3 x jaw chuck appointment. Lathe chucks

These fixtures serve to secure relatively short parts. They differ in the type of drive for manual and mechanized, and in the number of cams - for two-, three- and four-cam. Chucks can be self-centering and with independent movement of the jaws, universal and special. They also differ in design into wedge, lever-wedge, lever, spiral-rack, screw, etc.

Technical requirements for lathe chucks general purpose regulated by GOST 1654--71. Four classes of accuracy of cartridges have been established: H - normal accuracy; P - increased accuracy; B - high precision; A - especially high accuracy, depending on the magnitude of the permissible imbalance (imbalance) and maximum deviations from geometric shape and the location of the surfaces of the cartridges. The radial runout of the control band of self-centering chucks with a diameter of up to 630 mm should not exceed 10 µm for accuracy classes A and B and 20 µm for accuracy classes H and P.

Three-jaw self-centering chucks

Figure 1.1 - Designs of three-jaw spiral-rack self-centering chucks with a key clamp.

These cartridges are most widely used in industrial practice as the most convenient and reliable for fixing cylindrical parts. They are made with manual and mechanized drives.

Self-centering key three-jaw chucks for general purposes (GOST 2675--71) with a manual drive are made of a spiral rack type with solid or prefabricated jaws. In foreign practice, key spiral rack and pinion chucks with a flat (Archimedean) spiral and a bevel gear to the spiral disk are also most common. Chucks are attached to the ends of the spindles only with the help of intermediate flanges (GOST3889--71). The designs of three-jaw spiral-rack self-centering turning chucks for spindles with threaded and flanged ends are shown in Figure 1.1.

Figure 1.2 - Universal self-centering chuck with key clamp

A spiral disk 2 is installed in the cast-iron or steel body of the cartridge, which is engaged with the rails 3. During the rotation of the disk, the rails move in the T-shaped grooves of the body. Disk 2 is driven by one of three conical wheels 6 mounted in the radial holes of the body and locked in it with pins 8. Cover 7 keeps the spiral disk 2 from moving in the axial direction and at the same time serves to protect against dirt and small chips from entering the chuck . In the cross-shaped groove of the rails 3, straight or reverse overhead cams 5 are installed and fixed with screws 4. In some cases, cartridges are made with solid straight and reverse cams with rails cut on their bases for direct mating with the spiral disk 2. The general view of the cartridge is shown in fig. 2. In fig. 3 dan general form self-centering rack and pinion chuck, which is described below. Straight solid and overhead cams are designed to clamp parts along the outer surface with large prisms, and along the hole - with cam steps. Reverse solid jaws and top jaws are used for clamping workpieces with jaw steps over a large diameter outer surface.

Figure 1.3 - Universal self-centering rack chuck

The disadvantage of the chucks is the linear contact in the mating of the helix turns with the cam rails, which causes increased pressures in the mating, resulting in relatively rapid wear of the centering mechanism and loss of accuracy. At present, in our country and abroad, hardening and grinding of spiral turns and cam racks are used, which increases the wear resistance and durability of cartridges. However, the grinding operation requires the use of special equipment and needs further improvement. In this regard, a version of a universal three-jaw self-centering chuck with a screw centering mechanism has been developed and is being used.

Screw three-jaw self-centering chucks with a key clamp have been manufactured in Germany by Mundorf for a number of years as the main product and compete with rack and pinion chucks.

The three screws in these cartridges are connected by a common bevel gear driven by a key through a worm gear. The cams are half-nuts and, when the screws are rotated, they carry out radial movement and clamping of the parts.

The advantages of chucks with screw centering mechanism are as follows.

• 1. The contact of the helical surfaces, carried out across the entire width of the cam (which works like a half nut) determines reduced pressures mating and increased wear resistance.
• 2. The ability to harden and grind the thread of the screw pair on a conventional thread grinding machine.
• 3. The ability to use one set of reversible jaws, while in spiral rack and pinion chucks it is necessary to have two sets of jaws (a set of forward and a set of reverse).

Chucks of this design provide great clamping force, and with high-quality workmanship, high centering accuracy (according to the company, the runout is up to 0.02 mm); under normal operating conditions, centering accuracy must be maintained for a long period of time.

The main disadvantage of the kinematic scheme of screw chucks is that the centering accuracy depends on the manufacturing accuracy of two pairs: a conical gear and a screw, while in spiral rack and pinion chucks, the centering accuracy depends only on a pair of spiral - cam racks. The chuck is more difficult to manufacture, has only one socket for the key, and the time for moving the jaws during setup is relatively long.

Rack and pinion chucks (see Figure 1.3) or otherwise, wedge chucks with transverse wedges have limited jaw travel and are not universal.

Leading racks and driven racks on the bases of the cams have oblique teeth and work like wedge pairs. The movement of one of the rails perpendicular to the guide cams is carried out by means of a screw rotated by a key.

From this rail, the movement is transmitted to other rails either by means of a central gear, as shown in Figure 1.3, or by means of a rocker transmission carried out by a central ring (disk) with radial grooves, which include crackers sitting on the pins of the rails.

These chucks, like screw chucks, provide high clamping force and at the same time high centering accuracy (up to 0.02 mm). Surface contact across the entire width of the jaws, the ability to harden and grind mating surfaces on conventional machines, increase the durability of the chucks.

However, due to the comparative complexity in manufacturing, the limited stroke of the cams and the increased time spent on changeovers, these chucks, despite their long existence (about 45 years), could not displace universal spiral rack and pinion chucks or significantly reduce their use.

In conditions of serial and single-piece production, with frequent changes in workpieces, up to 30% of auxiliary time is spent on installation and manual clamping in universal key chucks.

The time spent on setting and clamping workpieces in a mechanized chuck is reduced by 3-5 times. Mechanization facilitates the work of the machine operator. In addition, mechanized chucks can be automated and included in the automatic cycle of the machine.

According to ENIMS, about 400,000 chucks are required each year to replace and replenish cartridges in service, so even small cartridge improvements can have a big effect on a national scale. Therefore, both here and abroad, they are intensively engaged in the mechanization of lathe chucks.

The drive of mechanized chucks is located at the rear end of the spindle, on the front end wall of the headstock, or is built into the chuck body.

The drive can be pneumatic, hydraulic, electromechanical, etc. Rotating pneumatic drives located at the rear end of the spindle with a hollow and conventional stem are most widely used. The front location of a non-rotating pneumatic actuator is also used, the main disadvantage of which is that when the part is clamped, the force of the pneumatic cylinder (directed towards the tailstock) is transmitted through the chuck to the machine spindle and acts on bearing assemblies designed to perceive axial forces in the opposite direction. Chucks with a built-in pneumatic drive, although they have a number of advantages, have increased axial dimensions and weight of the cartridge, which leads to a decrease in processing accuracy. Therefore, the tasks of mechanization of lathe chucks are still waiting for optimal solutions (although recent times and a lot of mechanized cartridges of various designs appeared).

The lathe chuck is the main element of the equipment of the lathe, a clamping device that secures the workpieces on the spindle. The use of cartridges allows processing on high speeds rotation, ensures the installation accuracy and the required clamping force.

This tooling element is made of durable grades of cast iron or hardened tool steel, has various versions that provide ample opportunities for processing parts of various configurations.

Purpose and main parameters

The lathe chuck is one of the main elements of technical equipment and is necessary for reliable fastening of workpieces of various sizes and shapes on the spindle. High clamping accuracy ensures centering and perpendicularity of the surface of the machining axis. The chuck is necessary for carrying out almost all turning operations; it is included in the mandatory set of equipment for metalworking manual, semi-automatic and automatic machines.

This type of clamp is installed on the headstock of the machine. The transmission of rotation is carried out from the electric motor through the gearbox and transfer case. To ensure the production of parts, several turning chucks are needed, which are selected taking into account the main operational and technical parameters:

• Version and number of cams (clamping elements) - determines the possibility of fixing one or another type of blanks, the location of the cams, the possibility of installing several blanks.
• Working diameter of the cartridge. This is the outer size, the diameter of the connecting belt, as well as the location and parameters of the mounting holes.
• Workpiece parameters. It is necessary to take into account the largest and smallest diameters, take into account the method of fastening - external or internal through reverse cams. It is also necessary to take into account the permissible mass of the part.
• The diameter of the hole in the chuck body. Necessary when processing a long bar.
• The maximum value of rotational speeds.

Basic design options

Lathe chucks are made of durable cast iron with a grade of at least SCh-30 or tool steel grades with a strength of at least 500 MPa.

There are various design options for lathe chucks, let's focus on the most commonly used in modern production:

• Cartridge lever. Clamping occurs due to the displacement of the cams with clamps due to the action of a two-arm lever. The main characteristic is the number of cams and the degree of displacement on the working disk. The disadvantages include the complexity of settings, especially when performing non-standard operations. The cams can be adjusted by simultaneously shifting with a key or by individually adjusting each jaw. This type of equipment is usually used for roughing or semi-finishing.

• Wedge lathe chucks are an advanced version of the lever clamp design. The high accuracy of fixation is ensured by the presence of its own mechanical or pneumatic drive for each cam. It has the ability to fix the workpiece with an offset relative to the center of rotation, which allows processing parts of complex configuration.

• Membrane lathe cartridges. They provide the highest fixation accuracy due to membranes made of elastic material. The workpiece is fixed by turning off the hydraulic drive, which leads to the expansion of the membrane. Characteristic features design is a large number of clamps with a relatively low compression force. Therefore, the main scope of this type of equipment is the finishing of parts at low speeds.

Types and classification of lathe chucks

One of the main parameters of the classification of cartridges, which determines the possibility of processing certain workpieces, is the number and design of the cams. According to the number of clamps, cartridges are divided into:

• Double jaw chucks. Optimal for clamping small asymmetrical workpieces - forgings, fittings, etc.
• Three-jaw chucks self-centering. Used for fixing round and hexagonal workpieces. Provides fast centering and locking.
• Four-jaw chucks with independent fixing clamps. This type of equipment is used to install rectangular and asymmetrical workpieces, square bars.
• Six-jaw chucks self-centering. Optimal for working with thin-walled parts due to the minimum crushing force. Six cams provide an even distribution of compression forces.

According to the type of clamping of the jaws, the chucks are divided into direct and reverse. The former provide clamping along the outer surface, the reverse - along the inner hole. The use of reverse cams allows you to process the entire surface of the part.

According to the accuracy class, this type of equipment is divided into 5 steps:

• N - normal;
• P - increased;
• B - high;
• A is especially high.

Basic dimensions and designations

If we take the most common three-jaw chucks (GOST 2675-80), then the current standard provides ten sizes determined by the total diameter of the tooling: 80, 100, 125, 160, 200, 250, 315, 400, 500 and 630 mm (see table. 1)

Depending on the method of installation on the spindle, the equipment is divided into three types:

• With belt and fixation by means of an auxiliary flange (Type 1);
• With fixation through the flange at the end of the spindle under the swivel washer (Type 2);
• With fixing through the flange at the end of the spindle (Type 3).

There is a unified designation system for the main parameters of the cartridge, consisting of 8 numbers and a letter indicating the accuracy class of the tooling. Using the table in GOST 2675-80 for product marking, you can determine:

• Number of clamps;
• Product diameter;
• Main dimensions;
• Type of fastening equipment on the spindle;
• Execution of clamps;
• Accuracy class.

So, for example, Chuck 7100-0032-P GOST 2675-80 designates the second type, diameter 200 mm, mounting on a spindle with 5 nominal size, prefabricated jaws and an increased accuracy class (P).

Current GOSTs

Regulates the parameters of turning chucks GOST 1654-86. It regulates the technical conditions of cartridges for general purposes. Many other standards also apply. So, self-centering 3-jaw chucks are regulated by GOST 2675-80. GOST 14903-69 applies to two-jaw clamps with self-centering.

Scroll chuck - important element lathe tooling. The accuracy of processing depends on how securely the workpiece is fixed on the machine. The duration of operation depends on the quality of manufacture of the cartridge. In the process of improving metalworking technologies, many designs of cartridges were developed, from which the most effective ones were selected.

Fixing chucks on a lathe

Mounting and centering of lathe chucks is carried out on the lathe spindle. The diameters of the cartridges and the methods of their fastening are standardized. Depending on the manufacturer, cartridges will be designated by type (according to ISO) or execution (according to GOST). A common spindle end design is a Type C or Type D (cam-lock) mount. There are other spindle designs.

For mounting lathe chucks, flanges and faceplates placed on the spindle are widely used. They have the same design as the lathe chuck flange, however, such fixtures can greatly increase versatility, since they can accept various chucks. The faceplates have numerous holes for draw bolts and a centering lug. When mounting the chuck on a faceplate or flange, high accuracy can also be achieved.

Types of lathe chucks

Lathe chucks are divided into the following types:

• Mechanical. The most common class of cartridges, divided into cam, leash, collet. The first group has now practically supplanted the second and, in turn, is divided into self-centering, usually with 3 cams, and non-self-centering, in which the number of cams can be 2, 4 or 6. Six-jaw chucks are used the least.
• Mechanized: Pneumatic, hydraulic, electric. Automate the process of clamping-unclamping the workpiece with a given force. Hydraulic chucks are more commonly used on machine tools with a chuck diameter greater than 200mm (imported chuck diameters are in 6, 8, 10, 12, 15 and beyond). Pneumatic chucks are used on automatic lathes. Collet chucks are used to clamp a bar stock of a relatively small diameter. Electrical. have not been widely adopted.

The outer diameter of turning chucks is in the range of 80-1000 mm, of which chucks with a diameter of 80-400 mm are the most popular. For the manufacture of lathe chucks, steel and cast iron are used. Cams for lathe chucks are especially durable, which experience significant surface and abrasive loads during operation. Therefore, high-quality steel, which is hardened, is used for their production.

Double jaw chucks

Three-jaw self-centering chucks with manual drive and centers have received the greatest use for fixing workpieces during processing on lathes. The main tool for turning on a lathe is a cutter, which is fixed directly in the tool holder of the machine with the help of spacers that allow you to set the cutter so that its top is exactly on the center line.

Self-centering three-jaw chuck

Self-centering three-jaw chuck(Fig. 6.2) consists of a body 6 with grooves in which the cams 1,2, 3 move. The movement of the cams from the periphery to the center of the cartridge occurs with the help of a spiral cutting made on the disk 4. The disk is driven in rotational motion using a special key, bevel gear 5 mounted in a square hole. The bevel gear J is engaged with the disk 4, on which the teeth are cut. Cams are made three-stage, which allows you to fix workpieces based on the inner diameter of various sizes. To increase the wear resistance of the cams, they are hardened.

Centers (Fig. 6.3), depending on the shape and size of the workpieces being processed, have different shape and sizes. The angle at the top of the working part 1 of the center, as a rule, is 60°. tail section 2 centers are made with Morse taper. To remove the center from the hole of the machine spindle or the tailstock quill, the support part 3 is used, the diameter of which is smaller than the diameter of the tail part of the cone, which allows you to remove the center without damaging its conical part.

The design of the center is selected depending on the design of the workpiece and the nature of the processing being performed.

When processing workpieces of small diameter (up to 4 mm), it is difficult to make a center hole in them, therefore the end part of such a workpiece is processed at an angle of 60 °, and its fastening is carried out using a center with an inverse cone (Fig. 6.3, b). If during processing it is necessary to cut the end of the workpiece fixed in the centers, then a center with a cut cone is used (Fig. 6.3, c), which is installed only in the tailstock quill. When the axis of the workpiece being processed does not coincide with the axis of the spindle, a spherical center is used to fix it (Fig. 6.3, d). A center with a corrugated working surface (Fig. 6.3, e) is used when processing workpieces with a large center hole without a driver chuck. Due to the fact that during processing large friction forces arise in the centers, hard alloy is used to increase the durability of the centers for their working part (Fig. 6.3, e); such centers are installed in the tailstock quill. Along with solid centers wide application find rotating centers (Fig. 6.4). Such a center consists of a body 4 with a tapered shank, in which two ball bearings 3 and 5 and one roller bearing 2 are installed. The rotating center 1 is mounted on the bearings.

For transmission rotary motion from the spindle to the workpiece are also driving chucks and collars.

Driver chucks

Driver chucks(Fig. 6.5) are used when processing workpieces 5 in centers 4 and 6. The movement is transmitted by a driving chuck 7 through a driving pin 2 and a clamp 3 fixed to the workpiece with a screw.

Clamp(Fig. 6.6) is put on the workpiece processed in the centers and fixed with a screw 1. With a shank 2, the clamp rests against the pin of the driving chuck.

Gaskets are designed for setting the top of the cutter along the line of centers; they are metal plates of various thicknesses with dimensions corresponding to the dimensions of the support surface of the cutter. The inserts are installed in the tool holder under the cutter, while the thickness of the set is selected so that the top of the cutter is on the center line. The position of the tip of the cutter is controlled by the top of the center installed in the tailstock quill. After adjusting the position of the tip of the cutter, it is fixed in the tool holder of the machine along with a set of selected inserts. The set should not contain more than three plates.

On lathes, two-, three- and four-jaw chucks with manual and mechanized clamping are used. In two-jaw self-centering chucks, various shaped castings and forgings are fixed; the jaws of such chucks are usually designed to hold only one part. In three-jaw self-centering chucks, workpieces of round and hexagonal shape or round bars of large diameter are fixed. In four-jaw self-centering chucks, square bars are fixed, and in chucks with individual jaw adjustment, rectangular or asymmetrical parts are fixed.

The most widely used three-jaw self-centering chuck (Figure below). Cams 1, 2 and 3 of the cartridge move simultaneously with the help of disk 4. On one side of this disk, grooves are made (having the shape of an Archimedean spiral), in which the lower protrusions of the cams are located, and on the other, a bevel gear is cut, mated with three bevel gears 5. When one of the wheels 5 is turned with a key, the disk 4 (thanks to the gearing) also rotates and, by means of a spiral, simultaneously and evenly moves all three cams along the grooves of the cartridge body 6. Depending on the direction of rotation of the disk, the cams approach or move away from the center of the chuck, clamping or releasing the part. Cams are usually made in three stages and are hardened to increase wear resistance. There are cams for fastening workpieces on the inner and outer surfaces; when fastening along the inner surface, the workpiece must have a hole in which the cams can be placed.

Cam chucks can be equipped with a mechanized drive - traction or built-in. Chucks with a traction drive have clamping elements connected by solid or hollow rods with a pneumatic or hydraulic cylinder. The figure below shows the design of a two-jaw lever chuck with interchangeable jaws 14, which are pre-installed along the workpiece (relative to the axis of rotation) by shifting crackers 12 (attached to the cams 14 with screws 13) along the grooves in the sliders 11. The sliders 11 are moved to the center of the cartridge by levers 10, which, when the stop 15 moves (together with the rod 3), rotate around the axis 9 in the housing 8. When turning, the levers 10 rest on the surfaces 7. The movement of the sliders 11 (together with the cams 14) from the center of the cartridge is made by the conical surface of the stop 15 during the reverse movement of the rod 3 , connected to the stop by means of a guide bushing 6 and fittings 2, 4 and 5. The chuck is attached to the machine with screws 1.

The cartridge with a built-in drive (figure below) has a built-in pneumatic cylinder 6 with a piston 5 and is attached to the machine with a flange 1. The rubber ring 11 softens the blows of the piston against the flange 4. O-rings 10 and 12 ensure the tightness of the pneumatic drive. The sliders 7 (with clamping jaws 8) have protrusions 9 that enter the grooves of the piston 5. The angle of the grooves is 40.5 degrees, which provides conditions for self-braking. When air is supplied through channels 2 and 3 to the left or right cavity of the cylinder, the sliders 7 move from the center of the cartridge or to its center and through the cams 8 open or clamp the workpiece.

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A four-jaw chuck with independent jaw movement (figure below) consists of a body 1 in which four grooves are made, in each groove a cam 4 is mounted with a screw 3 used to independently move the jaws along the grooves in the radial direction. Screw 3 is kept from axial displacement by cracker 2. When the cams are rotated 180 degrees, the chuck can be used to fasten workpieces along the inner surface. On the front surface of the cartridge, concentric circular marks are applied (the distance between the marks is 10-15 mm), with the help of which the cams are set at the same distance from the center of the cartridge.

Cam chuck for machining eccentric surfaces

Collets for three-jaw chuck

Three-jaw chuck with adjustable jaws

The processing of eccentric surfaces on lathes is carried out using various devices. However, most of them do not meet the requirements of modern production. Some of them are complex and cumbersome, others require time-consuming setup.

At the Leningrad plant of machine tools, the innovator S.V. Litvinov developed and introduced a cartridge that is easy to manufacture and adjust, and also has high rigidity and versatility. The main part of the cartridge (Fig. 1) is a mandrel 9, which has three parts: a taper shank with a Morse taper No. 5, a cylindrical belt with a diameter of D1 = 70 mm and a flange. A faceplate 4 is put on the cylindrical belt, connected to it with a key 8 and attached to the flange with three screws 12. At the end face of the faceplate, an annular “sample” is made with the axis // shifted from the axis /, common to the shank and the cylindrical surface of the mandrel, by 5 mm . Ring 5, adapter 3 and a standard three-jaw chuck / with a diameter of 130 mm are installed in this sample, fastened together with screws 2 and 13. Moreover, the cartridge is seated on an adapter belt with a diameter of D3, the axis /// of which is shifted by 5 mm from the axis //. Thus, the axis of the chuck, in which the part is installed in the position shown in the drawing, is eccentric with respect to the axis of rotation of the spindle by a maximum value of 10 mm.

In the sample, the entire block can be rotated to any angular position and secured with three T-bolts 6 and nuts 7. The bolts with their heads are inserted into the T-shaped circular groove of the ring 5 and passed into the faceplate hole.

On the front end of the faceplate, divisions 11 are applied. Each division corresponds to such an angular the position of the block, at which the axis /// is shifted towards the axis / by 1/10 of the maximum eccentricity of 10 mm, i.e. by 1 mm. To install the block in the required position, the adapter 3 has an angular risk (groove) 10.

To adjust the chuck / to the required processing eccentricity, it is necessary to loosen the nuts 7, turn the block, placing the mark 10 against the desired division on the faceplate, and tighten the nuts 7.

The accuracy of setting the eccentricity value depends on the accuracy of manufacturing the fixture parts and will practically not exceed the sum of the errors in the eccentricities of the surfaces D2 and D3. So, with the error of the latter ± 0.05 mm, which is technologically easily achievable, the tuning accuracy will not exceed ± 0.1 mm.

This device allows you to adjust the eccentricity with higher accuracy. To achieve it, you must use the indicator and make adjustments directly on the machine.

Cartridge overall dimensions: diameter - 260 mm, length - 170 mm. Weight - 15 kg.

The annual economic effect from the introduction of one cartridge amounted to 1.2 thousand rubles.

Lathe 3-jaw chucks

Lathe 3-jaw chucks are used as part of the front headstock of a lathe to clamp the workpiece. In some cases, this equipment is used as part of rotary tables and dividing heads.

There are self-centering 3-jaw chucks and chucks with independent jaws. The chuck can be mounted on the spindle axis: type 1 - with a cylindrical centering belt and with fastening through an intermediate flange (faceplate); type 2 - with fastening directly on the flanged ends of the spindles under the swivel washer; type 3 - with fastening directly on the flanged ends of the spindles.

The standard delivery set includes the three-jaw lathe chuck itself, reverse and straight jaws, and a clamping key.

A rotating turning center is used to install workpieces such as bodies of revolution when performing precise work on metal-cutting machines with manual and program control. Equipment of this type provides the possibility of clamping a workpiece of maximum diameter and dimensions for cutting on top speed rotation with minimal runout. According to technical parameters, standard and elongated turning centers are distinguished.

The tool holder is used to fix tools of various sections with the help of a replaceable bar and bolts, for example, turning tools on a 16K20 machine. This tool is characterized by high positioning accuracy and durability. The shank of the quick-detachable tool holder standardly complies with generally accepted GOSTs.