Figs. 7,8
Where cost is an object, a simple substitute for the boring collar is frequently made by the ordinary workman by a piece of board one inch thick, shaped like Fig. 9, with a single hole of the size most generally required; and the work is then fitted to the boring collar, instead of the latter to the work. In turning tool handles, for instance, where a few dozen are required all of the same size, or nearly so, a device of this kind, which can be made in a few minutes, is sufficiently effective. This form has been modified in two ways, and either will be found convenient. In the first, the conical hole is made of the largest size likely to be required, a set of boxwood plugs are then turned to fit this hole and are themselves bored in a similar way to suit various sizes of work. The form of these plugs is shown in Fig. 10, which is a side sectional view, and at B, where the same is shown in perspective. Two small screws or pins b, c, Fig. 10, fitting into the holes a, a, Fig. 9, prevent these flange-shaped plugs from turning round in the board as the work revolves. The pattern of A, Fig. 9, may be varied, and is better made of hard wood, and of a form which will afford a good bearing upon the lathe bed.
The second modification is more difficult to make, but equally effective. It is shown complete in Fig. 11. This form, arranged by the writer, has many advantages over the two last-named, and is very serviceable. A is the poppet, of the full height of the ordinary lathe heads, or a couple of inches higher. B, the slide forming the support of the piece to be bored. The form of the poppet without this attachment is shown in Fig. 12. If for nice work it should be made of metal and the face of it planed, but for general purposes hard wood will suffice. b, b, Fig. 11, are two pieces of brass forming a groove or guide in which a slide B, with dovetailed edges is fitted to work. This slide is bored, like the ordinary collar, with conical holes of different sizes, and should be made of metal and planed on back and edges. Over each hole is a mark, and this is to be brought to a similar mark on the face of the poppet. The plate is then clamped in position by a screw at the back of the poppet. One or more of such slides may be fitted at pleasure, and in case of wear or damage these are the only parts requiring to be renewed.
It is a good plan to arrange a socket and tee of a rest as b, c, Fig. 13, at the back of this boring collar, especially as the position of the tool will be always the same, so that the rest may be a permanent part of the poppet. There is sometimes a difficulty with the ordinary form of boring collar in advancing the rest T sufficiently near the work (the foot of the poppet, and that of the rest preventing it, by coming in contact.) There is another modification of boring collar, forming at the same time a guide for the drill, which in slender work, where the tool is long and fine, becomes almost a matter of necessity.
This consists in making such a guide cone as mentioned and shown in Fig. 10, B, but with a continuation containing a smaller hole for the drill, as Fig. 14. Both this and the other shorter cones above-mentioned may be made to screw into the poppet A, Fig. 9, instead of being kept in place by the pins at a, a, of that figure. In that case however the hole in the poppet must be cylindrical and only used as a support for the cones themselves. In addition to the use of these boring collars already alluded to, they serve for the purpose of turning up the points of screws like those of lathe centres. These are first formed between centres with carrier chuck, the back poppet is then removed and the extreme point fitted through one of the holes of the boring collar and the marks of the centre turned off.
Another useful adjunct to the lathe is the back rest for supporting long and slender articles, which would otherwise bend under the pressure of the tool. The ordinary and simplest form is shown in Fig. 15, and this is of general use with brush handle makers and others whose work is confined to a few sizes and shapes only. A better form is shown in Fig. 16. A support of wood or metal shaped like A is clamped to the lathe bed. Through the upper part the slide B passes and is wedged up so as to support the work—or the socket of a lathe rest may be arranged to take the upright part A, which must then be rounded, as shown at C.
A modification of the latter, communicated to the English Mechanic, is shown in Fig. 16A. Its construction and mode of application is sufficiently evident without a detailed description. Fig. 16B is another form made in metal. It consists of two similar plates with a triangular opening A, through which the work is passed, and which has an oval slot D, by which the apparatus is secured to the short poppet of the boring collar. Between the two plates slides a third, partly visible at C, which can be clamped by a screw at B, this screw also serving as a stud by which the plate may be moved. The work is allowed to take up its own bearing in the triangular opening as it revolves in the lathe. The clamping screw of the poppet is then secured, and the centering thus made certain. The plate C is then made to descend so as to touch the work, and clamped in that position. This is a very good central support for long slender articles.
There is a plan practised by German turners by which the back rest is in a measure superseded, and which may be mentioned here. It is simply the peculiar method of using the left hand. This is placed on the piece to be turned so that the fingers partly encircle the work while the thumb rests in the hollow of the gouge, or upon the end of the tool. The fingers thus form a back rest and keep the work pressed against the cutting edge, which is further steadied by the thumb. As the tool traverses the work the left-hand accompanies it, and with a little practice a ramrod or similar long and slender article may be readily and accurately turned. This position is shown in Fig. 17, and though the novice will find it difficult to work thus, it is well worth the trouble of mastering, as the method once acquired will be found of very great service.
We have now described more or less in detail the principal parts of the lathe as adapted for hand turning. Before we dismiss this part of the subject, however, it will be necessary to say a few words respecting the bed and lower fittings, the flywheel, treadle, and their adjuncts.
Beyond question the iron bed, planed as it now is at a moderate price, by machinery, is the best that can be adopted, especially if it is intended eventually to fit up the simple tool with slide rest and superior apparatus. Nevertheless, the pocket must in this case also frequently decide the question of material. If wood is preferred by necessity or otherwise, it should be hard wood, beech, or Spanish mahogany, unless it is proposed to plate the surface with iron. This latter plan costs little and, besides stiffening the bed, it prevents the wear and tear caused by the constant shifting of the back poppet and rest. A flat strip of iron one inch or an inch and a half wide can be picked out from the stores of any village blacksmith straight and level as it came from the rolls of the manufacturer. Selecting a piece of the required length and breadth, the eighth of an inch thick or rather more, the purchaser will have holes drilled and countersunk at intervals of nine or ten inches, to receive ¾-inch screws. These strips will have to be laid upon the top of the bed, at its inner edges; they need not be let in flush with the surface unless appearance is studied.
They must then be screwed down firmly, and by means of a file worked by both hands up and down their length (not across them) a good surface may be readily obtained. If the iron is let into the bed this filing will abrade the wood work, which is the reason why we prefer screwing it on the surface. This method produces a very excellent and durable lathe bed, and it will be free from much of the tremor which is so disagreeable while working upon a lathe entirely of cast iron unless the bed of the latter and the standards are more substantial than is usual with small lathes.
The standards supporting the axle of the fly wheel and bed may in like manner be of wood or iron. Even when the bed is of iron these may be of hard wood, although it is customary to make them of the same material as the bed. If of beech, oak, or mahogany, as in some of Holtzapffel’s best lathes with iron beds, the tremor before alluded to will be considerably lessened. Iron is nevertheless very neat, and is quite the fashion with the majority of makers, but is too often faulty in respect of solidity.
The standards as a rule are too slight, an elegant pattern being studied to the sacrifice of substance and weight, The bed and stand of a lathe cannot be too strong and stiff.
Respecting this matter of stiffness and solidity we seldom find it sufficiently considered, and, even with practical workmen, a defect in this particular is more frequently acknowledged and put up with than remedied, although the comfort of a steady lathe is beyond question, to say nothing of its superiority when good workmanship is studied (as it always should be). The old French lathes made in the form of a thick table with four stout legs, forming the bed and back-board, are by no means to be despised as patterns; and instead of the usual method of making but one standard at end of the bed, there can be no question that two additional ones add considerably to the stability of the machine.
The fly wheel should be sufficiently heavy and have three speed grooves on the rim and two additional ones to produce a slow motion, which is required for turning metal. The latter may be worked with ease in this way when the article to be turned is small, but if heavy work is likely to be encountered the back geared lathe, to be hereafter described, must be substituted, and the slide rest will then also replace the hand tools. The crank axle is generally supported by two centre screws, the points being hardened, and also the ends of the axles, which are accordingly made of steel, and the holes for the centre screws neatly drilled and countersunk.
This is however not the most perfect method, and as we are speaking of better class lathes, as well as those of more common and cheaper make, we must by no means omit to speak of a very superior way of fitting the crank axle. The latter must be turned at both ends, the wheel bored and slipped on, and keyed in its place.
Two wheels of brass about two inches diameter, must then take the place of the centre screws. These are called friction wheels, and they must be placed sufficiently near each other to support the end of the axle between them, as shown in Fig. 17B, a and b. A pair of these must be thus fitted to each standard, and after the axle is placed in position a third may be placed above it to prevent the lathe cord from lifting the axle out of place by its tension. The axle and friction wheels will thus work together with an exquisitely smooth rolling motion—there will be no tendency to thrust the lathe standards apart as must result from tightening the ordinary centre screws, and the friction of the axle on its bearings will be reduced to a minimum. Any person acquainted with the use of the lathe may readily fit up these friction wheels, and the time and trouble so expended will be amply repaid by the superior ease with which the lathe can be used. We may say the same of the chain and eccentric, which can replace with similar advantage the crank and hook in ordinary use.
For the latter the following arrangements are necessary. A is the eccentric keyed to the crank axle, and may be either in the middle of the same or, as in Muir’s patent lathes, at one end outside the standard. Around it passes the endless flat chain B (known as crank chain). This also passes round a roller in the treadle shown at C. This chain does not act as a mere link, but when the lathe is in action it moves round and over the eccentric and treadle roller. The motion of the whole is smooth and regular, and, what is almost as important, noiseless. In Muir’s and other lathes the crank chain is used without the eccentric, being applied to the crank instead. Perhaps there is not much to choose between the two, but no one who has studied the eccentric and observed its exquisitely gentle and smooth motion in an ordinary engine can have failed to be struck by these valuable qualities. It must however be remembered that its throw is half that of a crank of the same eccentricity and the latter will have the advantage in power size for size.
In whatever position the lathe may be set up let the rise of the treadle be moderate. It is exceedingly disagreeable to work at a lathe where the rise of the foot board is so great as to bring the knee into contact with the lathe bed, a consummation not infrequent in country made ones.
This is only to be escaped by giving up a certain portion of power. Let A, B, Fig. 19, be the line of the treadle when at rest; c, the crank. To gain power we should let part A, E, be longer than E, B, as in the sketch. But let this arrangement be made, and when the crank is at its highest point, the line G, B, will show the position of the treadle and foot board. Hence this kind of leverage is not practicably available to any extent, and the length taken from foot board to link may with advantage be even less than that from link to the axle on which the treadle works. In lathes, of all machine tools, it is essential that the workman should be able to stand easily, that the movements of the leg and body should not be communicated to the tool, the play of the treadle and such items of detail being of more consequence than might at first sight appear, and any method tending to diminish friction, vibration, and noise is well worth consideration in planning this machine.
We may now suppose the reader the happy possessor of a well made foot lathe, long or short in bed, high or low in poppet, according to his need, but, of whatever size, carefully made and firmly fixed in a well-lighted place, and if possible on the basement floor—an upstairs workshop is objectionable owing to the certain vibration of a boarded floor. He will now require certain chucks and tools, many of the former of which he will have to make for himself.