When, according to the conditions of the drawing, it is necessary to obtain a smooth and shiny mirror surface of a part, but the dimensional accuracy may be rough, polishing of this surface is used; if, in addition to cleanliness and shine, it is necessary to obtain the exact dimensions of the part, finishing or lapping is used.

1. Polishing

Polishing is carried out on lathes using emery cloth. Depending on the size of the emery grains, the following sandpaper numbers are distinguished: No. 6, 5 and 4 - with large emery grains, No. 3 and 2 - with medium ones, No. 1, 0, 00 and 000 - with small ones. The cleanest polishing is achieved with sandpaper No. 00 and 000. The sandpaper should be held as shown in Fig. 232, otherwise it may wrap around the part and pinch your fingers.

Polishing is much faster with simple device, called presses (Fig. 232, b). The presses consist of two wooden blocks connected at one end by a leather or metal hinge and having recesses in the shape of the part. Sandpaper is placed in the clamps or sanding powder is added. It is recommended to lubricate the polished surface machine oil or mix the powder with oil, then the surface will be more shiny.

The use of clamps eliminates the risk of injury to the turner’s hands and of the sleeve being caught by a rotating part, clamp or chuck.

Polishing is carried out with light pressure of the presses and large numbers revolutions of the workpiece.

2. Finishing or lapping

Finishing or lapping is used for final processing of external and internal cylindrical and conical, shaped and flat surfaces of parts in order to obtain accurate dimensions and high quality(cleanliness) of the surface or tightness of the connection.

This processing method has become widespread in tool production (finishing the cutting edges of carbide cutters and reamers; finishing cylindrical, conical, threaded gauges; finishing measuring tiles).

This processing method is also widely used in mechanical engineering, for example, finishing of crankshaft journals, injector plungers, wheel teeth, etc. The surface finish after finishing can be obtained from 10 to 14.

Finishing of external cylindrical surfaces It is made using cast iron, copper, bronze or lead bushings (laps), machined to the size of the workpiece. On one side the bushing is cut, as shown in Fig. 233.

Bushing 1 is lubricated from the inside with an even thin layer of corundum micropowder with oil or finishing paste. Then it is inserted into the metal clamp 2 and put on the part. Slightly tightening the clamp with bolt 3, rub evenly along the rotating part. When finishing, it is useful to lubricate the part with liquid machine oil or kerosene.

The finishing allowance is left on the order of 5-20 microns (0.005-0.020 mm) per diameter.

The speed of rotation of the part during finishing is from 10 to 20 m/min; The cleaner the treated surface should be, the lower the speed should be.

Finishing holes made with cast iron or copper bushings (laps), also cut on one side. The bushings are set to the exact size using flat conical mandrels onto which they are mounted. In Fig. 234 shows a sleeve 1 mounted on a conical mandrel 2 fixed in a self-centering chuck. For finishing, the part is put on sleeve 1, which rotates with mandrel 2 during finishing; in this case, the parts communicate a slow rectilinear-return movement along the bushing.

Finishing of external and internal surfaces is carried out with corundum micropowder mixed with oil, or with special GOI finishing pastes. These pastes give better results both in terms of surface quality and performance. They exert not only a mechanical force on the metal, but also chemical action. The latter is that thanks to the paste, a thin film of oxides is formed on the surface of the part, which is then easily removed.

3. Rolling

The cylindrical handles of various measuring instruments, caliber handles, micrometer screw heads and round nuts are made not smooth, but grooved to make them easier to use. This corrugated surface is called knurling, and the process of obtaining it is rolling. Knurling can be straight or cross.

For rolling, a special holder 1 is fixed in the tool holder of the machine support (Fig. 235), in which one is installed for simple rolling, and for cross rolling - two rollers 2 and 3 made of tool hardened steel with teeth applied to them.

The teeth on the rollers have different sizes and different directions (Fig. 236), which allows you to produce different knurling patterns.

When rolling, the holder is pressed against the rotating part. The rollers rotate and, pressing into the material of the part, form a knurling on its surface. It can be large, medium or small depending on the size of the teeth on the rollers.

When rolling, feed is performed in two directions - perpendicular to the axis of the part and along the axis. To obtain sufficient knurling depth, knurling can be carried out in 2-4 passes.

Rolling rules: 1) starting rolling, you should immediately apply strong pressure and check whether the teeth of the roller fall into the notches they made during the next revolutions;
2) the rollers must match the required pattern of the part;
3) double rollers must be exactly located one below the other;
4) before work, the rollers must be thoroughly cleaned from any remaining material with a wire brush;
5) during rolling, the working surfaces of the rollers should be well lubricated with spindle or machine oil.

Rolling modes. In table 10 and 11 indicate peripheral speeds and longitudinal feeds when rolling on lathes.

Table 10

Circumferential speeds during rolling

Table 11

Rolling feeds

The correct knurling is checked by eye.

4. Rolling the surface with a roller

To strengthen the surface layer of a part pre-treated, for example, by fine turning, rolling a cylindrical surface with a hardened roller with a polished surface is used.

The rolled part is given a rotational movement at a speed of 25-50 m/min, and the holder with a roller is given a longitudinal feed movement. The feed rate is 0.2-0.5 mm/rev - depending on the required surface cleanliness. Rolling is carried out with slight pressure of the roller on the surface being rolled. The number of roller passes is 2-3. To reduce roller wear, generously lubricate the surfaces of the roller and the part with spindle or machine oil mixed in equal quantities with kerosene.

Control questions 1. How is surface polishing done?
2. What materials are used when polishing surfaces?
3. What is the difference between finishing and polishing?
4. What tool is used to roll the surface?
5. How is the surface rolled with a roller?

Finishing operations - polishing, finishing, rolling, rolling, smoothing and rolling are performed to reduce roughness, increase dimensional accuracy and wear resistance of a previously treated surface or to apply corrugations of a certain pattern to it.

Polishing

Polishing is performed to reduce the roughness and increase the gloss of the surfaces of the part. On lathes it is carried out using sandpaper on paper or canvas. Steel and non-ferrous metals are treated with corundum skins 15A-25A, cast iron and others fragile materials- silicon carbide skins 54C-64C.

During operation, a strip of sandpaper is held with both hands, pressed against a rotating polished surface and moved back and forth along it. You cannot hold the skin with your hand, as it can wrap around the part and pinch your fingers. It is necessary to stand at the machine with the body turned to the right at approximately an angle of 45° to the center axis. Polishing is usually performed sequentially with several sandpapers with a gradual reduction in their grain size.

It is convenient to polish cylindrical surfaces with a “press”, consisting of two hinged wooden blocks. Sanding paper is placed in the radial recesses of the bars, which is pressed with a press to the surface to be treated. Holding the handles of the press with your left hand and supporting the hinge with your right, carry out a reciprocating longitudinal feed.

Polishing can also be carried out by securing the abrasive paper in the caliper tool holder using wooden block and metal strip .

The internal surfaces are polished with sandpaper secured and wound on a wooden mandrel.

The part being polished becomes very hot and elongates. Therefore, when it is pressed by the center, you need to periodically check how tightly it is clamped and, if necessary, loosen it a little.

To obtain a better surface, it is necessary to increase the rotation speed of the part as much as possible. In addition, during final polishing, it is recommended to rub the skin with chalk.

Finishing

Finishing is carried out to increase the accuracy of the surface (up to 5-6th quality) and reduce its roughness. Special tools - laps - together with abrasive materials The smallest irregularities are removed from the surface of the part.

Abrasive and binding materials. Working surface The lapping is saturated with hard abrasive materials: electrocorundum powders - for finishing steels and silicon carbide - for cast iron and other brittle materials.

The grain size of the powders is selected depending on the required roughness. Preliminary finishing is performed with micropowders M40-M14, finishing finishing with M10-M5 (the micropowder number corresponds to the grain size in microns).

Of the finishing pastes, the most commonly used are GOI pastes, made on the basis of a soft abrasive material - chromium oxide, mixed with chemically active and binding substances. According to finishing ability, such pastes are divided into coarse, medium and fine.

Kerosene or mineral oil are used as binders and lubricants during finishing.

Lapping bushings with a longitudinal cut, allowing them to be adjusted in diameter to compensate for wear.

The laps for preliminary finishing are equipped with longitudinal or helical grooves, in which residues of abrasive material are collected during operation. Final finishing carried out by lapping with a smooth surface.

The finishing of the outer surface is carried out using a lap, which is installed in the clamp and adjusted as necessary with a screw. .

To machine holes, the lap is mounted on a conical mandrel and adjusted by axial movement with nuts. The lap material is selected depending on its purpose and the abrasive material used.

When finishing with hard abrasive materials, the grains of which are pressed into the lap, the material of the latter must be softer than the material of the workpiece. In addition, the larger the grains of the powder used, the softer material should be selected for lapping. For rough finishing, laps made of mild steel, copper, brass are recommended, and for preliminary and finishing - from fine-grained gray cast iron of medium hardness.

To work with GOI pastes, the lap must have greater hardness than the part being finished. In this case, the use of laps made of hardened steel or gray cast iron of increased hardness gives good results.

The peripheral speed of the part or lap is assumed to be 10-20 m/min during preliminary finishing, and 5-6 m/min during finishing in order to reduce heating of the part.

Rolling

Purpose and tools. Rolling is performed to create on the surfaces of some parts (handles, screw heads, etc.) a specially designed roughness, made in the form of corrugations of a certain pattern. For this purpose, knurling tools are used, consisting of a knurling roller and a holder.

To apply a straight pattern, single-roller knurling is used, mesh-double-roller knurling, respectively, with the right and left directions of the corrugations.

Knurling rollers are made of tool steels and hardened to high hardness. On their cylindrical surface, corrugations are made with a profile angle of 70° for steel parts and 90° for parts made of non-ferrous metals with a pitch of 0.3 to 1.6 mm.

The knurling is fixed with the smallest overhang in the tool holder of the caliper so that the generatrix of the roller is strictly parallel to the axis of the part. Check this against the surface being treated against the light. The axis of the single-roller knurling roller must be at the level of the center axis of the machine. For double-roller knurling, the accuracy of height adjustment is not significant, since in

In this case, the rollers are self-aligned along the surface being processed due to the swivel connection between the holder and the holder. .

Rolling techniques. When rolling, the metal is squeezed out, so the surface of the part is ground to a diameter that is approximately 0.5 knurling pitch less than the nominal one.

The rollers are brought close to the rotating part and, using manual feed, are pressed into the surface to be processed to a certain depth. Turning off the rotation of the part, check the accuracy of the resulting pattern. Then the spindle rotation and longitudinal feed are turned on and rolling is performed to the required length in several passes in both directions until the full height of the corrugations is obtained. At the end of each pass, without breaking contact with the workpiece, the knurling is applied transversely to

required depth. Knurling rollers should be periodically cleaned with a wire brush to remove metal particles stuck in the recesses.

The longitudinal feed is taken to be approximately equal to twice the corrugation pitch (1-2.5 mm/rev), the rotation speed of the part is within 15-20 m/min.

The surface to be treated is lubricated with oil.

The IT-1M.64 grinding device is intended for external and internal grinding of parts installed in centers or chucks.

The grinding device is a special tool for screw-cutting lathes IT-1M, IT-1GM.

Specifications

Design and operation of the product

The base of the device is plate 1, in which the spindle is fixed. A grinding stone, covered with a casing, and a belt drive pulley are attached to the spindle. The electric motor is mounted on a movable bracket 4, which allows you to change the belt tension. The belt drive is covered by guard 3.

Drawing - grinding device for lathe IT 1M

Operating procedure

To operate, the grinding device must be installed on the upper carriage of the caliper instead of the tool holder and secured with nut 1 (Fig. 5).

Figure - Setting up the grinding device for external grinding

When internal grinding (Fig. 6), it is necessary to replace pulley 2 on the electric motor shaft, replace belt 3 to obtain the required grinding speed, and install extension 1 with a circle with a diameter of 25 mm.

Figure - Setting up the grinding device for internal grinding

Lathes perform grinding, knurling and other finishing work.

Grind when the dimensions and shape of the part are not made with high accuracy, and increased demands are placed on the cleanliness of the treated surface.

The part is placed on the machine in the same way as when turning, brought into rapid rotation and cleanly processed flat. The handle of the file is held in the left hand, and the toe is held with the right. Place the file across the axis of the part.

When filing, lightly press and slowly move the file away from you. During the reverse movement, the contact of the file with the workpiece is maintained, but the pressing force is reduced.

Sand with sandpaper. Small-diameter parts are processed using a device consisting of two wooden blocks, which are connected by a hinge and have concave surfaces corresponding to the cylindrical surface of the workpiece. The sanding paper is inserted into the device, pressed against the part and moved along it.

Rough processing is carried out with coarse-grained sandpaper, and finishing with fine-grained sandpaper.

To improve cleanliness, the surface to be treated is lubricated with machine oil.

Questions

1. When grinding parts lathe?
2. How do you grind parts on a lathe?

Rolling on a lathe

For ease of use, cylindrical handles of various measuring instruments, caliber handles, micrometric screw heads and round nuts are made not smooth, but grooved. This corrugated surface is called knurling, and the process of obtaining it is called rolling.

Knurling can be straight or cross. For rolling, a holder is attached to the tool holder, in which one is installed for simple rolling, and for cross rolling, two rollers made of tool hardened steel with teeth cut on them.

These teeth have different sizes and different directions, which allows you to produce different knurling patterns.

When rolling, the holder with rollers is pressed against the rotating part with a cross-feed screw. The rollers begin to rotate and, pressing into the material of the part, form a knurling on its surface. It can be large, medium or small, depending on the size of the teeth on the rollers. When rolling, feed is carried out in two directions - perpendicular to the axis of the part and along it. To obtain a sufficient depth of knurling, you need to knurl in 2 - 4 passes.

Rolling rules

1. When you start rolling, you should immediately press hard and check whether the teeth of the rollers fall into the notches they made during subsequent revolutions.
2. The rollers must match the required pattern of the part.
3. The two rollers must be exactly positioned one below the other.
4. Before work, you need to thoroughly clean the rollers with a steel brush to remove any remaining material.
5. During rolling, the working surfaces of the rollers should be well lubricated with spindle or machine oil.

The correctness of the knurling is checked by eye.

Questions

1. What parts are knurled on and why?
2. What elements does knurling consist of?
3. What kind of knurling is there?
4. Tell us about the knurling rules.

“Plumbing”, I.G. Spiridonov,
G.P. Bufetov, V.G. Kopelevich

Boring holes (internal cylindrical surfaces) is more difficult than turning external surfaces. The main difficulty is the low rigidity of the boring cutter. Through holes are bored using boring cutters shown in the figure. See figure - Boring cutter for a through hole. To do this, the workpiece being processed is secured in the chuck of a lathe. Check the reliability of fastening the workpiece and the cutter. They first bore with a roughing cutter, which, using...

Depending on the required measurement accuracy and hole diameter sizes, different measuring tool. Inaccurate cylindrical holes can be measured with a bore gauge and a measuring ruler. To determine the size, you need to measure the spread of the legs of the bore gauge with a ruler or caliper. Measuring a hole with a bore gauge When boring a hole for a machined shaft, first measure the diameter of the shaft with a caliper and then install the legs along them...

Holes are bored on lathes when drilling and reaming do not provide the required accuracy of hole sizes and cleanliness of the machined surface. Boring cutter for through holes During roughing and finishing machining, holes are bored using boring cutters. Depending on the type of holes being bored, boring cutters are distinguished for through holes(see picture above) and for blind holes (see picture...

To main

section five

Basic operations and work,
performed on a lathe

Chapter XI

Turning external cylindrical surfaces

Lathes can be used to process parts whose surfaces have the shape of bodies of rotation. Most parts used in mechanical engineering have cylindrical surfaces, such as rollers, bushings, etc.

1. Cutters for longitudinal turning

For longitudinal grinding, through cutters are used. Passing cutters are divided into rough And finishing.

Rough cutters (Fig. 99) are intended for rough grinding - stripping, carried out in order to quickly remove excess metal; they are often called peeling. Such cutters are usually made with a welded or soldered, or mechanically attached plate and are equipped with a long cutting edge. The tip of the cutter is rounded along a radius of r = 1-2 mm. In Fig. 99, and the cutter of the roughing straight line is shown, and in Fig. 99, b - bent. The bent shape of the cutter is very convenient for turning the surfaces of parts located near the chuck jaws and for trimming the ends. After turning with a rough cutter, the surface of the part has large marks; As a result, the quality of the processed surface is low.

Finishing cutters are used for final turning of parts, i.e., to obtain exact dimensions and a clean, smooth processing surface. Exist different kinds finishing cutters.

In Fig. 100, and shows the finishing cutter, which differs from the rough cutter mainly in its large radius of curvature, equal to 2-5 mm. This type of cutter is used for finishing work, which is carried out with a small depth of cut and low feed. In Fig. 100, b shows a finishing cutter with a wide cutting edge parallel to the axis of the workpiece. This cutter allows you to remove finishing chips at high feed rates and gives a clean and smoothly machined surface. In Fig. 100, c shows V. Kolesov’s cutter, which allows you to obtain a clean and smoothly machined surface when working with high feed (1.5-3 mm/rev) with a cutting depth of 1-2 mm (see Fig. 62).

2. Installation and fastening of the cutter

Before turning, you need to correctly install the cutter in the tool holder, making sure that the part of the cutter protruding from it is as short as possible - no more than 1.5 times the height of its shaft.

With a larger overhang, the cutter will tremble during operation, as a result the processed surface will be unsmooth, wavy, with traces of crushing.

In Fig. 101 shows the correct and incorrect installation of the cutter in the tool holder.

In most cases, it is recommended to set the tip of the cutter at the height of the machine centers. To do this, use pads (no more than two), placing them under the entire supporting surface of the cutter. Lining is a flat steel ruler 150-200 mm long, having strictly parallel upper and lower surfaces. The turner must have a set of such shims of different thicknesses in order to obtain the height necessary for installing the cutter. You should not use random plates for this purpose.

The shims must be placed under the cutter as shown in Fig. 102 on top.

To check the height position of the cutter tip, bring its tip to one of the pre-calibrated centers, as shown in Fig. 103. For the same purpose, you can use a mark placed on the tailstock quill, at the height of the center.

Fastening the cutter in the tool holder must be reliable and durable: the cutter must be secured with at least two bolts. The bolts securing the cutter must be tightened evenly and tightly.

3. Installation and fastening of parts in centers

A common way of processing parts on lathes is processing in centers(Fig. 104). With this method, center holes are pre-drilled at the ends of the workpiece - center detail. When installed on a machine, these holes fit into the center points of the machine's headstock and tailstock. To transmit rotation from the headstock spindle to the workpiece, it is used driving chuck 1 (Fig. 104), screwed onto the machine spindle, and clamp 2, secured with screw 3 on the workpiece.

The free end of the clamp is captured by the groove (Fig. 104) or finger (Fig. 105) of the cartridge and causes the part to rotate. In the first case, the clamp is made bent (Fig. 104), in the second - straight (Fig. 105). The pin driver cartridge shown in Fig. 105, poses a danger to the worker; A driver chuck with a safety casing is safer (Fig. 106).

The essential accessories of a lathe are centers. Typically the center shown in Fig. 107, a.

It consists of a cone 1, on which the part is mounted, and a conical shank 2. The shank must fit exactly into the conical hole of the headstock spindle and the tailstock quill of the machine.

The head center rotates with the spindle and the workpiece, while the tailstock center is mostly stationary and rubs against the rotating workpiece. Friction heats up and wears out both the conical surface of the center and the surface of the center hole of the part. To reduce friction, the rear center must be lubricated.

When turning parts at high speeds, as well as when processing heavy parts, working on a fixed center of the tailstock is impossible due to the rapid wear of the center itself and the development of the center hole.

In these cases, use rotating centers. In Fig. 108 shows one design of a rotating center inserted into the tapered hole of the tailstock quill. Center 1 rotates in ball bearings 2 and 4. Axial pressure is perceived by thrust ball bearing 5. The tapered shank 3 of the center body corresponds to the conical hole of the quill.

To reduce the time required to secure parts, clamps with manual clamping are often used instead of clamps. grooved front centers(Fig. 109), which not only center the part, but also act as a leash. When pressed by the rear center, the corrugations cut into the workpiece and thereby transmit rotation to it. For hollow parts, external (Fig. 110, a) are used, and for rollers, internal (reverse) corrugated centers are used (Fig. 110, b).

This fastening method allows you to grind the part along its entire length in one installation. Turning the same parts with a conventional center and collar can be done in only two settings, which significantly increases the processing time.

Used for light and medium turning work self-clamping clamps. One of these clamps is shown in Fig. 111. In the body 1 of such a clamp, a cam 4 is installed on the axis, the end of which has a corrugated surface 2. After installing the clamp on the part, the corrugated surface of the cam is pressed against the part under the action of the spring 3. After installation in the centers and starting the machine, finger 5 of the driving chuck, pressing on cam 4, jams the part and causes it to rotate. Such self-clamping clamps significantly reduce auxiliary time.

4. Setting up the machine for processing in centers

To obtain a cylindrical surface when turning a workpiece at centers, it is necessary that the front and work centers be on the axis of rotation of the spindle, and the cutter moves parallel to this axis. To check the correct location of the centers, you need to move the rear center towards the front (Fig. 112). If the centers do not align, the position of the tailstock housing on the plate must be adjusted as indicated on page 127.

Misalignment can also be caused by dirt or chips getting into the tapered holes of the spindle or pin. To avoid this, it is necessary to thoroughly wipe the spindle and quill holes, as well as the conical part of the centers, before installing the centers. If the center of the headstock still "beats" as they say, then it is faulty and must be replaced with another one.

During turning, the part heats up and elongates, creating increased pressure on the centers. To protect the part from possible bending and the rear center from jamming, it is recommended to release the rear center from time to time and then tighten it again until normal condition. It is also necessary to periodically additionally lubricate the rear center hole of the part.

5. Installation and fastening of parts in cartridges

Short parts are usually installed and secured in chucks, which are divided into simple and self-centering.

Simple chucks are usually made with four jaws (Fig. 113). In such chucks, each cam 1, 2, 3 and 4 is moved by its own screw 5 independently of the others. This allows you to install and secure various parts of both cylindrical and non-cylindrical shapes in them. When installing a part in a four-jaw chuck, it must be carefully aligned so that it does not hit when rotating.

The alignment of the part during its installation can be done using a thickness gauge. The surface scriber is brought to the surface being tested, leaving a gap of 0.3-0.5 mm between them; turning the spindle, watch how this gap changes. Based on the observation results, some cams are pressed out and others are pressed in until the gap becomes uniform around the entire circumference of the part. After this, the part is finally fixed.

Self-centering chucks(Fig. 114 and 115) in most cases three-jaw ones are used, much less often two-jaw ones are used. These chucks are very convenient to use, since all the cams in them move simultaneously, due to which a part having a cylindrical surface (external or internal) is installed and clamped exactly along the axis of the spindle; In addition, the time required to install and secure the part is significantly reduced.

In it, the cams are moved using a key, which is inserted into the tetrahedral hole 1 of one of the three bevel gears 2 (Fig. 115, c). These wheels are coupled to a large conical wheel 3 (Fig. 115, b). On the reverse flat side of this wheel, a multi-turn spiral groove 4 is cut (Fig. 115, b). All three cams 5 enter into the individual turns of this groove with their lower projections. When one of the gears 2 is turned with a key, the rotation is transmitted to the wheel 3, which, rotating, through the spiral groove 4 moves all three cams simultaneously and evenly along the grooves of the cartridge body. As the spiral-groove disk rotates in one direction or the other, the cams move closer or further from the center, respectively clamping or releasing the part.

It is necessary to ensure that the part is firmly secured in the chuck jaws. If the cartridge is in good condition, then a strong clamping of the part is ensured by using a key with a short handle (Fig. 116). Other clamping methods, such as clamping with a key and a long tube placed over the handle, should under no circumstances be permitted.

Chuck jaws. The cams used are hardened and raw. Usually hardened cams are used due to their low wear. But when clamping parts with cleanly machined surfaces with such jaws, traces remain on the parts in the form of dents from the jaws. To avoid this, it is also recommended to use raw (unhardened) jaws.

Raw jaws are also convenient because they can be periodically bored with a cutter and eliminate the chuck runout that inevitably appears during long-term operation.

Installing and securing parts in the chuck with support from the rear center. This method is used when processing long and relatively thin parts (Fig. 116), which are not sufficiently secured only in the chuck, since the force from the cutter and the weight of the protruding part can bend the part and tear it out of the chuck.

Collet chucks. To quickly secure short parts, do not large diameter applied to the external treated surface collet chucks. Such a cartridge is shown in Fig. 117. With a conical shank, 1 chuck is installed in the conical hole of the headstock spindle. A split spring sleeve 2 with a cone, called a collet, is installed in the recess of the cartridge. The workpiece is inserted into hole 4 of the collet. Then screw nut 3 onto the cartridge body using a wrench. When screwing the nut, the spring collet compresses and secures the part.

Pneumatic chucks. In Fig. 118 shows a diagram of a pneumatic chuck, which provides quick and reliable fastening of parts.

At the left end of the spindle there is an air cylinder, inside of which there is a piston. Compressed air through the tubes it enters the central channels 1 and 2, from where it is directed to the right or left cavity of the cylinder. If air enters through channel 1 into the left cavity of the cylinder, then the piston displaces air from the right cavity of the cylinder through channel 2 and vice versa. The piston is connected to a rod 3 connected to a rod 4 and a slider 5, which acts on the long arms 6 of the crank arms, the short arms 7 of which move the clamping jaws 8 of the cartridge.

The stroke length of the cams is 3-5 mm. Air pressure is usually 4-5 am. To activate the pneumatic cylinder, a distribution valve 9 is installed on the gearbox housing, turned by handle 10.

6. Screwing and screwing of jaw chucks

Before screwing the chuck onto the spindle, thoroughly wipe the threads at the end of the spindle and in the chuck hole with a rag and then lubricate them with oil. A light cartridge is brought with both hands directly to the end of the spindle and screwed in until it stops (Fig. 119). It is recommended to place a heavy cartridge on the board (Fig. 120), bringing its hole to the end of the spindle, screw the cartridge until it stops, manually, as in the first case. When screwing on the chuck, you need to ensure that the axes of the chuck and the spindle strictly coincide.

To prevent cases of self-unscrewing of chucks in high-speed cutting machines, additional fastening of the chuck to the spindle is used using various devices

(screwing on an additional nut, securing the cartridge with shaped crackers, etc.).

The cartridge is screwed together in the following way. Insert the key into the chuck and pull towards yourself with both hands (Fig. 121).

Other methods of make-up involving sharp blows to the chuck or jaws are unacceptable: the chuck is damaged and the jaws in its body become loose.

It is better to screw and unscrew a heavy cartridge with the help of an auxiliary worker.

7. Techniques for turning smooth cylindrical surfaces

Turning of cylindrical surfaces is usually carried out in two steps: first, most of the allowance is roughed out (3-5 mm per diameter), and then the remaining part (1-2 mm per diameter).

To obtain the specified diameter of the part, it is necessary to set the cutter to the required cutting depth. To set the cutter to the cutting depth, you can use the test chip method or use the cross feed dial.

To set the cutter to the cutting depth (by size) using the test chip method, you must:
1. Inform the details of the rotational movement.
2. By rotating the longitudinal feed handwheel and the cross-feed screw handle, manually move the cutter to the right end of the part so that its tip touches the surface of the part.
3. Having established the moment of contact, manually move the cutter to the right from the part and rotate the handle of the cross-feed screw to move the cutter to desired depth cutting After this, the part is turned with manual feed to a length of 3-5 mm, the machine is stopped and the diameter of the turned surface is measured with a caliper (Fig. 122). If the diameter turns out to be larger than required, the cutter is moved to the right and set to a slightly greater depth, the belt is machined again and the measurement is taken again. All this is repeated until the specified size is obtained. Then turn on the mechanical feed and grind the part along the entire specified length. When finished, turn off the mechanical feed, move the cutter back and stop the machine.

Finish grinding is performed in the same order.

Using the cross feed screw dial. To speed up the installation of the cutter to the depth of cut, most lathes have special device. It is located at the handle of the cross-feed screw and is a bushing or ring with divisions marked on its circumference (Fig. 123). This sleeve with divisions is called a limb. The divisions are counted according to the mark on the fixed screw hub (in Fig. 123 this mark coincides with the 30th stroke of the dial).

The number of divisions on the dial and the pitch of the screw can be different, therefore, the amount of transverse movement of the cutter when turning the dial by one division will also be different. Let's assume that the dial is divided into 100 equal parts and the cross feed screw has a thread with a pitch of 5 mm. With one full revolution of the screw handle, i.e., per 100 divisions of the dial, the cutter will move in the transverse direction by 5 mm. If you turn the handle by one division, then the movement of the cutter will be 5:100 = 0.05 mm.

It should be borne in mind that when the cutter moves in the transverse direction, the radius of the part after the passage of the cutter will decrease by the same amount, and the diameter of the part will decrease by doubled. Thus, in order to reduce the diameter of a part, for example from 50.2 to 48.4 mm, i.e. by 50.2 - 48.4 = 1.8 mm, it is necessary to move the cutter forward by half the amount, i.e. .by 0.9 mm.

When setting the cutter to the cutting depth using the cross-feed screw dial, it is necessary, however, to take into account the gap between the screw and the nut, which forms the so-called “backlash”. If you lose sight of this, the diameter of the processed part will differ from the specified one.

Therefore, when setting the cutter to the cutting depth using a dial, it is necessary to observe next rule. Always approach the required setting along the dial by slowly turning the screw handle to the right (Fig. 124, a; the required setting is the 30th division of the dial).

If you turn the handle of the cross-feed screw by an amount greater than the required value (Fig. 124, b), then to correct the error, in no case should you push the handle back by the amount of the error, but you need to make almost a full turn in reverse side, and then rotate the handle again to the right until the required division along the dial (Fig. 124, c). The same is done when it is necessary to move the incisor back; By rotating the handle to the left, the cutter is retracted more than necessary, and then by right rotation it is brought to the required division of the limb.

The movement of the cutter corresponding to one division of the dial is different on different machines. Therefore, when starting work, it is necessary to determine the amount of movement that corresponds to one division of the dial on a given machine.

Using dials, our high-speed turners achieve the specified size without testing chips.

8. Processing parts in steady rests

Long and thin parts, the length of which is 10-12 times greater than their diameter, bend during turning both from their own weight and from the cutting force. As a result, the part gets an irregular shape - it is thicker in the middle and thinner at the ends. This can be avoided by using a special support device called lunette. When using steady rests, you can grind parts with high precision and remove chips of a larger cross-section without fear of part deflection. The lunettes are motionless and movable.

Fixed rest(Fig. 125) has a cast iron body 1, to which a hinged cover 6 is attached using a hinged bolt 7, which makes installation of the part easier. The body of the steady rest is processed at the bottom according to the shape of the frame guides, on which it is secured by means of a bar 9 and a bolt 8. Two cams 4 are moved in the holes of the body using adjusting bolts 3, and one cam 5 is moved on the roof. Screws 2 are used to secure the cams in the required position This device allows the installation of shafts of various diameters into the steady rest.

Before installing the unturned workpiece into a stationary rest, you need to machine a groove in the middle for the cams, a width slightly larger than the width of the cam (Fig. 126). If the workpiece has a large length and a small diameter, then its deflection is inevitable. To avoid this, machine an additional groove closer to the end of the workpiece and, having installed a steady rest in it, machine the main groove in the middle.

Fixed steady rests are also used for cutting ends and trimming the ends of long parts. In Fig. 127 shows the use of a stationary rest when cutting the end: the part is fixed at one end in a three-jaw chuck, and the other is installed in the rest.

In the same way, you can machine a precise hole from the end of a long part, for example, bore a conical hole in the spindle of a lathe or drill such a part along its entire length.

Movable steady rest(Fig. 128) are used for finishing turning of long parts. The steady rest is secured to the support carriage so that it moves along with it along the part being turned, following the cutter. Thus, it supports the part directly at the point where the force is applied and protects the part from deflection.

The movable steady rest has only two cams. They are pulled out and secured in the same way as the cams of a fixed rest.

Steady rests with conventional cams are not suitable for high-speed machining due to rapid wear of the cams. In such cases, use Steady rests with roller or ball bearings(Fig. 129) instead of conventional cams, which makes the work of the rollers easier and reduces the heating of the workpiece.

9. Techniques for turning cylindrical surfaces with ledges

When processing on lathes a batch of step-shaped parts (stepped rollers) with the same length for all parts of individual steps, innovators use a longitudinal stop that limits the movement of the cutter and a longitudinal feed dial in order to reduce the time for measuring length.

Using the rip fence. In Fig. 130 shows a longitudinal stop. It is bolted to the front frame guide, as shown in Fig. 131; The place where the stop is secured depends on the length of the part to be turned.

If there is a longitudinal stop on the machine, it is possible to process cylindrical surfaces with ledges without preliminary marking, while, for example, stepped rollers are turned in one installation much faster than without a stop. This is achieved by placing a length limiter (measuring tile) between the stop and the support, corresponding to the length of the roller step.

An example of turning a stepped roller using stop 1 and measuring tiles 2 and 3 is shown in Fig. 131. Turning of step a 1 is carried out until the caliper rests against measuring tile 3. Having removed this tile, you can grind the next step of the roller, length a 2, until the caliper rests against tile 2. Finally, having removed tile 2, step a 3 is turned . As soon as the caliper reaches the stop, you need to turn off the mechanical feed. The length of the measuring tile 2 is equal to the length of the ledge a 3, and the length of the tile 3 is equal to the length of the ledge a 2.

Hard stops can only be used on machines that have automatic feed shutdown when overloaded (for example, 1A62 and other new machine systems). If the machine does not have such a device, then turning against the stop can only be done if the mechanical feed is turned off in advance and the support is brought to the stop manually, otherwise machine breakdown is inevitable.

Using the longitudinal feed dial Using the longitudinal feed dial. To reduce the time spent on measuring the lengths of workpieces, modern lathes are equipped with longitudinal feed dial. This dial represents a large-diameter rotating disk (Fig. 132), located on the front wall of the apron and behind the longitudinal feed handwheel. Equal divisions are marked on the circumference of the disk. When the handwheel rotates, the dial, connected by a gear transmission to the longitudinal feed wheel, also rotates. Thus, a certain longitudinal movement of the support with the cutter corresponds to a rotation of the dial by a certain number of divisions relative to the stationary mark.

When processing stepped parts, the use of a longitudinal feed dial is very rational. In this case, the turner, before processing the first part from the batch, first marks the length of the steps with a cutter using a caliper, and then begins to grind them. Having turned the first stage, he sets the longitudinal limb to the zero position relative to the stationary mark. While grinding the next steps, he remembers (or writes down) the corresponding dial readings regarding the same mark. When turning subsequent parts, the turner uses the readings established when turning the first part.

Using the Cross Stop. To reduce the time spent measuring diameters when machining stepped parts, a cross stop can be used on a number of lathes.

One of these stops is shown in Fig. 133. The stop consists of two parts. The fixed part 1 is installed on the carriage and secured with bolts 2; the thrust pin 6 is motionless. The movable stop 3 is installed and secured with bolts 4 on the lower part of the caliper. Screw 5 is set exactly to the required part size. The end of screw 5, resting against pin 6, determines the required size of the part. By placing 5-dimensional tiles between pin 6 and screw, you can grind parts with steps of different diameters.

10. Cutting modes when turning

Selecting cutting depth. The depth of cut when turning is selected depending on the processing allowance and the type of processing - roughing or finishing (see pages 101-102).

Feed rate selection. The feed is also selected depending on the type of processing. Typically, the feed rate for rough turning is from 0.3 to 1.5 mm/rev, and for semi-finishing and finishing from 0.1 to 0.3 mm/rev when working with normal cutters and 1.5-3 mm/rev when working with cutters designs by V. Kolesov.

Cutting speed selection. The cutting speed is usually selected according to specially developed tables depending on the durability of the cutter, the quality of the material being processed, the material of the cutter, depth of cut, feed, type of cooling, etc. (see, for example, Table 6, p. 106).

11. Defects when turning cylindrical surfaces and measures to prevent it

When turning cylindrical surfaces, the following types of defects are possible:
1) part of the surface of the part remained unprocessed;
2) the dimensions of the turned surface are incorrect;
3) the turned surface turned out to be conical;
4) the turned surface turned out to be oval;
5) the cleanliness of the treated surface does not correspond to the instructions in the drawing;
6) combustion of the rear center;
7) mismatch of surfaces when processing the roller in the centers on both sides.

1. Defects of the first type are caused by insufficient dimensions of the workpiece (insufficient allowance for processing), poor straightening (curvature) of the workpiece, incorrect installation and inaccurate alignment of the part, inaccurate location of the center holes and displacement of the rear center.
2. Incorrect dimensions of the turned surface are possible due to inaccurate setting of the cutter to the cutting depth or incorrect measurement of the part when removing test chips. The causes of this type of defect can and should be eliminated by increasing the turner’s attention to the work being performed.
3. The taper of the turned surface is usually obtained as a result of a displacement of the rear center relative to the front. To eliminate the cause of this type of defect, it is necessary to correctly install the rear center. A common cause of rear center misalignment is dirt or small chips getting into the tapered hole of the quill. By cleaning the center and conical hole of the quill, this cause of defects can also be eliminated. If, even after cleaning, the points of the front and rear centers do not coincide, you need to move the tailstock body on its plate accordingly.
4. The ovality of the turned part is obtained when the spindle runs out due to uneven wear of its bearings or uneven wear of its journals.
5. Insufficient surface cleanliness during turning can be due to a number of reasons: high cutter feed, use of a cutter with incorrect angles, poor sharpening of the cutter, small radius of curvature of the cutter tip, high viscosity of the part material, vibration of the cutter due to a large overhang, insufficiently strong cutter attachment in the tool holder, increased gaps between in separate parts caliper, vibration of the part due to its weak fastening or due to wear of the bearings and spindle journals.

All listed reasons defects can be eliminated in a timely manner.

6. Burning out of the hard center of the tailstock may be caused by for the following reasons: the part is fixed too tightly between the centers; poor lubrication of the center hole; incorrect alignment of the workpiece; high cutting speed.
7. The discrepancy between the processing surfaces when turning on both sides in the centers is obtained mainly as a result of runout of the front center or the development of center holes in the workpiece. To prevent defects, it is necessary to check the condition of the center holes of the workpiece during finishing processing, and also ensure that there is no runout in the center of the headstock.

12. Safety precautions when turning cylindrical surfaces

In all cases of machining on lathes, it is necessary to pay attention to the strong fastening of the part and the cutter.

The reliability of fastening the part processed in centers largely depends on the condition of the centers. You cannot work with worn centers, since the part under the influence of the cutting force can be torn from the centers, fly to the side and injure the turner.

When processing parts in centers and chucks, the protruding parts of the clamp and chuck jaws often catch the worker’s clothing. These same parts can cause injury to your hands when measuring a part and cleaning the machine while moving. To prevent accidents, safety guards should be installed at the clamps or safety clamps should be used, and the jaw chucks should be protected. The perfect type of safety clamp is shown in Fig. 134. Rim 3 covers not only the head of the bolt 2, but also the pin 1 of the driving chuck.

To protect the turner’s hands and clothing from protruding parts of the chuck or faceplate, a special guard is used on modern lathes (Fig. 135). The casing 1 of the device is hingedly connected to a pin 2 fixed to the headstock body.

When installing parts in centers, you need to pay attention to the correctness of the center holes. If their depth is insufficient, the part may fall off the centers during rotation, which is very dangerous. In the same way, after securing the part in the chuck, you need to check whether the key is removed. If the key remains in the chuck, then when the spindle rotates it will hit the frame and fly off to the side. In this case, the machine may break down and the worker may be injured.

The cause of accidents is often chips, especially drain chips, which when high speeds cutting comes off as a continuous strip. Such shavings should never be removed or torn off by hand; they can cause severe cuts and burns. Chip breakers should be used whenever possible. In extreme cases, when chip breaking is not achieved, it should be removed with a special hook.

When processing materials that produce short rebound chips, it is necessary to use safety glasses or use safety shields made of safety glass or celluloid (Fig. 136), attached to a hinged stand to the carriage. You need to sweep away small shavings resulting from processing brittle metals (cast iron, hard bronze) not with your hands, but with a brush.

Hand injuries may occur when installing and securing cutters as a result of the key being torn off the heads of the tool holder mounting bolts. The key breaks when the key jaws and bolt heads are worn out. Often, however, failure occurs because the turner uses a wrench whose size does not correspond to the size of the bolt.

Setting the cutter to the height of the centers using all sorts of unsuitable supports (metal scraps, pieces of hacksaws, etc.) does not ensure a stable position of the cutter during operation. Under the pressure of the chips, such pads are displaced, and the installation of the cutter becomes unstable. At the same time, the fastening of the cutter also weakens. As a result, the shims and the cutter can jump out of the tool holder and injure the lathe operator. In addition, when installing the cutter and when working on the machine, your hands may be injured by the sharp edges of the metal pads. Therefore, it is recommended that every turner have a set of backing blocks, varying in thickness, with well-finished supporting planes and edges.

Control questions 1. How to properly install the cutter in the tool holder?
2. How to check the position of the cutter tip relative to the center line?
3. How are parts installed and secured when turning cylindrical surfaces?
4. What is the difference between the operating conditions of the anterior and posterior centers?
5. How is the rotating center constructed and in what cases is it used?
6. How does the fluted front center work and what are its advantages?
7. How to check the correct installation of centers for turning a cylindrical surface?
8. How does a self-centering chuck work? Name its details, rules for installing and preparing it for work.
9. How to align a part when installing it in a four-jaw chuck?
10. What is the purpose of the cross feed screw dial?
11. What is the longitudinal feed dial used for? How is it built?
12. What are steady rests used for and in what cases are they used?
13. How does a fixed steady rest work?
14. How is the movable steady rest constructed?
15. How is the shaft blank prepared for installation in the steady rest?
16. Give an example of using a longitudinal stop; cross stop.
17. What types of defects are possible when turning cylindrical surfaces? How to eliminate the causes of marriage?
18. List the basic safety rules when turning cylindrical surfaces.