Читать книгу The Wood Turner's Handybook - A Practical Manual for Workers at the Lathe: Embracing Information on the Tools, Appliances and Processes Employed in Wood Turning - Paul N. Hasluck - Страница 13

THE lathes now commonly employed for general wood-turning are most simple and primitive. Some 3,500 years ago, the potter’s wheel, which may be considered to be the primogenitor of modern lathes, was known and used. In some of the oldest Egyptian monuments the God Ptah is represented working at a potter’s throw, or wheel. The modern throw possesses but slight modifications, and is substantially the same tool as that used for the production of antique pottery ware, some of which still remains unsurpassed for beauty and skilful execution.

The modern form of turning-lathe, in which the work is suspended on horizontal centres, was commonly used by the Greeks and Romans. Though none of the early writers have left anything like a graphic description of the lathe of their time, yet the tool is frequently mentioned by Herodotus, Cicero and Pliny—that is to say, at a date some centuries before the Christian era. Virgil, who lived from 70 to 19 B.C., gives particulars of the art of turning, from which it is evident that wood-turning was practised at that time. In his “Georgics” we learn not only that the ancients turned wood externally, but that they also hollowed it internally. Boxwood and lime tree, woods of very different natures, are spoken of as susceptible of being fashioned on the lathe.

Wind instruments were made of boxwood, and from Virgil’s “Æneid “we may glean an idea of the degree of perfection attained in his time. The instruments were, it seems, all flutes, and of these there was no lack some 2,000 years ago. Pandean pipes are probably meant by the flute spoken of in the Bible; but the flutes made by the Greeks were formed of ass’s bones, which, of course, did not require the use of a lathe in their preparation. It is difficult to decide with any degree of certainty the date at which wood-turning originated.

When turning between centres was first practised the work had an alternating rotary motion imparted to it. One method was by means of a cord, which encircled the work twice, having one end attached to an elastic pole, and the other formed into a stirrup for the foot. On pressing with the foot the work was rotated in the direction required for turning; it was similarly rotated in the opposite direction when the power was released, and the cord drawn back to its original position by the elastic force of the pole. During this latter movement the turning-tool had to be lifted from contact with the work. Another method was to pass a cord twice round the work, and an assistant, taking one end in each hand, would, by pulling alternately, produce the effect previously described. Both of these primitive methods of driving the work are still practised, the first by many workmen in their usual trade—for example, watch case makers—the second by the itinerant turners of India.

Before mandrels were employed, the work was suspended between centres only, then a portion of the article to be manipulated was utilised to form a pulley. The cord was passed round this part, which was generally hollowed out to receive it. When the work was finished, the superfluous pulley was severed from it and cast aside.

A bow having several strings, which were fastened to a roller at their middle, was next used to draw the cord to its original position, after applying the foot or other power. The roller had the cord coiled upon it, and when the treadle was pressed down the roller was rotated, thereby winding the several strings together, and bending the bow slightly. This bow was a considerable improvement on the pole. The power was more uniform, and could be adjusted to a great nicety, so that the influence of the spring would not be felt on delicate work. The bow could be fixed to the framework of the lathe, and from being more compact than the pole it rendered the whole machine more portable.

Bergeron’s book, published nearly one hundred years ago, contains illustrations of lathes driven by means of the bow-motion last described. A German book, dated 1568, contains an illustration of a pole-lathe with a sphere between the centres. A quantity of turned objects are represented lying about the workshop. This illustration appears to be the earliest record of a lathe mounted on standards. The tool had been previously confined to the Oriental nations, and had been kept low down to suit their habitual squatting position.

The centre-lathe, that is to say the lathe which has merely plain centre-points on which the work is mounted, and the mandrel-lathe, which is provided with a mandrel headstock, were described as distinct tools by Bergeron. The former has since become obsolete except in the form of the turn-bench used by watch and clockmakers. Lathes with mandrels are now in common use throughout Europe, and it is with these that a modern turner executes his work.

Modern workshops, where wood-turnery is executed, are fitted up with apparatus of very primitive design. Steam power, of course a modern invention, commonly serves as the motor, but the lathes themselves are the same as those that were used a century ago. Timber is the principal material employed in constructing them. At the present time, when cast-iron has superseded wood in so many of the mechanical arts, this is a somewhat curious fact. Before the advent of planing machines for iron, the shaping of that material was difficult and costly, and principally for those reasons wood was employed. Now cast-iron can be fashioned to almost any form in the mould, and may be finished with the greatest accuracy afterwards. It is cheap, and possesses some important advantages over wood in the construction of machinery. It is, therefore, not easy to understand why wooden lathes are still employed by woodturners.

The lathes commonly used for plain wood-turning are as simple and cheap as they can be. A plain bed, consisting of two strips of pine, as described below, supports the head-stocks. These are usually iron castings, made much lighter than the engineer’s usual pattern. The mandrel has a neck for the front bearing, instead of the cone generally applied to single-speed metal-turners’ lathes. The front head-stock bearing consists of a pair of brasses, to allow the mandrel to be put in the head-stock, not the usual steel collar driven into the head-stock casting. Gun-metal is most frequently used for these brasses, but no doubt phosphor bronze would prove more durable. This latter metal is now used extensively for the bearings of fast-running spindles in woodworking machinery, and apparently gives satisfaction.

The illustration, Fig. 1, shows a lathe of the type described above. It is intended to be driven by power from an overhead shaft. The bed is shown as capable of any extension towards the right. An extremely long bed would be further supported by additional standards placed between those at each end.

Fig 1. PLAIN WOOD TURNING LATHE.

Wooden beds are well suited to the requirements of the wood-turner. The work does not necessitate the use of a lathe possessing the solidity necessary for some classes of metal-turning, and hence the expensive planed iron bed may be dispensed with. Two strips of sound pine, two-and-half inches by five inches, form a convenient bed for an ordinary wood-turning lathe. The length is determined by circumstances; three feet six inches is about the shortest useful size, and frequently the bed is as long as the workshop will admit. The long bed will carry several head-stocks, and be more stable than several short ones. The two strips are usually bolted together parallel, with a space of from about one-and-half inches to two inches between; blocks of hard wood are used to separate them, and coach-bolts clamp them in position.

The bed is mounted on legs or struts, bolted to it, and firmly secured to the floor. The top surface of the bed should be at a height that will bring the lathe-centres level with the elbow of the turner when his arm is close to his side. This is the most convenient height for turning, and for men of average stature will be about three feet nine inches. A six-inch centre lathe, will require the top of the bed to be six inches below this; and the height of the bed is necessarily determined by the height of centres.

The rear side of the bed should be provided with a bench, or tray, on which various tools and appliances may be placed when temporarily out of use. This adjunct will be found very useful. It may consist of an inch board, a foot or so wide, secured to the bed by screws and supported at its outer edge by struts from the legs. The top of the bench should be placed about an inch below the top of the lathe-bed. The outer edge should have a fillet about an inch high fastened to it. This precaution will prevent the tools, &c., that may be laid on the tray from rolling off.

The head-stocks for a plain lathe may be made of beech-wood. A strip, four-and-a-half inches wide and one-and-a-half inches thick, should be planed up straight and smooth. Square one end, and cut off a piece eight inches long; this is to form the bottom of the head-stock. The two upright pieces should be of about the same height; these must be cut off likewise, also a similar piece for the back centre poppit. These three pieces have to be carefully placed together, with one set of ends quite level. At six inches from this end a hole is bored straight through the three; it should be as near as possible midway of the width. A three-eights of an inch hole will be about right for size. The pieces should be held together with cramps when boring.

One piece, to form the back centre, may now be fixed to a base, say four inches long, cut from the same strip. A holding-down bolt, consisting of a half inch coach bolt, long enough to go through the bed, with one-and-a-half inches to spare, is then fitted to it. A butterfly or winged nut is put on in place of the ordinary square or hexagon one, and a washer must be put over it to bear against the underside of the bed. The screw to form the back centre should measure half-an-inch to three-quarters of an inch in diameter, and be pointed. It can be obtained at an ironmonger’s. This is forced into the hole bored through the wood, and will hold well without further precaution.

The mandrel head-stock is fixed together by means of one or two long bolts going quite through it lengthways. A nut on each end will draw the two end uprights into close contact with the bottom piece, and will prevent the head-stock from spreading open when the mandrel tail-pin is screwed up tight. It is essential that this wooden head-stock should be made as solid as possible, and one made of iron would be more serviceable. The former can be made by a wood-worker, whereas the latter entails engineers’ work, and probably for this reason is not invariably met with in wood-turners’ workshops. The wooden head-stock may be bolted on to the bed by the aid of coach-bolts.

The mandrel, usually made of iron, and its collar, which may be of steel, or of some softer metal suited for bearings, must be procured from an engineer. It would be impossible for a wood-turner to make these with his usual appliances, and not only will it be better, but cheaper, to buy the mandrel and collar. These will have to be fitted to the head-stock. A tail-pin screw is wanted to support the tail end of the mandrel, and should be obtained with it. The making of the mandrel head-stock is work altogether more fit for an engineer. A fast and a loose pulley have to be fitted on the mandrel to take the strap from the driving-shaft.

The hand-rest—or T rest as it is more properly called—consists of a casting which forms the socket, and of a second one, which is the T. These may be bought at many iron foundries. A holding-down bolt is wanted to secure the socket-sole. For convenience of shifting, a butterfly or bow-nut is preferable to a hexagon or square one.

A skeleton lathe of the most simple and inexpensive form has been briefly described above, so that an idea of the very primitive tools now employed may be formed.

Fig. 2 shows a wood-turning lathe of more substantial construction. It has the bed and standards made of iron. The mandrel projects on the left end, and has a threaded nose to receive chucks; by this arrangement discs of large diameter, say up to six feet, such as table-tops can be turned. When used in this manner, the mandrel nose must either have a left handed thread or be run the reverse way. The chucks would be unscrewed from an ordinary right-handed thread by the action of the tools.

Fig. 3 shows a lathe specially adapted for ornamental work. It will produce spirals of any size, pitch and form; shape prisms of any sectional form, parallel or tapering; and may also be used as an automatic lathe working to a template. The slide-rest carries a revolving spindle, which is driven from an overhead countershaft, and cutters of any desired form can be fitted into this. When used for fluting, the cutter spindle is brought into action, and, if a spiral is desired, the mandrel is slowly rotated by means of gearing from the leading screw. Quick or slow twists are got by altering the wheels to suit. The chuck, shown on the mandrel-nose, serves the purpose of a division plate in spacing fluting. A template is shown in the illustration, and the upper slide of the rest is kept against it by the action of the weight, also shown.

Fig. 2. WOOD TURNING LATHE ON IRON BED.

Fig. 3. LATHE FOR STRAIGHT AND SPIRAL FLUTING.

In contrast with the lathe first sketched may be considered some of the automatic machines which are used in turnery. An American “Variety” lathe is illustrated in Fig. 4. This machine is constructed to produce large quantities of uniform articles at a minimum of cost, to effect which rapidity in working is most essential. An idea of the mode of operating this lathe may be inferred by reference to the illustration. The headstock to the left is fitted with a chuck, which receives the squared wood just as it comes from the saw mill; the right-hand end of the wood is supported by a collar, mounted on a carriage, which travels along the lathe-bed. This collar is fitted with a cutter, arranged to turn the square wood down to a parallel cylinder of definite diameter. The poppet-head is actuated by a lever handle, shown on the right, having its fulcrum about a pillar to the rear of the bed; the lever is jointed, and is attached to the barrel of the poppet. Suppose the rough wood is placed in position, ready for operating upon. By pulling the lever handle, the poppet-head is brought up towards the carriage, and as soon as the former touches certain regulating screws on the carriage the latter is also moved. The effect of this is to turn the wood to a certain diameter, the length being determined by regulating screws. Simultaneously with the operation, the wood may be bored to any diameter and depth required by means of a boring tool fixed in the poppet-barrel.

So far the process is merely to rough out the work. Any mouldings or shaping that may be wanted may then be made by a series of cutters fixed in the tool-box, shown just to the right of the collar. This tool-box is brought towards the work by pressing the knee-pad, shown near the centre, between the standards. The same operation also brings a parting tool into action, but this tool does not act till the last moment.

These operations, so difficult to describe clearly, are performed with such rapidity that about three seconds suffice for going through the whole series and producing a finished article from the rough material. The work that can be turned out in this machine is almost endless in variety and exact uniformity is assured.

Wooden boxes, bobbins, knobs, handles, egg-cups are amongst the many objects that can be successfully made on this machine at a speed of about 1,000 an hour. Turning, boring, and beading being carried on at the same time, the lathe running at some 3,000 revolutions per minute. The price of this lathe is from £50 to £65, including freight from the United States.

Fig. 4. AMERICAN VARIETY WOOD TURNING LATHE.

Fig. 5. WOODEN SHOE.

Fig. 6. SHOE LAST.

Fig. 7. PISTOL STOCK.

Though turning is often considered as limited to the formation of circular work, yet lathes are constructed to produce objects of a widely differing form, such as wheel spokes, gun stocks, boot lasts, curved handles, as used for axes, &c. Several specimens of this kind of turnery are illustrated in Figures 5 to 12. Such work is produced on copying lathes, and examples of these are shown and described in a subsequent chapter. The examples of work are introduced thus early in the book in order that the reader may not proceed with his ideas of turning limited to mere circular work.

Fig. 8. TOOL HANDLE.

Fig. 9. AXE HANDLE.

Fig. 10. HATCHET HANDLE.

Fig. 11. WHEEL SPOKE.

Fig. 12. GUN STOCK