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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Caliper. History of invention and production
Directory / The history of technology, technology, objects around us Caliper (from English and French support, from late Latin supporto - I support) - a unit designed for fastening and manual or automatic movement of a tool, for example, in machine tools. The caliper usually consists of a tool holder and intermediate parts such as a sled that provide a given direction of movement of the tool.
One of the most important achievements of mechanical engineering at the beginning of the XNUMXth century was the spread of machine tools with calipers - mechanical holders for the cutter. However simple and, at first glance, insignificant this appendage to the machine may seem, it can be said without exaggeration that its influence on the improvement and distribution of machines was as great as the influence of the changes made by Watt in the steam engine. The introduction of the caliper at once led to the improvement and reduction in the cost of all machines, gave impetus to new improvements and inventions. The lathe has a very ancient history, and over the years its design has changed very little. Perhaps the principle of its device was suggested to people by a potter's wheel. Bringing a piece of wood into rotation, the master with the help of a chisel could give it the most bizarre cylindrical shape. To do this, he pressed the chisel against a rapidly rotating piece of wood, separated circular chips from it, and gradually gave the workpiece the desired shape. In the details of their device, the machines could differ quite significantly from each other, but until the end of the XNUMXth century, they all had one fundamental feature: during processing, the workpiece rotated, and the cutter was in the hands of the master. Exceptions to this rule were very rare, and by no means can they be considered typical of this era. For example, cutter holders have become widespread in copy machines. With the help of such machines, a worker who did not have special skills could produce intricate products of a very complex shape. For this, a bronze model was used, which looked like a product, but larger (usually 2:1).
The desired image was obtained on the workpiece as follows. The machine was equipped with two calipers, which made it possible to turn products without the participation of the worker's hand: a copy finger was fixed in one, and a cutter in the other. The fixed copy finger looked like a rod, at the pointed end of which a small roller was placed. The model was constantly pressed against the roller of the copy finger by a special spring. During the operation of the machine, it began to rotate and, in accordance with the protrusions and depressions on its surface, made oscillatory movements. These movements of the model were transmitted through a system of gears to a rotating workpiece, which repeated them. The workpiece was in contact with the cutter, just as the model was in contact with the copy finger. Depending on the relief of the model, the workpiece either approached the cutter or moved away from it. At the same time, the thickness of the chips also changed. After many passes of the cutter over the surface of the workpiece, a relief appeared similar to that on the model, but on a smaller scale. The copy machine was a very complex and expensive tool. Only very wealthy people could buy it. In the first half of the 1712th century, when the fashion for turned wood and bone products arose, many European monarchs and titled nobility were engaged in turning work. For them, for the most part, copying machines were intended. For example, such a machine (produced, as one might assume, by the remarkable Russian mechanic Nartov) was installed in XNUMX in the workshop of the Russian Tsar Peter the Great.
Calipers were used on some machines in watchmaking, because they made it easier to turn high-precision parts of watch movements. At the end of the century, they began to be installed on lathes. In the 10th volume of Diderot's Encyclopedia, for the first time, an image of the simplest cross support of a large lathe was placed. This caliper could rotate around an axis and approach the workpiece with a screw, but it could not move along it. But these devices were not widely used in turning. A simple lathe fully satisfied all human needs until the second half of the XNUMXth century. However, since the middle of the century, it has become increasingly necessary to process massive iron parts with great accuracy. Shafts, screws of various sizes, gears were the first parts of machines, the mechanical manufacture of which arose immediately after their appearance, since they were required in huge quantities. Especially acute need for high-precision processing of metal blanks began to be felt after the introduction of the great invention of Watt. As already mentioned, the manufacture of parts for steam engines turned out to be a very difficult technical task for the level reached by the engineering industry of the XNUMXth century. Usually the cutter was fixed on a long hook-shaped stick. The worker held it in his hands, leaning like a lever on a special stand. This work required great professional skills and great physical strength. Any mistake led to damage to the entire workpiece or to too large a processing error.
In 1765, due to the impossibility of reaming with sufficient accuracy a cylinder two feet long and six inches in diameter, Watt had to resort to a malleable cylinder. The bore of a cylinder nine feet long and 28 inches in diameter was accurate to "the thickness of a small finger." Needless to say, such "accuracy" in the manufacture of a steam engine was completely insufficient. The situation could be corrected in only one way: it was necessary to create machines for the production of machines. The machines were supposed to replace highly skilled workers, who were scarce, and to ensure the mass production of cheap and reliable machines. Since the beginning of the XNUMXth century, a gradual revolution in mechanical engineering began. In place of the old lathe, new high-precision automatic machines equipped with calipers come one after another. The beginning of this revolution was laid by the screw-cutting lathe of the English mechanic Henry Maudsley, which made it possible to automatically turn screws and bolts with any thread.
In general, cutting screws has long remained a difficult technical task, since it required high precision and skill. Mechanics have long thought about how to simplify this operation. Back in 1701, in the work of C. Plume, a method for cutting screws using a primitive caliper was described. To do this, a piece of screw was soldered to the workpiece as a shank. The pitch of the soldered screw had to be equal to the pitch of the screw to be cut on the workpiece. Then the workpiece was installed in the simplest detachable wooden headstock; the headstock supported the body of the workpiece, and a soldered screw was inserted into the back. When the screw rotated, the wooden nest of the tailstock was crushed in the shape of a screw and served as a nut, as a result of which the entire workpiece moved towards the headstock. The feed, on the contrary, was such that it allowed the fixed cutter to cut the screw with the required pitch. A similar kind of device was on the screw-cutting lathe of 1785, which was the immediate predecessor of the Maudsley machine. Here, the threading, which served as a model for the screw being made, was applied directly to the spindle, which held the workpiece and set it in rotation. (The spindle is called the rotating shaft of a lathe with a device for clamping the workpiece.) This made it possible to cut the screws by machine: the worker rotated the workpiece, which, due to the thread of the spindle, just like in the Plume fixture, began to move progressively relative to the fixed chisel, which the worker held on a stick. Thus, a thread was obtained on the product that exactly corresponded to the thread of the spindle. However, the accuracy and straightness of processing here depended solely on the strength and hardness of the hand of the worker who guided the tool. This was a great inconvenience. In addition, the thread on the spindle was only 8-10 mm, which only allowed very short screws to be cut. The screw-cutting machine designed by Maudsley represented a significant step forward. The history of its invention is described in this way by contemporaries. In 1794-1795, Maudsley, still a young but already very experienced mechanic, worked in the workshop of the famous inventor Brama. The main products of the workshop were water closets and locks invented by Brahma. The demand for them was very wide, and it was difficult to make them manually. Brahma and Maudsley were faced with the task of increasing the number of parts produced on machine tools. However, the old lathe was inconvenient for this. Starting work on its improvement, Maudsley in 1794 supplied him with a cross caliper. The lower part of the caliper (sled) was mounted on the same frame with the tailstock of the machine and could slide along its guide. In any of its places, the caliper could be firmly fixed with a screw. On the lower slide were the upper ones, arranged in a similar way. With the help of them, the cutter, fixed with a screw in a slot at the end of a steel bar, could move in the transverse direction. The movement of the caliper in the longitudinal and transverse directions occurred with the help of two lead screws. By moving the cutter with the help of a caliper close to the workpiece, rigidly setting it on a cross slide, and then moving it along the surface being machined, it was possible to cut off excess metal with great accuracy. In this case, the caliper served as the worker's hand holding the cutter. In the described design, in fact, there was still nothing new, but it was a necessary step towards further improvements. Leaving Brahma shortly after his invention, Maudsley founded his own workshop and in 1798 created a more advanced lathe. This machine became an important milestone in the development of machine tool industry, as it allowed for the first time to automatically cut screws of any length and any pitch. As already mentioned, the weak point of the old lathe was that it could only cut short screws. It could not be otherwise - after all, there was no support, the worker's hand had to remain motionless, and the workpiece itself moved along with the spindle. In the Maudsley machine, the workpiece remained motionless, and the caliper with the cutter fixed in it moved. In order to make the caliper move on the lower slide along the machine, Maudsley connected the headstock spindle to the caliper lead screw using two gear wheels. A rotating screw was screwed into a nut, which pulled the caliper sled along with it and made them slide along the bed. Since the lead screw rotated at the same speed as the spindle, the workpiece was threaded with the same pitch as that screw. For cutting screws with different pitches, the machine had a supply of lead screws. Automatic cutting of the screw on the machine was as follows. The workpiece was clamped and turned to the required dimensions, not including the mechanical feed of the caliper. After that, the lead screw was connected to the spindle, and helical cutting was carried out in several cutter passes. The return of the caliper each time was done manually after turning off the self-propelled feed. Thus, the lead screw and the caliper completely replaced the worker's hand. Moreover, they made it possible to cut threads much more accurately and faster than on previous machines. In 1800, Maudsley made a remarkable improvement to his machine - instead of a set of interchangeable lead screws, he used a set of interchangeable gears that connected the spindle and lead screw (there were 28 of them with a number of teeth from 15 to 50). Now it was possible to obtain various threads with a variety of pitches with a single lead screw. Indeed, if it was required, for example, to obtain a screw whose stroke is n times less than that of the lead screw, it was necessary to make the workpiece rotate at such a speed that it made n revolutions while the lead screw made only one revolution. Since the lead screw received its rotation from the spindle, this was easily achieved by inserting one or more gear wheels between the spindle and the screw. Knowing the number of teeth on each wheel, it was not difficult to obtain the required speed. By changing the combination of wheels, it was possible to achieve different effects, for example, cut the right thread instead of the left one.
On his machine, Maudsley performed threading with such amazing precision and accuracy that it seemed to his contemporaries almost a miracle. He, in particular, cut the adjusting screw and nut for an astronomical instrument, which for a long time was considered an unsurpassed masterpiece of precision. The screw was five feet long and two inches in diameter with 50 turns to each inch. The carving was so fine that it could not be seen with the naked eye. Soon, the improved Maudsley machine became widespread and served as a model for many other metal-cutting machines. In 1817, a planer with a caliper was created, which made it possible to quickly process flat surfaces. In 1818, Whitney invented the milling machine. In 1839, a carousel appeared, etc. The outstanding achievement of Maudsley brought him loud and well-deserved fame. Indeed, although Maudsley cannot be considered the sole inventor of the caliper, his undoubted merit was that he came up with his idea at the right time and put it in the most perfect form. His other merit was that he introduced the idea of a caliper into mass production and thus contributed to its final distribution. He was the first to establish that each screw of a certain diameter must have a thread with a certain pitch. Until screw threads were applied by hand, each screw had its own characteristics. For each screw, its own nut was made, usually not suitable for any other screw. The introduction of mechanized cutting ensured the uniformity of all threads. Now any screw and any nut of the same diameter fit together, regardless of where they were made. This was the beginning of the standardization of parts, which was extremely important for mechanical engineering.
One of Maudsley's students, James Nesmith, who later became an outstanding inventor himself, wrote in his memoirs of Maudsley as the initiator of standardization: in mechanical engineering. Before him, there was no system in the ratio between the number of turns of cutting screws and their diameter. Each bolt and nut was suitable only for each other and had nothing to do with a bolt of neighboring sizes. Therefore, all bolts and their corresponding nuts received special markings , indicating that they belonged to each other. Any confusion of them led to endless difficulties and expenses, inefficiency and confusion - part of the machine park had to be constantly used for repair. Only someone who lived in the relatively early days of machine production can have a correct idea of the troubles , obstacles and costs that caused a similar situation, and only he will correctly assess the great merit rendered by Maudsley to mechanical engineering. Author: Ryzhov K.V.
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