To meet these conditions, it is usual in the driving apparatus of all lathes, whether driven by hand, foot or power, to have a variety of grooves or steps of different diameters in the fly wheel and in the pulley; that different steps may be employed to give different speeds, upon the simple law of the velocities being inversely as the diameters. The diameters being equal, the wheel and the pulley on the mandrel move turn for turn; the groove on the wheel being six times the diameter of that on the pulley, the latter will move with six times the rapidity of the former and so on.

The one extreme or face of the conical mandrel pulley, is generally made as large as the lathe head will admit, the smallest groove at the reverse end, being usually about half that diameter. Sometimes the smallest grooves of the pulley are proportionately much less, as in the lathes of the soft wood turner, whose work offers the least resistance and requires the highest velocity. The edge of the foot wheel is formed as a bevil nearly the same as that of the mandrel pulley, turned into grooves of about a corresponding number. For slower speeds, additional bevils of less diameter turned with grooves, are carried on the front of the spokes; the foot wheels being termed single, double or triple bevil wheels according to the number of the series.

The hand fly wheel has been very generally supplanted by power, nevertheless it still remains in use for many industries, it is convenient for occasional purposes in all workshops, while it has the recommendation over most motors, of simplicity and almost impossibility of derangement. The largest and lightest handwheels are those used by the soft wood turners; these are made of wood with spokes very like the wheel of a carriage, and measure from six to eight feet in diameter. Occasionally they are provided with speed grooves, but a plain rim with a light, flat strap, running to different steps on the mandrel pulley, is more general. The wheel is mounted on a stand, that is pulled along the floor to tighten the band, but occasionally its axis is carried by an adjustable swing upright.

The cutler's or grinder's wheel is very largely used, this is of the same kind but rather smaller in diameter. Two long, parallel wooden bearers, about eighteen inches high, carry the centers for his buffs and grinding wheels; the bearers run along the floor of the shop and the workman sits astride or with his legs between them. The fly wheel is mounted behind him, frequently upon the same bearers, its lower half revolving in a pit or recess in the ground. The potter, when engaged upon the largest specimens of his art, requires a slow rate of speed in the revolution of the throw; which he also obtains by means of the hand fly wheel, in this case of from about three to four feet in diameter, turned by an assistant.

The Driving Wheel Considered As To Momentum And As 40030

Fig. 35.

The hand fly wheel for general purposes, fig. 35, and its frame, are entirely of iron, the five speed grooves being from about eight, to about forty inches in diameter; which, combined with the speed grooves of the pulley, give suitable rates for most metal work. For wood turning of small diameter, one band would be carried from the largest groove of the hand wheel, to one of the smaller on the foot wheel of the lathe, and a second band from the largest of the foot wheel, to one of the smaller on the pulley. The weight of the wheel and stand is sufficient to maintain the tension of the band. The hand fly wheel, suitable to the amateur, fig. 36, has a triple bevil wheel mounted on a swing upright, the tension of the band being regulated by screw adjustment; the speed grooves measure from about eight to about thirty inches in diameter. In both these fly wheels the two handles stand at right angles, and can be placed at different radii.

The Driving Wheel Considered As To Momentum And As 40031

Fig. 36.

The amateur sometimes desires to drive the lathe by other means than by the foot or the hand wheel, and seeks assistance in some variety of engine or water power; the latter is not very generally available, but the former is frequently attempted. Except for manufactories, power is a less convenience than would at first appear, and its uniform pace prevents the gradations of increasing or decreasing speed, so valuable in the practice of hand turning, and easily, almost intuitively given by the foot, after moderate practice. This advantage is so considerable, that in manufactories where steam power is applied to all the lathes, many of them are also provided with the ordinary treadle, which is almost always resorted to for the more delicate operations. In those cases where steam power is already in use for other purposes, and therefore under separate control; it may be applied to the amateur's foot lathe with advantage, for occasional use as for heavy works. But, when both using the lathe and driving the engine have to be performed by the same individual, the divided attention becomes irksome, and leads to errors and accidents to the work, and experience has shown that such attempts have usually been abandoned as less convenient than troublesome. The ordinary manner of applying steam power to the foot lathe, is by attaching fast and loose pulleys, with a lever for shifting the band from the one to the other, at the end of the crank shaft opposite the foot wheel. This arrangement does not interfere with the variation of the speeds by the grooves of the fly wheel and pulley, and allows the treadle to be employed when the driving band is running on the loose pulley.

In a well made foot lathe, the friction of the working parts is usually so slight, that when the tool is not cutting, the mechanical exertion of working the treadle is soon scarcely felt. While in light hand turning, and in driving the revolving cutting frames in ornamental turning; the foot is often entirely withdrawn from the treadle that the workman may stand upon both feet, to obtain greater steadiness for an exact or delicate cut, or for making adjustments with the division plate and index. At these times the momentum of the fly wheel will cause the lathe to continue very many revolutions before its speed materially slackens, and the speed is again immediately increased, so soon as the foot is placed on the treadle to take up and continue the motion.

The turn bench, fig. 28, but of rather larger dimensions, is sometimes provided with a small hand wheel of from ten to eighteen inches diameter, together with the additions represented in fig. 37, when it becomes the clockmaker's throw or dead center lathe. The wheel is turned by the left hand and the tool as before is held in the right: the horizontal framework is grasped in the vice, but, it is also occasionally permanently screwed down to the bench. The work revolves between fixed centers, but the pulley, which is no longer fixed upon it, as in the turn bench, revolves freely on the center on the left; shown by the detached views of the fixed center and pulley. A movable square piece, fastened by a thumb screw to the front of the pulley, filed square to receive it, carries a projecting pin which catches against a screw clamp or carrier fixed on the work; the pulley communicates its motion to the work driving it before it, the two parts in contact being called the driver and the carrier. The driving wheel is adjustable upon the arm by which it is carried, to regulate the tension of the band, and the latter is usually crossed as a figure of eight, to obtain increased wrapping contact around the pulley; the driving wheel being also slightly inclined from the perpendicular to prevent the band chafing when so crossed, and the work may now be removed and replaced, without deranging the band. The continuous revolution renders the clock throw much more expeditious than the turn bench, and fig. 37, is a very convenient little lathe for much small turning.

The Driving Wheel Considered As To Momentum And As 40032

Fig. 37.

The dead center lathe with loose pulley, of which the clock throw is the smallest variety, may be considered as a permanent tool, derived from the fixed centers of the reciprocating lathe; lathe heads embodying this principle constructed of considerable size, are sometimes met with, and they are well adapted both to heavy works and for accurate results. Fig. 38, is a dead center head forming a part of a lathe for oval turning, copied from Plumier; this was driven by a band on its grooved pulley. In the more modern form fig. 39, used for larger works; when the hold of the catgut or rope in the grooves of the pulley affords insufficient power, these are replaced by a strap and a broad pulley, shown by the dotted lines. In turning work of still greater size, the strap and pulley in their turn are insufficient, and a wheel and pinion are then employed for the rotation. A large toothed wheel replaces the pulley, and a pinion of about one-third or onefourth the diameter of the wheel, is attached to the same standard by a separate axis. The dead center lathe from its simplicity and efficiency, was long a favorite in the hands of the millwrights; with them, the pinion axis terminated in a winch handle or in a fly wheel; when now employed, it usually carries a pulley and is driven by power.

Fig. 38.

The Driving Wheel Considered As To Momentum And As 40033

Fig. 39.

The Driving Wheel Considered As To Momentum And As 40034

Fig. 40.

The Driving Wheel Considered As To Momentum And As 40035