The Spiral Chuck (Fig. 319)
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 already spoken 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 of virtu. 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. 320 shows 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 of the 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 seem preferable, 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.
The details of the arrangement are as follows:—The several parts being drawn of full size, Fig. 321 A is an eccentric capable of slight adjustment by the use of either hole, one being further from the centre than the other. Fig. 322 gives 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 like Fig. 320 B. This apparatus will completely alter the character of a spiral, which, if cut through a hollow cylinder (as in the case of detached twists) 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 work revolving cutters are preferable to fixed ones, unless, indeed, it is required to finish up a perfectly round thread, when Figs. 3 and 4 of the tools drawn are required. Revolving cutters must be placed in the 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 face work drills are specially to be used to produce patterns like Fig. 325, and others derived from this simple one. An additional apparatus, represented in Fig. 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 as Fig. 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.
It is evident that the variations producible by working intersecting spirals and waved lines are very numerous, and these may be additionally varied by the combination of eccentric and spiral movements.
The following six patterns are re-engraved from Valicourt’s Hand Book, which is almost identical with that of Bergeron. They were not engraved in time to be inserted under the head of eccentric chuck work. The notation and description annexed is from a manuscript book kindly lent to the writer by an amateur. “Bed-plate,” 4 deg., must be taken to mean that the work is shifted (on one of the beds of the chuck) four of the marked divisions for eccentricity, counting from the axial line of the mandrel.
“Slide rest, 4 deg.,” means that the cutting tool is moved four corresponding divisions in its bed for radius of the circle to be cut; and so throughout.
“4 *,” means four times repeated.
The cutting tools, unless otherwise expressed, are double angled, and “25 cutting tool,” means 25 deg. of cutting edge.
If bed-plate and slide rest are both equally diminished at each cut, a shell results, with the close part internal. If bed-plate is increased and slide rest diminished, the close part of the shell is external.
SPECIMEN I.—Tools 25, 32, 36; Click-plate 96 or 288.
| Bed-plate moved. | Slide rest moved. | Circles done. | Tool. | |
| 3 | 2 | 12* | (1 done 7 missed) | 25 |
| 6 | 1 | 12* | (1 done 7 missed) | |
| 10 | 3 | 48* | (1 done 1 missed) | 36 |
| 3 | 16 | 24* | (1 done 3 missed) | |
| 23 | 4½ | 4* | (16 done 8 missed) | |
| 29½ | 2 | 96* | 25 | |
| 33 | 1 | 96* | ||
| or 33 | ⅝ | 288* |
SPECIMEN II.—Tools 28, 36; Click-plate 288.
| Bed-plate. | Slide rest. | Circles done. | Tool. | ||
| 1 | ½ | 12 | 28 | ||
| 4 | 1½ | 12 | |||
| 7½ | 2 | 4 | (8 done 4 missed) | 36 | |
| 13 | 3½ | 24 | 28 | ||
| 19¾ | 3½ | 4 | (16 done 8 missed) | 36 | |
| 19¾ | ½ | 4 | (in spaces) | ||
| 21¾ | 1 | 4 | (above last) | ||
| B 17¾ | 1 | 4 | (below last) | 36 | |
| 30 | ½ | 12 | (20 done 4 missed) | 28 | |
| 29⅜ | ½ | 12 | ( 1 ″ 18 ″ ) ( 1 ″ 4 ″ ) | ||
| 28¾ | ½ | 12 | Ditto. | ||
| 28⅛ | ½ | 12 | |||
| 27½ | ½ | 12 | (15 done 4 missed) ( 1 ″ 4 ″ ) | ||
| 26⅞ | ½ | 12 | (1 ″ 18 ″ ) (1 ″ 4 ″ ) | ||
| 26¼ | ½ | As before | |||
| 25⅝ | ½ | Ditto. | |||
| 25 | ½ | 12 | (20 done 4 missed) |
From B to here, border, if with 96 click-plate, not good-looking; tool a boring-bit.
| 331/16 | ⅞ | 12 | (7 done 1 missed) | ||
| 319/16 | 13/16th | 12 | (1 ″ 5 ″ ) (1 ″ 1 ″ ) | ||
| 291/16 | ¾ | 12 | (1 ″ 1 ″ ) (5 ″ 1 ″ ) | ||
| 279/16 | 11/16th | 12 | (1 ″ 1 ″ ) (1 ″ 5 ″ ) | ||
| 25¾ | ¾ | 12 | (1 ″ 1 ″ ) (7 ″ 1 ″ ) |
SPECIMEN III.—Click-plate 96.
| Bed-plate. | Slide rest. | Circles done. | Tool. | |
| 1¼ | 1⅛ | 8 | 36 | |
| 4¼ | 2⅛ | 24 | ||
| 5⅛ | 11¾ | 24 | ||
| 21½ | 4¾ | 96 | ||
| 27¾ | 1½ | 96 | 28 |
SPECIMEN IV.
The centre of this is a star of six curved rays, described by fixing the cutter at the centre and turning the mandrel by hand through so many divisions—for convenience so many 48ths of the circumference. These rays are marked by B. (The segment stop is constructed for this very kind of work, and is to be used in the present case):—
| Bed-plate. | Slide rest. | Arcs done for star. |
| 5 | B 5 | 6 (12/48ths of the circle) |
| 5 | B 5 | 12 (11/48ths ″ ) |
| 5 | B 5 | 12 (10/48ths ″ ) |
| 5 | B 5 | 12 ( 8/48ths ″ ) |
| 14⅛ | 5 | 24 (2 done, 2 missed) |
| 19¾ | ½ | 96 |
| 24¼ | 4 | 32 |
| 29½ | 2½ | 32 (intersecting) |
| 30½ | 2 | 32 |
SPECIMEN V.—Catherine wheel; tool 28.
The ground grailed by concentric circles contiguous to each other. The arcs by fours, all of same radius.
| Bed-plate. | Rest. | Arcs done. |
| 0 | ½ ¾ 1¼ &c. (for grailing) | |
| B 30 | 30 | 12 (16/48) |
(Repeat at three next divisions.)
SPECIMEN VI.—Tools 28, 36; Click-plate, 288.
| Bed-plate. | Rest. | Number. | |
| 1¼ | 1 | 8 | done |
| B 12 | 12 | 127/48 | (to meet next circle) |
| 4⅜ | 17 | 24 | |
| 30 | ½ | 12 | |
| 29½ | 1 | 12 | |
| (On same radius as the last, and surrounding it.) | |||
| 29 | 1½ | 12 | |
| 28½ | 2 | 12 | |
| 28 | 2½ | 12 | |
| 27½ | 3 | 12 | |
| 27 | 3½ | 12 | |
| 26½ | 4 | 12 | |
| 23½ | 1 | 12 | |
| (3 done, 21 missed between last, or if click-plate 96.) | |||
| 25 | 1 | 12 | (between last) |
Although in the matter of beauty the patterns here given are by no means comparable to many others, especially to some lately published from blocks cut by Mr. George Plant, for the English Mechanic; they are, by their comparative simplicity, well selected to give the learner a good idea of designing and working with the eccentric chuck. It is not, indeed, proposed by the writer to multiply patterns, as mere copying of such is of small interest to those who are really endued with taste and skill; and the variations producible by combinations of different numbers of divisions of the click-plate and slide rest are of such infinite number, that printed designs of a score or two would not serve to teach the nature of this work better than the half dozen now before the reader. When a new chuck, indeed, is brought out, it is well to give a few specimens of its work, to show the possible purchaser its value as a means of ornamentation and the extent of its capabilities; but when these are understood, the purchaser had much better design for himself, instead of becoming a lazy imitator and copying patterns laid down by others. Details of designs that are presented in a tabular form remind us sadly (for we are married) of the old “knit one, drop two,” “purl” or some such mysterious and, to us, detestable jargon wherewith ladies were, or are, wont to worry the ears of mankind.
The chuck of Professor Ibbetson, and the elliptic cutting frame of Captain Ash, are not introduced here, partly because this work has reached its intended limit, and partly because the inventors themselves have published separate works entirely devoted to a description of the arrangements and capabilities of their respective chucks. A brief notice is appended of Plant’s geometric chuck, contributed by the inventor to the pages of the English Mechanic.24
The author now concludes his pleasant labours, the result of which is contained in the preceding pages. These labours have been lightened, and the work itself benefited, by several kindly-written remarks received from various readers of the English Mechanic, while the articles were in course of production in that paper. Criticisms and suggestions also came to hand in which no such kindly feelings appeared. These also have, nevertheless, had an equal share of attention, and where they appeared to be of value they have been turned to profit, and have resulted in various more or less important alterations and additions. “The Lathe and its Uses,” thus re-arranged and modified, must now take its chance in the world with other productions of a similar character; and the writer hopes it may suffice to help those who need such assistance, and may be well received by others who though able to walk alone may yet cherish a kindly feeling for the friendly walking-stick.
Notes
24 See Appendix.