Sidebilder
PDF
ePub

it to run freely and evenly upon it. The screw-tool must then be selected which fits the guide. And now, then, for the method of cutting the required screw. Advance the screw-guide on the screw in the edge of the brass plate below it about half its length, having previously, of course, turned the piece of wood or ivory on which the screw is to be cut, and attached it in its chuck to the mandril. Then place the screw-tool on the rest M, allowing its end to come in contact with the work, when it must be held perfectly steady. The large driving-wheel must then be moved with the treadle about half-way round, and reversed. It will be readily seen that the mandril as it revolves moves forwards and backwards by the motion thus given to it, and of course in exact proportion to the "pitch" of the thread employed; and after a few turns the screw is complete. The inside screw is cut in precisely a similar way, substistuting the inside screw-tool. For making " working " screws, i.e., those which in boxes, &c, are intended to be opened and shut, this apparatus is invaluable, as the screws thus made fit most accurately. Where a joint is made, not intended to be disturbed, the screws may be cut well enough by hand ; but when time is no object, we would advise all screws to be made by this apparatus. Care should be taken that the screw-tool be placed on the rest so that its side comes exactly against the "shoulder" of the work, where the bottom of the screw finishes. A groove should always be cut round the work at this spot, rather deeper than the intended thread, which glides nicely into it without leaving a ragged edge. We will next attempt to describe the

"universal chuck," so called from its being capable of holding in the lathe any sized piece of wood or ivory from half an inch up to four or five inches. This chuck is not absolutely necessary, although a very useful tool. It is a plate of brass, A, about half an inch thick, having a screw in its centre at the back to fit the nose of the mandril (which all chucks must do), and having three steel screws, B, B, B, passing through slots and converging to the centre, as shown in the engraving. The holes which appear in the plate are of no other use than that of lessening the weight of the chuck. It is as well to have ten or twelve concentric circles cut on the face of the plate, as it enables the turner to adjust his work in it with greater facility as regards the centre of the chuck. In order to fix the work in this chuck, the screws should be turned, with a key made to fit them, until the jaws, or "dogs," as they are called, are drawn sufficiently far from the centre to admit of its being inserted ; they must then be screwed tight against it, and it is thus held quite firmly. Some of these chucks are made so that by turning one screw all three of these jaws move equally towards the centre; but this is practically a disadvantage, and for this reason: that it requires the work to be exactly circular, in order to grip it firmly, which is not the case if the screws act independently of each other In the latter case the turner is able to chuck work of almost any shape, and this is a great consideration in preparing the material, particularly ivory, for the lathe, in which it is. of course, desirable to avoid cutting, as much as possible, to waste.

[graphic]

Another very useful tool is the "boring collar," which is attached to the lathe in the same way as the " back poppit," F. It is composed of a circular plate of cast iron, A, having eight circular holes bored through it, as shown in the drawing, varying in size from half an inch up to two inches, or even more, and slightly tapered.

It is for the purpose of supporting any long piece of work while boring it, in order to get rid of the vibration. It is used in this way: the " back poppit" must be taken from the bed of the lathe, and the " boring collar" put in its place, with its standard next to the mandril; the distance from which must, of course, be regulated by the length of the work required to be bored. One end of the work being fixed in the chuck, the "boring collar" must be pushed forward, and the plate turned round, until the hole in the plate, fitting the work is at the top, when it will be found to be exactly opposite the end of the mandril, and concentric with it; the plate must then be made fast by means of the nut in the centre, by the binding-screw beneath, and the boring collar itself fixed in its place. The lathe must then be worked in the ordinary way, and the end of the work can then be easily bored or hollowed as required with- Fig. 4.

out fear of its giving way.

We have, we trust, described the lathe itself sufficiently so far as common or hand turning is concerned; and we will now proceed to describe the various additions to it which are necessary for the accomplishment of Ornamental Tuining.

The Overhead Motion.

This is a bar of wrought iron, H (p. 398), fitting movably into two stout rings of the same material, attached to the left-hand bearer of the lathe, as shown in the drawing, and having a screw, L, beneath it, and working in a third ring to enable it to be raised or depressed about three inches at pleasure by means of a screw, for the purpose of tightening or loosening the band which passes over the pulley, hereafter described. The upper end of this bar is bent, as shown in the engraving, and carries a frame and spindle, 1, on which are two pulleys about three inches in diameter.

In common or hand turning the work revolves in the lathe, and the tools are held against it; but in ornamental turning it is just the reverse, for while the tools revolve, the work remains stationary. The band connecting the drivingwheel with the pulley is removed, and a long band connecting the drivingwheel with the small pulleys on the overhead motion is substituted, and a second band, connecting the other pulley on the spindle with the wheels on different parts of the apparatus connected with the slide-rest (presently described), causes the different tools to revolve.

[graphic]

The above description will, we trust, be sufficiently clear to enable our young readers at once to comprehend this part of the apparatus; and we will, therefore, at once proceed to describe the slide-rest, an indispensable adjunct to the lathe, and without which no attempt can be made in this branch of our subject.

The Slide-rest,

so called from the cradle connected with it, which carries several slides, in which the various tools are fixed. When in use it is attached to the lathe by removing the rest, M, described in Fig. 1, and placing the slide-rest in its place. We will now attempt to describe it as correctly as we can.

[graphic][merged small]

A is a piece of cast iron, most accurately planed and finished, of the shape shown in the engraving, having a slot cut through it nearly its entire length, through which a flat threaded screw works and carries the slide B, which, by means of this screw, can be moved from one end of A to the other, so that the tool can be brought to bear on any part of the work; and as the small wheel, D, attached to the end of the screw is graduated with twenty divisions, and the "pitch " of the screw is twenty turns to the inch, it will be seen at once that the very finest adjustments may be arrived at. The upper part of the rest is fastened to the lower part by means of a stout standard fixed to it exactly at right angles, which falls into a receptable made for it, and the upper part can be secured at any angle with the lower by means of the binding-screw, F, and can be raised or depressed by turning a ring of brass working on a screw which is placed between them. E is a key which turns the screw carrying the cradle, B ; c is the slide which fits into the cradle, B, and which carries the "eccentric cutting-frame." the " universal cutting-frame," and the "vertical cutting-frame," all of which will be described in their turn. G G are two binding-screws, which keep them firmly in their places. H is the binding-screw for attaching it to the lathe; and 1 1 are two small standards, one attached to the slide C, and the other to the cradle B, by means of which and the two levers, A and B, Figs. 6 and 7, they are advanced or withdrawn to and from the work, by placing the hole at

[graphic][merged small]

the end of the lever over the standard on the slide, and the slot over that on the cradle, the straight one, A, being used for the tool-slide (Fig. 8), and the drill-slide (Fig. 9) and the bent one, B, for the slides carrying the eccentric cutting-frame, universal cutting-frame, and vertical cutting-frame.

The Tool-slide.

This slide is used almost exclusively with what are called the slide-rest tools, which need no further description than that they are straight tools about two and a quarter inches long, with round, square, pointed, or grooved ends, according to the pattern required to be produced. They fit into the boss c on the slide A, and are kept in their place by the binding-screw D. - B is the standard before described, E being a small stud or handle for withdrawing the slide. F and G are two screws, F regulating the depth of the cut in the work, and G, by being turned slowly, allowing the tool to advance gradually to it, thus diminishing the risk of the very delicate points of the tools being broken, and

[graphic][merged small]

avoiding the chance of a ragged gash or scratch being made on the work, which would be the case if the tools were pushed suddenly against it. These screws, it will be observed, are attached to all the slides used in the slide-rest.

The slide (Fig. 8), although it enables the turner to produce very beautiful patterns in connection with the eccentric chuck, hereafter described, is comparatively very little used for ornamental purposes, excepting as it is indispensably necessary in ensuring a perfectly true and even surface on the wood or ivory, preparatory to the introduction upon it of the various and innumerable patterns which are capable of being produced by the other tools. The method of using this slide will be described and treated of in the concluding remarks and instructions of this article.

The Drilling-frame, Or Drill-slide.

This instrument is one of the most useful of all these slides, as by its use such a great variety of patterns may be produced. It fits, like all the other slides, in the cradle, B, on the slide-rest. A is the slide itself; B, the spindle, having a steel wheel at its lower end (by which motion is given to it by passing

[graphic][merged small]

the band from the overhead motion over it), and a receptacle, E, into which the various tools are inserted. C is the standard before described; G, the regulating-screws, and F a small piece of steel attached to the slide, which (the head of the screw being graduated) enables the turner to alter the depth of the cut by equal degrees.

The Eccentric Cutting-frame.

This instrument, as its name implies, is used in cutting eccentric patterns on the prepared surface of wood or ivory, and the diversity of work which may be accomplished by it is almost incalculable.

A is a steel shaft, which also fits into the slide on the cradle, B, of the slide-rest, having a spindle working through its entire length, which, like the drillingframe, has a steel wheel, E, at its lower end, moved in the same way. At the upper end is a steel frame, B, having a four-threaded steel

[graphic]
« ForrigeFortsett »