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Caliper


Caliper
One of the most important engineering achievements in the beginning of the XIX century was the distribution of machine tools with calipers - mechanical cutter holders. No matter how simple and, at first glance, this may seem insignificant appendage to the machine, we can say without exaggeration that its impact on the improvement and dissemination of machines was as great as the impact of the changes made in the Watt steam engine. Introduction slide again resulted in an improvement and cheapening of all machines, gave rise to new improvements and inventions.

The lathe has a very long history, and over the years its design has changed very little. Perhaps the principle of his device was prompted people potter's wheel. Is driven to rotate a piece of wood, the master using the bit could give it the most bizarre cylindrical shape. To do this, he held fast to the bit rotating piece of wood, separated from him a pie chips and gradually give the desired workpiece shape. The details of your device machines could pretty much different from each other, but until the end of the XVIII century, they all had one fundamental feature: the workpiece is rotating and the tool in the hands of the master.

Exceptions to this rule are very rare, and in any case can not be considered typical for that era. For example, the tool holders have proliferated in copy machines. With the help of these tools the employee does not have special skills, can produce intricate products of very complex shapes. To do this, use a bronze model, which had a kind of products, but larger (usually 2: 1). Receiving the desired image on the workpiece follows. The machine is equipped with two slides, allows you to grind out the product without the employee's hands: one was fixed stylus, the other - with a chisel. Fixed stylus had a view of the bar, on the pointed end which prevented small roller. By copying roller finger special spring constantly pressed model. During operation, the machine is started and rotated in accordance with the projections and depressions on its surface oscillates. These movement patterns through a system of gears transmit the rotational workpiece, which repeated them. The preform was in contact with the cutter, just as the model is in contact with the copying finger. Depending on the terrain model workpiece is approached to the tool, then removed from it. Thus it changed and chip thickness. After many cutter passes over the workpiece surface topography arose, had a similar model, but on a smaller scale.

The copy machine was very complicated and expensive instrument. Buy it might only very wealthy people. In the first half of the XVIII century, when it became the fashion for Turned items made of wood and bone, turning operations involved many European monarchs and titled nobility. For them, and for the most part intended Lathes. For example, such a machine (made, as might be supposed, a remarkable Russian mechanic Nartov) was established in 1712 in the studio of the Russian Tsar Peter the Great.

Calipers were used on some of the machines in the watchmaking because with their help, it was easier to grind precision parts clockworks. At the end of the century they begin to set on turning machines. In the 10th volume of "Encyclopedia" Diderot was first plotting the simplest compound slide of a large lathe. This support could rotate around its axis by a screw and to approach the workpiece, but it can not move along it.

But the widespread practice in turning these devices have not received. Simple lathe fully satisfy all human needs until the second half of the XVIII century. However, from the middle of the century it has become increasingly be necessary to handle with great precision massive iron parts. Shafts, screws of various sizes, the gears were the first parts of machines, the mechanical production of which the question arose immediately after their arrival, as they were required in large numbers. Particularly acute need for high-precision machining of metallic workpieces began to be felt after the introduction in the life of the great invention of Watt. As already mentioned, the production of parts for steam engines proved to be very difficult technical problem to the level that has reached mechanical engineering of the XVIII century. Usually the cutter strong in the long hook stick. Work holding it in his hands, relying both on the lever on a special stand. This work demanded great skills and great physical strength. Any error resulted in damage to the entire workpiece or too large processing error. In 1765, due to the inability drilled with sufficient precision cylinder length two feet in diameter and six inches Watt was forced to resort to the malleable cylinder. Cylinder Boring nine feet long and 28 inches in diameter allowed accuracy to the "little finger thickness." Needless to say, this "precision" in the manufacture of the steam engine was completely inadequate.

The situation could improve only one way: it was necessary to create a machine for the production of cars. Machines were replaced by a highly-skilled workers, which was a little, and to ensure mass production of cheap and reliable machines. Since the beginning of the XIX century began a gradual revolution in mechanical engineering. In place of the old lathe, one by one come to the new high-precision automatic lathes equipped with calipers. The beginning of this revolution put lathe cutting lathe English engineer Henry Maudsley, allows you to automatically grind screws and bolts from any thread.

Generally cutting screws remained difficult technical problem for a long time, since the required precision and skill. Mechanics have long thought about how to simplify this operation. Even in 1701 in the work of Sh Plumet describes a method of cutting screws using primitive support. To this end soldered to the workpiece as the screw shank segment. Step soldered screws had to be equal to the pitch of the screw, which had to be cut into the workpiece. Then, the workpiece set in simple wooden split pasterns; headstock support body blanks and inserted into the rear screw soldered. By rotating the screw a wooden nest tailstock rumpled shape of the screw and nut served, so that the entire workpiece is moved in the direction of the headstock. Submission on the contrary was such that allowed the fixed cutter to cut the screw to the required step.

A similar type of device was on the screw-cutting lathe 1785, which was a direct predecessor of Maudsley machine. There threading, which served as a model for manufactured screws are applied directly to the spindle holding the workpiece and drives it into rotation. (Spindle called a rotating shaft turning machine with a device for clamping a workpiece.) This made it possible to make cuts on the screws by machine: work led to rotate the workpiece, which is due to the spindle thread, just as in the adaptation of the plume began to steadily move relative to a stationary cutter, who kept working on the stick. Thus it was obtained on the product carving, exactly corresponding to the spindle thread. However, the precision and the straightness of treatment depended here purely on the strength and hardness of the working hands, point the tool. This is a big inconvenience. In addition, the spindle thread was only 8-10 mm, which allows to cut only a very short screws.

Cutting machine, designed Mawdsley, was a significant step forward. The history of its invention as described by contemporaries.

In the years 1794- 1795 Maudsley, still young, but already very experienced engineer, he worked in the studio of the famous inventor of Brahma. The main products of the workshop were invented Brahma Waterski closets and castles. The demand for them was very wide, and manually make them was hard. Before Brahma and Mawdsley had a task to increase the number of parts manufactured on the machines. However, the old lathe was this inconvenient. Starting work on its improvement, Mawdsley in 1794 provided him with a cross slide. The lower part of the slide (slide) was placed on one frame with the tailstock of the machine and can slide along the rail. In any caliper its place could be firmly secured with a screw. On top of the lower slide are arranged in a similar manner. With them, the cutter attached to the screw groove on the end of the steel rod, can move in the transverse direction. Slide movement in longitudinal and transverse directions occur via two spindles. Sliding the tool via a support against the workpiece firmly placing it on the cross slide, and then moving along the surface to be treated, can be very accurately cut excess metal. At the same time he served as the support of the working hands, holding the cutter. In the described structure, in fact, there was still nothing new, but it was a necessary step for further improvements.

After retiring soon after his invention of Brahma, Mawdsley founded his own studio and in 1798 created a more perfect lathe. This machine was an important milestone in the development of the machine tool, as it allowed for the first time automatically produce cutting screws of any length and any step. As already mentioned, the weak point of the old lathe was that it could be cut only short screws. Otherwise, it could not be - because there was no support, working hand should remain stationary and moving the workpiece itself, together with the spindle. The machine Mawdsley billet remained stationary and moving caliper with fixed cutter in it. In order to make the lower support sled movable along the machine, Maudsley connected via two gears spindle headstock with the spindle support. Rotary screw screwed into the nut, which is pulled behind a slide caliper and forced them to slide along the bed. As the lead screw rotates at the same speed as the spindle, the workpiece is threaded at the same pitch that was on this screw. For cutting screws with a different step in the machine had a stock of spindles. Automatic tapping screws on the machine is as follows. The preform clamped and grind to the desired size, not including mechanical feed support. Then connect the spindle to spindle and screw cutting was carried out in several cuts. Reverse withdrawal slide each time to do manually after switching off the supply of self-propelled. Thus, the spindle and the caliper arm completely replaced desktop. Moreover, they allow threaded much more accurate and faster than on previous machines.

In 1800 Mawdsley has made a remarkable improvement in your machine - instead of a set of interchangeable spindles he used a set of replacement gears that connect the spindle and the spindle (there were 28, with the number of teeth from 15 to 50). It was now possible with a single lead screw with threads to receive various different step. In fact, if required, for example, to receive the screw, which move in the n times smaller than that of the lead, it was necessary to force the preform to rotate at a rate such that it is made n revolutions during the time until the spindle made only one turn. As the lead screw received his rotation of the spindle, this was easily achieved by inserting between the spindle and screw one or several toothed gear wheels. Knowing the number of teeth on each wheel, it was easy to obtain the required speed. By changing the combination of wheels, you can achieve different effects, for example, cut the thread right instead of the left.

At its machine Mawdsley performing threading with such amazing accuracy and precision that it seemed to contemporaries almost a miracle. He, in particular, sliced ​​adjusting screw and nut for the astronomical unit, which for a long time was considered the unrivaled masterpiece of precision. The screw had a length and five feet two inches in diameter with 50 turns per inch. The thread was so small that it was impossible to see with the naked eye. Soon the machine was improved Mawdsley ubiquitous and served as a model for many other metal-cutting machines. In 1817 planer caliper was created, allowing you to quickly process the flat surface. In 1818 Whitney invented the milling machine. In 1839 she appeared boring machine, etc.

Maudsley outstanding achievement earned him a loud and well-deserved fame. Indeed, although the Maudsley can not be considered the sole inventor of a support, his undoubted merit was that he came up with his idea at the right time and clothed it in the most perfect form. Another was to his credit that he introduced the idea of ​​a support to mass production and so contributed to its final distribution. He first established that each screw should have a certain diameter thread with a certain pitch. Until screw thread is applied by hand, each screw had its own peculiarities. For every screw nut was manufactured its own, it is not usually suitable to any other screws. Introduction of mechanized cutting of all threads to ensure uniformity. Now any screw and nut of any diameter approached to each other regardless of where they were produced. This was the beginning of standardization of parts, which had a crucial importance for the engineering industry.

One of the Maudsley disciples, James Nasmyth, later he did an outstanding inventor, wrote in his memoirs about the Maudsley as a pioneer of standardization: "He went to the spread of the most important things uniformity screws. You can call it an improvement, but rather would call it a revolution, produced by Maudsley in mechanical engineering. Before he had no system in the ratio between the number of turns of the screw and the cutting diameter. Every bolt and nut were suitable only for each other, and had nothing in common with the neighboring bolt sizes. Therefore, all the bolts and corresponding nuts received special markings designating them belonging to each other. Any mixing them led to endless difficulties and costs, inefficiencies and confusion - of the machine park was constantly used for the repair. Only those who lived in the relatively early days of the production of machines, can have a correct idea of ​​the troubles, obstacles and costs that caused this situation, and only the properly appreciate great service rendered to the Maudsley engineering. "

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