WOOD-TURNERS’ LATHES.
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.
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