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§ 74. Countersinking, countersinking, countersinking.

Countersinking. Provides the necessary accuracy and cleanliness of holes produced by casting, forging or stamping.

Countersinks are made from high-speed steel P9, alloy steel 9ХС or tool carbon steel U12A. Countersinks differ from drills in the design of the cutting part and the large number of cutting edges. The bridge connecting the cutting edges is much larger than that of the drill, and the apex angle is cut off. A larger number of guide strips ensures the correct and more stable position of the countersink relative to the axis of the hole being machined, and the distribution of forces over 3-4 cutting edges ensures smoother operation and a clean and fairly accurate hole. According to their design, countersinks are either solid or with insert plates, and according to the number of teeth (feathers) - three- and four-flute (Fig. 138).

Rice. 138. :

1 - ribbon, 2 - cutting edge

Solid countersinks have three or four cutting edges, and with insert plates - four cutting edges. To process holes with a diameter of 12-20 mm, solid countersinks are used.

With insert plates, countersinks are used when processing holes with a diameter of over 20 mm. They are connected to the mandrel using a protrusion on the mandrel and a cutout on the countersink. Now countersinks are manufactured with a number of teeth reaching up to 8 or more. Several countersinking operations can be performed with one combination countersink. Combined countersinks come in two types: stepped and prefabricated. The latter can be combined with other types of tools - drills, reamers, boring plates, etc.

Countersinking is mostly an intermediate operation between drilling and reaming, so the diameter of the countersink must be less than the final size of the hole by the amount of allowance removed by the reamer.

The use of countersinks significantly improves the quality of machined holes: it reduces taper, ovality, marks, scratches, etc., however, it cannot provide high dimensional accuracy and surface cleanliness of the hole. Therefore, the hole obtained after countersinking is processed with a reamer, which, cutting off very thin chips, calibrates and smoothes the surface of the hole.

Countersinking. It is produced by countersinks, which have cutting edges at the end of the tool (Fig. 139). By design, countersinks are cylindrical, conical and flat.

Rice. 139. Countersinking of cylindrical recesses(A), conical(b), counterbore(V)

(Fig. 139, a) are used for processing sockets with a flat bottom for the heads of bolts and screws. To ensure alignment, the countersinks have a guide pin.

(Fig. 139, b) have a sharpening angle of the conical part equal to 60; 70; 90 or 120°.

The number of cutting teeth may vary depending on the size of the tool. Conical countersinks are used to produce conical recesses for countersunk rivet heads, as well as to remove conical chamfers.

Flat countersink in its design it is a modified drill bit with a pin at the end. With such a countersink you can chamfer or countersink holes for the heads of bolts, screws and rivets, if the sharpening angle is made equal to 90; 75 or 60° (Fig. 139, a). The guide pin is soldered (or screwed) into the body of the countersink, which greatly facilitates regrinding.

When countersinking, chips are removed from light parts by tipping (rather than blowing them off), and from large parts - by a jet of compressed air.

Countering(cleaning of end surfaces). Counterbodies are made in the form of mounted heads with four teeth at the end (Fig. 139, c). Counters are used to process bosses for washers, thrust rings, and nuts.

The cutting mode for countersinking, countersinking and countersinking is selected according to reference tables.

Among the metalworking tools used to create holes, countersinks and countersinks deserve special importance. With their help, openings are made with specified characteristics, for example, stability of important geometric parameters, roughness, narrowing of a cylindrical hole. Let's look at what a countersink and a countersink are.

Terminology

– is a multi-blade cutting tool used for making holes in metal parts. After processing, conical/cylindrical type recesses are obtained, you can create a reference plane near the holes, and chamfer the center hole.

Countersinking of holes– this is the secondary preparation of finished holes for placing hardware heads - bolts, screws, rivets

– a cutting tool with a multi-blade surface. Used in machining cylindrical/conical holes in workpieces to expand the diameter, improve surface characteristics and accuracy. This type of processing is called countersinking. This is a semi-finish cutting process.

A - drilling with a drill B - boring on a lathe C - countersinking with a countersink D - reaming with a reamer E, F - counterbore with a counterbore G - countersinking with a countersink H - thread cutting with a tap

Countersinking holes- the process of cultivating the top of an opening in order, for example, to remove burrs from the edge of the hole or to create recesses to hide the head of rivets or screws and level them with the surface of the part. The tool used for this task is called a countersink.

Types of countersinks and countersinks

The production of metal cutting tools is subject to the main category of country standards (GOST) and technical regulations for the use of the finished product. On units with partially automated control, the following types of countersinks are used:

• Cylindrical, with diameters from 10 to 20 mm. This set of blades is produced with a coating of wear-resistant elements. Regulated by GOST 12489-71.
• Indivisible conical, from 10 to 40 mm. Manufactured from alloy steel with wear-resistant coating. Subject to TU 2-035-923-83.
• Whole, in the form of attachments, with a diameter from 32 to 80 mm. Regulated by GOST 12489-71.
• Conical or mounted, subject to GOST 3231-71. They are marked by the presence of special plates made from hard iron alloys.

A countersink is also a tool with numerous blades, but it has clear differences from a countersink in terms of use. These devices are divided into several types:

• Conical countersink. It has an operating head with a cone angular coefficient of 60,90, 120 degrees. It is mainly used for cultivating bases for fasteners and removing chamfers, that is, to blunt sharp edges. Regulated by GOST 14953-80 E.
• Rounded countersink (cylindrical). The device can have a rounded or conical end, having a wear-resistant coating on the base. Mainly implemented as a treatment for supporting bases.

What is a countersink, systematization

A cutting tool for metal (countersink) allows you to countersink an opening in a part up to accuracy group 5. It is widely used for semi-finishing parts before mechanical reaming. According to its structure, it is divided into types:

• holistic;
• nozzles;
• tail;
• connected.

Externally, metal-cutting devices look like a simple small drill, but have an increased number of cutting edges. The correct dimensions of the opening of the workpiece being processed is determined by the gauge. The tools are fastened in the unit's chuck with the support of the shank.

To cultivate openings with a diameter of up to 10 cm, attachments with 4 points are used. Their main feature is fastening through a mandrel. The presence of a chamfer on the teeth of the element made it possible to achieve correct adjustment of the cut.

Cone countersink design

This device is intended for passing cone-shaped openings of small depth. The main feature in the design of the element is the presence of straight teeth and an absolutely flat outer base. The number of cutting elements, in accordance with calibration, can vary from 6 to 12 units.

Countersinking holes is considered a manual procedure, carried out through a turning unit on which the countersink is mounted. The workpiece is clamped in the machine's grip, and its correct location in the recess is checked. The axial centers of the electric spindle and the rear assembly of the machine must be at the same level. This reduces the risk of the technically movable sleeve (quill) flying out. The tip of the tool is inserted into the hole to be finished manually.

To obtain an opening of the required diameter after the countersinking operation, an allowance of 2-3 mm is made during drilling. The exact allowance values ​​depend on the calibration of the recess in the workpiece being processed. It is more difficult to implement the countersinking process for forged and dense products. To simplify your task, you should bore the countersunk hole by 5-9 mm in advance.

Countersinking can be done in cutting order. In this situation, the tool feed is doubled than when drilling, but the travel speed remains the same. The cutting recess with a countersink is laid at approximately 50 percent of the allowance for the diameter. Countersinking of holes with a tool is carried out using cooling materials. The mechanism made of hard alloys does not require the introduction of auxiliary coolant.

When processing openings, a countersink guarantees high accuracy, but defects cannot be avoided at all. The most common processing defects are:

• Increased opening diameter. The main reason for the occurrence of such a defect is considered to be the use of a device with incorrect sharpening.
• Reduced diameter of the recess. It happens that the wrong tools were chosen for the job or a damaged countersink was used.
• Defiant purity. This flaw can be caused by a number of reasons. Usually, a decrease in cleanliness lies in poor sharpening of the device. In practice, the cause of the defect can also be excessive viscosity of the product material. Therefore, the element sticks to the tool belts. Damage is also caused by the error of the turner, who made an incorrect feed and acceleration of the cut.
• Partial processing of the opening. This reason usually occurs as a result of incorrect fixation of the part or an incorrect countersink allowance saved after drilling.

Types and purpose of countersinks

A countersink resembles a type of drill that is used for countersinking. The operation is similar to countersinking, but the final task differs. The countersinking procedure is needed in situations where there is a need to form rounded recesses to hide the marks of the fastener heads.

The cultivation of parts by countersinking is considered a semi-finishing method, and is carried out before the deployment operation.

According to the design of the countersinks, they are divided into:

• Rounded;
• Conical.

A separate category includes countersinks consisting of hard alloys. They are used as grinding actions. To process openings and remove chamfers in difficult areas, another type of tool is used - a reverse countersink. To ensure the necessary processing of metal products and wood, it is recommended to purchase a countersinking kit rather than using individual tools.

The structure of the cone-type countersinks accommodates the shank and the operated element, with an angular index of 60, 75, 90 and 120 degrees. The number of teeth varies from 6 to 12 units, depending on the diameter of the tool. To ensure the alignment of the cultivated opening, a trunnion is used.

The rounded countersink has a wear-resistant coating. This mechanism is used for chamfer cutting. In design, it resembles a drill, but has a large number of blades - from 4 to 10, it all depends on the diameter of the device. There is a guiding pin at the end of the element. With its help, the position of the tools during operation is recorded. The trunnion can be detachable or integral. In practice, devices with detachable pins are used due to ease of use. You can also attach an attachment cutter to the countersink.

To process several openings into equal recesses, you should use a countersink with holders, which includes various stops. When processing a product, the cutting element is installed in the holder and moves out of the stop by an amount equal to the recess of the opening.

Countersinks are made from various types of steel, including carbide. Tools made of carbide alloys are excellent for processing metal parts, as they can withstand extreme loads for a long time. For processing products made of non-ferrous metal alloy or wood, devices made of high-speed steel are used, since it is subjected to minor loads. It is worth noting that when processing, for example, cast iron products, it is necessary to introduce additional cooling of the tools. For this purpose, special emulsion compositions are used.

The principle of countersinking metal products

When processing an opening created in a part during its casting, it is recommended to bore it several millimeters deep at once so that the countersink selects the correct initial direction.

During the period of work when processing steel workpieces, it is recommended to use emulsion cooling compounds. The procedure for countersinking non-ferrous metals and cast iron does not require additional coolant. A very important stage is the correct selection of tools for carrying out the work. In this regard, attention is focused on the following aspects:

1. The type of tools is selected in accordance with the harvesting materials and the nature of cultivation. The factors of hole location and the number of processes are taken into account.
2. Countersinks and a device for countersinking are selected depending on the specified parameters: the size of the recess, diameter, accuracy of work.
3. The design of a metal-cutting tool is determined based on the method of its fastening on the machine.

The choice of countersink is made according to reference literature or using the normative act of the GOST 12489-71 standard:

• Blanks made from structural steel with openings up to 40 mm in diameter are processed with a countersink made from high-speed iron, including 3-4 teeth and a diameter of 10-40 mm. In holes up to 80 mm, nozzles with a diameter of 32-80 mm are used.
• For hardened iron, when boring, equipment is provided with plates made of hard alloys, with a diameter of 14-50 mm and 3-4 teeth.
• For boring blind openings of cast iron products and non-ferrous metal parts, a feather countersink is used.

A necessary condition for the countersinking procedure is the observance of allowances. As a result, the diameter of the selected tooling must coincide with the final diameter of the opening after processing. If, after countersinking, the opening is to be expanded, then the diameter of the device is reduced by 0.15-0.3 mm. If rough boring or drilling for countersinking is planned, then the edge allowance should be maintained from 0.5 to 2 mm.

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GENERAL INFORMATION

1. FEATURES OF TECHNOLOGICAL OPERATIONS

Drilling used for processing blind and through holes of cylindrical, conical and multifaceted internal surfaces.

Two types of drilling are used:

actual drilling(obtaining holes in solid material);

reaming(increase in the diameter of a hole previously drilled, cast, punched during stamping, stitched, obtained by electrophysical or electrochemical processing methods).

Drilling and reaming ensure accuracy of hole processing according to 10 - 11 qualifications and surface quality Rz 80... 20 microns (when processing small diameter holes in non-ferrous metals and alloys up to Ra 2.5 µm). To obtain more accurate holes, countersinking and reaming are used.

Countersinking, like drilling, they are used to increase the diameter of a previously obtained cylindrical hole, as well as to obtain conical (with conical countersinks) and flat (with the ends of countersinks when processing stepped holes) surfaces. When countersinking after drilling, accuracy of 9-10 grades is obtained, surface quality up to Ra 2.5 microns.

Deployment used for final (finishing) processing of mainly cylindrical holes, less often - for finishing of conical and end surfaces. Accuracy according to 6 - 8 qualifications, surface quality Ra 2.50...0.32 microns.

2. GEOMETRICAL PARAMETERS OF THE CUTTING PART OF DRILLS, COUNTERSINKERS AND REAMERS

Elements of the cutting part of the most common twist drill are shown in Fig. 1 a, b.

A twist drill has two teeth, each of which has its own tip, main and auxiliary cutting edges, its own front surface, main and auxiliary rear surfaces. The drill also has a cross cutting edge (web) that allows the drill to machine holes in solid material.

The geometry of the twist drill is determined by the following sharpening angles.

Front corner g x at the point in question X the main cutting edge is measured in plane I-I, normal to the main cutting edge, between the tangent to the rake surface at the point in question X and the normal to the surface formed by the rotation of the main cutting edge around the axis of the drill.

Back angle a x measured in a plane tangent to a cylinder coaxial with the drill, on the surface of which the point in question lies X main cutting edge, between the tangent to the flank surface at the point X cutting edge and tangent at the same point to the circle of its rotation around the axis of the drill. At the outer surface the angle g X largest, and the angle a x- the smallest.

Drill tip angle 2j measured between the main cutting edges. Angle 2 j prescribed depending on the material being processed: for processing steel, hard bronze 2j= 116... 118°, for processing non-ferrous metals and their alloys of medium hardness 2 j= 130... 140°.

Rice. 9.1. Elements of the cutting part of the drill (a, b), countersink ( c, d) and sweeps (d, f):

1 - main cutting edge; 2 - main back surface; 3 - top of the tooth; 4 - auxiliary rear surface [ribbon]; 5 - auxiliary cutting edge; 6 - groove; 7 - back of the tooth; 8 - front surface; 9 - jumper (at the drill); 10 - guide part (at the reamer); L,l slave, l w, l x, l r, l to, l l, l c. l o .k- the length, respectively, of the tool, its working part, neck, shank, cutting part, calibrating part, foot of the cylindrical section and section with a reverse taper; D r - main movement; d- drill diameter; (j, j 1 - main and auxiliary plan angles; g x, a x - front and back angles at point x; a 0- rear corner of the jumper at point O; w - tooth inclination angle; y- angle of inclination of the jumper; AB - jumper; a l- back corner on ribbon; q- tooth back diameter

Angle of transverse cutting edge y measured between the projections of the transverse and main cutting edges onto a plane perpendicular to the axis of the drill.

The inclination angle of the helical groove w is measured along the outer diameter. As the angle с increases, the rake angle g increases X1 At the same time, the cutting process is facilitated and chip yield is improved. Recommended geometric parameters of the drill are given in the reference literature.

The auxiliary angle j x is created by a reverse taper on the working part of the drill within 0.03...0.12 mm per 100 mm of length. The back surfaces of drills are sharpened along a conical surface, along a plane and along a helical surface.

Elements of the cutting part of countersinks and reamers are shown in Fig. 1.1, V- e. The working part of countersinks consists of a cutting part and a calibrating part - with a reverse taper. The cutting part is inclined to the axis at an angle j and performs the main cutting work.

A twist countersink has 3 to 4 teeth, with almost the same geometry as the teeth of a twist drill.

The working part of the reamers consists of a guide cone with a length l N, cutting part with length i p and calibrating part with length l K. The calibrating part of reamers consists of two sections: a cylindrical length l C and conical 7 0 k long with reverse taper. Reverse taper is made to reduce the friction of the tool on the machined surface and reduce the size of the hole.

The reamer has 6 - 12 teeth. Angles g, a to And w sweeps are usually equal to zero.

Drills, countersinks and reamers are made from tool and high-speed steels, hard alloys VK6, VK8, VK3M, VK6M, VK8V. Carbide drills are widely used for machining holes in heat-resistant and stainless steels and alloys, titanium and its alloys, and thermosetting plastics.

3. ELEMENTS OF CUTTING MODE AND CUT LAYER

The main movement when drilling, reaming, countersinking and reaming is rotational D r, and the feed movement is forward D s. Cutting patterns for drilling, reaming, countersinking and reaming are shown in Fig. 2. Cutting speed, m/min or m/s, at the periphery of the tool

Where D- diameter of the treated surface, mm; n- tool rotation speed, rpm.

Rice. 1.2. Cutting patterns:

a - drilling; b - drilling; V - countersinking; g - deployment; 1 - workpiece; 2 - drill; 3 - countersink; 4 - scan; D, D 0- diameters of machined and machined surfaces; D r- main movement; D s- feed movement; A, And b- thickness and length of the cut layer; s- feed per revolution; s z - feed per tooth; t- cutting depth; j- main plan angle

Innings s- the amount of movement of the tool along the axis per revolution. Innings s z , per one tooth of the tool, s z = s/z (z- number of tool teeth).

Thickness A the cut layer is measured in the direction perpendicular to the main cutting edge of the tool, and the width b of the cut layer - along this cutting edge.

When drilling below cutting depth t imply the distance from the machined surface to the drill axis (t = D/2), and when drilling, countersinking and reaming - the distance from the processed to the processed surface: t = (D - D 0)/2.

When drilling axial force P 0(feed force, N), calculated using the formula

P o = C p D zp s yp k p.

Torque M cr, N m, cutting when drilling

M k p = C M D zM S yM k M .

When drilling, countersinking and reaming, the tool is subject to an axial force (usually a small amount) and a torque M cr, N m, cutting

M Kp =C M D zM t xM S yM k M

Where S R And Cm- constant coefficients characterizing the material being processed and the conditions for its processing; z P , y P, z M , x m, y m- degree indicators; D mm, t, mm, and s, mm/rev, - respectively the diameter of the machined surface, depth of cut, and feed; to R And k m- general correction factors taking into account specific processing conditions. Effective power, kW, cutting

Where M cr- cutting torque, N m; n- rotation speed of the tool or product, rpm.

When drilling, cutting speed, m/min or m/s,

When drilling, countersinking and reaming

Where C v- a constant coefficient characterizing the material being processed and the specific processing conditions; z v , x v , y v- degree indicators; T- indicator of relative resistance; kv- general correction factor taking into account specific processing conditions; T - period of durability.

The drilling and boring group of machines, the second group according to the ENIMS classification, consists of two subgroups: drilling and boring. Drilling machines are designed to work with drills, countersinks, reamers, taps, etc., and boring machines, in addition, are mainly designed to work with boring tools of various designs. Depending on the location of the spindle, drilling machines are divided into vertical and horizontal drilling, and depending on the number of spindles - into single and multi-spindle. Tabletop drilling machines are produced for drilling holes with a diameter of up to 16 mm; vertical drilling and radial drilling - for drilling holes with a diameter of up to 100 mm. Horizontal drilling machines are designed to produce deep holes using special drills.

CUTTING TOOLS AND TECHNOLOGICAL EQUIPMENT FOR DRILLING MACHINES

CUTTING TOOLS

Holes on drilling machines are processed with drills, countersinks, reamers and taps. All these tools are axial. Processing with these tools is carried out with a main rotational movement D r tool or workpiece and with one feed movement D s(usually a tool) along the axis of the tool or the machined surface.

When processing with axial tools, three kinematic schemes are possible:

the main movement and the feed movement are transferred to the tool. This scheme is implemented on drilling, jig-boring, aggregate-drilling and aggregate-boring machines. With this scheme, the tool axis shifts if this axis does not coincide with the direction of feed of the workpiece or tool;

the main movement is transferred to the workpiece, and the feed movement is transferred to the workpiece or tool. Used on lathes, turret lathes and automatic lathes. The drift of the tool axis can occur in this case only due to the uneven sharpening of the tool teeth;

rotational motion is also transmitted to the workpiece (v 3, m/min or m/s), and tool (v and m/min or m/s). Main movement D r in this case, it will be the one whose speed is greater (usually this is the rotation speed of the tool v i).

Cutting speed (total), m/min or m/s, is determined by the formula v= v 3+ v i.

The feed motion is communicated to either the tool or the workpiece.

This scheme is used only for drilling on some automatic machines and special machines. The diametrical size is more accurate than with the previous scheme.

Drill According to design and purpose, they are divided into spiral, centering and special. The most common tool for drilling and reaming is a twist drill (see Fig. 1.1, a, b), consisting of a working part l slave, cervix l w, shank l x and paws l l.

In the working part l slave distinguish between cutting l r and calibrating guide l to parts with helical grooves. Neck l w connects the working part of the drill to the shank. Shank l x necessary for installing a drill in the machine spindle. Paw l l serves as a stop when knocking the drill out of the spindle hole.

The elements of the working part and the geometric parameters of the twist drill are shown in Fig. 1.1, b. The drill has two main cutting edges 1, formed by the intersection of the front 8 and main rear 2 blade surfaces and performing the main cutting work; transverse cutting edge 9 (jumper) and two auxiliary cutting edges 5. On the calibrating (guide, with reverse taper) part of the drill, two narrow ribbons are located along the helical groove 4 (auxiliary rear surfaces), providing the direction of the drill during cutting and the required accuracy and quality of the machined surface.

countersinks According to the type of holes processed, they are divided into spiral cylindrical (see Fig. 1.1, c, G), conical (Fig. 1.3, A) and end (Fig. 9.3, b). Countersinks can be solid with a conical shank (see Fig. 1.1, c, d) and mounted (see Fig. 1.3, b).

A spiral cylindrical countersink differs from a twist drill mainly in the large number of teeth (three to four) and the absence of a bridge.

Countersinking, as stated earlier, is used when processing previously produced holes and end surfaces.

Sweeps, as stated in subsection. 1.1, finalize the holes. Based on the shape of the hole being machined, they are classified as cylindrical (Fig. 1.1, d and 1.3, c) and conical (Fig. 1.3, d) developments. Reamers have 6 - 12 main cutting edges l K located on the cutting part l r with guide cone l N, auxiliary cutting edges are located on the calibrating part 7 K.

According to the design of fastening, the reamers are divided into tail ones (see Fig. 1.1, d and 1.3, c, d) and mounted (Fig. 1.3, d, which shows a machine mounted reamer with mechanical fastening of cutting blades in its body).

Fig.1.3. Tools for processing holes on drilling machines: a, b – countersinks, c, d, e – reamers, f – tap; l n, l r, l k -

Taps used for cutting internal threads. The tap (Fig. 9.3, e) is a screw with cut straight or helical grooves that form cutting edges. The working part of the tap has a cutting l r and calibrating l K parts. The thread profile of the tap must match the profile of the thread being cut. The tap is secured in a special chuck.

For countersinks, reamers, taps, as well as for drills, the cutting parts perform the main cutting work. Calibrating parts serve to guide the tool in the hole and provide the necessary accuracy and quality of the machined surface.

During operation, the cutting elements of axial tools are subject to abrasion along the front, main rear and auxiliary surfaces with simultaneous thermal exposure. This leads to wear on the tool surfaces (Fig. 9.4, a, b), in contact with the workpiece and the cut layer. The wear rate of drill pads, countersinks and reamers depends on the cutting mode, the material of the cutting part and the workpiece, and other processing conditions.

Wear of a high-speed drill (see Fig. 9.4, a) occurs along the front 1, main 2 and auxiliary 3 rear surfaces. The heaviest wear occurs on the auxiliary flank surfaces 3 (ribbons) having a significant friction surface, and along the rear surface in the area where the main and auxiliary cutting edges meet. By the value of ii 3, which characterizes this wear, one judges the possibility of further use of the drill.

Allowable flank wear h 3 for different drilling cases is given in the reference literature. For example, for a high-speed drill with a diameter of 20 mm h 3 = 0.8 mm. Failure to comply with the recommendations on the permissible amount of wear reduces the service life of the tool: if there is a lot of wear, a lot of material has to be removed when regrinding the tool, and if there is little wear, you have to do a lot of resharpening.

Wear of countersinks and reamers occurs along the strip and back surface of the fence, forming the most vulnerable spot of the tool (see Fig. 1.4, b). Permissible wear is determined by the value h 3 . For high speed countersinks with diameter D= 10...50 mm this value lies within 1...2 mm, for carbide 0.4...0.6 mm. The wear of high-speed reamers should not exceed 0.6...0.8 mm.

Rice. 1.4. Places of wear of the drill (a) and countersink (b) and patterns for sharpening drills on a conical surface (V), along the plane (g), along the helical surface (d):

1 - front surface; 2, 3, 4 - main, auxiliary, additional rear surfaces; K 1, K 2- cams; P 1 t, P 2, P 3- clamping force of the drill in the fixture; D Snp- longitudinal feed; D S to p- circular reciprocating rotational feed of the drill; D Sy 1, D Sy 2- installation rotational movements of the cams K 1 And K 2; D s 2 p And D s 2 b- respectively, the working and auxiliary strokes of the transverse feed of the drill; h 3 - wear width

When the specified amount of wear is reached, the axial tools are sharpened to restore their cutting properties. Resharpening of drills, countersinks and reamers is carried out along the main rear surfaces and, in some cases, along the front surface. Special sharpening machines are used to sharpen twist drills. Some drill sharpening schemes are shown in Fig. 9.4, c, d, d.

TECHNOLOGICAL EQUIPMENT OF DRILLING MACHINES

When processing on drilling machines, various devices are used to install and strengthen workpieces on tables and tools on machine spindles.

The workpieces are installed on a machine table equipped with T-shaped slots in the following ways: by securing with clamping bars or in a machine vice; on a square with a table that can be rotated to the required angle and which has T-shaped slots that allow you to secure a device with the workpiece on this table; in three- or four-jaw chucks (cylindrical blanks); onto a prism with the workpiece secured with clamps; using jigs equipped with guide bushings, which ensure a certain position of the cutting tool relative to the workpiece fixed in the jig body. There is no need for markings when using conductors.

The cutting tool in the spindle of the drilling machine is secured with the help of auxiliary tools: adapter bushings for drill chucks and mandrels. The tool mount can be rigid or floating. Rigid tool mounting is used when machining imprecise holes.

When reaming holes with 7th grade accuracy and directing the tool along the drill bushings or along a previously machined hole, it is necessary to use self-aligning chucks (oscillating and floating), which eliminate deformations of the tool and spindle and freely orient the tool relative to the drill bushings or the hole being machined.

Cutting tools with a tapered shank are clamped directly into the tapered hole of the drill press spindle. If the size of the tool shank cone is smaller than the size of the spindle conical hole, then tapered adapter bushings are used. Tools with a cylindrical shank are mounted in two-, three-jaw or collet chucks.

SCHEMES FOR PROCESSING WORKPIECES ON DRILLING MACHINES

Drilling machines perform drilling, reaming, countersinking, reaming, counterbore, countersinking, threading and processing of complex holes.

Schemes for processing workpieces, cutting tools and the possibilities of drilling, reaming, countersinking, and reaming are given in subsection. 1.1 and 1.2.

Let's add that drilling And reaming- this is rough processing.

Depending on the required accuracy and the size of the batch of workpieces being processed, holes are drilled in the jig or according to the markings.

The diameter of the hole for drilling is chosen so that the transverse cutting edge does not participate in the work. In this case, the axial force decreases.

Countersinking refers to a semi-finish type of processing of hole surfaces; with this method, small allowances of 0.5...3 mm are removed. A countersink is a more rigid tool than a drill, and therefore it corrects the curvature of the axis of the hole being machined after the drill has been withdrawn, and improves the processing accuracy and surface quality of the cylindrical hole.

Deployment- finishing method for processing holes. For reaming, a small allowance is left on the side of 0.05... 0.5 mm, and therefore reaming cannot correct the curvature of the hole axis, but it increases the accuracy of the diametrical size and the quality of the machined surface.

Single, double and triple deployments are used. Single deployment is carried out with a rough development; it ensures accuracy of 8-9 grades; double reaming is carried out with rough and semi-finish reaming, accuracy - according to the 7th grade; triple reaming is carried out with rough, semi-finishing and finishing reaming, accuracy - up to 6th grade.

Countering- processing the end surface of the hole with an end countersink to achieve perpendicularity of the flat end surface to the axis (Fig. 1.5, a).

Rice. 1.5. Schemes for processing workpieces on a vertical drilling machine:

a - counterlining; b, c - countersinking; g - thread cutting; d - combined processing; - fixed support;<|- - зажим

Countersinking cylindrical or conical recesses are obtained in the existing holes for the heads of screws, bolts, rivets and other parts. In Fig. 9.5, b, c shows the countersinking of a cylindrical recess with a cylindrical countersink and a conical recess with a conical countersink.

Threading- obtaining a helical groove on the inner cylindrical surface using a tap (Fig. 9.5, d).

Drilling deep holes(the length of the hole is more than five of its diameters) is performed on special horizontal drilling machines. When processing deep holes with twist drills, the drill moves away and the hole is “broken,” making it difficult to supply coolant and remove chips. Therefore, deep holes are drilled with drills of a special design. The cutting fluid supplied to the cutting zone flushes chips through the internal channel of the drill.

Combined hole processing used in serial and mass production in order to increase productivity and improve the quality of workpiece processing.

It is carried out using a combined tool. Combined tools allow you to combine sequential roughing and finishing processing of one surface in one pass, to process the shaped surface of one or several holes in one pass, to combine various operations: drilling and countersinking, drilling or countersinking and reaming, drilling and threading, drilling and milling, countersinking and countersinking (Fig. 1.5, d).

Replacing several operations or transitions performed sequentially with normal tools with one operation performed with a combined tool not only increases labor productivity and reduces processing costs, but also increases the accuracy of part manufacturing. The combined tool also includes centering drills (see pos. 14 in Fig. 1.1, a).

When processing stepped holes with combined tools, stricter alignment and accuracy of the axial dimensions of the steps and perpendicularity of the end sections to the hole axis are ensured compared to sequential processing with several normal tools.

Some types of combination tools for machining stepped holes are shown in Fig. 9.6. Flaws The disadvantage of a combined tool is the labor intensity of its manufacture and some difficulty in sharpening it.

Rice. 9.6. Combination tools:

a - two-stage twist drill; b - feather three-stage drill; V- two-stage scanning; d 1 , d 2 , l 1 , l 2 - diameters and lengths of tool steps; D1, D2- diameters of machined holes; a - tooth thickness at the 1st stage; L- length of the ribbon; d 0 , b 0- the smallest and largest thickness of the drill bit

This is a tool for countersinking holes (for example, or a screw). Countersinking is necessary in order to hide the screw head flush - to level it with the surface of the part.

Countersinking- This is the processing of the top of the hole to obtain a chamfer. Countersinking is performed using countersinks or a larger diameter drill.

I prefer to do my countersinking using countersinks. A larger diameter drill may cause chips. And we don't need them. In addition, the drill must be sharpened at 90 degrees.

Here are some examples of countersinks that suit us:

It turned out that countersinks are not so easy to find for sale in stores or markets. But there is no need to be upset. It is quite possible to use a whetstone as a countersink, for example, like one from this set:

Of course, it is not suitable for large volumes of work, because it wears out quickly. But for making furniture with your own hands fits better than a larger diameter drill, and is not as problematic (in terms of acquisition) as a countersink. How to countersink a hole using such a sharpening stone, see the video:

Countersinking holes

The technological process of changing the sizes and shapes of parts, as a rule, cannot be done without such a type as countersinking. Translated from German, the word means “to pass”, “to deepen”. More precisely, this is a process during which the diameter of the holes is increased. It can be compared to drilling. Countersinking is a mechanical operation during which holes are bored in order to improve their surface quality and accuracy.

Getting holes

In order to thoroughly understand what countersinking is, you need to have an idea of ​​how holes are made in parts. Let's say it is necessary to drill a hole of the fifth accuracy class with a diameter of 12 mm in a workpiece.

An important indicator that affects the maximum and minimum values ​​is the required quality. For example, it is necessary to finish countersinking a hole with a diameter of 85 mm with grade H11. Based on the tables of tolerance fields for holes with nominal sizes from 1 to 500 mm, for quality 11 (for diameters from 80 mm to 120 mm) the tolerance field is: the upper value is “+220”, and the lower value is “0”, that is, 85 +220 mm. The maximum diameter of the drilled hole cannot exceed 85.22 mm, and the minimum - 85 mm.

In this case, the size tolerance is the difference between D max and D min, that is, it will be 0.22 mm. If we talk about defects, then for a hole a diameter above the value of 85.22 mm will be considered irreparable, and a diameter less than 85 mm will be considered reparable.