The normal turning process is determined to a large extent by the correct installation of the cutter in the tool holder. Before installing the cutter, it is necessary to wipe the supporting surfaces of the holder. The cutter is installed with a minimum overhang, usually no more than 1.5 of its core thickness (to avoid vibrations), perpendicular to the center line and exactly at their height. To check the correct installation of the cutter in height, it is necessary to insert the center into the tailstock quill and bring the top of the cutter to the top of the center. If the tip of the cutter is below the top of the center, you need to put dimensional pads under the support surface of the cutter (no more than three). The cutter must be firmly secured with at least two bolts when turning the socket wrench with two hands.

Setting the cutter at an angle to the axis other than 90°, or bringing another cutter fixed in the tool holder to the working position, is done by turning the tool holder counterclockwise to the desired angle. You must first unscrew the clamping handle. Sometimes, instead of a standard tool post, designed to hold four cutters with rectangular holders, special tool posts are used.

The universal tool holder is mounted on the support of the lathe and serves to secure round cutters. The housing has four through holes located at an angle of 90° to each other. Split bushings with eccentrically located holes are inserted into the holes. This allows you to quickly set the cutting edge of the cutters in height without spacers. The tool holder is equipped with rigid and spring holders for boring deep holes, cutting internal threads, etc.

A special tool holder can be recommended for small repair shops that perform a variety of jobs. It consists of a body, two holders and interchangeable mandrels. The body with its central hole is put on the caliper bolt and fastened with a handle.

The movement of the holders vertically is carried out by turning the screws provided with a rectangular thread.

Fixing of holders on height is made by locking screws. Each holder can hold two cutters at the same time. The middle screw presses both cutters through the clamping bar. To install drills, reamers and other tools, there are mandrels installed in the grooves of the body.

Setting the cutter to the required depth of cut can be carried out using the test chips method, according to finished product or using a cross feed dial. In the first case, the cutter is brought to the rotating part until it touches its surface, then it is retracted to the right and the depth of cut is set by eye. The part is manually machined to a length of 5-7 mm, stops and the diameter of the groove is measured. If the diameter turned out to be greater than the required one, the process is repeated with a new depth of cut until a required size. After that, automatic feed is turned on, and the part is machined along the entire length.

In the manufacture of several identical products, the cutter is set to a depth only for the first part. After turning the first part, it is removed without violating the installation of the cutter, the caliper is retracted to the right position, a new part is installed and it is processed without additional adjustment. The check is made only to compensate for the wear of the cutter.

To speed up the installation of the cutter to the depth of cut, lathes are equipped with a special device. It is a graduated ring that fits over the front of the caliper cross feed screw. This ring is called a limb, it rotates with the screw. The countdown of the rotation of the screw is carried out relative to the risks on a fixed sleeve, sitting on the same axis with the limb. Usually on the machine there is an indication of the price of the division of the limb, i.e., the amount of movement of the cutter when the screw is turned. per division of the limb. To adjust the cutter to the required depth of cut, you first need to measure the diameter of the workpiece with a caliper and find the thickness of the metal layer to be removed. After that, move the cutter until its tip touches the rotating workpiece and, turning the dial, align its zero division with the risk on the fixed bushing. Pull the caliper back and to the right and, turning the screw by the counted number of divisions, set the required depth of cut. The rotation of the screw when setting the size should be done in only one direction (clockwise) to eliminate the influence of the gaps between the screw and the nut.

Setting example. The diameter of the workpiece is 52 mm, the diameter of the product after turning should be 50 mm. The price of division of a limb is 0.05 mm. Calculate how many divisions you need to turn the cross feed screw.

When the screw is turned one division, the cutter moves forward by 0.05 mm, i.e., the radius of the part decreases by 0.05 mm, and the diameter by 0.1 mm. We need to reduce the diameter by 2 mm or move the cutter forward by 1 mm. To do this, turn the screw 20 divisions of the dial.

To main

section five

Basic operations and work,
performed on lathe

Chapter XI

Turning external cylindrical surfaces

On lathes, it is possible to process parts whose surfaces have the form of bodies of revolution. Most of the parts used in mechanical engineering have cylindrical surfaces, such as rollers, bushings, etc.

1. Cutters for longitudinal turning

For longitudinal turning, through cutters are used. Passing cutters are divided into draft and finishing.

Rough cutters (Fig. 99) are designed for rough turning - peeling, carried out in order to quickly remove excess metal; they are often called rough. Such cutters are usually made with a welded or soldered or mechanically attached blade and are provided with a long cutting edge. The top of the cutter is rounded along the radius r = 1-2 mm. On fig. 99, but shows the cutter of the rough straight line, and in fig. 99, b - bent. The bent shape of the cutter is very convenient when turning the surfaces of parts located near the jaws of the cartridge, and for trimming the ends. After turning with a rough cutter, the surface of the part has large risks; the quality of the machined surface is therefore low.

Finishing cutters are used for the final turning of parts, i.e., to obtain accurate dimensions and a clean, even surface of processing. There are various types of finishing cutters.

On fig. 100, a shows a finishing cutter, which differs from the draft one mainly in a 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. On fig. 100b shows a finishing cutter with a wide cutting edge parallel to the axis of the workpiece. This cutter allows for fine chip removal at high feed rates and produces a clean and smooth surface finish. On fig. 100, c shows the cutter of V. Kolesov, which allows you to get a clean and smoothly machined surface when working with a large feed (1.5-3 mm / rev) with a cutting depth of 1-2 mm (see Fig. 62).

2. Installing and fixing the cutter

Before turning, it is necessary 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 of the height of its core.

With a longer overhang, the cutter will tremble during operation, as a result, the machined surface will turn out to be uneven, wavy, with traces of crushing.

On fig. 101 is shown correct and not correct installation cutter in the cutter holder.

In most cases, it is recommended to set the tool tip at the height of the machine centers. For this, linings are used (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 linings of different thicknesses in order to obtain the height necessary for installing the cutter. Random plates should not be used for this purpose.

Linings should be placed under the cutter as shown in Fig. 102 on top.

To check the position of the top of the incisor in height, bring the top of it to one of the pre-calibrated centers, as shown in Fig. 103. For the same purpose, you can use the risk drawn on the quill of the tailstock, at the height of the center.

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

3. Installing and fixing parts in centers

A common way to process 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 the machine, the points of the centers of the front and tailstocks of the machine enter these holes. To transfer rotation from the headstock spindle to the workpiece, driver chuck 1 (Fig. 104), screwed onto the machine spindle, and clamp 2, fixed with screw 3 on the workpiece.

The free end of the clamp is captured by the groove (Fig. 104) or the 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 chuck shown in fig. 105, poses a danger to the worker; safer is a driver chuck with a safety cover (Fig. 106).

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

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

The front center rotates with the spindle and workpiece, while the tailstock center is in most cases stationary and rubs against the rotating part. 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, it is necessary to lubricate the rear center.

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

In these cases, apply rotating centers. On fig. 108 shows one of the designs of the 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 tapered hole of the quill.

To reduce the time for fixing 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 (Fig. 110, b).

This method of fastening allows you to turn the part along the entire length in one installation. Turning the same parts with regular center and collar can be produced in only two installations, which greatly increases the processing time.

For light and medium turning work self-locking clamps. One of these collars is shown in Fig. 111. In the body 1 of such a collar, a cam 4 is installed on the axis, the end of which has a corrugated surface 2. After installing the collar 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, the pin 5 of the driving chuck, pressing the cam 4, jams the part and sets it into rotation. These self-locking clamps significantly reduce the non-productive time.

4. Setting up the machine for processing in centers

To obtain a cylindrical surface when turning the workpiece in the centers, it is necessary that the front and reference centers are 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 to the front (Fig. 112). If the center points do not align, the position of the tailstock housing on the platen must be adjusted as indicated on page 127.

Center misalignment can also be caused by dirt or chips getting into the taper holes of the spindle or pi-zeros. To avoid this, it is necessary to carefully wipe the spindle holes and quills, as well as the conical part of the centers, before installing the centers. If the center of the headstock after that, as they say, "beats", then it is faulty and must be replaced with another one.

When turning, the part heats up and elongates, while creating increased pressure on the centers. To prevent 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 to normal. It is also necessary to periodically additionally lubricate the rear center hole of the part.

5. Installing and securing parts in chucks

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

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

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

Self centering chucks(Fig. 114 and 115) in most cases, three-cams are used, much less often - two-cams. These cartridges are very convenient to use, since all the cams in them move at the same time, so that a part that has a cylindrical surface (outer or inner) is installed and clamped exactly along the axis of the spindle; in addition, the time for installation and fixing of 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 with 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 separate turns of this groove with their lower protrusions. When one of the gears 2 is turned with a key, the rotation is transferred to the wheel 3, which, rotating, moves through the grooves of the cartridge body simultaneously and evenly all three cams. When the disk with a spiral groove rotates in one direction or another, the cams approach or move away from the center, respectively clamping or releasing the part.

It is necessary to ensure that the part is firmly fixed in the jaws of the chuck. 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 methods of clamping, such as clamping with a key and a long pipe that goes over the handle, should in no case be allowed.

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

Raw cams are also convenient in that they can be periodically bored with a cutter and eliminate the beating of the cartridge, which inevitably appears during its long operation.

Inserting and clamping parts in a chuck with rear center support. This method is used when processing long and relatively thin parts (Fig. 116), which are not enough to be fixed 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 fasten short parts of small diameter to the outer machined surface, they are used collet chucks. Such a cartridge is shown in Fig. 117. Tapered shank 1 cartridge is installed in the tapered bore 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 the hole 4 of the collet. Then they screw nut 3 onto the chuck body with a wrench. When screwing the nut, the spring collet is compressed and secures the part.

Pneumatic chucks. On fig. 118 shows a diagram of a pneumatic chuck that provides fast and reliable fastening of parts.

An air cylinder is fixed at the left end of the spindle, inside of which there is a piston. Compressed air through the tubes 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 levers, 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 actuate the pneumatic cylinder, a distribution valve 9 is installed on the gearbox housing, which is turned by the handle 10.

6. Screwing in and out of jaw chucks

Before screwing the chuck onto the spindle, carefully wipe the threads at the end of the spindle and in the chuck bore 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 on to failure (Fig. 119). It is recommended to put a heavy cartridge on the board (Fig. 120), bringing its hole to the end of the spindle, screw the cartridge to failure, as in the first case, by hand. When screwing the chuck, make sure that the axes of the chuck and the spindle are exactly the same.

To prevent cases of self-unscrewing of cartridges in machines for high-speed cutting, additional fastening of the cartridge on the spindle using various devices is used.

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

The screwing of the cartridge is carried out as follows. Insert a key into the cartridge and with both hands make a jerk towards yourself (Fig. 121).

Other methods of make-up, associated with sharp blows to the chuck or jaws, are unacceptable: the chuck is damaged, the cams in its body are loosened.

Screwing on and screwing off a heavy cartridge is best done with the help of an auxiliary worker.

7. Techniques for turning smooth cylindrical surfaces

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

To obtain a given diameter of the part, it is necessary to set the cutter to the required depth of cut. To set the cutter to the depth of cut, you can use the test chips method or use the transverse feed dial.

To set the cutter to the depth of cut (per size) using the test chips method, you must:
1. Report details of rotational movement.
2. By turning the longitudinal feed handwheel and the cross feed screw handle, manually bring the cutter to the right end of the part so that its top touches the surface of the part.
3. Having set the touching moment, manually move the cutter to the right of the part and, by turning the cross feed screw handle, move the cutter to the desired cutting depth. After that, the part is turned with manual feed at 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 more than required, the cutter is retracted to the right and set to a slightly greater depth, the girdle is again machined and the measurement is taken again. All this is repeated until the desired size is obtained. Then turn on the mechanical feed and grind the part along the entire specified length. At the end, turn off the mechanical feed, take the cutter back and stop the machine.

Finishing is done 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 a special tool. It is located at the handle of the cross feed screw and is a sleeve or ring, on the circumference of which divisions are marked (Fig. 123). This sleeve with divisions is called a limb. The divisions are counted according to the risk on the fixed screw sleeve (in Fig. 123 this risk coincides with the 30th stroke of the limbus).

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 the dial is rotated by one division will also be different. Assume that the dial is divided into 100 equal parts and the cross feed screw is threaded in 5mm pitch. With one full turn of the screw handle, i.e., 100 divisions of the limb, 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 is moved in the transverse direction, the radius of the part after the cutter passes will decrease by the same amount, and the diameter of the part will double. Thus, in order to reduce the diameter of the 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, i.e. . by 0.9 mm.

When setting the cutter to the cutting depth with the help of the transverse feed screw dial, it is necessary, however, to take into account the gap between the screw and the nut, which forms the so-called "dead stroke". If you lose sight of this, then the diameter of the machined part will differ from the specified one.

Therefore, when setting the cutter to the depth of cut using a limb, the following rule must be observed. 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 in order to correct the error, in no case do not feed 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 to the required division along the limb (Fig. 124, c). They do the same when it is necessary to take the cutter back; turning 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 limbus.

The movement of the cutter, corresponding to one division of the limb, is different on different machines. Therefore, when starting work, it is necessary to determine the amount of movement corresponding to one division of the limb on this machine.

Using limbs, our high-speed turners achieve a given size without test chips.

8. Processing parts in steady rests

Long and thin parts, the length of which is 10-12 times 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 turns out to be thicker in the middle, and thinner at the ends. This can be avoided by using a special supporting device called lunette. When using steady rests, it is possible to grind parts with high precision and remove chips of a larger cross section without fear of part deflection. The lunettes b, move motionless and mobile.

steady rest(Fig. 125) has a cast-iron body 1, with which a hinged cover 6 is fastened with a hinged bolt 7, which facilitates the installation of the part. The body of the steady rest is processed at the bottom according to the shape of the frame guides, on which it is fixed by means of a bar 9 and a bolt 8. Two cams 4 move in the holes of the body with the help of adjusting bolts 3, and one cam 5 moves on the roof. Screws 2 are used to fix the cams in the required position Such a device allows you to install shafts of various diameters in the steady rest.

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

Stationary steady rests are also used for cutting off the ends and trimming the ends of long parts. On fig. 127 shows the use of a fixed rest when cutting the end: the part is fixed at one end in a three-jaw chuck, and the other end 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 tapered hole in the spindle of a lathe or drill such a part along its entire length.

Movable steady rest(Fig. 128) is used for fine turning of long parts. The lunette is fixed on the caliper carriage so that it moves along with it along the workpiece, following the cutter. Thus, it supports the part directly at the point of application of force and prevents the part from deflecting.

The steady rest has only two cams. They are extended and fixed in the same way as the cams of a fixed lunette.

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

9. Techniques for turning cylindrical surfaces with ledges

When processing on lathes a batch of stepped 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 limb in order to reduce the time for measuring the length.

Using the longitudinal stop. On fig. 130 shows the longitudinal stop. It is bolted to the front bed rail as shown in fig. 131; the place of fixing the stop 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 setting much faster than without a stop. This is achieved by laying 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 with stop 1 and measuring tiles 2 and 3 is shown in Fig. 131. Turning step a 1 is carried out until the caliper rests against the measuring tile 3. By removing this tile, you can grind the next step of the roller with a length of a 2 until the caliper rests against the tile 2. Finally, removing the tile 2, grind step a 3 . As soon as the caliper reaches the stop, it is necessary 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 an automatic shutdown of the feed when overloaded (for example, 1A62 and other new machine systems). If the machine does not have such a device, then turning along the stop is possible only if the mechanical feed is turned off in advance and the caliper is brought to the stop manually, otherwise the machine will break.

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 limb represents a rotating disk of large diameter (Fig. 132), located on the front wall of the apron and behind the longitudinal feed handwheel. Equal divisions are applied to the circumference of the disk. When the handwheel rotates, the limb connected by gearing to the longitudinal feed wheel also rotates. Thus, a certain longitudinal movement of the caliper with a cutter corresponds to the rotation of the limb by a certain number of divisions relative to the fixed risk.

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, preliminarily 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 fixed risk. Turning the next steps, he memorizes (or writes down) the corresponding indications of the limb regarding the same risk. When turning subsequent parts, the turner uses the indications set when turning the first part.

Using the cross stop. To reduce the time spent on measuring diameters when machining stepped parts, it is possible to use a cross stop on a number of lathes.

One of these stops is shown in Fig. 133. The emphasis consists of two parts. The fixed part 1 is installed on the carriage and fixed with bolts 2; thrust pin 6 is fixed. The movable stop 3 is installed and fixed with bolts 4 on the lower part of the caliper. Screw 5 is set exactly to the required size of the part. The end of the screw 5, resting against the pin 6, predetermines the required size of the part. By placing measuring tiles between pin 6 and screw 5, it is possible to grind a part with steps of various diameters.

10. Cutting conditions for turning

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

Feed rate selection. The feed is also chosen depending on the type of processing. Usually, feed is taken for rough turning 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.

Choice of cutting speed. The cutting speed is usually chosen according to specially developed tables depending on the tool life, the quality of the material being processed, the material of the cutter, the depth of cut, the feed, the type of cooling, etc. (see, for example, Table 6, page 106).

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

When turning cylindrical surfaces, it is possible the following types marriage:
1) part of the surface of the part remained untreated;
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 machined surface does not correspond to the instructions in the drawing;
6) combustion of the rear center;
7) non-coincidence of the surfaces during the processing of the roller in the centers on both sides.

1. The marriage of the first type is obtained due to insufficient dimensions of the workpiece (insufficient machining allowance), poor straightening (curvature) of the workpiece, incorrect installation and inaccurate alignment of the part, inaccurate location of 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 depth of cut or incorrect measurement of the part when removing test chips. It is possible and should eliminate the causes of this type of marriage by increasing the attention of the turner to the work performed.
3. The taper of the turned surface is usually obtained as a result of the displacement of the rear center relative to the front. To eliminate the cause of this type of marriage, 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 bore of the quill. By cleaning the center and the conical hole of the quill, this cause of marriage can also be eliminated. If, even after cleaning, the tips of the front and rear centers do not match, it is necessary to move the body of the tailstock on its plate accordingly.
4. The ovality of the turned part is obtained when the spindle beats due to uneven wear of its bearings or uneven wear of its necks.
5. Insufficient surface finish during turning can be due to a number of reasons: high cutter feed, use of a cutter with irregular angles, poor sharpening of the cutter, small radius of curvature of the cutter tip, high viscosity of the part material, jitter of the cutter due to a large overhang, insufficiently strong attachment of the cutter in the tool holder, increased gaps between the individual parts of the caliper, trembling of the part due to its loose fastening or due to wear of the bearings and spindle necks.

All of the above causes of marriage can be eliminated in a timely manner.

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

12. Safety precautions when turning cylindrical surfaces

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

Reliability of fastening of the workpiece processed in the centers largely depends on the state of the centers. It is impossible to work with worn centers, since the part under the action of cutting force can be torn out of the centers, fly off to the side and injure the turner.

When processing parts in centers and chucks, the protruding parts of the clamp and the cams of the chuck often capture the worker's clothes. These same parts can cause damage to hands when measuring a part and cleaning the machine on the go. To prevent accidents, safety shields should be arranged at the clamps or safety clamps should be used, and cam chucks should be protected. perfect type safety collar is shown in fig. 134. The rim 3 covers not only the head of the bolt 2, but also the pin 1 of the driving chuck.

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

When installing parts in the centers, you need to pay attention to the correctness of the center holes. If their depth is insufficient, the part can break off the centers during rotation, which is very dangerous. In the same way, after fixing the part in the chuck, you need to check if the key is removed. If the key remains in the chuck, then when the spindle rotates, it will hit the bed and fly off to the side. In this case, both the breakdown of the machine and the injury to the worker are possible.

The cause of accidents is often chips, especially drain chips, which, when high speeds cutting comes off a continuous tape. In no case should such chips be removed or cut 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 give short bouncing chips, it is necessary to use goggles or use protective shields made of safety glass or celluloid (Fig. 136), attached to the carriage on a hinged rack. It is necessary to sweep away small chips resulting from the processing of brittle metals (cast iron, hard bronze) not with hands, but with a brush.

There may be injuries to the hands when installing and fixing the cutters as a result of the wrench being torn off the heads of the fixing bolts of the tool holder. Breaking the key occurs when the jaws of the key and the heads of the bolts are worn. Often, however, a breakdown also occurs from the fact that the turner uses a key whose size does not match the size of the bolt.

Installing the cutter along the height of the centers with the help of all kinds of linings that are not adapted for this (metal scraps, pieces of hacksaws, etc.) does not provide a stable position of the cutter during its operation. Under the pressure of the chips, such linings are displaced, and the installation of the cutter goes wrong. At the same time, the fastening of the cutter also weakens. As a result, the pads and the cutter may jump out of the tool holder and injure the turner. In addition, during the installation of the cutter and when working on the machine, injuries to the hands on the sharp edges of the metal linings are possible. Therefore, it is recommended that each turner have a set of linings of various thicknesses, with well-finished supporting planes and edges.

test questions 1. How to install the cutter in the cutter holder?
2. How to check the position of the tip of the cutter relative to the center line?
3. How are parts installed and fixed when turning cylindrical surfaces?
4. What is the difference between the working conditions of the front and rear centers?
5. How is the rotating center arranged and in what cases is it used?
6. What is the knurled front center 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, the 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 arranged?
12. What are steady rests for and in what cases are they used?
13. How is the steady rest arranged?
14. How is a movable steady rest arranged?
15. How is a shaft blank prepared for installation in a steady rest?
16. Give an example of the use of a longitudinal stop; cross stop.
17. What types of marriage are possible when turning cylindrical surfaces? How to eliminate the causes of marriage?
18. List the basic safety rules for turning cylindrical surfaces.

What is the correct installation of the cutter on a lathe and how to carry out the installation correctly? Basic rules, as well as some subtleties.

The entire course of the turning process on lathes from the very beginning to the final result is mainly determined by the competent installation of the cutter in the tool holder. Otherwise, if it is in the wrong position, the machine will face rather rapid wear of the cutting edge.

Not infrequently, serious equipment breakdowns also occur due to this malfunction, which often entail tangible material losses in production.

Before starting, you must first thoroughly clean the support surfaces of the holder. The main rule for installing a cutter on a lathe is, in fact, that its top must necessarily be at the level of the line of centers of the machine.

Remember that setting below this line will cause the part to be pushed out of centers when running over, and setting it higher will result in unacceptable heat and extremely rapid wear.

But in other cases, minor deviations are allowed to further improve the work of the cutter. For example, in the process of roughing, the part is set with a slight excess above the center level, which is from 0.3 to 1.2 mm (it depends solely on the diameter of the workpiece).

A completely different case is fine turning, in which the installation of the cutter is carried out with a decrease by the same amount.

Being fixed in the tool holder with at least two bolts, the cutter must be brought strictly to the center of the tail or front headstock and adjusted in height, while laying no more than three linings under it. This will give maximum accuracy when installing the part.

The linings themselves also deserve special mention: they should be prepared as a whole set immediately in advance. Do not replace them with pieces of metal or other other materials.

Linings must be placed on the support surface of the tool holder, while controlling the tool overhang - it should not exceed 1.5 of the rod height, otherwise vibration of the part during machine operation cannot be avoided.

Further adjustment of the cutter to the required depth can be done in two ways: by trial chips or with a transverse feed dial. Choosing the first technology, the cutter is brought close to the first touch to the surface of the rotating part.

Video: fitting (installation) of cutters for a lathe.

1.7 General rules setting the cutter in the cutter holder

So that the cutter does not vibrate during operation, as a result of which chipping of its cutting edge is possible, the length of the overhanging part of the cutter, or, as they say, overhang, should be as small as possible. On fig. 6, a shows the correct one, and in fig. 6, b - incorrect position of the incisor.

For the same purpose, the lining under the cutter, used when installing the top of the cutter relative to the line of centers of the machine, should be positioned as shown in Fig. 6, c. The incorrect position of the pads is shown in fig. 6, d. It is better to take one thick lining, and not several thin ones, since they are not always tightly pressed against one another (even with the tool holder bolts tightened), which can also cause the tool to vibrate.

The cutter must be installed at a right angle to the part (Fig. 6, e). If you install the cutter according to Fig. 6, e, then during operation under the pressure of the chip being removed, it can turn to the right and go deeper into the workpiece.

1.8 Some features of working with carbide cutters with negative rake angles

Working with cutters with negative rake angles allows you to increase cutting conditions, but causes an increased load on the machine mechanisms and the workpiece. Therefore, to ensure normal operation the following basic rules must be observed.

Rice. 6 - Installing the cutter in the tool holder: correct (a, c, e) and incorrect (b, d, f)

1. The machine on which the work is being done must be in perfect order. Bearings must be properly tightened; the transmission belt and the clutch on the machine must be well fitted; the caliper of the machine should move smoothly, without jerking.

2. The part being machined both in the chuck and in the centers must be securely clamped.

3. The back center when working at high speeds of the part must be carbide or rotating.

4. When installing the cutter relative to the center of the machine during rough turning, its top should be set above the center by 0.01 of the diameter of the workpiece.

5. In order to avoid vibrations of the cutter, its overhang should not exceed the height of the holder.

6. You should work only with a finished cutter.

7. The cutter should be brought to the part only when it is rotating. The insertion of the cutter into the part should be carried out manually and gradually, so that the rear auxiliary surface does not touch the surface to be machined. Only after the insertion is completed, you can turn on the automatic feed of the caliper.

8. Retract the cutter before stopping the machine, after turning off the automatic feed.

9. When turning on the crust, you should work with the largest allowable depth of cut and avoid sliding the cutter on the mill scale.

10. The width of the cut should not exceed 2/3 of the length of the cutting edge of the cutter.

1.9 Cutting conditions for rough turning with carbide tools

The depth of cut for rough turning is usually slightly less than the total machining allowance. The layer of metal, which remains uncut, forms an allowance for further processing. The feed is selected taking into account the section of the cutter, the depth of cut and the diameter of the workpiece. Feed values ​​for the most frequently performed jobs on machines medium size are given in table. 6, 8, 10 and 12.

Table 6 - Feeds (in mm / rev) for rough turning of steel with carbide cutters

Table 7 - Cutting speeds (in m / min) for rough turning of carbon, chromium, chromium-nickel steels and cast steel with carbide cutters

Table 8 - Feeds (in mm / rev) for rough turning of steel with carbide cutters with an additional cutting edge (φ 1 \u003d 0)

The determination of the cutting speed for a given machining is carried out in two steps:

1) according to one of the tables (tables 7, 9, 11 or 13), the cutting speed is determined for conditions closest to the given ones;

2) the numerical value of this speed is multiplied by correction factors that take into account the specific conditions of the forthcoming processing.

The most important of these conditions are the tool life (K1 coefficient), the mechanical properties of the material being machined (K2 coefficient), the state of the machined surface (Kz coefficient), the material of the cutter (K4 coefficient) and its main angle (K5 coefficient) - The values ​​of these coefficients are given in table. fourteen.

Table 9 - Cutting speed (in mm / rev) during rough turning of carbon, chromium, chromium-nickel steels and steel casting with carbide cutters with an additional cutting edge (φ 1 \u003d 0)

Table 10 - Feeds (in mm/rev) for rough turning of gray cast iron with carbide cutters

Table 11 - Cutting speeds (in m/min) for rough turning of gray cast iron with carbide tools

Table 12 - Feeds (in mm / rev) for rough turning of gray cast iron with carbide cutters with an additional cutting edge (φ 1 \u003d 0)

Table 13 - Cutting speeds for rough turning of gray cast iron with carbide cutters with an additional cutting edge (φ 1 = 0)

Table 14 - Correction factors for table values ​​of cutting speeds with carbide cutters

Obtaining a workpiece for each of the methods by comparing them by cost value. The cost of production of blanks, excluding the cost of pre-machining, is determined by the dependence: (7), where Gd is the mass of the part, kg Gzag is the mass of the blank, kg coefficient, ...

... ;v=6 kg/mm2 – tensile strength of the deformed material at the stamping end temperature. Mm = 1781.9 kg = 1.8 tons. In accordance with the calculation for stamping the gear blank according to OST 2KP12 - 1 - 87, we select a steam-air hammer with a mass of falling parts of 2 tons. 2. Metal cutting 2.1 Introduction Metal cutting - technological processes for processing metals by ...

Of all technological operations produced on metal blanks, processing on turning equipment is the most common. That is why sharpening cutters for metal is a very important process that should be done correctly. The features of the implementation of such a procedure depend both on the material to be processed and on the type of the cutting tool itself (shaped, through-hole, thread-cutting, boring, and others).

The design of turning tools

Sharpening turning tools cannot be done correctly if you do not understand the design features of such a tool. The main elements of its design are the rod-holder, with which the cutter is fixed on the machine, as well as the working head: it is precisely its cutting part that must be sharpened regularly.

Let's take a closer look at the working head turning tool. It is formed by two types of surfaces: front and rear. The front one is very easy to distinguish: it is through it that chips are removed. Back same called those sides of the cutters, to which the workpiece is facing in the process of performing its processing. They can be primary or secondary, depending on their location.

The most important element of any cutter (including for a metal lathe) - its cutting edge - is formed at the intersection of the rear main and front surfaces. In the design of any cutter, there is also an auxiliary edge formed by the intersection of its rear surfaces: the main and auxiliary. The top of the tool, which is mentioned in the specialized literature, is the intersection of its cutting and auxiliary edges.

The main characteristics of turning tools for metal, which determine them functionality, are sharpening angles, divided into main and auxiliary. In order to determine the values ​​of the main ones, they are measured in the plane that is formed when the cutting edge is projected onto the main plane.

In general, two planes are used to determine the angles of a cutting tool:

• the main one, superimposed on the supporting side of the turning tool, located in its lower part (in relation to the direction of machine feeds, such a plane is parallel);
• cutting plane located tangentially relative to the surface of the workpiece being machined (this plane intersects with the main cutting edge of the tool).

In the design of the working part of the turning tool, several types of angles are distinguished:

• sharpening - located between the front surface of the cutter and the rear main;
• rear main - located between the rear main surface and the cutting plane;
• front main - located between the front side of the tool and the plane perpendicular to the cutting plane.

Checking the correctness of their definition is quite simple: their sum is always 90 degrees.

In addition to the above, the design of the working head of the turning tool characterizes several more angles between:

• the direction of feed and the projection that the main cutting edge lays;
• processing plane and the front surface of the cutter;
• projections that lay the main and auxiliary cutting edges.

Tools for turning equipment

In order to understand the rules for sharpening cutters for metal lathes, it is not enough just to watch the training video. It is necessary to have an idea of ​​how such instruments are classified. The most important parameter by which turning tools are classified as various types, is the type of processing performed by them. On this basis, the following are distinguished.

Such cutters workpieces are processed along the axis of rotation.

Using these cutters on a lathe, they reduce ledges and perform trimming of workpieces.

As the name implies, they form the outer and inner grooves on the surfaces of a cylindrical shape. It is also possible to create grooves on the outer sides of workpieces using cut-off cutters for metal. In addition, such cutters allow you to cut off parts of the workpiece at right angles.

With the help of such tools, holes are machined on machines.

These cutters are specially designed for threading.

With the help of cutters of this type, shaped protrusions or grooves are formed on the outer side of cylindrical blanks.

With the help of these cutters, chamfers are removed on the workpieces.

Turning cutters are also divided into types depending on the direction in which they are used to machine the workpiece. So, among them there are right (processing is performed towards the headstock) and left (processing towards the tailstock).

The turning tool is also classified according to the material of manufacture, according to the method of connecting the cutting part to the holder, as well as according to a number of other parameters.

Rules for sharpening turning tools

In order for the metal to be efficient, high-quality and accurate, it is necessary to regularly sharpen the cutters, thereby giving their working part the necessary shape and obtaining angles with the required parameters. Only the tool, the cutting part of which is made in the form of a disposable carbide plate, does not need sharpening. To perform such an important procedure in large manufacturing enterprises machines with special devices are used, and a separate structural unit is engaged in this.

In order to sharpen a turning tool with your own hands on a home machine or to do it in a small business, you can use various techniques. This procedure can be performed using chemical reagents or using conventional grinding wheels. It should be noted that sharpening a turning tool on specialized or universal machines that use is the most inexpensive, but effective method giving the cutters the required geometric parameters.

Of course, the most high-quality turning tools for metal are sharpened on a machine specially designed to perform such a procedure. If such equipment is not at your disposal, you can use universal machine with a grinding wheel. When choosing such a circle, it is important to pay attention to the material from which it is made. working part processed tool. So, in order to effectively sharpen carbide cutter, you will need a circle of carborundum, which has a characteristic green color. Tools, the working part of which is made of carbon or, are perfectly machined on machines with medium-hard circles made of corundum.

Sharpening of turning tools for metal can be performed without cooling or with cooling, which is more preferable. If sharpening is performed with cooling, then cold water should be evenly supplied to the place where the turning tool is in contact with the grinding wheel. In the case when cooling is not used during the sharpening process, after sharpening it is impossible to cool the tool immediately: this can lead to cracking of its cutting part.

You can learn how to sharpen turning cutters on a grinding machine with your own hands from the training video. In the process of performing such a procedure, it is important to adhere to a certain sequence. First of all, on the grinding wheel, the back main surface is processed, then the back auxiliary, and lastly, the front is sharpened. The last stage of sharpening is the processing of the tip of the cutter - giving it the required radius of curvature.

In the process of sharpening, the cutter is constantly moved in a circle, trying not to press it very hard (this can be seen in the video). It is necessary to adhere to such a recommendation so that the surface of the circle wears out evenly, and also so that the cutting edge of the turning tool is as smooth as possible.

Features of sharpening cutters for a lathe

There are certain nuances that should be considered when sharpening turning tools with your own hands using a grinding machine. Thus, the processing of the rear surface of the cutter is carried out in three stages.

• Initially, the back surface is machined at an angle equal to the back angle of the holder itself. As a rule, it turns out to be slightly larger than the clearance angle of the cut (approximately 5 degrees).
• At the second stage, the back surface of the cutting insert itself is processed. At the same time, it is sharpened at an angle exceeding the rear cutting angle by 2 degrees.
• The third stage is the formation of the required rear angle with the help of finishing. It is important that such an angle is formed not on the entire rear surface of the cutter, but only on a narrow chamfer directly adjacent to the cutting edge.

In several stages, sharpening is also performed on the front surface of the turning tool. So, it is pre-sharpened at an angle equal to the angle of the cutting insert itself. This angle, as in the case of the back surface, slightly exceeds the front cutting angle. Directly, the cutting angle that needs to be formed on the front surface of the cutter is obtained by fine sharpening or finishing. These processes are subjected to a narrow strip adjacent to the cutting edge of the carbide insert.

For greater convenience of sharpening turning tools on grinding machines, as well as to obtain angles with specified parameters, special linings are used, which are installed between the tool's support surface and the machine table where it is located. To achieve even more accurate and high-quality sharpening, you can modify the design of the machine table with your own hands, making it adjustable in height and angle of rotation. After such a refinement of the machine, the need to use linings of a certain thickness disappears.

When sharpening a turning tool, it is important to pay attention to the fact that its cutting edge is on the same level with the center of the grinding wheel, but not lower than 3–5 mm in relation to it. The direction of rotation of the grinding wheel should also be taken into account. This is necessary in order to make the sharpening process safer, and also to minimize the risk of the cutting insert breaking off from the tool holder. The grinding wheel during the sharpening process must rotate so as to press the cutting insert, and not tear it off the holder.