Part 7

The next class of spirals is that in which no central core exists, but the coils stand separate and distinct, two or more rising from the same base. The coils are sometimes flat, sometimes rounded, and still more frequently, in the best work, exquisitely, and (as a casual spectator would say) _impossibly_ carved. The process is as follows:--Turn a cylinder of ivory or hard wood, forming at the end any required mouldings as a base and capital. Determine the number of coils and the pitch, and by one of the previous methods mark out the same. The cylinder is now to be bored out from end to end, leaving sufficient for the thickness of the required cords. This bore may with advantage be slightly larger at one end than at the other, so that a mandrel of wood may be fitted into it, to be afterwards easily withdrawn. This will certainly be necessary if the ivory cords are to be of light substance, as they require support to enable them to bear the action of the tool. After the cylinder has been bored as above directed, let a mandrel of common wood be inserted, and the lines, marked as shown, be cut quite through. The intermediate parts between the intended threads must then be removed carefully (with a round rasp, if of ivory) with any convenient tool if of wood. The cords must then in a similar way be rounded or otherwise moulded, and afterwards the common and now damaged mandrel removed. In the case of ivory the piece of work will not only be strengthened by the insertion of a polished mandrel of ebony, but its appearance will be improved. Sometimes, however, it may be preferable to line it with red velvet or silk, or it may be left entirely open. The further ornamentation of the cords, depending on the eccentric chuck or eccentric cutters, will not be described in the present paper. These open spirals are worth a vast amount of patience and trouble, which their elegant appearance when finished will amply repay.

The reader is not to suppose that this method of cutting spirals by rasp and file is the only or best method, especially when ivory is the substance operated upon. Further on will be described various modes of accomplishing the same ends by self-acting machinery, and by the spiral apparatus designed for use with the ordinary lathe, but all these need the slide rest, whereas it is quite possible in the foregoing manner to make spirals by hand tools alone, which for correctness and finish may vie with those which may have been worked with more elaborate and costly apparatus.

Before quitting the subject of plain hand turning in wood, a few more words may be necessary in respect of certain details of lathe manipulation, foremost among which comes Chucking work. This is often carelessly done, especially by amateurs, who, in consequence, are frequently annoyed by the shifting of the material under the influence of the cutting tool. If this is hard and valuable--as are many of the best woods for ornamental turning--the fork or prong chuck will not enter sufficiently to sustain the piece, and at the same time the stuff is too valuable to allow of the waste incurred in screwing it direct to the mandrel, or inserting it sufficiently far into a brass cup chuck. In such cases the best plan is to screw a piece of common wood upon the mandrel, face it truly, and cut a few shallow concentric circles upon the end thus levelled, both for the purpose of a guide to centrality, and also to give a hold to the glue by which the more precious material is to be attached to it. For this purpose, both chuck and work are to be well warmed, and the glue--boiling hot--brushed upon the parts to be united. The latter are then to be rubbed together a few seconds, and when the piece to be turned runs truly, the back poppet with boring flange attached--if the right hand end of the piece is level, otherwise, the point allowed to remain--is to be brought up and screwed as a clamp against it till dry. This process requires time, but is well worth the trouble, as the material will be securely held, and can be safely operated on. None but those who have had to contend personally with a tyro's difficulties, and have, in consequence, seen the work shift in the chuck when nearly completed, can truly appreciate the advantages of efficient chucking. In the case detailed, there is absolutely no waste of material, no possibility of the work becoming loose or out of truth; and the ornamentation by eccentric cutters, drills, and so forth, can be proceeded with, and carried out with that confidence which never fails to promote good workmanship. Even with the above arrangement the back poppet should be used while the excrescences are turned down, and retained as long as the gouge has to be used in bringing the design into an approximation to its intended form. This should be removed, however, before taking the final cut, as the work will generally seem to drop a little when the support is taken away, in consequence of the mandrel, which has been forced against the back centre, returning to its place in the collar.

Pieces of six or seven inches in length, and of one or two inches diameter, requiring to be hollowed out, may frequently be turned by reversing the usual method and boring out the interior, previous to shaping the outside. A case for pencils, for instance, or a bodkin case, may be thus worked:--Mount in the square hole chuck, an American screw auger, sets of which are now to be had beautifully finished and polished. The kind meant has a scooping kind of edge above the screw, Fig. 102, and cuts cleanly and rapidly. The piece of wood--soft wood alone is meant--is brought against the tool, being grasped by the left hand, while the back centre, with flange, is steadily advanced with the right hand against the opposite end. This auger will run straight through several inches without requiring to be withdrawn, as the borings pass freely along the polished threads of the instrument and escape. If necessary, however, it can be readily withdrawn by reversing the action of the lathe, and replaced without difficulty. The piece thus bored may then be mounted in the lathe and finished on the outside. To do this satisfactorily, an arrangement is requisite by which the centrality of bore is insured, else in the process of cutting the external surface, the material will, in all probability, be cut through in one part, while in another it will remain of considerable thickness. If the piece is bored quite through, so as to become a tube, Fig. 103 will be satisfactory, as the cones preserve centrality, whilst the use of the carrier will prevent the necessity of screwing the cones up so tightly as to endanger splitting the wood. This is the best way to chuck small cylinders and brass tubes. The more obtuse the angle of the cones the better.

In this method the bottom of the case must be turned as a plug and glued into its place. If the bottom of the case is left solid, an arrangement like Fig. 104 will answer well. The plug chuck, A, must not be at all conical, and the part that enters the work must be at least an inch long. If this is attended to, and the face of the work and of the chuck is square, the tube will be truly centred, only requiring the back poppet to take off the strain upon A, when the tool is applied. If A is chalked, there will be no slipping, provided it has been accurately fitted. Observe, nevertheless, that as a general rule, hollow work should be placed _inside_ and not _upon_ a chuck, unless you have to work upon the _whole_ exterior surface. By this plan, there will be no likelihood of splitting the object, an undesirable consummation which not unfrequently takes place when the contrary method is pursued.

Thin discs of wood or brass are most conveniently turned upon a face-plate, to which they can be attached by turners' cement, already described. If, however, one surface only has to be worked, and the plate is not of less thickness than 1/8th of an inch, it may be mounted on a flat chuck with small projecting points, the back poppet being used to keep it firmly against the face of the chuck. Even a plate of brass may be thus turned if placed first of all against the chuck and gently tapped so as to mark the position of the points, and then drilled to suit them. Bread-platters are thus easily chucked, first of all _face downwards_, and then reversed with the bottom against the points, so that in the latter position, the chisel or broad may be applied to the face and the marks removed. The larger designs on these platters are carved by hand after their removal from the lathe, and the small figures forming the ground, which often appear round the main design, are made by figured punches.

_Chucking Egg Shells_:--The method of doing this so as to enable the turner to cut the shell evenly in two parts, is given by Holtzapffel, in his "Mechanical Manipulation," and has been copied elsewhere. It is ingenious and effective. The object is simply to obtain a pair of delicate vases, to be edged with ivory, and mounted on a pedestal, as a curiosity. The following account is from the pen of the inventor, Mr. G. D. Kittoe, as communicated to Mr. Holtzapffel:--"In the accompanying figure--Fig. 105--is represented the nose of a lathe, with an egg chucked ready for cutting." Fig. 106 is the chuck used first "to prepare the egg, to be mounted in the above way. The latter is generally termed a spring chuck, and is made by rolling stout paper with glue upon a metal or hardwood cylinder, the surface of which has been greased to prevent the paper sticking to it, and upon which it must remain until perfectly dry, when it may be removed and cut or turned in the lathe as occasion may require." [N.B. Nothing is said in the above account of the evident necessity of fixing the paper cylinder to a wooden block, in which a screw must be cut to mount it on the nose of the lathe.] "This sort of chuck is very light--easily made and well adapted for the brittle material it is intended to hold. Before fixing the egg in it, the inner surface should be rubbed with some adhesive substance (common diachylon answers exceedingly well); when this is done the egg should be carefully placed in the chuck, the lathe being slowly kept in motion by one hand whilst with the other the operator must adjust its position until he observes that it runs perfectly true, then, with a sharp pointed tool he must mark the centre and drill a hole sufficiently large for the wire in the chuck, Fig. 105, to pass freely through. When this is done the egg must be reversed, and the same operation repeated on the opposite end, its contents must then be removed by blowing carefully through it. It is now ready for cutting, for which purpose it must be fixed in the chuck, Fig. 105. A is a chuck of box or hard wood having a recess turned in it at _a, b_, into which is fitted a piece of cork as a soft substance for the egg to rest against. B is a small cup of wood with a piece of cork fitted into it serving the same purpose as that in A. A piece of brass, _d_, is to be firmly screwed into the chuck A, and into this a steel wire screwed on the outer end, on which a small brass nut _e_ is fitted to work freely in a recess in the piece B. When the egg is threaded on the wire through the holes previously made in it, this nut is to be gradually tightened up until it presses the cup B against the egg sufficiently to hold it steady and firm enough to resist the action of a finely-pointed graver used to cut it. The tool requires to be held very lightly, as a little undue violence would crush the shell. Neither should the latter be pinched unduly tight in the chuck, as otherwise when the point of the tool divides the shell the two parts might spring together, and be destroyed by the pressure. It requires some delicacy of hand to attach the rings to the edges of the shell to constitute the fitting. The foot and top ornaments are fixed by very fine ivory screws, the heads of which are inserted within the shell."

Box wood is decidedly the best material for ordinary chucks, as it takes a screw almost as well as brass, is pleasant to work, holds the material firmly, and is of good appearance, which last is not unimportant to those who possess good lathes, and like to see everything in decent order about the workshop, and it is certain that a disorderly workman will commonly produce slovenly work. This wood, however, though tolerably plentiful, is sufficiently costly to be worth preserving, and by a little management chucks may be made to answer for a longer period than might be at first supposed. A chuck, for instance, too large to hold the work, may be plugged with a worn-out chuck of smaller bore, or with wood of inferior character, to save the necessity for hollowing out a new piece of box wood. The latter material, moreover, excellent as it is, may be replaced by other kinds of wood, provided the latter will bear a good screw.

_Beech_, if dry, will answer very well for the purpose.

_Pear_ is tough and screws well.

_Apple_ is little inferior.

_Ilex_ or _evergreen oak_ is sufficiently hard and tough and will be found quite satisfactory. Elder of large size is good, and screws well.

_Sycamore_ screws well, but is not always equally tough.

All hollow or cup chucks should be furnished with rings of iron or brass to prevent splitting. About six sizes of rings will suffice for a great number of chucks. Bergeron, speaking of the barrel stave chucks already alluded to, prefers the encircling rings plain and not screwed. He gives the following reason:--"If a piece of work entered in such a chuck does not run quite truly, a tap on the ring in the proper place will, by closing the sawgates more in that part, rectify the error, whereas with a screwed ring this is impossible." There is reason in this, but at the same time it would be easy to unscrew the ring a turn or so, give a light tap to the work, test its position by putting the lathe in motion, and when true fix it securely by screwing up the ring. There is, however, one precaution to be taken in making these useful chucks--namely, to cut the staves of equal width, else they will not yield equally to pressure, and the work will not be so readily centred truly. A grip chuck of inexpensive make (one additional pattern of which is introduced from a design by contributors to the _English Mechanic_) should always be provided. A rough block of ivory for instance may be seized in its jaws, and the exterior useless part cut off by a parting tool as a ring, leaving the nicely rounded material ready for chucking. Ivory nuts or _corosos_ which are peculiarly awkwardly shaped for mounting in the lathe, may also be thus seized, and one portion faced up and rounded so as to allow of being fixed on a face chuck by glue or cement, or fitted into a cup chuck. Rough pieces, too, thus mounted may be faced up, bored and tapped to fit the mandrel as chucks, and a thousand similar works may thus be handled. The simple grip chuck in question is important as having the very useful addition of a centre point which the writer would, if he did not abominate and eschew puns, direct attention to, as the chief "point" of interest--"I call it," says the inventor, a "Universal Self-Centering Grip Chuck." The drawings 1, 2, and 3, almost speak for themselves, to practical turners.

1, is an elevation of one of the grips. 2, a section through centre of chuck. 3, a side section of ditto. The body of the chuck is made of cast iron, to screw on to the mandrel; and the grips, 1, are moved simultaneously by a right and left-handed screw acting in a circular groove. The jaws of the grip are serrated and tempered, the same as in ordinary vices. In the centre of the grips, when closed, a three-sixteenth hole is bored true to the centre of the lathe. Behind this there is a true centre point screwed into the body of the chuck, as marked at _a_. The above hole and this centre point are to be particularly attended to, as on their truism depends the correctness of your work.

If I want to turn a solid cylinder I make the usual centre at each end; put one on the above centre point and the other on the back centre of lathe, and then screw up the grips tight; but if the work is short you need not apply the above centre point or the back centre, as the grips are alone sufficient. The hole in the jaws of the grips admit of any kind of drill or other tool being put into them without using any centres, and the grips will admit anything up to two inches. In fact, I do almost every sort of thing with this chuck, and I think amateurs, if not others, will find it a most valuable and handy contrivance.

Fig. 108, A and B, represents a modified form--a chuck already spoken of and recommended for ordinary plain turning, in which the work is supported at both ends. The present form is to a great extent self-centering and will hold the work also without the saw-cuts otherwise needed, the sharp edges of the double fork entering the work with the pressure caused by the back centre. The chuck is useful not only for ordinary work, but for re-mounting pieces centrally, which it may have been necessary to remove when partly finished, and to return to the lathe for completion. A still further addition to this chuck of a steel point sliding through the centre, as in the section, Fig. 109, makes it a very complete and serviceable apparatus, as by this means it is easy to reverse the work without destroying its centrality. The point is intended, as in the chuck of Wilcox, to slide back stiffly (being if necessary kept up by a spiral spring as shown), as it is only intended as a guide to assist in mounting the piece. If the mandrel is not bored the chuck must be long enough to receive the pointed wire within its substance. This will be found in every way a most serviceable chuck. It may be of iron or brass, or even of wood, if a round plate of brass is mounted on its face, to which the holding pieces can be soldered or brazed.

HOLLOWING OUT SOFT WOOD.

This is done, as already described, by the regular soft wood turners in Tunbridge and elsewhere, by means of hook tools. A great number of workmen, however, use only the gouge, and for boring out chucks, hollowing boxes, small bowls, and similar work, the latter tool will be found effectual if rightly held and carefully managed. It must not, however, be applied to the inner surface of the work at the point usual with scraping tools, but beyond the centre, Fig. 109A. The rest, B, does not require to be turned across the face of the work, but remains parallel to the bed of the lathe. The blade of the gouge is to press against the near side of the hollow as the work proceeds, which considerably aids in securing the position of the tool. The back of the gouge is to face the bottom of the hollow (next the mandrel), but the tool is generally rolled on the rest a little, so that its hollow side is often more or less below, towards the lathe bed, and the point is also lightly raised as it approaches the finish of the cut. Begin with the tool almost horizontal, and at the centre of the piece, the back against the wood, and, depressing the handle as the shaving is removed, finish at the top _outer_ edge of the hollow, rolling over the tool, so that it shall leave the work with its back upwards and hollow downwards. Thus used it will not stick in its course, and, after a few trials, will be found to cut out the wood cleanly and rapidly.

Another grip chuck, or self-centering scroll chuck may here be introduced, from the source of information previously alluded to. The writer thus describes it--

AMERICAN SCROLL CHUCK.

This chuck is made upon the same principle as the Warwick Drill Chuck--namely, a flat spiral so acting on three jaws sliding in radial grooves as to make them recede from the centre to admit any object between certain sizes, and then to be tightened upon it. Fig. 1 is a plan of a 4-inch chuck. Fig. 2 is a vertical section of the same. Fig. 3 is a view of the outside of the chuck, and Fig. 4 is a separate section of the principal part _a, a_, taken through the line _z, z_ (Fig. 1).

In Fig. 2, _a, a_ is this piece, _b, b_, has the spiral cut on it which actuates the jaws 1, 2, 3 (Fig. 1), _c, c_ screws on the piece _a, a_ to keep _b, b_ in its place and _d, d_ is the plate which screws on the mandrel, and which is fixed to _c, c_, by three countersunk screws, one of which is shown in section.

If the foregoing observations are carefully studied the further practice of plain hand-turning in wood will not be difficult, and we shall proceed to speak of metal turning, before passing to a description of the Slide Rest and other apparatus usually added to the lathe. We may, however, observe here, that, for ivory and hard wood--especially the former, the first roughing down cannot be done with the gouge. A point or small round-ended tool must in these cases take its place, to be succeeded by one or more of those tools which rather scrape than cut, as described in detailing the process of hollowing out boxes and similar work.

METAL TURNING BY HAND TOOLS.

The first requisite for the above work is a well made and sharp tool, for, strange as it may appear, a keen edge is as necessary for making good work in metal as in turning wood. The principle of this cutting edge must be well understood, and this has been well explained by Nasmyth and others.