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 15

THIS chapter deals with the tools used for producing plain cylindrical work, such as curtain poles, broom-handles, dowel-pins, &c. A large quantity of cylindrical wood is used in many ways other than for the purposes named, but it would be of little use even to attempt to enumerate them all. Hard and soft woods are alike used in all sizes, from about a quarter inch diameter upwards.

Rounding machines are employed when the work has to be produced in large quantities. The wood, rough as it comes from the saw-mills, is fed by rollers into a hollow revolving mandrel, which carries an internal cutter. This reduces the material to a cylindrical form, and rollers with hollow grooves draw it out on the other side. It is not easy to say whether a rounding machine may be termed a lathe or not. The distinguishing characteristics of this latter tool have not been definitely determined.

Hollow planes are frequently employed for making cylindrical work; the accuracy of the result is not to be compared with that produced by rounding machines, or even by rounding planes or rounders, of which more hereafter. In a workshop where curtain-poles are the staple produce, I found the hollow plane holding the post of honour. The wood, having been sawn into rods of square section, is laid on a shooting-board, which is grooved to receive it, and the corners are taken off with a jack-plane, thus the material is reduced roughly to hexagonal form. A hollow plane is then used, and the wood is quickly shaved down to a circular section. A practised hand will make very good cylinders, but, of course, there is no means of ensuring perfect accuracy. The work is done quickly, and it is sufficiently true for the purpose for which it is intended; hence it is saleable, and the tools used for producing it are not costly. This latter consideration is probably the chief cause for adopting this primitive method, instead of using some of the modern machinery for the purpose. A few shillings will suffice to purchase the necessary hollow planes, but a rounding machine costs something like ten times as many pounds, and, moreover, involves the employment of steam power and other incidental expenses.

Fig. 21. ROUNDING TOOL.

Rounding planes, or rounders, are used to make cylindrical rods. The tool consists of a wooden stock, or handle, with a round hole through it. See accompanying illustration, Fig. 21. A plane iron is fitted to the stock, and projects slightly inside the hole. The work has to be rotated, and the rounder is forced on to it, the rough wood entering the hole, which forms a guide for it. The plane iron reduces the irregular pole to a perfect cylinder as it passes through the tool. In many respects the rounder acts in a manner similar to the rounding machine. The chief difference is that in the latter the machine revolves, whilst in the former the work is rotated whilst the rounder is held stationary. This tool forms the connecting link between the implements used by turners and carpenters. The ordinary rounder is suited to round one size only, but adjustable tools are made with which any sized cylinder, within the limit of the tools’ range, can be made.

Hollow augers, used for cutting tenons on wheel spokes and many other purposes, are very similar in construction to the rounder which has just been described. Universal hollow augers to cut all sizes, from three-eighths of an inch to one inch and a half are made, and very useful tools they are.

Fig. 22. CONCENTRIC SLIDE.

Fig. 22 shows an apparatus intended for use on a lathe, and adapted for turning cylindrical work straight, tapering, or any contour that has not abrupt alterations in its form. The apparatus is shown on the lathe illustrated on page 32, Fig. 23. It consists of an iron casting, fitted to slide along the lathe bed, to which several cutters are fixed. A circular plate, having a series of graduated holes, serves as a guide and steady for the work, which is turned to fit one hole by the knife shown slanting upwards. The knife placed vertically against the guide plate is placed at a slight angle, and serves as a self-acting feed, causing the apparatus to move automatically. The arm, which bears the name of the maker, rocks on the bolt, which is also shown, and carries the finishing tool. This arm rests upon a template fixed to the front of the lathe bed, and thus shapes the work to any desired form. This apparatus will take work from half an inch to two-inches diameter, and turn out from eighty to one-hundred-and-fifty objects per hour.

Fig. 23. LATHE FOR TURNING TAPER HANDLES, &C.

Fig. 23 shows a lathe arranged for turning long tapering handles. The action is automatic, and from 1,200 to 1,400 handles, thirty inches long, can be produced in ten hours. Skilled labour not being required to work the machine. The action is obtained by means of the apparatus illustrated at Fig. 22, which is fitted to an ordinary wood-turning lathe, such as shown at Fig. 2. The wood is square when placed on the lathe, a cutter reduces it to fit a hole in the guide collar by which it is held steady. The finishing cutter is attached to an arm jointed to the sliding part, and this arm, by moving over a guide, causes the finishing cutter to produce work of any required form within not very wide limits. The advance of the apparatus is made self-acting by means of a knife placed at a slight angle. A glance at Fig. 22 will best explain the action.

The two forms of rounding machines next illustrated are manufactured by Messrs. W. Furness & Co., of Liverpool.

Fig. 24 shows a machine for turning pins and rods of all diameters, from one-quarter inch to three inches, and of any length. The hollow mandrel is mounted in bearings on a headstock, which is bolted to a substantial cast-iron stand. The mandrel is driven by a belt from a countershaft. The right-hand end of the mandrel carries a cutter-head, which is also shown separately in the engraving. This cutter-head carries two cutters, one a gouge and one a chisel; the former reduces the wood roughly to form, and the latter, acting on the part already made circular, makes it quite true and smooth. The wood is shown entering on the right hand end, square as it leaves the saw mill, and issuing on the left a true cylinder. On the right is a stop flange or holder, which prevents the wood from turning round by the motion of the mandrel. The stop rests against one of the faces of the square wood.

The material is fed into this machine by hand, while a second person is employed in withdrawing the finished cylinders. A hand-fed machine cannot be worked to its full capacity, and is much less economical than an automatic machine. With self-acting motion the work is fed in at a speed of from ten to twenty feet per minute, the speed being regulated according to the size and hardness of the material. A hand-fed machine could not be supplied so fast. About one horse-power is necessary to drive the machine which has been described. A smaller machine, which will turn work from one-quarter inch to one-and-a-quarter inches in diameter, is made by the same firm. It is similar in all other respects, and only requires about half the before mentioned power to drive it.

Fig. 24. SIMPLE ROUNDING MACHINE.

Fig. 25 shows a rounding machine with automatic feed motion. It is similar in its general principles to Fig. 24. The square timber is fed in at the left-hand end between two rollers, which have V-shaped grooves, These rollers are made to grasp the wood by the pressure of the weight shown above. The lower wheel is revolved by means of the gear-wheels, shown driven by the tangent screw. A cutter-head comes next; this carries a chisel and a gouge, as previously described. By these tools the wood is shaped to a cylindrical form, and it then passes through the hollow mandrel to the rollers at the right-hand end. These rollers are covered with india-rubber, so that they do not indent or damage the smooth and finished cylinders. They are held in contact with the wood by the weight, shown above. The tangent screw turns the wheel which drives the lower roller. Thus both pairs of rollers are driven at the same speed from the screw-shaft, which carries at the right-hand end a fast and loose pulley for a driving-belt.

Fig. 25. AUTOMATIC ROUNDING MACHINE.

The hollow mandrel is mounted in bearings on a head-stock. The speed at which this should be driven is determined by the diameter of the work produced. For three-inch rods five to seven thousand revolutions per minute would be a fair rate, and the smaller the work the higher should be the speed. The lower rollers in the pairs are adjusted to a suitable height, according to the diameter of the work to be turned, by means of the hand-wheels, shown at both ends, below the bearings of the tangent screw shaft. The weights above bring the upper rollers in contact. The pressure is regulated by adjusting the weights along the lever arms to which they are fixed with set screws.

The necessity of driving revolving cutters at a high speed in wood-working machinery is now fully recognised. Not only does increased speed of the cutters allow the wood to be fed at a correspondingly faster rate, but increased velocity of the cutting edge produces a cleaner and better surface. It is only during recent times that wood-working machinery has been driven at the very high speeds named. Formerly it was considered to be impossible to manufacture bearings that would work satisfactorily under these high speeds. It has, however, now been ascertained that cutters will do more work of a better quality when driven at high velocities, and though the machines which carry them have to be constructed with extra caution, yet the consequent extra initial cost is inconsiderable when compared with the increased productive capacity.

Great attention must be paid to the correct balancing of cutter-heads which are driven at a high speed. Any deviation in the equipoise will impart a tremor, or spring, to the tool, and bad work will result. The bearings must be kept plentifully supplied with a suitable lubricant. A channel should be cut the whole length of the plummer-block bearing for the oil to flow in, and thus ensure a constant supply.

Spindles which have to be driven very fast should have their bearings as small in diameter as possible, consistent with the duty the spindle has to perform. The bearings are generally made very long in proportion to their diameters: twelve diameters long is perhaps a safe average. The greater the amount of bearing surface the longer it will wear. It is not superfluous to remind readers that to increase the length of a bearing does not increase the friction, and whether a spindle runs in bearings one inch or twelve inches long the same power will drive it, providing always that the diameters of the bearings are the same. An increase in the diameter will necessitate an increase in the power required to drive, and thus the necessity of keeping the diameters of bearings as small as possible is manifest.

The speed at which cylindrical work can be turned in a rounding machine of the construction illustrated may be judged by the figures given above. With cutter-heads running at over 5,000 revolutions per minute, the material may be turned at the rate of from thirty to forty feet length per minute. The enormous quantity of rod that can be turned out by a machine in constant work is surprising.