Classification of Lathes

The essential elements of a lathe. The bed. The head-stock. The tailstock. he carriage. The apron. The turning and supporting rests. The countershaft. Taper attachments. Change-gears. Classification applied to materials, labor accounts, and the handling of parts in the manufacture of lathes. The four general classes of lathes. The eighteen sub-divisions of these classes. The first class: hand lathes, polishing lathes, pattern lathes, spinning lathes and chucking lathes. The second class: engine lathes without thread-cutting mechanism, Fox brass lathes, forge lathes, and roughing lathes. The third class: complete engine lathes with thread-cutting mechanism, precision lathes, rapid reduction lathes, and gap lathes. The fourth class : forming lathes, pulley lathes, shafting lathes, turret lathes and multiple spindle lathes. Rapid change gear devices. Bancroft and Sellers device. The Norton device. Lathe bed supports. The precision lathe. The rapid production lathe. The gap lathe. Special lathes. Forming lathes. Pulley lathes. Shafting lathes. Turret lathes. Screw machines. Multiple spindle lathes. Variety of special lathes.

IN considering what are the essential elements of a lathe they may be briefly stated, if we assume that in a simple lathe the work is to be what was originally intended, that is, held on centers, and may be stated in these terms, viz. The essential elements of a simple metal turning lathe are : suitable means for supporting and holding the work upon centers; proper mechanism for rotating the work; and a cutting-tool properly held and supported upon a traveling device actuated by suitable mechanism.

The first of these essentials comprise the bed, head-stock, and tail-stock, with their proper parts and appendages, so far as the fixed parts and centers are concerned, and including legs or other supports for the bed. The second essential comprises the driving mechanism, consisting of the driving-cone, back gearing, etc., and the third essential consisting of the carriage, tool block, and cutting-tool, with the necessary gearing for moving it, and the connecting parts for transmitting power for that purpose from the main spindle of the lathe.

This classification of the essential elements of the lathe naturally suggests certain groups of related parts which compose a complete lathe, and correspond with the experience and practice of the author in the designing and construction of the various types of lathes. They are as follows :

1. Bed and appendages, including the legs or cabinets, lead-screw and its boxes, the feed-rod, its boxes and supports, carriage rack, tail-stock, moving rack (when the lathe is large enough to require one), stud-plate and studs, and such necessary bolts and screws as are needed to fasten these parts.

2. Head-stock and appendages, including such feed-gears as are necessary to connect with the feed-rod in case of a geared feed. Also the holding-down bolts and binders (if used), for fastening the head-stock to the bed, and the large and small face-plates. (Where a quick change gear device is used and is not an integral part of the bed or head it forms a separate class.)

3. Tail-stock and appendages, such as holding-down bolts, binders, and, when the lathe is large enough to require it, the mover bracket, gears, shafts and crank; and if the tail-spindle is handled by a hand-wheel in front, the brackets, shafts, spur and bevel gears, etc.

4. Carriage and appendages, including gibs and a solid tool block if one is used, but not a compound rest where these are furnished at the order of the purchaser. If the lathes are habitually built with compound rests they may be classed with the carriage.

5. Apron and appendages, including the apron in its complete assembled form ready to attach to the carriage, together with the screws for making such attachment.

6. Rests, including the compound rest (when not classed with the carriage, the full swing, pulley or wing rest (as it is variously named), center rest, back rest, (when one is furnished), together with bolts, binders, and similar means of attachment.

7. Countershaft and its appendages, including the hangers, boxes, shipper rod, etc., and any similar parts for tight and loose pulleys or friction pulleys as may be necessary to make it complete and ready to put up.

Taper attachments, special tool holders, or tool-rests, and all similar parts are deemed extras and not included in regular lists.

Change-gears are sometimes listed as a part of the bed and appendages. When these are a part of a special quick change device they are made a separate class. This is understood to be when the change gear device is detachable. When made a part of the head-stock or the bed such parts as are attached to the one or the other of these main parts will be listed with it and become a portion of its appendages.

This classification is carried into all lists of materials of whatever kind and into all accounts of labor in the designing, constructing, and handling of these parts, whether in groups or as single pieces, during their progress through the various departments of the shop.

The classification of these lathes as entire and complete machines, and according to their various types of design and construction and the uses to which they are to be put, will be next considered, and in so doing it seems appropriate to commence with the more simple forms, and to proceed with such types as are commonly recognized and in use at the present time, dividing them into four general classes and these into such sub-divisions as their construction and uses seem to demand By this method of classification we shall have:

In the first class we understand by speed lathes a lathe without back gears and without the -carriage and apron of an engine lathe, although as chucking lathes they may be provided with back gears, as they are frequently used for boring quite large holes, and are therefore made much larger and heavier than those of the other sub-divisions of this class.

Hand lathes are supposed to be for the usual operations of hand tool turning, filing and light metal turning by means of a detachable slide-rest. They may have legs of sufficient height to support them from the floor as in Fig. A Hand Lathe, or with very short legs, making them convenient for setting upon the usual machinists’ bench as in Fig. A Bench Lathe. Otherwise their design and construction is the same.

A Hand Lathe
A Hand Lathe
A Bench Lathe
A Bench Lathe

Polishing lathes are, as their name implies, mostly used for polishing cylindrical work, although a hand-rest or a slide-rest is sometimes used upon them.

Pattern lathes, as shown in Fig. A Pattern Lathe, are usually so called when used by wood pattern-makers and while usually used with hand tools, as chisels and gouges with the support of a hand-rest, at the present time a majority of them are provided with a slide-rest. Those of larger swing have the rear end of the main spindle threaded for attaching a face-plate upon which is fixed large face-plate work of too great a diameter to be turned on the ordinary face-plate, as this supplemental face-plate overhangs the end of the bed and consequently the diameter of the work that can be turned is only limited by the height of the main spindle above the floor. In this class of work a hand-rest is supported by a tripod stand that may be moved to any desired position on the floor and is heavy enough to stand steadily wherever it may be placed.

A Pattern Lathe
A Pattern Lathe

Spinning lathes are used for forming a great variety of shapes from discs of quite thin metal, usually brass, with various shaped tools held either by hand or in the tool post of a slide-rest. These tools form the metal in a manner similar to the action of a burnisher instead of cutting it, usually over a former, by which the same shape is produced in all the pieces. Such work is not usually of large diameter, therefore a spinning lathe is generally of small and medium swing and is of substantially the same construction as the ordinary hand lathe, except when built for large or special work.

Chucking lathes, shown in Fig. A Chucking or Turret Head Lathe, are used to a great extent for boring and reaming circular castings, as pulleys, gears, hand-wheels, balance-wheels, sleeves, bushings, flanges, and all similar work that require only the formation of the hole, although some of these machines are provided with a cross-slide and tool-post by means of which the hubs or bosses of the work may be faced. Many of them are now provided with a turret, by means of which several tools may be carried so that not only boring and reaming, but recessing, facing, etc., may also be done without removing the work from the chuck. These lathes usually have a very large driving-cone with a broad belt surface, or they are constructed with back gears similar to those in an engine lathe. It was from this form of lathe that the elaborate lathes built by Jones & Lamson and others of similar design and construction originated.

A Chucking or Turret Head Lathe
A Chucking or Turret Head Lathe

In the second class we have what used to be called the “plain engine lathe,” that is, one not provided with any thread-cutting mechanism. Formerly the smaller sizes of these lathes did not usually have the power cross-feed, although at the present time there are very few of them built by any of the manufacturers, unless by a special order, practically all the modern engine lathes having the thread-cutting mechanism, and frequently it is made an elaborate and expensive feature and covers a wide range of work. When these lathes were built to a considerable extent the feeding mechanism was nearly always driven by a belt, gears being very seldom used for this purpose. No sub-division has been here given for foot-power lathes, as any of those so far described can and have been operated by foot-power when not too large to be thus driven.

The Fox brass lathe, Fig. A “Fox” Brass Finishing Lathe, is built upon similar lines as the engine lathe without a carriage or apron, but in place of it there is a swinging tool post slide whose rear end is journaled upon a lead screw which gives a longitudinal feed when the slide is brought over to the front by means of a handle for that purpose. With this driver, straight turning, facing, and thread cutting is quickly and conveniently done. There is also a hand-rest and sometimes a cutting-slide or cross-slide. The tail spindle has a long run and is sometimes worked with a lever, particularly when chucking work is to be done. Occasionally the tail-stock is replaced by a turret carrying a variety of tools such as are convenient for the brass finisher. These lathes are usually made without back gears. They are run at very high speeds and in the hands of an expert brass finisher do the work very rapidly, both as to turning and boring or inside finishing, while they cut threads very rapidly by means of “chasers.”

A "Fox" Brass Finishing Lathe
A “Fox” Brass Finishing Lathe

Forge lathes are a very heavy design of the plain engine lathe, without thread-cutting mechanism (although some manufacturers add this feature so as to make the lathes available as a complete engine lathe for much work that cannot be classed as forge work). The purpose of these lathes is to rough down large forgings, the users claiming that it is more economical to thus bring the work to the “forging sizes” than to do so by the process of hammering, and that all the chips thus removed may be worked into other forgings by which this waste is economically recovered. It is therefore their practice to forge the work (cylindrical work, of course) to dimensions much over the forge sizes, and by the use of the heavy forge lathe to finish them to customers “rough turned” to within reasonable limits of “finish sizes.”

By the term “roughing lathe” we understand that the design is heavy and massive with a very powerful driving mechanism, lateral and cross feeds and a very rigid tool holding device. Such a lathe is seen in Fig. A Roughing Lathe. While it is somewhat analogous to the forge lathe it is usually understood to be of much less capacity. And while the forge lathe, being for handling forgings almost exclusively, holds the work on centers, the roughing lathe should be made with a large hole in the spindle so that work may be “roughed out” from the bar as well as when held on centers, or with one end in a chuck and the other on a center. And here it encroaches upon what may be considered the field of the so-called “rapid reduction lathe “; with this difference, however, that in the former lathe the work is simply roughed out, while in the latter it is supposed to be not only roughed out or rapidly reduced to near finished sizes, but in many cases entirely finished, or finished to dimensions suitable for being finished by grinding.

A Roughing Lathe
A Roughing Lathe

In the third class we commence with the complete engine lathe, with thread-cutting mechanism, back geared or triple geared, with a compound rest which in the larger sizes is capable of power feed at all angles. Such a lathe should also be supplied, especially in the larger sizes, with a tool-rest to attach to the front wing of the carriage on the left-hand side for turning the full swing of the lathe. The larger lathes, particularly those that are triple geared, should have a tail-stock arranged with two sets of holding-down bolts, by means of which one set may be loosened and the tail-stock set over for turning tapers without removing the work from the lathe, as the other set of bolts still holds the tail-stock to its place on the bed. There should also be a tail-stock moving device consisting of a rack attached to the bed, with which is engaged a pinion fixed to a shaft journaled in a bracket attached to the tail-stock base. By means of a crank on this shaft the tail-stock can be easily moved to any desired point upon the bed.

In lathes of 42-inch swing and larger, this arrangement should be back-geared by the introduction of a second shaft, the gears being in ratio of 2 to 1. In lathes of 60-inch swing and larger this ratio should be 3 to 1. The tail-spindle in the smaller lathes has the usual screw and hand wheel for moving it back and forth. In large lathes this is inconvenient and laborious. The hand wheel should be placed in front of the tail-stock and near the center, being
mounted upon a short shaft at right angles to the spindle and journaled in a bracket fixed to the tail-stock. Upon this short shaft is also a miter gear engaging with another fixed to a shaft parallel to the spindle and extending to the rear end of the tailstock where it passes through another bracket and has fixed upon it a spur pinion which engages a spur gear fixed to the tail-spindle screw, and by which mechanism it is operated. The ratio of this spur gear and pinion is usually 2 to 1 on lathes of 42-inch swing, and proportionately more on larger lathes. By the use of this mechanism the operator may stand opposite the tail center in adjusting his work and easily reach the hand wheel controlling the movement of the spindle, which would otherwise require an assistant to operate.

In the triple-geared head-stocks of this class of lathes it is customary to attach the face-plate to the main spindle by a force-fit and key instead of making it readily removable by a coarse thread, for the reason that it is to be driven by means of a very large internal gear bolted to its rear side and engaged by a pinion fixed to a shaft driven by the cone through a suitable system of triple back gearing. In this case the cone is not placed upon the main spindle, but upon a separate shaft placed sometimes in front and sometimes in the rear of it. The front position is the more convenient for the operator in making the necessary changes of speed.

It is upon this class of lathes that many improvements have been made in the last few years in the thread-cutting devices, the original idea having been to avoid removing and replacing “changegears” when threads of different pitches were required to be cut. The first attempt in this line, so far as the patenting of a device shows, was made by Edward Bancroft and William Sellers in 1854, and taken up by various inventors with more or less success but never brought prominently into the market until the patent was granted to Wendel P. Norton in 1892, when somewhat later on the mechanism was adopted by the Hendey Machine Company, since which time it has been manufactured with much success. In the meantime many other devices for the same purpose have been devised and built, so that now every tool room and nearly every machine shop making any pretense to modern equipment possesses lathes having some one of these “rapid change gear attachments “included in their design or arranged to be attached when desired by the customer.

In the development of the engine lathe proper, much attention has been paid to the supports for the bed, and instead of the former pattern of light and, later on, heavy legs, substantial cabinets of liberal dimensions and weight, have been designed and are now used upon nearly all such lathes, the only exceptions seeming to be upon those where the selling price renders economy in the use of cast iron essential; upon lathes too small and light to justify their use; and upon lathes built by the more conservative manufacturers who have not yet come to consider this class of improvements as necessary to the efficiency of their machines.

A precision lathe is designed to be a lathe in which fineness and exactness in all its parts is the prime consideration rather than a great range of work or capacity, or from which a large output may be realized. It is therefore not necessary that it should be very heavy or massive except in so far as its weight may render it capable of greater precision. While the entire design and construction of the lathe is as exact as possible, the effort is also made to provide against all conditions and causes that shall be detrimental to its one object, that of turning out its work in as perfect a manner as possible.

These being the conditions under which it is designed and built, it is an expensive lathe, as the most skillful labor is used in its construction and the time devoted to this work is always liberal. It is, therefore, essentially a lathe for the tool room and the laboratory rather than the manufacturing department, and with it master screws of very great exactness and all similar work is performed. It is, of course, an engine lathe in its general design, although there are more or less changes of form and manner of assembling the parts introduced for the purpose of avoiding the effects of strains, protecting bearings from dirt, insuring accuracy of movement of the several parts, and so on, everything in the design and construction being subordinated to the one condition of the greatest precision and accuracy, not only in the entire machine but in all its individual parts.

A Rapid Reduction Lathe
A Rapid Reduction Lathe

The rapid-reduction lathe, shown in Fig. A Rapid Reduction Lathe, is another form of a complete engine lathe, built heavy and strong, with a powerful and somewhat complicated driving mechanism and very strong feed. The tool holding device should accommodate at least two tools and hold them very rigidly. It should have thread-cutting facilities so that pieces requiring threads may be entirely finished in this respect. It should be an accurately working machine so that it may not only rapidly reduce the stock to near the finishing dimensions, but finish all ordinary work to the given sizes, or to such dimensions as may be called for when the piece is to be finished by grinding. Such a lathe may be arranged with a series of stops both for diameters and lengths and thus do much of the work done in a very much more expensive turret lathe. It will be of much convenience to have a hollow spindle, bored out as large as possible so as to admit of running a bar of round stock through it, holding it in a chuck and forming one end of the pieces, then cutting them off, leaving the remainder of the work on the opposite end of the piece to be done at a second operation in this lathe or some similar machine. In working up round stock in this manner the lathe should be provided with a cutting-off slide constructed similar to that on a turret lathe.

A Gap Lathe
A Gap Lathe

A gap lathe, shown in Fig. 23, is one in which the top of the bed is cut away for a space immediately in front of the face-plate for the purpose of increasing the swing of the lathe so that much larger work may be turned or bored, either when held upon centers or in a chuck. This type of lathe is more in favor in English machine shops than those of this country, where the gap lathe is seldom seen. When the work of the lathe is not of such a nature as to require the gap, it is usually closed up in one of two ways. The first method is to have a portion of bed exactly like the main part and of such a length that it will exactly fit in the space form ing the “gap.” The other method is to have that portion of the bed upon which the head-stock is attached, of the full height, while the remainder of the bed is lowered sufficiently to furnish a support for a sliding supplemental bed whose depth is equal to the depth of the gap. This supplemental bed when closed up to the face of the head-stock completes the bed by filling the entire cut-away portion completely to the rear end. When it is desired to form a “gap” this supplemental bed is moved, toward the rear end of the bed proper to any desired distance to leave the required space or gap for the work in hand, and secured by bolts arranged for that purpose. In a large machine shop, with the proper lathes for handling whatever work the shop is called upon to do, the gap lathe is not usually necessary and will seldom be found, but in jobbing shops, particularly those with a modest equipment of tools, the gap lathe may often be found convenient for doing exceptionally large jobs such as pulleys, balance-wheels and the like, as these jobs may come along so seldom that it would not be advisable to incur the expense of a lathe large enough to swing them, and which would be liable to be idle a large portion of the time.

The gap lathe is provided with the usual thread-cutting mechanism and is in all respects a complete engine lathe. It is not usually as rigid as a solid bed lathe and therefore not as efficient in taking heavy cuts.

The fourth class, including the various types of special lathes, would of necessity be a very large one if an attempt were made to enumerate them all, and the list might prove tiresome to the busy reader. Those introduced in the foregoing list are of the well-known and recognized types and seem to be sufficient for the purposes of this work.

Forming lathes are of heavy and massive design and construction, and provided with powerful driving mechanism, adapted to rather slow speeds, and with fine feeds, owing to the large extent of the cutting surface of the tools used in them. These tools require special forms of rest for supporting them which are of strong but simple design, as many of the forming tools are simply flat steel plates with the form to be turned cut in the edge, so that when dull they may be sharpened by grinding the top face and not changing the form. Forming lathes should have hollow spindles, bored out much larger in proportion than in other types of lathes. The author has designed and built these lathes of 28-inch swing with a spindle 7 ½ inches in diameter and bored out to 5J inches, so as to take in a bar of 5-inch steel. As this size weighs about 85 pounds to the foot, or a bar 16 feet long weighs over 1 ,300 pounds, it will be seen that ample provision was needed  for the weight to be borne upon the main spindle bearings in addition to the weight of the lathe parts, and that while the driving power necessary for operating with a wide forming tool on steel of 5 inches diameter was a serious matter, that of providing for the rotating of this unusual load was a considerable addition to it. However, they met the required conditions and succeeded in turning out much work even of this comparatively large diameter.

Naturally the forming lathe requires no provision for thread cutting, but a geared feed should be used and will need to be of ample power to withstand the very severe strain to which it will be put.

Pulley lathes, as they are commonly termed, might more appropriately be called pulley-turning machines, or even pulley-making machines, since some of them make the pulley complete, with the exception of splining and drilling and tapping for the setscrews. In some of these machines the boring is going on and the reaming is also done while the turning is taking place. In other forms, one machine does the boring and reaming, which may be done at quite high relative speed, while the turning must be comparatively slower and is done in another machine. Thus one machine for boring and reaming may furnish work enough for several turning machines.

In the pulley-turning lathes there must be a strong driving mechanism since comparatively large diameters are turned, although even the roughing cut is light when compared with that frequently taken by other lathes. Two and sometimes more tools are used, being located both at the front and back of the bed, (those at the back being bottom side up) . In some machines the tools commence the operation in the center of the face of the pulley, and each tool or pair of tools (one roughing and one finishing), are fed away from the center, and with the slide upon which the tool block travels set in a slightly inclined position with reference to the axis of the lathe so as to produce the properly “crowned face” of the pulley. With four tools thus arranged, the pulley is completely turned during the time necessary for a tool to travel across one half of the face of the pulley plus the distance apart of the roughing and the finishing tool, say from an inch to an inch and a half.

When the pulley-turning lathe is arranged for turning cone pulleys it is customary to have as many tools as there are steps to the cone pulley, each held in a separate tool post fixed in a single tool block having a lateral power feed and a transverse adjustment for setting to the proper diameter. The tool posts set in T-slots and the tools are set with relation to each other so as to turn the proper relative diameters of the several steps. The tool block and the slide upon which it runs is adjustable to the right inclination or “taper” to properly crown all the steps of the cone at once, and when the tools have passed over one half the face of the steps, this block and slide may be shifted and properly adjusted to turn the other half of each step. In this form of pulley turning it is usual to make two cuts, a roughing and a finishing cut, and when turning up to the face of the different steps to draw back the entire number of tools by means of the transverse slide which may be fed back by hand for that purpose.

Pulley-turning and boring lathes or machines are built very  road as compared with an engine lathe and with very short beds, as the width of a pulley face, or the combined faces of the several steps of a cone pulley, is the extent of their lateral feed in any case.

The boring and reaming mechanism should have a power feed so as not to require the constant attendance of the operator, who may easily run one boring and reaming machine and two surface turning machines.

Shafting lathes or shaft-turning lathes may be arranged from any good engine lathe provided the bed is long enough for the purpose, by adding to it a three-tool shafting rest and a shaft straightener. Still a lathe that is especially designed as a shaft-turning lathe will be better adapted for the purpose and will turn out more good shafting with the same expenditure of capital and labor than the engine lathe arranged with attachments for the purpose. In the properly designed shaft-turning lathe there is a heavy shaft running the length of the lathe bed and arranged to communicate power to a face gear and driver journaled on the front end of the tail-stock, by means of which the shaft to be turned may be driven from this end as well as from the head-stock end. This is very useful in turning long shafts in which the torsional strain would be great, as the power may be applied at the tail-stock to turn one half of the shaft and then applied direct from the head-stock, or it may be applied at both ends continuously and simultaneously.

There should be a force pump to keep the cutting-tools constantly supplied with a stream of whatever lubricant is being used. This pump may be driven from the shaft above mentioned, which is located at the center of the bed and below the bridge of the carriage. The three-tool rest carries its own center rest, but it is customary to support the shaft being turned by easily removable rests used between the carriage and the head-stock or tail-stock, as the operator finds necessary. These are generally composed of two wooden blocks resting on the V’s of the lathe and somewhat lower than the lathe centers. The upper block has a V-shaped groove for the shaft to rest in and is raised up and held in place by a wooden wedge inserted just far enough to give proper support to the shaft so as not to permit it to sag during the process of turning. There are three turning tools usually employed. The first is a roughing tool; the second cuts the shaft very closely to size, while the third takes an extremely light cut, completing the work, so that by running once over the shaft from end to end it is completely finished. Two tools are placed at the left of the center rest fixed to the tool block, and one, the final finishing tool, at the right. As these three tools and the center rest occupy considerable length upon the shaft the lathe is provided with extra long centers so as to reach the work. The center rest is provided with split collars bored to the size that the second tool leaves the shaft.

A Turret Lathe
A Turret Lathe

The turret lathe, shown in Fig. A Turret Lathe, now so well and favorably known, is a comparatively recent invention and doubtless originated in the use of a multiple tail-stock which was formerly used on small work where more than one tool was desirable. Our English friends recognize its value and usefulness, and one author speaks of it as “the common capstan tool-rest.” In this country much has been done to develop and bring into popular form the turret lathe by such builders as Jones & Lamson, Warner & Swasey, Potter & Johnson, Bullard and others.

While the turret lathe in its perfected form is now a complete machine, the turret idea was first applied to engine lathes, and turret attachments are so universally popular that most of the lathe manufacturers now make them of dimensions suitable for their lathes, and attach them either to the lathe carriage or to a special bed which may be fastened to the lathe bed upon the removal of the tail-stock. A great variety of work may be done in the turret lathe, its principal rival being the automatic screw machine, whose economy lies principally in the fact that one operator may take care of a number of machines, each of these machines depending principally for their success upon the turret with its multiplicity of tools. And this idea of a turret carrying from four to eight tools is applied in a great variety of ways and to a large variety of machines on account of the ease with which any desired tool may be brought into a working position.

The head-stock of a turret lathe is made in several ways, from that of a plain head without back gears to one with a large variety of speeds, controlled by handles operating clutches, or friction driving devices, or both, and which may be operated while the machine is in motion. In some cases the head-stock is cast in one piece with the bed, in others fitted to it in a similar manner to that of an ordinary lathe. In still others the head has a transverse
movement on the bed upon which it slides and its movement is easily controlled by the operator.

The turret is designed and constructed in a variety of forms, but principally either circular or hexagonal. It is mounted usually in a horizontal position, that is with its axis vertical, but still in some of the best machines, notably the Gisholt, it is pivoted in an inclined position, the object being to bring the long tools, made necessary by a large machine, up out of the way of the operator as they swing over the front of the machine.

In the smaller hand machines and in many of the turrets furnished upon ordinary engine lathes the turrets are rotated by hand as each change is required, but in the larger and more complete machines the sliding movement of the turret effects its rotation at the proper time near its extreme rear position.

There is no carriage, properly so called, upon a regular turret lathe. A cutting-off slide carrying two tool-posts, one in front and one in the rear, serve to carry a cutting-off tool and a facing tool, or one for doing forming within certain limits. The spindle being hollow, and a large part of the work of the turret lathe adapted for steel work being made direct from the bar, these tools are very useful.

Some turret lathes are particularly adapted for a large variety of chucking and forming work, which they perform very accurately and economically, an elaborate system of stops for the turret slide rendering them very efficient for this work.

The tools that may be used in a turret are almost without number, and the expert operator readily attacks the most complicated pieces and brings them out with excellent finish and with surprising accuracy. Internal and external threads are readily cut very true to size and with rapidity.

The screw machine is very closely allied to the turret lathe, so called, and the smaller sizes are fitted with what is called a “wire feed,” which will automatically feed in the bar against the turret stop as soon as it is released by opening the chuck. This is in the hand screw machine. In the automatic screw machine all these movements are made automatically when once the machine is set up, the tools properly adjusted, the bar of stock once introduced and the machine started, and, barring accidents, the machine continues to run, dropping its work into a pan as it is completed and cut off, until the bar of stock is almost entirely used up.

Multiple spindle lathes are usually those having two spindles. These may be side by side for the purpose of performing two similar operations simultaneously; or one spindle may be considerably higher than the other, above the bed, thus giving two different capacities as to the diameter of work that can be accommodated on the same lathe; the larger swing being frequently used for boring or similar work. Notably of this type of lathe is that put in the market by J. J. McCabe.

While the general and well-marked types of lathes have been specified in this classification it must not be understood that the list is complete, as there are many special lathes, each of excellent mechanism and well adapted to the special work for which it is designed, that do not appear here, and that it is manifestly impossible to classify and describe in detail. Frequently they may be assigned to some one of the classes or sub-divisions here set forth, as all lathes must partake in some respect of the essential parts of those described.

Further on in this work many practical examples of the lathes described in this chapter will be found, their builders’ names being given and their particular features pointed out and commented upon, and to them the reader is referred for the better examples of each of the classes enumerated in this chapter.

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