The enormous steel lathes which are seen in engineering shops to-day are the outcome of Henry Maudslay’s invention of the screwcutting lathe. Even the huge modern boring and drilling machines can be related to this epoch-making invention
THE RADIAL DRILLING MACHINE engaged in drilling the cylinder block of a large diesel engine. Smaller mobile radial machines are often used in locomotive works, and can easily be moved from one place to another. The drilling arm of the mobile type can be moved round in a complete circle and it has also a motion of 30 degrees in a vertical plane.
AT the push of a button, the hundreds of tons of steel which make up the modern lathe are galvanized into life. Turnings, smoking hot from the speed of cutting, writhe off at the rate of three and a half tons an hour. The huge machines dwarf the men who plan and build them, yet the giant lathes acknowledge as their immediate forebears of only a few centuries back a primitive contraption of wooden poles and ropes. The pole lathe, as this earliest machine tool was called, is still to be seen in operation in some parts of England and Wales, worked vertically, passes once round the work by old craftsmen who produce extremely fine turning despite the limitations of their equipment. The early history of the lathe records the development of machine tools generally. Even at the present time the lathe is still one of the most important individual machine tools in production technique. Almost any job can be carried out with its aid and many of the specialized machines now current are simply elaborate offshoots of the same basic idea.
In the pole lathe the work to be shaped is held between two fixed centres, while to a pole, about three feet above the work, a rope is tied. The pole must be fairly pliable and is fixed at one end, the rope being tied to the free end. From here the rope descends vertically, passes once round the work and is then joined to a treadle on the ground. In this manner movement of the treadle causes the work to rotate backwards and forwards, shaping of the work being effected by pressing a chisel into it as it rotates towards the turner.
An obvious advance over this crude arrangement was the introduction of the crank and flywheel, which together enable the work to rotate consistently in the same direction. The evolution of the lathe through all its phases makes an interesting study. Henry Maudslay’s invention of the screwcutting lathe was one of the most important advances in the development of the lathe.
It was towards the end of the eighteenth century that Maudslay built the first workshop machine for producing screw threads by means of a lead screw and change wheels. This historic relic is now preserved in the Science Museum, London. The bed is made up of two triangular bars and is about three feet long. The height of the centres is 1½ in. Between the two guide bars comprising the bed is arranged the lead screw of 1-in. diameter and ¼-in. Pitch.
It is geared to the lathe spindle through the change wheels in the same way as is practised to-day. All the features of the modern small lathe are almost exactly in accordance with the principles laid down in Maudslay’s original design. Changes have been made in the construction of the bed, by the introduction of the back gear and completely automatic traverse of the saddle. These, however, are absurdly minor changes to have to record after nearly 200 years of development. The changes have been slight because the original design was sufficiently sound to meet all general machining requirements within the capacity of the small lathe.
Maximum Diameter of 110 in.
The needs of industry always spur on the designer of engineering tools to evolve new, larger and more powerful machines; yet each machine is linked to its predecessor by similar fundamental principles. The giant modern milling machines, multiple drills, shapers or planers may appear to have little in common with Maudslay’s lathe, but the starting point may reasonably be identified with the introduction of the first screwcutting lathe.
Maudslay could turn work up to a maximum diameter of 3 in. in his lathe. A striking contrast in size is afforded by one of the largest lathes ever built in Great Britain. Work up to a maximum diameter of 110 in. may be mounted in the machine and a maximum total length of 60 feet may be accommodated. The length of the lathe bed is 86 ft. 8 in. and its width is 12 feet.
Despite their huge proportions, machines of this type may be controlled by a single operator, probably with more ease than a 6-in. capstan lathe.
The machine is electrically operated, the main drive being through the medium of a 250 horse-power motor. An instrument panel informs the operator of the spindle revolutions per minute and the current taken by the motor.
ONE OF THE LARGEST LATHES ever built in Great Britain weighs 270 tons and can accommodate work with a maximum diameter of 110 in. and a maximum length of 60 feet. The machine is operated by an electric motor of 250 horse-power and can be controlled by push buttons operated by one man.
By means of push buttons the operator may start or stop the machine altogether or individual motions separately. Similar control panels are mounted on each saddle. Separate motors, each of 3 horse-power, control the movement of the saddles and one of 5 horse-power provides motion for the tailstock. The suds (cutting lubricant) pump requires a ¾ horsepower motor to drive it. Right underneath the machine, fitted into the foundations, is a chip conveyer powered by a 10 horse-power motor.
This conveyer provides for the removal of the chippings as they fall into a longitudinal trough in the middle of the bed. The cuttings are conveyed to a bin at the tail end of the lathe by an endless conveyer chain fitted with scraper plates which scrape the bottom of the trough.
The total weight of this machine is 270 tons — 85 tons less than another large British lathe built about 1935. This has a centre height of 54 in. and its builders in 1937 were engaged on the making of three single lathes to swing work of 188-in. diameter and 33 feet in length. One of the largest machines of its type ever built was a 51-in. centre tube-boring machine completed in 1936. It has an overall length of 260 feet and is capable of boring tubes 100 feet in length and 100 tons in weight.
High-speed production has given rise to the evolution of entirely automatic machines which are not, in general, remarkable for their size, but are outstanding in the ingenuity of their design. The automatic is a common tool in the modem machine shop and is generally to be seen engaged on the making of screws and other small repetition jobs which it is able to turn out with amazing rapidity and accuracy.
Metal stock (long rods) is initially fed in at the headstock end, where it is held firmly in a collet chuck. (A chuck is an appendage which holds the work firmly in position on the lathe.) At the tailstock end of the machine is a turret head, this being a heavy circular piece of metal with holes drilled round its periphery to take various toolholders. In these holes the various turning tools, taps and dies are mounted, the turret rotating automatically, so that each tool is brought into the correct position at the right time.
Movement of the turret head is controlled by a cam specially cut to suit the work in hand. Where the slide rest would be positioned on a normal type lathe, forming and parting-off tools are mounted. These are brought into use at the. correct time also by cams. Finally the design generally includes an automatic arm which, for screw production, descends at the moment the screw is parted off. Having picked it up, the arm carries it along to be slotted in the head to a predetermined depth. At this stage the article is ejected, complete, to the collection tray.
Drilling 60 Holes At Once
Except for feeding in new stock at intervals and for occasionally checking, by micrometer, the work turned out, these automatics will carry on throughout a complete day’s work without further attention. Sperm whale oil is continuously spurted on to the work to prevent the temperature from rising and tools from being blunted.
For heavier and slower repetition work the capstan lathe is generally adopted. This has a turret head similar to the automatic, but movement of the head is contrived by a lever handled by a young operator. Setting up the capstan is a skilled man’s task, although its subsequent operation is simply a question of feeding in each tool in turn and parting off the completed component when the whole range of operations has been gone through. By furthering the demand for specialized machine tools the automobile industry has done a great deal to expedite development. Multiple drilling machines are now fairly common in all branches of industry. In the production of automobile engines fifty or sixty holes are drilled in components simultaneously, to accuracy limits of plus or minus a few thousandths of an inch. For dealing with crankshafts special machines have been evolved which drill six holes, ream two, countersink six and tap four, all in the flange end. A modification of the same design drills, faces, recentres and taps the holes in the pulley end of the shaft.
Four unit heads are mounted on a central column, round which the table carrying the fixture rotates freely by hand on a special ball-bearing track, with positive stop positions at the various stations. Provision is made on the table at the back of the machine for clearing the swarf (turnings). Each of the operating units consists of a sliding member, independently motor-driven, controlled by a cam which brings the tools quickly to a working position, feeds them through the work at the correct rate of penetration, and then returns them rapidly to the starting position.
A GIGANTIC PUNCH PRESS by means of which motor car bodies may be stamped out of sheet steel. The top photograph shows the dies which are used for pressing the wings. The ram of a large press of the enclosed type is driven by two horizontally arranged crankshafts with four connecting rods. This system prevents the ram from tilting when the die pressure is uneven. The drive is enclosed and is separated into two units, one for the sheet holder and one for the ram.
Several internal combustion engine cylinder blocks are now machined simultaneously on a continuous rotary milling machine. This consists of a huge table, on which the blocks are mounted, which rotates in the horizontal plane. Above the table two or more machine heads are suspended vertically. These carry cutters, 2½ feet in diameter, which also rotate in the horizontal plane. The feed is adjustable by varying the height of the heads above the table. Lubrication is of the utmost importance in a machine of this type. The tracks in which the table rotates are permanently submerged in oil and general lubrication is achieved by pumping oil continuously up to a reservoir at the top of the structure. From here the oil is allowed to cascade through all the oilways down to the sump for the process to be repeated.
It is a short step from the combination vertical miller to the giant single upright boring and turning mill. The largest of its type in the world is the product of a French firm of engineers and has been evolved for extra heavy duty. When engaged on facing work it virtually comprises a gigantic lathe which has been up-ended and has had its bed shortened. The likeness is further marked in the mode of operation, the work being bolted to the table, which rotates. The vertical column overhead carries tools which are fed into the work for machining purposes.
Outstanding features of the mill are the movable work table and open side construction. By reason of the first property, occasional parts of large diameter can be machined when normally they would be too large for the mill. Its open side construction facilitates rapid and easy loading. The weight of the table alone is 9 tons and the maximum weight that it can support is 291- tons. A 40 horse-power motor provides the main drive and this is used in conjunction with an auxiliary motor of 6 horse-power. The total weight of the complete machine is 70 tons.
Presses for Heavy-Gauge Steel
One of the most remarkable developments in recent years is the evolution of the gigantic punch press. Such is the terrific pressure exerted by these presses that complete car bodies, running boards and wings can be pressed out from relatively heavy-gauge sheet steel.
The ram of a large four-point action bodywork drawing press of this type is driven by two horizontally arranged crankshafts with four connecting rods. This feature prevents any ram tilt when the die pressure is uneven. When the ponderous ram is driven down to the die, some means must be adopted of absorbing some of the heavy shock when the two meet. No steel, of even the finest grade, could for long stand up to such continued shocks.
In this machine controlled pneumatic bolsters are fitted in the table and in the ram so that the press has four different possible motions — sheet holder, ram, table drawing pad and ram drawing bolster. These features enable the press to be used for the most difficult operations.
There are other machines which act on the same principle, but with the drive gearing housed inside the body of the press. This allows greater accessibility at the operating position — a feature of great importance when fitting or removing tools. Further, the drive of this enclosed type is separated into two units, one for the sheet holder and one for the ram. The sheet holder motion is therefore quite independent of the ram movement and can be controlled instantly.
HUGE MODERN LATHE weighing 355 tons. This machine, seen in the centre of the production shop of an engineering works, has a centre height of 54 in. Enormous machines such as these are directly driven by electric motors and not by belts.
The inevitable complaint, when machines of such marvellous capabilities as the modern punch press are evolved, is that the skill of the individual craftsman is nullified and that his services can no longer be used. On the other hand, the highest standards of toolroom skill and craft of the most individual type are necessary for the production of dies suitable for press work.
The exigencies of industrial production frequently necessitate the machining, drilling or boring of a job which cannot easily be dealt with by ordinary means. A whole series of small machine tools has been developed for dealing with work in position. High-speed portable filing and chipping tools are available and by their aid a surprising amount of metal can be removed in a few minutes. The portable electric drill has found its way into the everyday equipment of even small engineering concerns. In their spheres the portable riveter and scraper perform extremely valuable service.
Through the whole range of portable apparatus of these types alternative designs, providing for their operation by compressed air instead of by electricity, are marketed. The compressed-air drive is achieving an ever-increasing popularity in present-day practice, not only as a convenient form of primary drive but also for the control of auxiliary equipment. An example of such applications is afforded by its use for the opening and closing of lathe chucks and the ejection of finished work. Chuck control of this nature saves much time on repetition work.
The surprising speed of over 1,000 revolutions a second is attained by some of the tiny portable pneumatic grinders. Speeds for drilling are not so high, the maximum being about 13,000 revolutions a minute for 3/16-in. holes through thin-gauge metal. Machines of this type are extensively used in aircraft construction, dealing with duralumin sheets. To an observer, the effect is that the hole is punched through the thin metal, so rapidly does the small drill eat through it.
An important feature of these small compressed-air tools is that they can be successfully used under water for ship repairs, salvage operations, and the like.
There are many varieties of mobile or semi-mobile machines which, although they cannot be classed as truly portable, are also capable of being taken to the site of the job. The portable universal radial type of drilling machine is often seen in locomotive works, where it is used for the drilling of the side frames, cylinders, fireboxes and the like.
Mobile Drilling Machines
On partly-erected components which are too large to move, the heavy mobile drill has full play for its outstanding abilities. The drilling arm can be positioned at any angle through a full 360 degrees, and it also has a motion in the vertical plane of 30 degrees. The whole outfit, which is massive by ordinary standards, can be readily moved about either on its own wheels or by a lifting shackle.
One of the most modern of the many other machine tools is the broaching machine, which is almost comparable to a gigantic file, though, in contrast to the file, it does its work with a single stroke. Then there is the planing machine and its smaller companion the shaping machine. In both the cut is made by a reciprocating movement, the work moving in the planer and the tool in the shaper. There is a whole family of grinding machines; metal saws of many kinds; cold forging machines; punching and shearing machines and so forth.
Throughout a survey of machine tool development a resemblance — although slight at times — can nearly always be noted to that fundamental tool, the lathe. Perhaps in the punch press the relationship would be strained beyond credibility, but here the dies emanate from the toolroom and in most instances the lathe will have contributed largely to their production. Maudslay must rank with those many others who “builded better than they knew”.
CONTINUOUS ROTARY MILLING MACHINE used for the simultaneous machining of internal combustion engine cylinder blocks. The blocks are mounted on a huge table which rotates in the horizontal plane. Two or more machine heads are carried on slides above the table. These carry cutters, 21 feet in diameter, which also rotate in the horizontal plane.