Three-jaw chuck purpose. Jaw chucks
A lathe chuck is the main element of lathe equipment, a clamping device that ensures the fixation of workpieces on the spindle. The use of chucks allows processing at high rotation speeds, ensures installation accuracy and the required clamping force.
This element of equipment is made of durable grades of cast iron or hardened tool steel, and has various designs that provide wide possibilities for processing parts of various configurations.
Purpose and main parameters
A lathe chuck is one of the main elements of technical equipment and is necessary for reliable fastening of workpieces of various sizes and shapes to the spindle. High clamping accuracy ensures centering and perpendicularity of the surface of the processing axis. The chuck is necessary for 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 lathe chucks are needed, which are selected taking into account the main operational and technical parameters:
- Design option and number of cams (clamping elements) - determines the possibility of fixing a particular type of workpiece, the location of the cams, and the possibility of installing several workpieces.
- 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 cartridge body. Necessary when processing long rods.
- Maximum value of rotation speed.
Main 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; we will focus on the most commonly used in modern production:
- Cartridge lever. The 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 difficulty of setting up, especially when carrying out non-standard operations. The cams can be adjusted by moving them simultaneously using a key or by individually adjusting each clamp. This type of equipment is usually used for roughing or semi-finishing.
- Wedge Lathe chucks are an improved version of the lever clamp design. 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 makes it possible to process parts of complex configurations.
- Membrane lathe chucks. Provide the highest fixation accuracy thanks to membranes made of elastic material. The workpiece is fixed by turning off the hydraulic drive, which leads to expansion of the membrane. Characteristic features of the design are a large number of clamps with a relatively low compression force. Therefore, the main area of application of this type of equipment is finishing of parts at low rotation speeds.
Types and classification of lathe chucks
One of the main parameters for the classification of cartridges, which determines the processing capabilities of certain workpieces, is the number and design of the jaws. Based on the number of clamps, cartridges are divided into:
- Double jaw chucks. Optimal for clamping small workpieces of asymmetrical shape - forgings, fittings, etc.
- Three jaw chucks self-centering. Used for fastening round and hexagonal workpieces. Provides the ability to quickly center and lock.
- Four jaw chucks with independent fixation of clamps. This type of equipment is used for installing rectangular and asymmetrical workpieces, square rods.
- Six-jaw chucks self-centering. Optimal for working with thin-walled parts due to minimal crushing force. Six cams ensure even distribution of compression forces.
Based on the type of jaw clamping, chucks are divided into direct and reverse. The first provide clamping along the outer surface, the reverse - along the internal hole. The use of reverse jaws allows the entire surface of the part to be processed.
According to the accuracy class, this type of equipment is divided into 5 stages:
- N – normal;
- P – increased;
- B – high;
- A – especially high.
Basic dimensions and designations
If we take the most common three-jaw chucks (GOST 2675-80), then the current standard provides for ten standard sizes determined by the overall diameter of the equipment: 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 a flange at the end of the spindle under a rotary washer (Type 2);
- With fixation through a 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 equipment. Using the table in GOST 2675-80 based on product labeling, you can determine:
- Number of clamps;
- Product diameter;
- Basic dimensions;
- Type of fastening of equipment to 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 standard size 5, prefabricated jaws and increased accuracy class (P).
Current GOSTs
Regulates the parameters of lathe chucks GOST 1654-86. It regulates the technical conditions of general-purpose cartridges. Many other standards also apply. Thus, self-centering 3-jaw chucks are regulated by GOST 2675-80. GOST 14903-69 applies to two-jaw clamps with self-centering.
The most widely used for securing workpieces when processing on lathes are three-jaw self-centering chucks with manual drive and centers. The main tool for processing on a lathe is a cutter, which is fixed directly in the tool holder of the machine using spacers that allow you to install the cutter so that its tip is exactly on the center line.
Self-centering three-jaw chuck
Self-centering three-jaw chuck(Fig. 6.2) consists of a housing 6 with grooves in which cams 1,2, 3 move. The movement of the cams from the periphery to the center of the cartridge occurs using a spiral thread made on disk 4. The disk is driven into rotation using a special key, bevel gear 5 installed in the square hole. The bevel gear J is meshed with disk 4, on which teeth are cut. The cams are made in three stages, which makes it possible to clamp workpieces based on the internal 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 shapes and sizes. The angle at the top of the working part 1 of the center is usually 60°. The tail part 2 of the center is made with a Morse taper. To remove the center from the hole of the machine spindle or the tailstock quill, a support part 3 is used, the diameter of which is less 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 performed.
When processing workpieces of small diameter (up to 4 mm), it is difficult to make a center hole in them, so the end part of such a workpiece is machined at an angle of 60°, and its fastening is carried out using a center with a reverse cone (Fig. 6.3, b). If during processing it is necessary to trim the end of a 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 secure it (Fig. 6.3, d). A center with a grooved working surface (Fig. 6.3, e) is used when processing workpieces with a large center hole without a driving chuck. Due to the fact that during processing large friction forces arise in the centers, to increase the durability of the centers, a hard alloy is used for their working part (Fig. 6.3, f); Such centers are installed in the tailstock quill. Along with solid centers, rotating centers are widely used (Fig. 6.4). Such a center consists of a housing 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 installed on the bearings.
Drive chucks and clamps are also used to transmit rotational motion from the spindle to the workpiece.
Lead cartridges
Lead cartridges(Fig. 6.5) are used when processing workpieces 5 in centers 4 and 6. The transmission of motion is carried out by a driver chuck 7 through a driver pin 2 and a clamp 3, secured to the workpiece with a screw.
Clamp(Fig. 6.6) is put on the workpiece being processed in the centers and secured with screw 1. With shank 2, the clamp rests against the pin of the driver chuck.
Gaskets are intended to set the tip of the cutter along the center line; they are metal plates of various thicknesses with dimensions corresponding to the dimensions of the supporting surface of the cutter. The plates are installed in a tool holder under the cutter, and the thickness of the set is selected such that the tip of the cutter is on the center line. The position of the cutter tip is controlled by the center tip mounted 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 drives are used. Various shaped castings and forgings are secured in two-jaw self-centering chucks; The jaws of such chucks are usually designed to secure only one part. Three-jaw self-centering chucks hold round and hexagonal workpieces or large diameter round rods. In four-jaw self-centering chucks, square-section rods are fixed, and in chucks with individual adjustment of the jaws, parts of rectangular or asymmetrical shape are fixed.
The most widely used is a three-jaw self-centering chuck (figure below). Cams 1, 2 and 3 of the cartridge move simultaneously using disk 4. On one side of this disk there are grooves (shaped like an Archimedean spiral) in which the lower projections of the cams are located, and on the other there is a cut bevel gear mated to three bevel gears 5. When you turn one of the wheels 5 with a key, disk 4 (thanks to gearing) also turns 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 move closer to the center of the chuck or move away from it, clamping or releasing the part. The cams are usually made in three stages and are hardened to increase wear resistance. There are cams for securing workpieces on the internal and external surfaces; when fastening on the inner surface, the workpiece must have a hole in which the cams can be placed.
The jaw chucks can be equipped with a motorized drive - traction or built-in. Chucks with traction drive have clamping elements connected by solid or hollow rods to a pneumatic or hydraulic cylinder. The figure below shows the design of a two-jaw lever chuck with replaceable jaws 14, which are pre-installed on the workpiece (relative to the axis of rotation) by displacing the crackers 12 (fastened to the jaws 14 with screws 13) along the grooves in the sliders 11. The sliders 11 are moved to the center of the chuck by levers 10, which, when moving the stop 15 (together with the rod 3), rotate around the axis 9 in the body 8. When turning, the levers 10 rest on the surface 7. The movement of the sliders 11 (together with the cams 14) from the center of the cartridge is carried out by the conical surface of the stop 15 when the rod 3 moves in reverse , connected to the stop by means of a guide sleeve 6 and connecting parts 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 by flange 1. The rubber ring 11 softens the impacts of the piston on the flange 4. O-rings 10 and 12 ensure the tightness of the pneumatic drive. The sliders 7 (with clamping jaws 8) have projections 9 that fit into the grooves of the piston 5. The angle of inclination of the grooves is 40.5 degrees, which ensures self-braking conditions. When air is supplied through channels 2 and 3 into 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, unclench or clamp the workpiece. 
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A four-jaw chuck with independent movement of the jaws (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, which is used to independently move the jaws along the grooves in the radial direction. Screw 3 is held against axial displacement by block 2. When the cams are rotated 180 degrees, the chuck can be used to fasten workpieces on the inner surface. On the front surface of the chuck there are concentric circular marks (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 chuck.
Jaw chuck for machining eccentric surfaces
Collet chucks for three-jaw chuck 
Three-jaw chuck with adjustable jaws
Processing of eccentric surfaces on lathes is carried out using various devices. However, for the most part they do not meet the requirements of modern production. Some of them are complex and cumbersome, others require time-consuming setup.
At the Leningrad Automatic Machine Tools Plant, innovator S.V. Litvinov developed and introduced a cartridge that is easy to manufacture and configure, and also has high rigidity and versatility. The main part of the chuck (Fig. 1) is the mandrel 9, which has three parts: a conical shank with a Morse taper No. 5, a cylindrical belt with a diameter of D1=70 mm and a flange. A faceplate 4 is placed on the cylindrical belt, connected to it by a key 8 and attached to the flange with three screws 12. At the end of the faceplate there is an annular “recess” with an axis // offset from the axis /, common to the shank and the cylindrical surface of the mandrel, by 5 mm . In this sample, ring 5, adapter 3 and a standard three-jaw chuck with a diameter of 130 mm are installed, fastened together with screws 2 and 13. Moreover, the cartridge is seated on the 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 using three T-shaped 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 hole in the faceplate.
On the front end of the faceplate there are divisions 11. Each division corresponds to such an angular 
the position of the block at which the /// axis shifts 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, adapter 3 has an angular mark (groove) 10.
To adjust the chuck / to the required machining eccentricity, it is necessary to loosen the nuts 7, rotate 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 manufacturing accuracy of the device parts and will practically not exceed the sum of the errors in the eccentricities of surfaces D2 and D3. Thus, with an error of ±0.05 mm, which is technologically easily achievable, the adjustment accuracy will not exceed ±0.1 mm.
This device allows you to adjust the eccentricity with higher accuracy. To achieve this, you need to use the indicator and make adjustments directly on the machine.
Overall dimensions of the cartridge: 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.
3-jaw lathe chucks
3-jaw lathe chucks are used as part of the 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 to the flanged ends of the spindles under the rotary washer; type 3 – with fastening directly to the flanged ends of the spindles. 
The standard delivery set includes the three-jaw lathe chuck itself, reverse and straight jaws, and a clamping wrench.
The rotating turning center is used for installing workpieces such as bodies of rotation when performing precision work on metal-cutting machines with manual and program control. Equipment of this type provides the ability to clamp a workpiece of maximum diameter and dimensions for cutting at maximum rotation speed with minimal runout. According to technical parameters, a distinction is made between standard and extended rotating turning centers.
The tool holder is used to secure tools of various sections using a replaceable bar and bolts, for example, turning tools on a 16K20 machine. This technical equipment is characterized by high positioning accuracy and durability. The shank of the quick-detachable tool holder standardly complies with generally accepted GOST standards.
For turning operations we use a three-jaw chuck. Such chucks are made with two or three eccentric cams with a notch, which, at the beginning of processing, under the action of cutting forces, clamp the workpiece installed in the centers of the machine and transmit torque to it from the machine spindle. Uniform clamping of the part by all jaws is ensured by the use of floating jaws or jaws with independent movement. Self-clamping driver chucks allow jaws to be installed on different workpiece sizes.
The part is fixed on the untreated surface with simultaneous centering by the center 8. By the pressure of the part, the center 8 is recessed and ensures that the end of the part reaches the stop against the base surface of the sleeve 14. The faceplate 6 of the cartridge is installed with a conical hole on the machine spindle and secured with ties 7 to the faceplate. The flange 1 of the chuck is connected to the faceplate with screws 24 and is fixed with a screw 23. The cams 3 are secured in the chuck with screws 4. To simultaneously clamp the part with two cams, the flange 1 can move relative to the faceplate 6 in the direction of its grooves and is rotated by a spring to the initial position. Cams 3 are connected to counterweights 15 using pins 20.
At the moment the machine is turned on, the spindle with the chuck begins to rotate and the cams 3, under the influence of centrifugal forces from the counterweights, instantly turning on the fingers, pre-clamp the part, and prevent it from turning at the beginning of cutting from the components of the cutting forces. After processing the part, the machine is turned off, the spindle does not rotate, the cams 3, pushers 19, under the action of springs, are rotated on the fingers to their original position and the part is pressed out.
Calculation of cartridge for accuracy
When calculating accuracy, the total error when processing a part should not exceed the tolerance value T of the size.
The total error depends on a number of factors and in general the accuracy of the device is calculated using the formula:
pr = T - K t1 ·
where, T is the tolerance of the size being performed, mm;
b - basing error,
b = 0, mm since the part is fixed in the centers;
z - fastening error, z = 0 mm when fixing the workpiece in the centers;
y is the error in installing the device on the machine,
y = 0.025 mm, since the chuck is installed in a spindle with a Morse taper No. 6;
and - error in the position of the part due to wear of the installation elements of the device, and = 0.014 mm;
pi is the displacement error of the cutting tool, pi = 0 mm, since there are no guide elements in the device;
K t1 is a coefficient that takes into account the deviation of the scattering of the values of the component quantities from the law of normal distribution, K t1 =0.8;
Economic precision of processing;
k t1 is a coefficient that takes into account the reduction in the maximum value of the basing error on configured machines, k t1 =1;
k t2 - coefficient taking into account the share of processing error in the total error caused by factors independent of the device, k t2 = 0.6;
Substituting the values of all errors into the formula, we obtain the following device error.
A lathe chuck is an important element of lathe equipment. The accuracy of the processing depends on how securely the workpiece is secured to the machine. The duration of operation depends on the quality of manufacture of the cartridge. In the process of improving metalworking technologies, many cartridge designs were developed, from which the most effective were selected.
Securing chucks on a lathe
Fastening and centering of lathe chucks is carried out on the spindle of the lathe. The diameters of the cartridges and methods of their fastening are standardized. Depending on the manufacturer, the cartridges will be designated by type (according to ISO) or version (according to GOST). A common spindle end design is a Type C or Type D (cam-lock) mount. There are other spindle designs.
For fastening lathe chucks, flanges and faceplates placed on the spindle are widely used. They have the same design as a lathe chuck flange, but these attachments offer significant versatility since they can accommodate a variety of chucks. The faceplates have numerous holes for tightening 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 is divided into cam, drive, and collet. The first group has now practically replaced the second and, in turn, is divided into self-centering, usually with 3 jaws, and non-self-centering, in which the number of jaws can be 2, 4 or 6. Six-jaw chucks are used the least often.
- Mechanized: Pneumatic, hydraulic, electric. They automate the process of clamping and releasing a workpiece with a given force. Hydraulic chucks are more often used on machines with a chuck diameter greater than 200 mm (diameters of imported chucks are indicated in inches 6, 8, 10, 12, 15 and further inches). Pneumatic chucks are used on automatic lathes. Collet chucks are used to clamp rod workpieces of relatively small diameter. Electrical. are not widely used.
The outer diameter of lathe chucks ranges from 80-1000 mm, of which chucks with a diameter of 80-400 mm are the most popular.
