Turning grooves on a lathe. External groove turning and cutting. Cutting cutters

Narrow grooves are machined with slotted cutters. The shape of the cutting edge of the cutter corresponds to the shape of the groove being machined. Slotted incisors can be straight or bent, which in turn are divided into right and left. The most commonly used slotted incisors are right straight and left bent. In Figure 29: a) - straight left, b) - straight right, c) - bent left, d) - bent right

Rice. 29. Slotted incisors

The rigidity of the part does not always allow cutting grooves of a given width in one cutter pass. When it is necessary to machine a groove wider than 5 mm in a non-rigid part, this is carried out in several passes of a cutter with a transverse feed (Figure 30). At the ends and along the diameter of the groove, an allowance of 0.5-1 mm is left for finishing, which is performed with the same cutter or a groove cutter with a cutting edge size equal to the specified groove size.

Rice. 30. Grooving

Workpieces and parts are cut with cutting tools. The width of the cutting edge of the cutting tool depends on the diameter of the workpiece being cut and is taken equal to 3; 4; 5; 6; 8 and 10 mm. The length L of the head of the cutting cutter should be slightly more than half the diameter D of the rod from which the workpiece is cut (L>0.5D). Cut-off cutters are manufactured in one piece or with inserts made of high-speed steel or carbide. To reduce friction between the cutter and the material being cut, the cutter head tapers towards the rod at an angle of 1-2 degrees (on each side of the cutter), angle l=0, clearance angle a=12 degrees (Figure 30: d, g). In parting cutters, the auxiliary lead angle must be less than the auxiliary clearance angle. An incorrect ratio of these angles can lead to increased friction of the rear auxiliary surface of the cutter on the machined surface of the part and, as a result, to increased wear or breakage of the tool.

Cutting cutters should be installed at right angles to the axis of the workpiece (Figure 30b). Installing the cutting edge of the cutter above the axis of the workpiece (even by 0.1-0.2 mm) can lead to its breakage, and when installing the cutting edge of the cutter below the axis of the workpiece an unprocessed protrusion remains at the end of the part. The distance o from the end of the device for securing the rod to the machined end of the rod should be minimal and not exceed the diameter of the rod being cut (Figure 30a).

When cutting brittle material, the workpiece breaks off before the cutter reaches the center of the workpiece, resulting in a protrusion (boss) remaining at the end of the workpiece. For

Rice. 30. Cutting blanks and parts

To obtain a smooth end, the cutting edge of the cutter is made at an angle of 5-10 degrees (Figure 39d). After cutting off the part, the cross feed is not turned off and the boss on the workpiece is cut off. You can cut the part with a curved cutting cutter: “Goose” (Figure 30c), while the spindle should rotate clockwise. To reduce the surface roughness obtained after cutting, chamfers 1-2 mm wide are made on the rear auxiliary surfaces of the cutter. Transverse feed when processing grooves - 0.05-0.3 mm/rev (for steel parts with a diameter of up to 100 mm). The cutting speed when processing grooves and cutting off workpieces is 25-30 m/min (for cutters made of high-speed steels) and 125-150 m/min (for carbide cutters).

Narrow grooves are machined with slotted cutters. The shape of the cutting edge of the cutter corresponds to the shape of the groove being machined. Slotted incisors can be straight or bent, which in turn are divided into right and left. The most commonly used slotted incisors are right straight and left bent. In the picture on the right: a) - straight left, b) - straight right, c) - bent left, d) - bent right

The rigidity of the part does not always allow cutting grooves of a given width in one cutter pass. When it is necessary to machine a groove wider than 5 mm in a non-rigid part, this is done in several passes of a cutter with a transverse feed (figure on the right). At the ends and along the diameter of the groove, an allowance of 0.5-1 mm is left for finishing, which is performed with the same cutter or a groove cutter with a cutting edge size equal to the specified groove size.

Workpieces and parts are cut with cutting tools. The width of the cutting edge of the cutting tool depends on the diameter of the workpiece being cut and is taken equal to 3; 4; 5; 6; 8 and 10 mm. The length L of the head of the cutting cutter should be slightly more than half the diameter D of the rod from which the workpiece is cut (L>0.5D). Cut-off cutters are manufactured in one piece or with inserts made of high-speed steel or carbide. To reduce friction between the cutter and the material being cut, the cutter head tapers towards the rod at an angle of 1-2 degrees (on each side of the cutter), angle φ=0, clearance angle α=12 degrees (figure below: d,g). In parting cutters, the auxiliary lead angle must be less than the auxiliary clearance angle. An incorrect ratio of these angles can lead to increased friction of the rear auxiliary surface of the cutter on the machined surface of the part and, as a result, to increased wear or breakage of the tool.

Cutting cutters should be installed at right angles to the axis of the workpiece, figure b) Setting the cutting edge of the cutter above the axis of the workpiece (even by 0.1-0.2 mm) can lead to its breakage, and when installing the cutting edge of the cutter below the axis of the workpiece, an unprocessed protrusion remains at the end of the part. The distance o from the end of the device for securing the bar to the machined end of the bar should be minimal and not exceed the diameter of the bar being cut (Figure a).

When cutting brittle material, the workpiece breaks off before the cutter reaches the center of the workpiece, resulting in a protrusion (boss) remaining at the end of the workpiece. To obtain a smooth end, the cutting edge of the cutter is made at an angle of 5-10 degrees, figure e). After cutting off the part, the cross feed is not turned off and the boss on the workpiece is cut off. You can cut off the part with a curved cutting cutter: “Goose” figure c), while the spindle should rotate clockwise. To reduce the surface roughness obtained after cutting, chamfers 1-2 mm wide are made on the rear auxiliary surfaces of the cutter. Transverse feed when processing grooves - 0.05-0.3 mm/rev (for steel parts with a diameter of up to 100 mm). The cutting speed when processing grooves and cutting off workpieces is 25-30 m/min (for cutters made of high-speed steels) and 125-150 m/min (for carbide cutters).

Control of external ledges, ends and grooves.

The depth of the grooves on the outer surface of the part is measured with a ruler, picture on the right a), a caliper, picture on the right b), a depth gauge, picture on the right c) and a step gauge, picture on the right d). The width of the treated area to the ledge is measured with a ruler if great measurement accuracy is not required. With more high requirements For measurement accuracy, it is better to use a caliper, and in mass production of parts, a step gauge. When measuring, the passing side of the template (PR) should rest against the machined cylindrical surface of the part, and the non-passing side (NOT) should rest against the outer cylindrical surface of the part.

Grooving cutters. For cutters intended for turning grooves, the shape of the cutting edge must accurately reproduce the profile of the groove. Cutters for turning grooves are called slotted.

Since the width of the grooves is usually small, the cutting edge of the slotted tool is made narrow (Fig. 147), which creates the risk of its breakage. This danger is further increased by the fact that the cutter head is narrowed towards the rod by 1-2° on each side (Fig. 148) to reduce friction of the side surfaces against the groove walls. To increase the strength of slotted cutters, the height of their heads is made several times greater than the width of the cutting edge. For the same purpose, the head is given a small rake angle or a radius (curvilinear) sharpening is made.

Parting cutters. For cutting, cutters similar to slotted ones are used, but with a longer head (Fig. 149). To reduce material loss during cutting, cutting tools are made with the narrowest possible cutting edge. The length of the cutter head should be slightly more than half the diameter of the bar or workpiece being cut.

Grooving and parting cutters are usually made as composites (see Fig. 149): holder 2 is made of carbon steel, plate 1, welded or soldered to the holder, is made of high-speed steel or hard alloy.

Parting cutters from production innovators. High-speed turners successfully use cutting tools equipped with carbide plates. In Fig. 150 shows a carbide cutting cutter designed by the innovative turner T. Mekhontsev. The cutter has a groove on the front surface that facilitates the flow of chips: resting against the ledge, the chips break off in separate half rings and fly out of the groove.

Technician D. Ryzhkov developed a turning cutting cutter with mechanical fastening of a hard alloy plate (Fig. 151) for cutting parts with a diameter of up to 80 mm.

The cutter body consists of a prismatic holder 4 and a narrow head 5. A groove is milled in the head, thanks to which its upper part springs and, when tightening the screw 3, presses the carbide plate 1. A carbide plate 2 is also installed in the head, which serves for curling and breaking chips. To protect the plate 1 from shifting, there are grooves in its lower surface. The same corrugations are present in the head body.

Innovative turner at the Krasnoye Sormovo plant V. Godyaev proposed an improved design of a cutting carbide cutter (Fig. 152). In this cutter, the carbide plate is obtained by grinding into a wedge shape with an angle of 60°. The same wedge shape is given by milling the groove of the holder. The angular shape of the plate and groove increases the soldering area of ​​the plate by 1.5 times and helps create a strong fastening that prevents the plate from moving under the influence of lateral forces. This allows processing with higher cutting conditions. The cutting speed when cutting reaches 100 m/min and the feed is 0.4-0.5 mm/rev.

Installation of slotting and parting cutters. When cutting or cutting deep grooves, special attention must be paid to accurate installation and good fastening of the cutter in the tool holder, since a small installation error (distortion of the cutter) causes friction of the groove walls against the side surface of the cutter. In this case, defects and breakage of the cutter are inevitable.

To check the correct installation of the cutter, use the already machined cylindrical part of the part, and when cutting from the workpiece, install a precisely machined roller in the centers. Then apply a square on both sides of the cutter. In this case, an angular gap of at least 1° must be clearly visible on both sides and along the entire length of the cutter head (see Fig. 148).

Cutters for turning grooves, as well as cutting tools, must be installed strictly at the height of the centers of the machine; This is especially important when working with cutting tools. Their location above or below the center axis can easily lead to breakage of the incisors.

2. Grooving and cutting techniques

Turning narrow grooves. To make grooves, parts are installed in chucks or centers, or in a chuck supported by the rear center.

The place where the groove should be machined or the part should be cut is determined using a measuring ruler. Narrow grooves are machined in one cutter pass.

Turning wide grooves. Wide grooves are machined in several passes. The procedure for turning wide grooves is as follows:
1. First, use a ruler or template to mark the boundary of the right wall of the groove and bring in the tool holder with the cutter (Fig. 153, a). Having installed the cutter correctly, it is given transverse movement to the depth of the groove minus 0.5 mm per finishing pass.
2. Then, moving the cutter to the left, as shown in Fig. 153, b, expand the groove, and before the last pass (Fig. 153, c) mark the border of the left wall of the groove using a ruler.
3. The final cutter pass is shown in Fig. 153, e: first, the cutter is fed along the dial of the cross-feed screw to the full depth of the groove, and then the cutter is allowed to move longitudinally from left to right and the groove is processed completely.

Cutting off. When cutting, the rod is inserted into the spindle hole and secured in the chuck so that the length a remaining after cutting does not exceed the diameter of the rod (Fig. 154). When cutting, do not allow the cutter or part to shake, as in this case the cutter may break.

A part mounted on centers or in a chuck with its end supported by the rear center cannot be cut to the end unless the end to be cut is installed in the rest. Otherwise, a very thin rod may form at the site of the cut, which will break under the pressure of the cutter and the weight of the part being cut, the cutter will become pinched and will inevitably break.

If the cutting edge of a cutting tool is sharpened parallel to the axis of the centers, then the part being cut may break at the moment when the cutter has not yet reached the center. In this case, a protrusion (in the form of a boss) will remain on the cut part, which will then need to be cut off. If, for cutting, you use a cutting cutter, in which the right corner of the cutting edge goes in front of the left (Fig. 155), then the cutting will occur to the very center.

The boss remaining on the right side of the workpiece is cut off with a scoring cutter during subsequent processing.

When cutting large diameter parts, a cutter with a long head is required. To reduce jitter, it is recommended: 1) to cut with the spindle rotating in reverse, using a curved cutting tool, which is installed with the cutting edge down (Fig. 156); 2) tighten the caliper wedges and tighten the caliper clamp screw against longitudinal displacement; 3) increase the feed to the maximum permissible values; 4) apply abundant cooling.

3. Cutting modes when turning grooves and cutting off

When turning grooves and cutting, the cutting depth t is taken to be the width of the cut (see Fig. 148), and the feed s is the amount of movement of the cutter perpendicular to the axis of the part in one revolution.

Due to the low rigidity of the cutter and poor conditions for heat dissipation when turning grooves and cutting, the following feeds and cutting speeds are used:

at work high-speed cutters for medium-hard steel, the feed rate is taken from 0.07 to 0.2 mm/rev, and the cutting speed is in the range of 15-30 m/min;

at work carbide cutters for medium-hard steel, the feed rate is taken from 0.07 to 0.1 mm/rev, and the cutting speed is 150-180 m/min. Thus, the productivity of carbide slotting and parting cutters is 5-6 times higher compared to high-speed steel cutters.

4. Groove measurement

Grooving is carried out with transverse feed, using the dial of the transverse feed screw.

The diameter of the machined groove is measured with a caliper (Fig. 157), of course, if the groove is wider than the legs of the caliper. Often, it is not the diameter of the groove that is measured, but its depth, using a measuring ruler, a template (Fig. 158), a caliper or a vernier depth gauge.

The width of the groove is measured with a ruler, caliper, template, gauge.

5. Defects during grooving and cutting and measures to prevent it

When turning grooves and cutting, the following types of defects are possible:
1) incorrect location of the groove along the length of the part;
2) incorrect groove width (more or less than required);
3) incorrect groove depth (more or less than required);
4) incorrect length of the cut part;
5) insufficient cleanliness of the surface of the groove or the end of the cut part.

1. The first type of defect occurs when the space for the groove is incorrectly marked or the cutter is installed incorrectly and is the result of the lathe’s carelessness. Marriage is irreparable. You can prevent defects by carefully marking the marks for the grooves, checking the marks applied and correctly installing the cutter along the length of the part.

2. The groove width is larger or smaller than required if the cutter width is chosen incorrectly. The defect is irreparable when the groove width is larger than required; If the groove width is less than the required one, correction is possible by additional turning.

3. A groove depth greater than required is obtained with an incorrect cutter passage length. Marriage is irreparable.

4. The incorrect length of the cut part is obtained due to the inattentive work of the worker. The defect is irreparable if the length of the cut part is less than the required length.

5. Insufficient cleanliness of the surface of the groove, as well as the end of the cut part, occurs for the reasons stated above (p. 158) for the same type of defect. In addition, the cause may be incorrect installation of the cutter, which touches the side edge of an already machined surface.

Control questions 1. What are the design features of grooving cutters?
2. Why does the head of the slotted cutter taper towards the shaft?
3. What is the difference between parting cutters and slotting cutters?
4. How are parting and slotting cutters installed?
5. How is the cutting tool designed for cutting when the spindle rotates in reverse (see Fig. 156)?
6. How and with what do you measure the location of the grooves being machined on a part?
7. How do you check the width and depth of the groove being machined?
8. Indicate the main types and causes of defects when turning grooves and cutting.

Cutters for cutting external grooves. The slotted cutter is shown in Fig. 114. The most important size of this cutter is its width, which is selected depending on the adopted method of processing the groove.

If cutting a groove is carried out with one pass of the cutter, then its width is taken equal to the width of the groove. When processing a groove is carried out with two passes of the cutter, its width is taken to be slightly more than half the width of the groove, etc.

The length of the working part of the cutter should be slightly greater (2-3 mm) than the depth of the groove. The back angle of the slotted incisors is made equal to 12°; auxiliary rear angles are taken equal to about 2°; The rake angle is selected as for through cutters, depending on the material of the cutter and the material of the workpiece. Auxiliary plan angles are made from 1 to 2°. The deeper the groove being cut, the larger these angles should be.

Rice. 114. Slotting tool for external grooves

Grooving Techniques. Grooving is done with one or more passes of the cutter.

The ability to cut a wide groove in one pass is limited by the vibration of the part. Therefore, this method is used when cutting grooves up to 5 mm wide in non-rigid (thin and long) parts. In more rigid parts (short and large diameters), grooves up to 10 mm wide can be cut with one pass of the cutter, and in very rigid parts, even up to 20 mm wide. Installation of a cutter for cutting a groove located at a distance from the end of the part using a ruler is shown in Fig. 115, a.

Rice. 115. Cutting grooves with one (a) and several (b) passes of the cutter

For wide grooves that are imprecise (in width and position), the cutter should be installed during the first pass as shown in Fig. 115, a, i.e., so that the distance from the right wall of the groove to the end of the part is obtained immediately. The groove depth obtained after the first pass of the cutter should be 0.5-1 mm less than the required one. The same allowance for finishing the groove bottom must be left for all subsequent transverse passes of the cutter.

During the last pass of the cutter, its installation relative to the end of the part (distance L 2) is checked using a ruler, as shown in Fig. 115, b. During this passage of the cutter, it moves forward so that the depth of the groove is equal to the required one. Stopping the transverse feed of the cutter and moving it longitudinally from left to right, you should clean the bottom of the groove.

When cutting precise grooves (in width and position) in several passes, it is necessary to leave an allowance of 0.5-1.0 mm for finishing on the right wall of the grooves during the first pass of the cutter (Fig. 115, a). The same allowance should be left on the left wall of the groove. Finishing of these walls is carried out with a groove cutter with a transverse feed (to the center of the part), and the first to be machined is the wall up to which the size is specified, which determines the position of the groove. So, for example, when cutting a groove (Fig. 116, a) it is necessary to maintain the size L 1. Therefore, the left wall of this groove is processed first, and the size L 1 is measured (for example, with a ruler). If the position of the groove was determined by the size L 2 (Fig. 116, b), then the right wall should first be processed, measuring the size L 2, for example, with a template.

Rice. 116. Measurements when checking groove position

Finishing of the groove wall is sometimes carried out using scoring cutters (right and left), using the same techniques as when cutting ledges.

In some cases, finishing of the groove walls is carried out with a slotted cutter, the width of which is equal to the width of the groove. In this case, it is only important to ensure that the cutter is installed in such a way that the position of the groove is correct.

Finishing the bottom of fine (width) grooves is carried out in the same way as was indicated above for processing the bottom of coarse grooves.

Cutting modes when cutting grooves. Feed when cutting grooves is usually manual. The cross feed should be small - from 0.05 mm/rev with a cutter width of 2 mm and up to 0.20 mm/rev if the cutter width is close to 10 mm.

Cutting speeds when cutting grooves should be low.

Due to the peculiarities of their design, groove cutters (also called slotting cutters) are considered multifunctional tools that can be used to form grooves on workpieces of cylindrical and conical configurations. Such technological operations (especially those associated with radial grooving) are characterized by significant loads, which are successfully carried by a cutter of this type, characterized by high structural rigidity. Moreover, groove cutters are successfully used for axial grooving and facing, making them versatile turning tools.

Grooving cutters for internal and external grooves with mechanical fastening of replaceable cutting inserts

It is advisable to use grooved ones to obtain parts with complex configurations. The versatility of cutters of this type in such cases allows us to minimize the number of tools used and reduce the time for equipment changeover. It is also noteworthy that the use of a groove cutter when performing many technological operations makes it possible to form surfaces with higher quality characteristics than when using a conventional turning tool.

Particularly successful is the use of a groove cutter when creating wide grooves on the surface of workpieces. When performing this technological operation, such a tool demonstrates exceptional durability; wear of its cutting plate occurs evenly even when performing large quantity passages. What is also important is that when using a groove cutter, the chip separation process is well controlled.

Requirements for groove-type cutters, which are produced in a wide variety of standard sizes, are specified by the provisions of GOST 18874-73.

GOST 18885-73 and 18874-73 regarding groove cutters

The contents of GOST 18874-73 “Slotting and cutting lathe cutters from” and GOST 18885-73 “Threaded lathe cutters with hard alloy plates” can be found below:

Types of groove cutters

Turning tools for forming grooves include cutters for internal and external machining. Both the first and second can be made entirely of carbide materials or have a replaceable cutting part. Carbide cutters are a fairly expensive tool, so their use must be economically feasible. When performing external work, products with replaceable inserts are usually used; using carbide groove cutters in such cases does not make sense.

The situation is completely different with the processing of internal grooves. Here it is necessary to take into account the diameter of the hole into which the cutter is to be inserted, as well as the rigidity of the tool. The requirements for which the cutter has minimum size their holder and sufficient rigidity for metal processing are satisfied only by carbide grooving tools.

Naturally, when the processing conditions and geometric parameters of the workpiece allow it, it is more advisable to use an inexpensive tool with replaceable inserts to form external and internal grooves.

Geometry and dimensions of groove type cutters

Since groove-type cutters experience significant load during processing, which determines increased requirements for their rigidity, they are manufactured with soldered carbide plates, the characteristics of which are specified in GOST 2209-82. The requirements for the cutter itself, as stated above, are given in GOST 18874-73.

The main feature of the geometry of groove-type cutters is that the shape of their cutting part must exactly match the shape of the groove that is planned to be obtained with their help. The grooves created on the surface of the workpiece are usually small in width. Accordingly, the cutting part of the tool with which they are formed is also quite narrow, which makes it very vulnerable to mechanical damage. In addition, the working head on each side has a narrowing towards the holder (by 1–2 degrees). Such a narrowing of the sides of the cutting part is necessary in order to reduce their friction against the walls of the groove being formed.

To increase the strength of the cutting head of a groove turning tool, its height is made significantly larger than its width. This also requires a small rake angle and a sharpening of the cutting edge with a small radius (curvilinear). The optimal cutting angles for groove-type cutters are 15–25 0 (front), 8–12 0 (rear).

The width of the working part of the groove tool, which, according to the requirements of GOST 18874-73, can vary over a wide range, is selected depending on the width of the groove that needs to be formed on the outer or inner surface of the workpiece.

Selection rules

The first thing you should focus on when choosing a groove turning tool is a drawing of the finished product, which indicates both the dimensions and shape of the grooves, as well as the tolerances for their accuracy geometric parameters. Naturally, the choice of cutter and its geometric parameters is influenced by the material from which the workpiece is made.

When forming grooves on parts small size It is especially important to maintain low cutting forces to minimize deformations that occur during machining. Compliance with this requirement is ensured by the sharp sharpening of the groove tool, which, however, can lead to its breakage if the carbide plate material and cutting conditions are selected incorrectly - the rotation speed of the workpiece and the feed rate.

When choosing a groove cutter, you should also take into account the shape of its cutting edge, which can be straight and sharpened with a small radius. Naturally, you should not choose a product with a curved sharpening of the cutting edge if the bottom of the groove, according to the provided drawing, should be straight.

Features of turning using a groove cutter

The cutting modes when using groove-type cutters have some differences from the modes of processing the workpiece with other types of turning tools. Thus, the depth of cut is taken to be a value equal to the width of the groove being formed, and the tool feed per revolution of the part is measured in the direction perpendicular to its axis. The feed rate, depending on the material from which the cutting part of the groove tool is made, is selected in the range of 0.07–0.2 mm/rev, and the cutting speed is 15–180 m/min.

Several types of grooves can be obtained on the surface of the workpiece.

• Narrow grooves, the width of which corresponds to the width of the cutting part of the tool, are made in one pass of the cutter, which is fed manually. Before this, the exact location of the groove is determined on the surface of the part, and then the cutter is placed opposite this place and fed.
• The grooves on the ledges and ends of the part are made according to the same principle; their diameter is set using the transverse feed dial, and their depth is set using the longitudinal movement dial of the caliper.
• Wide grooves are made in several passes according to the following scheme. First, determine the location of the right edge of the groove and place the cutter opposite this location. Using a transverse feed, the cutter is cut into the part to a depth that is 0.5 mm less than the depth of the groove being cut (this allowance is left for finishing). Then, using a longitudinal feed, the groove tool begins to move to the left edge of the groove being cut, the boundary of which has been previously marked. After the rough groove is formed, its bottom is processed cleanly - to the required depth, carrying out the longitudinal feed of the cutter from left to right. In the event that it is necessary to form a groove with a very precise location of its left and right edges, allowances can also be left on them during roughing, which are then removed using the transverse feed of a groove or scoring cutter.

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