whole ought to be so well constructed, that the various wheels revolve with perfect smoothness and without shake or noise.

[23]The wordbuckleis used to signify the small loops—not the large curves.

Fig. 316.

Fig. 317.

Fig. 318.

There is no class of work on the whole more interesting than that executed by the aid of the spiral chuck, especially with an addition to be described here. This apparatus has grown, almost as a matter of course, from the adaptation to the ordinary lathe of the system of change wheels for the production of screws of various pitches. A spiral is, in fact, a screw with very extended pitch, the threads either closely enwrapping a cylinder which forms the core or body of the screw, or being entirely separate and independent of such core, the latter being by far the most light and elegant. The chuck here described is used with the same arm or bracket as has been alreadyspoken of, standing out from the poppet to carry change wheels, and is itself adjustable to suit different diameters of the same. In the sectional view of this chuck given here, A, H, is the body with internal screw as B, to fit the mandrel. The cog wheel of the chuck which gears into the first on the movable arm or standard, is cast with a large central hole to allow it to be stopped on at D, where it is retained by a nut C. This permits a change of such wheel for one of different size or for the apparatus to be presently described.

Thus far the chuck is only applicable to the production of screws or spirals with a single thread. F, is a dividing plate with racked edge acted on by the tangent-screw E, and carrying the screw, G, a counterpart of that upon the mandrel. This plate carries 96 divisions or teeth. The latter may be used with a spring click if preferred; but the racked edge gives perhaps the more delicate power of adjustment. The spiral chuck constructed in this way is capable of producing any required number of screw threads or spirals, solid or detached, and of any ordinary pitch. It is, however, chiefly intended for the production of spirals or twists for articles ofvirtu. The method of proceeding has already been described in a previous page. It is one rather of care than skill, as the lathe apparatus ensures the correct movement of the tool where the shape of the latter determines the form of thread, angular, round, or moulded at pleasure. A few of the tools required are shown in the drawing. For finishing the rounded threads, Nos. 3 and 4 may be used, which are similar to those required for turning ivory rings, the one completing half the thread, the other applied in the opposite direction, meeting the cut of the first and finishing the operation. As it is necessary to get round to the back of the threads in this case, no inner mandrel can be used to support the work, and, therefore, great care and delicate handling are necessary to prevent breaking the twists. The stops should also be used upon the bed of the slide-rest, to limit the traverse of the tool and prevent it from striking the shoulder, and destroying any bead or other moulding formed there. This is more specially needed, when there are two or more such twists rising from the same base (that is when there are two or more threads to the screw). The additional apparatus now to be described, adds considerably to the powers of the spiral chuck. It is called the reciprocating apparatus, and its effect is, to cause a to and fro movement of the work, at the same time that the motion of the tool is continued in a horizontal direction.Fig. 320shows the simplest of the effects thus produced. The screw is commenced and carried to any desired distance on the cylinder. The action and horizontal traverse of the tool is continued, but that ofthe cylinder reversed, and the cut is thus carried upwards. The tool may be a revolving cutter, the action of which, being continuous and in the same direction, would seempreferable, as the greater the speed with which the tool attacks the material the better is generally the result in work of this kind. A fixed tool, moreover, must have a central edge chamfered above and below, and there is also a tendency with any such fixed tool to unscrew the chuck, as the resistance occurs in that direction in the upward cut.

Figs. 320, 321, 322, 323, 324, 325.

The details of the arrangement are as follows:—The several parts being drawn of full size,Fig. 321A is an eccentric capable of slight adjustment by the use of either hole, one being further from the centre than the other.Fig. 322gives another view of this eccentric, which is precisely similar to that used in model engines. It is turned as a circular plate of gun-metal, with one flange. The plate being five-tenths of an inch thick, a second plate, forming another flange, is attached by four small screws, after the ring of the eccentric is in place. This ring is of iron, or, still better, of steel, and is made in one piece, with the arm B, which is six inches long; the main part of it is flat, but it is rounded towards the end, and turned at E, after which it is again flattened to work against the arm D, or still better forked to embrace the latter. It will be seen that D is also a flat plate, with a turned ring similar to the first, but without the enclosed eccentric. In this is drilled a series of ten holes, into any of which a pin can be fitted, so as to unite the arms B and D, the pin becoming a hinge or centre of oscillation. The circular ring of the part D fits on the part D, D of the chuck, on which it can be secured by the ferrule C, the arm D being then in a vertical position. The holes in the eccentric can (either of them) be fitted over and secured to the end of the leading screw of the slide-rest. The handle being then placed on the other end of the screw and turned by the hand, the eccentric will cause the arm D to oscillate to and fro through the medium of the connecting rod B, thereby giving to the chuck, and to the work attached to it, a similar to and fro movement. The extent of this movement depends upon the length of the lever D brought into action. With the pin in the holes 1, 2, 3, the oscillation will be inconsiderable, but with the pin in either hole numbered 8, 9, 10, it will be much increased. In the first, therefore, a short wave,Fig. 320, will result; in the second case these will be more likeFig. 320B. This apparatus will completely alter the character of a spiral, which, if cut through a hollow cylinder (as in the case ofdetachedtwists) becomes a zigzag of curved sides curious enough to behold. The apparatus, it must be understood, is worked entirely by the handle of the slide-rest, the lathe-cord being thrown off unless the latter is carried to the overhead instead, to put in action revolving cutters. The reciprocal action is, in fact, a self-acting segment engine.

It has been already stated that for the production of spiral workrevolving cutters are preferable to fixed ones, unless, indeed, it is required to finish up a perfectly round thread, whenFigs. 3 and 4of the tools drawn are required. Revolving cutters must be placed inthe frame of the universal cutter and set to the rake of the thread. Drills may be used for the reciprocating movement, as they make very clean work, and the rake need not with these be attended to. In facework drills are specially to be used to produce patterns likeFig. 325, and others derived from this simple one. An additional apparatus, represented inFig. 323, is required for the latter process, to enable the rest to be turned in its socket so as to face the work, and notwithstanding the alteration of its position still to keep up the gearing of the wheels. A rest socket to be made and mounted as usual is fitted with a stem surmounted by an accurately drilled boss A, through which passes a spindle fitted with the wheel C, to gear with that on the arm carrying the change-wheels, and which may be changed for one of larger or smaller size. This is for cutting such work asFig. 324, representing, of course, only a single spiral, very open and of itself of no beauty, but which by intersection of other spirals can be converted into a pattern of great elegance. When it is desired to produce the waved spiral the eccentric is fixed to the rod instead of the wheel C, and the work proceeds the same as when a cylindrical surface is to be worked. In the Fig. shown the division plate of this chuck is of course used.

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