Cutting is a locksmith operation, in which, with the help of a cutting (chisel, cross-cutting tool, etc.) and percussion (locksmith's hammer) tool, excess layers of metal are removed from the surface of the workpiece (part) or the workpiece is cut into pieces.
Depending on the purpose of the workpiece, cutting can be fine and rough. In the first case, a layer of metal with a thickness of 0.5 to 1 mm is removed with a chisel in one working stroke, in the second - from 1.5 to 2 mm.
The processing accuracy achieved during cutting is 0.4 ... 1 mm.
When cutting, cutting is carried out - the process of removing an excess layer of metal in the form of chips from a workpiece (part) with a cutting tool.
The cutting part (blade) is a wedge (chisel, cutter) or several wedges (hacksaw blade, tap, die, cutter, file).
A chisel is the simplest cutting tool in which the shape of the wedge is especially pronounced. The sharper the wedge, i.e., the smaller the angle formed by its sides, the less force will be required to deepen it into the material.
On the workpiece, the machined and machined surfaces, as well as the cutting surface, are distinguished. The machined surface is the surface from which the layer of material will be removed, and the machined surface is the surface from which the chips are removed. The surface along which the chips come off during cutting is called the front, and the opposite back.
Cutting tools
Cutting tools. A bench chisel is a steel rod made of tool carbon or alloy steel (U7A, U8A, 7HF, 8HF).
The chisel is made with a length of 100, 125, 160, 200 mm, the width of the working part is 5, 10, 16 and 20 mm, respectively. The working part of the chisel at a length of 0.3 ... 0.5 is hardened and released. The degree of hardening of the chisel can be determined with an old file, which is carried out along the hardened part.
Kreuzmeisel differs from a chisel in a narrower cutting edge and is designed for cutting narrow grooves, keyways, etc. For cutting profile grooves - semicircular, dihedral and others - special crosscuts are used, called groovers. Ditchers are made of steel U8A with a length of 80, 100, 120, 150, 200, 300 and 350 mm with a radius of curvature of 1; 1.5; 2; 2.5 and 3 mm.
Sharpening the tool on the machine manually. Sharpening of chisels and crosscuts is carried out on a grinding machine. Before sharpening the tool, the handpiece is installed as close as possible to the grinding wheel. The gap between the handpiece and the grinding wheel should be no more than 2 ... 3 mm so that the tool being sharpened cannot get between the wheel and the handpiece.
Checking the sharpening angle of the tool. After sharpening the chisel or cross-meisel, the burrs are removed from the cutting edges. The taper angle is checked with a template, which is plates with angular cuts of 70, 60, 45 and 35 degrees.
A metalwork hammer is a tool for working with various metalworking tools.
Locksmith hammers with a round head are made from six numbers:
No. 1 (200 g) is used in marking and editing;
No. 2 (400 g), No. 3 (500 g) and No. 4 (600 g) - for locksmith work;
No. 5 (800 g) and No. 6 (1000 g) are rarely used.
Locksmith hammers with a square buoy produce eight numbers:
No. 1 (50 g), No. 2 (100 g) and No. 3 (200 g) - for metalwork and tool work;
No. 4 (400 g), No. 5 (500 g) and No. 6 (600 g) - for metalwork, cutting, bending, riveting, etc.;
No. 7 (800 g) and No. 8 (1000 g) are rarely used. For hard work, hammers weighing 4 ... 16 kg, called sledgehammers, are used.
In some cases, for example, in the manufacture of products from thin sheet steel, wooden mallets are used, which come with a round or rectangular striker.
Safety. When manually cutting metals, the following safety rules should be followed:
The handle of a manual machinist's hammer must be well fixed and not cracked;
When chopping with a chisel and a cross cutter, goggles must be used;
When cutting hard and brittle metal, it is imperative to use a fence: a mesh, a shield.
Metal straightening and straightening (cold method)
Editing and straightening are operations for straightening metal, blanks and parts that have dents, bulges, waviness, warping, curvature, etc. Editing and straightening have the same purpose, but differ in the methods of execution and the tools and devices used.
The metal is straightened both cold and hot. The choice of method depends on the deflection, dimensions and material of the product. Dressing is done manually on a straightening plate or anvil - machine-made on rollers or presses.
Correct plates (Fig. a) are made massive of steel or cast iron with a size of 400 x 400; 750 x 1000; 1000 x 1500; 1500 x 2000; 2000 x 2000;
1500 x 3000mm.
Straightening headstocks (Fig. b) are used for straightening (straightening) hardened parts; They are made from steel and hardened.
For dressing, hammers with a round smooth polished head are used.
For straightening hardened parts (straightening), hammers with a radius striker are used; the hammer body is made of U10 steel; the mass of the hammer is 400 ... 500 g.
Hammers with plug-in heads made of soft metals are used when dressing parts with a finished surface.
Smoothers (wooden or metal bars) are used when editing thin sheet and strip metal.
Metal dressing
The curvature of the parts is checked by eye or by the gap between the plate and the part.
When editing, it is important to choose the right places to hit. Editing is carried out on an anvil, a regular plate or reliable linings, excluding the possibility of parts slipping from them upon impact.
Editing of strip metal is carried out in the following order.
The strip is placed on the correct slab so that it lies with the bulge up, in contact with the slab at two points. Impacts are applied to the convex parts, adjusting their strength depending on the thickness of the strip and the magnitude of the curvature; the greater the curvature and the thicker the strip, the stronger the blows should be. The result of editing (straightness of the workpiece) is checked by eye, and more precisely, on a marking plate along the clearance or by applying a ruler to the strip.
Editing a bar. After checking by eye on the convex side, the boundaries of the bends are marked with chalk. Then the bar is placed on a slab or anvil so that the curved part is convex upwards and struck with a hammer.
Sheet metal dressing is more complex than previous operations.
When straightening workpieces with bulges, warped areas are identified, and it is established where the metal is more bulging. Editing begins from the edge closest to the bulge, along which one row of hammer blows is applied within the limits indicated by black circles. Then they strike on the second edge.
After that, a second row of blows is applied along the first edge and again they go to the second edge, and so on until they gradually approach the bulge.
Thin sheets are ruled with light wooden hammers - mallets, copper, brass or lead hammers, and very thin sheets are placed on a flat slab and smoothed with metal or wooden bars.
Straightening (straightening) of hardened parts. After hardening, steel parts sometimes warp. The straightening of parts that are bent after hardening is called straightening. The straightening accuracy can be 0.01 ... 0.05 mm.
Depending on the nature of straightening, hammers with a hardened head or special straightening hammers with a rounded side of the head are used.
Products with a thickness of at least 5 mm, if they are not hardened through, but only to a depth of 1 ... 2 mm, have a viscous core, therefore they are straightened relatively easily; they need to be straightened, striking at convex places. In the case of warpage of the product along the plane and along a narrow rib, straightening is performed separately - first along the plane, and then along the rib.
Straightening of short bar material is carried out on prisms, straightening plates or simple linings. Straightness is checked by eye or by the gap between the bar and the plate.
Shafts (up to 30 mm in diameter) are straightened using hand presses using a prism.
Straightening by hardening is carried out after laying the curved shaft on a flat plate with the bulge down, applying frequent and light blows to the surface of the shaft with a small hammer, after the appearance of a hardened layer on the surface of the hardened layer, the gap between the shaft and the plate disappears - straightening is stopped.
Straightening equipment
Basically, enterprises use machine dressing on straightening rollers, presses and special devices.
Bending rolls are manual and driven. On manual and driven three-roll bending rolls, workpieces are corrected, straight and curved along the radius, having bulges and dents on the surface.
The three-roll sheet bending machine has rolls located one above the other, which are adjusted depending on the thickness of the workpiece, moving away from each other or approaching. The billet is placed between two front rolls and, turning the handle clockwise, is passed between the rolls until the bulges and dents are completely eliminated.
Dressing shafts and angle steel on screw presses is used in cases where dressing with a hammer does not provide the desired result.
Editing of angular steel has some features. The deformed corner is installed in a prism on the press table, a hardened steel roller is installed between the shelves of the corner. When pressed with a press screw, the roller gives the corner the appropriate shape. Sheets, strips and tapes are straightened on straightening machines, horizontal stretching machines and pneumatic hammers.
Warped welded joints are cold straightened.
Manually using wooden and steel hammers on plates, anvils, etc. Cold straightening is carried out with particular care.
Safety. When straightening and straightening metals, the following safety requirements must be met: work only with a serviceable tool (correctly mounted hammers, no cracks on the handles and no chips on the hammers); to protect hands from shocks and vibrations of the metal, work in gloves: hold the workpiece firmly on the stove or anvil.
metal bending
Bending is a method of metal forming by pressure, in which a workpiece or part of it is given a curved shape. Bench bending is performed with hammers (preferably with soft heads) in a vice, on a plate or with the help of special devices. Thin sheet metal is bent with mallets, wire products with a diameter of up to 3 mm - with pliers or round-nose pliers. Bending is subjected only to ductile material.
When bending parts at a right angle without rounding on the inside, the allowance for bending is taken from 0.5 to 0.8 of the thickness of the material.
Staple dimensions: a=70mm; b=80mm; c=60mm; t=4mm. Workpiece development length L=a+b+c+0.5t=70+80+60+2=212mm.
Example 2. Calculate the length of the development of the square blank with internal rounding (Fig. c). We break the square according to the drawing into sections. Substituting their numerical values (a=50mm; b=30mm; t=6mm; r=4mm) into the formula L=a+b+3.14/2(r+t/2), we get L=50+30+3 .14/2(4+6/2)=50+30+1.57x7=0.99=91mm.
We divide the bracket into sections, put their numerical values (a=80mm; h=65mm; c=120mm; t=5mm; r=2.5mm) into the formula L=a+h+c+3.14(r+t/ 2), we get L=80+65+120+3.14(2.5+5/2)=265+15.75=280.75mm.
Bending this strip into a circle, we get a cylindrical ring, and the outer part of the metal will stretch somewhat, and the inner one will shrink. Therefore, the length of the workpiece will correspond to the length of the middle line of the circle, passing in the middle between the outer and inner circumferences of the ring.
The length of the workpiece L=3.14xD. Knowing the diameter of the average circle of the ring and substituting its numerical values into the formula, we find the length of the workpiece:
L=3.14x108=339.12mm. As a result of preliminary calculations, it is possible to manufacture a part of the established dimensions.
Bending of sheet and strip metal parts
Bending of a rectangular bracket made of strip steel is performed in the following order:
determine the length of the workpiece development by adding the length of the sides of the bracket with an allowance for one bend equal to 0.5 of the strip thickness, i.e. L=17.5+1+15+1+20+1+15+1+17.5= 89mm;
mark the length with an additional allowance for processing the ends of 1 mm per side and cut off the workpiece with a chisel;
straighten the cut blank on the plate;
sawn to size according to the drawing;
inflict bending risks;
the workpiece is clamped in a vice between the squares - with the muffs at the risk level and with hammer blows, the end of the bracket is bent (first bend);
rearrange the workpiece in a vice, clamping it between a square and a bar - a mandrel longer than the end of the bracket;
bend the second end, making the second bend;
remove the workpiece and take out the bar - mandrel;
mark the length of the legs at the bent ends;
they put a second square on the vise and, having put the same bar inside the bracket - the mandrel, but in its other position, clamp the bracket in the vise at the level of the marks;
bend the first and second legs, make the fourth and fifth bends of the first and second legs;
check and straighten the fourth and fifth bends along the square;
remove the burrs on the ribs of the staple and file the ends of the legs to size.
The bending of a double square in a vice is carried out after marking, cutting out the workpiece, straightening on the plate and sawing in width to the specified size. At the end of bending, the ends of the square are filed to size and burrs are removed from sharp edges.
Clamp flexible. After calculating the length of the workpiece and marking it in the places of bending, the mandrel is clamped in a vice in a vertical position. The diameter of the mandrel must be equal to the diameter of the collar hole. The final formation of the clamp is carried out on the same mandrel with a hammer, and then on the correct plate.
Ear bending with round nose pliers. An eyelet with a thin wire rod is made using round-nose pliers. The length of the workpiece should be 10 ... 15 mm longer than required by the drawing. After finishing work, the excess end is removed with wire cutters.
Sleeve bending. For example, it is required to bend a cylindrical sleeve from strip steel on round mandrels. First determine the length of the workpiece. If the outer diameter of the sleeve is 20mm and the inner diameter is 16mm, then the average diameter will be 18mm. Then the total length of the workpiece is determined by the formula L=3.14x18=56.5mm.
Mechanization of bending works.
Profiles (strip, bar metal) with different radii of curvature are bent on three- and four-roller machines. The machine is pre-adjusted by installing the upper roller relative to the two lower rollers by rotating the handle. When bending, the workpiece must be pressed by the upper roller to the two lower ones.
Profiles with a large bending radius are obtained on three-roller machines in several transitions.
The four-roller machine consists of a frame, two drive rollers that feed the workpiece, and two pressure rollers. Such machines are used for bending profiled rolled products along an arc of a circle or a spiral.
Bending and expanding pipes
Pipes are bent by manual and mechanized methods, in hot and cold condition, with and without fillers. The bending method depends on the diameter and material of the pipe, the value of the bending angle.
Hot bending of pipes is used with a diameter of more than 100mm.
During hot bending with filler, the pipe is annealed, marked, one end is closed with a wooden or metal cork.
The diameters of plugs (plugs) depend on the inner diameter of the pipe. For pipes of small diameters, plugs are made of clay, rubber or hardwood; they are made in the form of a conical plug with a length equal to 1.5 ... 2 pipe diameters, with a taper of 1:10. For pipes of large diameters, the plugs are made of metal.
The length L (mm) of the heated section of the pipe is determined by the formula L=ad/15, where a is the bending angle of the pipe, deg; d - outer diameter of the pipe, mm; 15 - constant ratio (90:6=15; 60:4=15; 45:3=15).
When bending pipes in a hot state, they work in mittens. The pipes are heated with blowtorches in the forges or with the flame of gas burners to a cherry-red color. Pipes are recommended with one heating, as repeated heating degrades the quality of the metal.
Cold bending of pipes is carried out using various devices. The simplest devices for bending pipes with a diameter of 10 ... 15 mm are a plate with holes, in which pins are installed in appropriate places, which serve as stops during bending.
Pipes of small diameters (40 mm) with large radii of curvature are cold-bent using simple hand tools with a fixed frame. Pipes up to 20 mm in diameter are bent in a fixture that is attached to the workbench using a hub and a plate.
Bending copper and brass pipes. Copper or brass pipes to be cold-bent are filled with molten rosin, molten stearin (paraffin) or molten lead.
Copper pipes to be bent in a cold state are annealed at 600 ... 700 degrees and cooled in water. The filler for bending copper pipes in a cold state is rosin, and in a heated state - sand.
Brass pipes to be bent in a cold state are pre-annealed at 600 ... 700 degrees and cooled in air. Fillers are the same as for bending copper pipes.
Duralumin pipes before bending are annealed at 350 ... 400 degrees and cooled in air.
Pipe bending mechanization. In the mass production of parts from pipes of the largest diameters, manual pipe bending devices and lever pipe benders are used, and for bending pipes of large diameters (up to 350 mm), special pipe bending machines and presses are used.
Bending of pipes into a ring is carried out on a three-roller bending machine.
New methods of pipe bending are widely used. Bending with stretching of the workpiece consists in the fact that the workpiece is subjected to the combined action of tensile (exceeding the yield strength of the metal) and bending forces. This method is used in the manufacture of pipes for aircraft, cars, ships, etc.
When bending pipes with heating by high-frequency currents, heating, bending and cooling occur continuously and sequentially in a special high-frequency installation such as pipe bending machines. Installation allows bending of pipes with a diameter from 95 to 300 mm. It consists of two parts - mechanical and electrical.
Flaring (rolling) of pipes consists in expanding (rolling out) the ends of the pipes from the inside with a special tool (rolling).
The flaring process consists in putting a flange with grooves machined in its hole on the end of the pipe, then inserting a flaring with rollers into the pipe and rotating it. The most productive is rolling on special rolling machines and various mechanisms.
Defects. When bending metal, defects are most often oblique bends and mechanical damage to the treated surface as a result of incorrect marking or fastening of parts in a vise above or below the marking line, as well as improper impact.
When bending pipes, the following conditions must be observed:
carefully monitor the uniformity of the stretching of the outer wall and the fit of the inner wall of the pipe; take into account that stretching the outer wall of the pipe is easier than fitting the inner wall;
bend the pipe smoothly, without jerking;
in order to avoid rupture, it is impossible to bend the pipe and straighten the folds if the pipe has cooled to a light cherry color (800 degrees), therefore pipes of large diameters are bent with repeated heating.
Safety. When bending, the following safety requirements must be met: secure the workpiece in a vice or other devices firmly; work only on working equipment; Before starting work on bending machines, read the instructions; work carefully so as not to damage the fingers; work in mittens and buttoned gowns.
metal cutting
Cutting is the separation of parts (blanks) from bar or sheet metal. Cutting is performed with or without chip removal.
The essence of the cutting process with scissors is the separation of metal parts under the action of a pair of cutting knives. The sheet to be cut is placed between the upper and lower knives. The upper knife, descending, presses on the metal and cuts it. Knives are made from steels U7, U8; the side surfaces of the blades are hardened to HRC-52…58, ground and sharpened.
Cutting with hand scissors
Ordinary manual scissors are used for cutting steel sheets with a thickness of 0.5 ... 1 mm and non-ferrous metal sheets with a thickness of up to 1.5 mm. Hand shears are made with straight and curved cutting blades.
According to the location of the cutting edge of the blade, the scissors are divided into right ones (the bevel on each part of the cutting half is on the right side); left - (the bevel on each part of the cutting half is on the left side).
The length of the scissors is 200, 250, 320, 360 and 400 mm, and the cutting part (from the sharp ends to the hinge) is 55 ... 65, 70 ... 82, 90 ... 105, 100 ... 120 and 110 ... 130 mm, respectively. Well-sharpened and adjusted scissors should cut paper.
Chair scissors differ from ordinary ones in large sizes and are used when cutting sheet metal up to 3 mm thick.
Chair scissors are inefficient, require considerable effort during operation, therefore they are not used for cutting large batches of sheet metal.
Manual compact power shears are used for cutting sheet steel up to 2.5 mm thick and bars up to 8 mm in diameter. Scissor blades are interchangeable and attached to levers with countersunk rivets. These blades are interchangeable and fit into the disc slot. For cutting bolts (studs) in the bushings of one of the disks there is a thread (several threads), which protects the thread of the bolts from crushing during cutting.
Lever shears are used for cutting sheet steel up to 4mm thick, aluminum and brass - 6mm thick. The upper hinged knife is actuated by a lever. The lower knife is fixed.
Knives are made of steel U8 and hardened to hardness HRC-52…60. The angles of sharpening of the cutting edges are 5 ... 85 degrees.
Before work, check the presence of lubrication on the rubbing surfaces, the smoothness of the lever, and the absence of a gap between the cutting edges.
Fly shears are widely used for cutting sheet metal with a thickness of 1.5 ... 2.5 mm with a tensile strength of 450-500 MPa (steel, duralumin, etc.). These scissors cut metal of considerable length.
Shears with inclined knives (guillotine) allow cutting sheet metal up to 32 mm thick, sheets with dimensions of 1000 ... 32000 mm, less often - flat products, as well as sheet non-metallic materials.
Hacksaw cutting
A manual hacksaw (saw) is a tool designed for cutting thick sheets of strip, round and shaped metal, as well as for cutting slots, cutting grooves and cutting blanks along the contour and other works.
A hacksaw blade is a thin and narrow steel plate with two holes and teeth on one or both edges. Cloths are made from steels U10A and Kh6VF, their hardness is НRCе61 ... 64. Depending on the purpose, hacksaw blades are divided into manual and machine.
The size (length) of a manual hacksaw blade is determined by the distance between the centers of the holes for the pins, the length of the blade for a hand saw is L = 250 ... 300 mm, height b = 13 and 16 mm, thickness h = 0.65 and 0.8 mm.
For cutting metals of different hardness, the angles of the teeth of the hacksaw blade are as follows: the rake angle is 0 ... 12 degrees; and the back angle of the teeth is 35 ... 40 degrees; the taper angle is 43 ... 60 degrees.
For cutting harder materials, blades are used, in which the angle of sharpening of the teeth is larger, for cutting soft materials, the sharpening angle is smaller. Cloths with a large angle of sharpening are more wear-resistant.
Setting the teeth of a hacksaw blade. When cutting with a hand saw, at least two to three teeth should participate in the work (at the same time cutting metal). To avoid jamming (jamming) of the hacksaw blade in the metal, the teeth are bred so that the width of the cut made by the hacksaw is much greater than the thickness of the blade. In addition, it will greatly facilitate the work.
The wiring of the hacksaw blade should end at a distance of no more than 30 mm from the end.
Preparing to work with a hacksaw. Before working with a hacksaw, the material to be cut is firmly fixed in a vice (the level of fastening must correspond to the growth of the worker). For long cuts, hacksaw blades with a large tooth pitch are used, and for short cuts, with a fine one.
The hacksaw blade is installed in the slot of the head so that the teeth are directed away from the handle, and not towards it. In this case, the end of the web is first inserted into the fixed head and fixed with a pin, then the second end of the web is inserted into the slot of the movable pin and also fixed with a pin. At the same time, because of the fear of breaking the blade, the hacksaw is kept away from the face. The degree of tension of the canvas is checked by lightly pressing it with a finger from the side; if the canvas does not flex, the tension is sufficient.
The position of the worker's body. When cutting with a hand saw, they stand in front of the vise straight, freely and steadily, half a turn in relation to the jaws of the vise or the axis of the workpiece being processed. The feet are placed so that they form an angle of 60 ... 70 degrees with a certain distance between the heels.
Hand position (grip). The handle is clasped with four fingers of the right hand so that it rests on the palm; the thumb is placed on top along the handle. The fingers of the right hand wrap around the nut and the movable head of the hacksaw.
Knife work. When cutting with a hacksaw, as well as when filing, strict coordination of efforts (balancing) must be observed, which consists in the correct increase in hand pressure.
In the process of cutting, two moves are made - a worker, when the hacksaw moves forward from the worker, and idle, when to the worker. When idling, the hacksaw is not pressed, as a result of which the teeth only slide, and during the working stroke, light pressure is created with both hands so that the hacksaw moves in a straight line.
When working with a hacksaw, the following rules must be observed:
Cut short workpieces on the shortest side; when cutting rolled corner, tee and channel profiles, it is better to change the position of the workpiece than to cut along the narrow side;
the entire hacksaw blade should be involved in the work;
when cutting, do not allow the blade to heat up; to reduce the friction of the blade against the walls in the cut of the workpiece, periodically lubricate the blade with mineral oil or graphite grease, especially when cutting viscous metals;
cut brass and bronze only with new blades, since even slightly worn teeth do not cut, but slide;
in case of breakage or chipping of at least one tooth, immediately stop work, remove the remains of a broken tooth from the cut, replace the blade with a new one or grind off two or three adjacent teeth on the machine; after that you can continue working.
Cutting round, square, strip and sheet metal with a hacksaw.
Cutting round metal. Round metal of small sections is cut with hand saws, and workpieces of large diameters are cut on cutting machines, powered hacksaws, circular saws, etc. The blade is pre-lubricated with oil with a brush.
For the correct start of the cut on an unmarked workpiece, at the place of the cut, the thumb of the left hand is placed with the nail and the hacksaw blade is placed close to the nail. The hacksaw is held only with the right hand. The index finger of this hand is pulled along the side of the handle, which ensures a stable position of the workpiece during cutting.
Cutting square metal. The workpiece is fixed in a vice and in the place of the future cut with a trihedral file, a shallow cut is made for a better direction of the hacksaw. Then the workpiece is cut with a hacksaw in a horizontal position. With very deep cuts, the left hand is rearranged, grasping the top of the frame.
Cutting of strip metal. It is more rational to cut strip metal not along the wide, but along the narrow side.
Cutting with a hacksaw with a turn of the blade is carried out with long (high) or deep cuts, when it is not possible to complete the cut due to the fact that the hacksaw frame rests on the end of the workpiece and prevents further sawing. In this case, you can change the position of the workpiece and, crashing into it from the other end, finish cutting. You can cut with a hacksaw, in which the blade is rearranged 90 degrees. This method cuts metal in parts with closed contours.
Cutting thin and profile metal. Blanks, parts made of thin sheet metal are clamped between wooden bars one or more pieces and cut together with the bars.
Cutting along curved contours. To cut a shaped window (hole) in a metal (sheet), drill or cut a hole with a diameter equal to the width of a hacksaw or jigsaw blade.
Slots of large sizes are cut with ordinary hacksaws with one or two (depending on the width of the slots) blades joined together.
Cutting pipes with a hacksaw and pipe cutter
Before cutting, the pipe is marked out according to a template made of tin, bent along the pipe. The template is applied to the place of the cut and marking marks are applied around the circumference of the pipe with a scriber. Pipes are cut with hacksaws and pipe cutters.
Cutting with a hacksaw. The pipe is clamped in a parallel vise in a horizontal position and cut at risk. When cutting the pipe, the hacksaw is held horizontally, and as the blade cuts into the pipe, it is slightly tilted towards itself. If the hacksaw is swept away from the marking risk, the pipe is rotated around the axis and cut along the risk in a new place.
Cutting with a pipe cutter is much more productive than with a hacksaw. Pipe cutters are manufactured in three sizes: No. 1 - for cutting pipes with a diameter of ¼…3/4”; No. 2 - 1…2S”; No. 3 - 3…4”.
Cutting is done like this. At the pipe cutter installed on the pipe, turn the handle ¼ of a turn, pressing the movable roller to the surface of the pipe so that the marking line coincides with the sharp edges of the rollers. The pipe cutter is rotated around the pipe, moving the movable roller until the pipe walls are completely cut through.
The length of the cut pipes is checked with a ruler, and the plane of the cut in relation to the outer wall is checked with a square. If it is necessary to obtain a smooth surface without significant burrs at the cut point, a pipe cutter designed by A.S. Misyuta. This is a conventional three-roller pipe cutter, between the rollers of which a cutter is fixed on a lever in a special frame (its reach can be adjusted), accelerating the cutting process.
Mechanized cutting
Mechanized cutting is carried out using various mechanical, electric and pneumatic hacksaws and scissors, circular saws or other universal or special equipment.
Hacksaws (driven hacksaws) are used for cutting sectional and shaped metal. Hacksaw 872А, which has electric and hydraulic drives, processing accuracy on such a machine is + 2 ... -2 mm, surface roughness Ra = 20 μm (Rz = 80 μm).
Clamping vise. A vice with flat jaws is used to secure workpieces of large sections - from 40 to 250 mm, with V - shaped jaws up to 120 mm. These vise are rotary, in them the cut material is fixed at an angle of 45 degrees.
Installing a hacksaw blade. The blade is installed with one end on the pin of the fixed bar of the saw frame so that the teeth of the blade are directed towards the working stroke. The hacksaw plate is adjusted for cutting hard metals at 85, and for cutting soft metals - at 110 double strokes per minute.
When starting to cut metal on the saw, the hydraulic drive crane handle is set to the “Descent” position and the electric motor is turned on. The handle is then moved towards the "Fast Action" position and the desired cutting feed is set.
Manual electric scissors C - 424 of vibration type consist of an electric motor, a gearbox with an eccentric and a handle. The gap between the knives is set depending on the thickness of the metal being cut according to the tables and checked with a probe (with a thickness of 0.5 ... 0.8 mm, the gap is 0.03 ... 0.048 mm, with a thickness of 1 ... 1.3 mm - 0.06 ... 0.08 mm , with a thickness of 1.6 ... 2 mm - 0.1 ... 0.13 mm).
Pneumatic scissors are designed for straight and curved cutting of metal and are driven by a pneumatic rotary motor. The largest thickness of the cut steel sheet of medium hardness is 3mm, the highest cutting speed is 2.5m/min, the number of double knife strokes per minute is 1600.
The pneumatic hacksaw is powered by compressed air. The maximum thickness of the cut metal is 5mm, the smallest radius is 50mm, the cutting speed is 20m/min.
The pneumatic circular saw is used for cutting pipes directly at the pipeline assembly site.
When using a pneumatic saw, there are no sags and burrs on the cut surfaces of the pipes.
The pneumatic saw allows cutting pipes with a diameter of up to 50 ... 64 mm. The diameter of the cutter is 190…220mm, its rotation frequency is 150…200 rpm.
Special types of cutting
Abrasive cutting. This method is advisable to use for cutting materials of various profiles with a size of 200x200mm and pipes with a diameter of up to 600mm.
The main advantages of cutting with abrasive discs:
high process productivity;
the ability to cut high hardness steel;
small cutting width, which reduces metal loss;
significantly higher quality of the cut surface than with other cutting methods;
tolerances for the length and perpendicularity of the cut are kept within narrower limits.
Abrasive discs are made from electrocorundum, silicon carbide and diamond.
Arc cutting is used for cutting scrap, cast iron, non-ferrous alloys, removing gates and profits in castings, as well as in the absence of gas cutting equipment. The disadvantage of arc cutting is the unevenness of the edges of the cut, its large width and the formation of metal sagging.
When cutting metal with a thickness of more than 20 mm, metal electrodes and alternating current are used.
Metal cutting under water is used in emergency recovery and ship lifting operations.
When gas cutting under water, cutters of a special design are used, which have caps that are put on the cutting head. When cutting at a depth of 20 m, acetylene is used as a fuel, and when cutting at a depth of 20 ... 40 m, hydrogen is used. As the depth increases, the pressure of the gas or compressed air increases.
Safety. When cutting metals, the following safety requirements must be met:
protect hands from injury on the cutting edges of a hacksaw or burrs on metal;
monitor the position of the left hand, supporting the sheet from below;
do not blow off the sawdust and do not remove it with your hands in order to avoid clogging the eyes or injuring the hands;
do not clutter up the workplace with unnecessary tools and parts;
do not remove or lubricate moving and rotating parts; do not move the belt from step to step when the hacksaw is in operation.
filing metal
General information. Files.
Filing is an operation for processing metals and other materials by removing a small layer with files manually or on filing machines.
With the help of files, planes, curved surfaces, grooves, grooves, holes of any shape, surfaces located at different angles, etc. are processed. Sawing allowances are left small - from 0.5 to 0.25 mm. The accuracy of processing by filing is 0.2 ... 0.05 mm (in some cases - up to 0.001 mm).
Files. A file is a steel bar of a certain profile and length, on the surface of which there are notches (cuts) that form depressions and sharpened teeth (teeth) that have a wedge shape in cross section. Files are made of steel U10A, U13A, ShKh15, 13Kh, after notching they are subjected to heat treatment.
Files are subdivided according to the size of the notch, its shape, along the length and shape of the bar.
Types and main elements of notches. The notches on the surface of the file form teeth that remove chips from the material being processed.
Single cut files can cut wide chips equal to the length of the entire cut. They are used when filing soft metals and alloys with low cutting resistance, as well as non-metallic materials. A single notch is applied at an angle of 25 degrees to the axis of the file.
Files with a double (cross) notch are used for filing steel, cast iron and other hard materials with high cutting resistance.
Files with a rasp (point) notch (rasps) are used for processing very soft metals and non-metallic materials - leather, rubber, etc.
A rasp (point) notch is obtained by pressing the metal with special chisels.
Files with an arc notch are used in the processing of soft metals.
The arc notch is obtained by milling; it has large tooth gaps and an arcuate shape for high productivity and improved surface quality.
File classification
By appointment, files are divided into the following groups: general purpose; special purpose; needle files; rasps; machine.
General purpose files are designed for general plumbing work. According to the number n of notches (teeth) per 10 mm of length, files are divided into six classes, and the notches are numbered 0, 1, 2, 3, 4, and 5;
the first class with a notch No. 0 and 1 (n = 4 ... 12) is called bastard;
the second class with a notch No. 2 and 3 (n = 13 ... 24) is called personal;
the third, fourth and fifth grade with a notch No. 4 and 5 (n = 24 ... 28) are called velvet.
Files are divided into the following types:
A - flat, B - flat pointed files are used for filing external or internal flat surfaces;
B - square files are used for sawing square, rectangular and polygonal holes;
G - trihedral files are used for filing sharp corners equal to 60 degrees or more, both from the outside of the part, and in grooves, holes and grooves;
D - round files are used for sawing round or oval holes and concave surfaces of a small radius;
E - semicircular files with a segmental section are used for processing concave curved surfaces of a significant radius and large holes (with a convex side);
Zh - rhombic files are used for filing gears, disks and sprockets;
Z - hacksaw files are used for filing internal corners, wedge-shaped grooves, narrow grooves, planes in trihedral, square and rectangular holes.
Flat, square, trihedral, semicircular, rhombic and hacksaw files are made with notched and cut teeth.
Rhombic and hacksaw files are made only with notches No. 2, 3, 4 and 5 with a length of 100 ... 250 mm and 100 ... 315 mm, respectively.
Special-purpose files for processing non-ferrous alloys, unlike general-purpose metalwork files, have other, more rational notch angles for this particular alloy, and a deeper and sharper notch, which ensures high productivity and file durability.
Files for processing bronze, brass and duralumin have a double notch - the upper one is made at angles of 45, 30 and 50 degrees, and the lower one is at angles of 60, 85 and 60 degrees, respectively. The files are marked with the letters TsM on the shank. And also there are for processing products from light alloys and non-metallic materials, calibrated and diamond files.
Files are small files used for curved, engraving, jewelry work, as well as for cleaning in hard-to-reach places (holes, corners, short sections of the profile, etc.).
Needles are made of steel U13 or U13A (U12 or U12A is allowed). The length of the needle files is set to 80, 120 and 160mm.
Depending on the number of notches per 10 mm of length, the needle files are divided into five types - No. 1, 2, 3, 4 and 5. The needle files have notch numbers applied on the handle: No. 1 - 20 ... 40; No. 2 - 28 ... 56; No. 3, 4 and 5 - 40 ... 112 notches per 10mm of length.
Diamond needle files are used for processing hard-alloy materials, various types of ceramics, glass, as well as for finishing cutting hard-alloy tools. When processing with needle files, surfaces with a roughness of Ra 0.32 ... 0.16 are obtained.
Rasps are designed for processing soft metals (lead, tin, copper, etc.) and non-metallic materials (leather, rubber, wood, plastics), when ordinary files are unsuitable. Depending on the profile, the rasps are blunt-nosed and sharp-nosed, as well as round and semi-circular with notches No. 1 and 2, 250 ... 350 mm long.
Types of filing
Filing of external flat surfaces begins with checking the machining allowance, which could ensure the manufacture of the part in accordance with the drawing. When filing flat surfaces, flat files are used - bastard and personal. Sawing is carried out with cross strokes. The parallelism of the sides is checked with a caliper, and the quality of filing is checked with a straightedge in various positions (along, across, diagonally).
Lekalnye rulers are used to check the straightness of sawn surfaces for clearance and for paint. When checking the straightness in the light, a curved ruler is applied to the controlled surface and, according to the size of the light gap, it is determined in which places there are irregularities.
Filing square surfaces located at right angles is associated with fitting the inner corner and is associated with some difficulties.
Sawing the end of the rod into a square begins with filing the edge, the size is checked with a caliper.
Safety. When filing work, the following safety requirements must be met:
when filing workpieces with sharp edges, do not press the fingers of the left hand under the file during the reverse stroke;
the chips formed during the filing process must be swept from the workbench with a hair brush; it is strictly forbidden to dump chips with bare hands, blow them off or remove them with compressed air;
when working, use only files with firmly attached handles; it is forbidden to work with files without handles or files with cracked, split handles.
drilling
Drilling is the formation by removing chips of holes in a solid material using a cutting tool - a drill. Drilling is used to obtain holes of a low degree of accuracy, and to obtain holes for threading, countersinking and reaming.
Drilling is applied:
to obtain irresponsible holes of a low degree of accuracy and significant roughness, for example, for mounting bolts, rivets, studs, etc.;
to obtain holes for threading, reaming and countersinking.
Drilling, you can get a hole with an accuracy of 10th, in some cases - 11th grade and surface roughness Rz 320 ... 80.
Drills are of various types (Fig. a-i) and are made of high-speed, alloy and carbon steels, and are also equipped with hard alloy plates.
The drill has two cutting edges. For processing metals of different hardness, drills with different angles of the helical groove are used. For drilling steel, drills with a groove angle of 18 ... 30 degrees are used, for drilling light and viscous metals - 40 ... 45 degrees, when processing aluminum, duralumin and electron - 45 degrees.
Shanks for twist drills can be conical and cylindrical. Tapered shanks have drills with a diameter of 6…80mm. These shanks are formed by a Morse taper.
The neck of the drill, connecting the working part with the shank, has a smaller diameter than the diameter of the working part.
Drills are equipped with hard alloy plates, with helical, straight and oblique grooves, as well as with holes for supplying coolant, carbide monoliths, combined, centering and feather drills. These drills are made from tool carbon steels U10, U12, U10A and U12A, and more often from high speed steel R6M5.
Sharpening twist drills
To increase the durability of the cutting tool and get a clean hole surface, when drilling metals and alloys, coolant is used (see below).
material liquid
Steel Soap emulsion or mixture of mineral and
fatty oils
Cast iron Soapy emulsion or dry blasting
Copper Soap emulsion or rapeseed oil
Aluminum Soapy emulsion or dry blasting
Duralumin Soap emulsion, kerosene with castor or
rapeseed oil
Silumin Soap emulsion or mixture of alcohol and
turpentine
Rubber, ebonite, fiber
Sharpening is carried out in goggles (if the machine does not have a transparent screen).
The sharpening angle significantly affects the cutting mode, drill durability and, consequently, productivity. The quality of sharpening drills is checked with special templates with cutouts. The three-cut template allows you to check the length of the cutting edge, the sharpening angle, the sharpening angle, as well as the angle of the transverse edge.
To improve the working conditions of drills, special types of sharpening are used (Table 1).
Features of drilling difficult-to-machine alloys and plastics
Drilling of heat-resistant steels is carried out with abundant cooling with a 5% emulsion or an aqueous solution of barium chloride with the addition of 1% sodium nitrate.
Drilling light alloys requires special attention. Drills for machining magnesium alloys have large rake angles; small angles at the top (24 ... 90 degrees); large rear corners (15 degrees). For processing aluminum alloys, drills have large corners at the top (65 ... 70 degrees), the angle of inclination of the helical grooves (35 ... 45 degrees), the clearance angle is 8 ... 10 degrees.
Drilling plastics can be done with any type of drill, but their mechanical properties must be taken into account. When drilling some, air is used for cooling, others are cooled with a 5% solution of emulsol in water. To prevent the output side from crumbling during drilling, a rigid metal support is placed under it. Drilling of plastics is carried out only with sharp cutters.
Safety. When working on a drilling machine, the following safety requirements must be observed:
correctly install, securely fix the workpiece on the machine table and do not hold them with your hands during processing;
do not leave the key in the drilling machine after changing the cutting tool;
start the machine only with firm confidence in the safety of work;
do not take on the rotating cutting tool and spindle;
do not remove broken cutting tools from the hole by hand, use special tools for this;
to remove the drill chuck, drill or adapter sleeve from the spindle, use a special key or wedge;
do not transfer or receive any items through a working machine;
do not work on the machine in gloves;
do not lean on the machine while it is in operation.
Countersinking, countersinking and reaming holes
Countersinking is the process of processing cylindrical and conical raw holes in parts obtained by casting, forging, drilling with countersinks in order to increase their diameter, surface quality, increase accuracy (reduce taper, ovality).
Zenkers. In appearance, the countersink resembles a drill, but has more cutting edges (three to four) and spiral grooves. The countersink works like a drill, making a rotational movement around the axis, and translational - along the axis of the hole. Countersinks are made of high-speed steel; they are of two types - one-piece with a conical tail and mounted. The first for preliminary, and the second for the final processing of holes.
When countersinking parts made of steel, copper, brass, duralumin, cooling with a soapy emulsion is used.
To obtain a correct and clean hole, the diameter allowance for countersinking should be 0.05 diameter (up to 0.1 mm).
Countersinking is the process of processing cylindrical or conical recesses and chamfers of drilled holes for the heads of bolts, screws and rivets with a special tool.
Countersinking tool. The main feature of countersinks in comparison with countersinks is the presence of teeth on the end face and guide pins, with which the countersinks are inserted into the drilled hole.
There are countersinks; cylindrical having a guide pin, a working part consisting of 4 ... 8 teeth and a shank; conical has a cone angle at the top of 30, 60, 90 and 120 degrees; a holder with a countersink and a rotating stop allows you to countersink holes to the same depth, which is difficult to achieve when using conventional countersinks; countersinks in the form of socket heads, have end teeth, they are used to process bosses for washers, thrust rings and nuts. The fastening of countersinks and countersinks does not differ from the fastening of drills.
Reaming holes.
Reaming is a process of finishing holes, providing an accuracy of 7 ... 9 grades and a surface roughness of Ra 1.25 ... 0.63.
Reamers are tools for reaming holes by hand or machine. The reamers used for manual reaming are called manual reamers (Fig. a, b), and for machine reaming - machine reamers (Fig. c).
According to the shape of the hole being processed, the reamers are divided into cylindrical and conical. Manual and machine reamers consist of three main parts: working, neck and shank. For manual reamers, the inverse cone is 0.05 ... 0.1 mm, and for machine reamers - 0.04 ... 0.3 mm.
Machine reamers are made with a uniform distribution of teeth around the circumference. The number of teeth of the reamers is even - 6, 8, 10, etc. The more teeth, the higher the quality of processing.
Manual and machine reamers are performed with straight (spur) and helical (spiral) grooves (teeth).
Reamers are divided into several types:
manual cylindrical reamers;
machine reamers with a conical and cylindrical tail;
machine-mounted reamers and with plug-in knives;
machine reamers with a square head;
machine reamers equipped with hard alloy plates;
sliding (adjustable) machine reamers.
Deployment techniques
Reaming is always preceded by drilling and countersinking. The depth of cut is determined by the thickness of the cut layer, which is half the diameter allowance. It should be borne in mind that for holes with a diameter of not more than 25 mm, an allowance of 0.01 ... 0.15 mm is left for black reaming, and 0.05 ... 0.02 mm for finishing.
Manual deployment. Getting started with the deployment, first of all, you should:
select the appropriate reamer, then make sure that there are no crumbled teeth or nicks on the cutting edges;
carefully install a reamer in the hole and check its position along a 90 degree square; after making sure that the axis is perpendicular, insert the end of the reamer into the hole so that its axis coincides with the axis of the hole; rotation is carried out only in one direction, since rotation in the opposite direction may crumble the blade.
For the sequence of processing a hole with a diameter of 30 mm in a steel part according to the 6th ... 7th grade:
I - drilling a hole with a diameter of 28mm;
II - countersinking with a countersink with a diameter of 29.6 mm;
III - reaming with a rough reamer with a diameter of 29.9 mm;
IV - reaming with a fine reamer with a diameter of 30 mm.
Processing of conical holes. -First, the hole is processed with a stepped countersink, then a reamer with chip breaking grooves is used, and then a conical reamer with smooth cutting blades is used.
Defects. The main defects during deployment, their causes and ways to eliminate them.
Safety. When reaming holes, the same safety requirements must be met as when drilling.
Threading
The concept of carving. Formation of a helix
Thread cutting is its formation by removing chips (as well as plastic deformation) on the outer or inner surfaces of workpieces.
The thread is external and internal. A part (rod) with an external thread is called a screw, and with an internal one - a nut. These threads are made on machines or by hand.
Basic thread elements
- 1 - thread profile
- 2 - thread top
- 3 - thread cavity
H - thread height
S - thread pitch
Y - thread angle
D1 - internal
D2 - outdoor
D3 - top
Thread profile
The thread profile depends on the shape of the cutting part of the tool with which the thread is cut.
- A) cylindrical triangular thread. This is a fastening thread, cut into studs - a nut, bolts.
- B) a rectangular thread has a rectangular (square) profile. Difficult to manufacture, fragile and rarely used.
- C) trapezoidal tape thread has a section in the form of a trapezoid with a profile angle of 30 degrees. It is used to transmit movements or high forces in metal-cutting machines (lead screws, jacks, presses, etc.)
- D) the thrust thread has a profile in the form of an unequal trapezoid with a working angle at the top equal to 30 degrees. The bases of the turns are rounded, which provides a strong profile in a dangerous section.
- E) a round thread has a profile formed by two arcs conjugated with small straight sections and an angle of 30 degrees. In mechanical engineering, this thread is rarely used, it is used in joints that are subject to severe wear (fire pipe fittings, wagon ties, hooks of hoisting machines, etc.).
The thread can be left and right, according to the number of threads, the threads are divided into single-pass and multi-pass.
The main types of threads and their designation. In mechanical engineering, as a rule, three thread systems are used - metric, inch and pipe.
The metric thread has a triangular profile with flat-cut tops, and the pitch is expressed in millimeters, they are divided into threads with a normal pitch M20 (the number is the outer diameter of the thread), with a fine pitch M20x1.5 (the number is the outer thread pitch). They are used as fasteners: with a normal pitch - with significant loads and for fasteners (nuts, bolts, screws), with a fine pitch - with small loads of fine adjustments.
An inch thread has a triangular flat cut profile with an angle of 55 degrees (Whitworth thread) or 60 degrees (Sellers thread). All dimensions of this thread are expressed in inches (1”=25.4mm). The pitch is expressed as the number of threads (turns) on a length of one inch with diameters from 3/16 to 4 "and the number of threads per 1", equal to 24 ... 3.
Cylindrical pipe thread is standardized, it is a small inch thread, but unlike the latter, it mates without gaps and has rounded tops.
Pipe threads are standardized in diameters from 1/8 to 6 "with the number of threads per inch from 28 to 11.
Threading tool.
General information. Threads on parts are obtained on drilling, threading and turning machines, as well as by rolling, i.e., by the method of plastic deformation. Thread rolling tools are knurling dies, knurling rollers and knurling heads. Sometimes the thread is cut by hand.
The internal thread is cut with taps, the external thread is cut with dies, runs and other tools.
Tool for cutting internal threads. Taps. Taps are divided: by purpose - into manual, machine-hand and machine; depending on the profile of the thread being cut - for metric, inch and pipe threads; by design - into solid, prefabricated (adjustable and self-switching off) and special ones.
The set, consisting of three taps, includes rough, medium and fine taps (Fig. I, II, III).
The tap consists of the following parts: the working part - a screw with longitudinal grooves is used for threading. The working part consists of the intake (or cutting) part - it performs the main work when cutting and the calibrating (guide) part - the threaded part of the tap adjacent to the intake part - it directs the tap into the hole and calibrates the hole being cut; the shank-rod serves to secure the tap in the chuck or collar.
The threaded parts of the tap, limited by grooves, are called wedge-shaped cutting feathers.
Cutting edges are the edges on the cutting feathers of the tap, formed by the intersection of the front surfaces of the groove with the joined surfaces of the working part.
The core is the inner part of the body of the tap. Taps for cutting threads in stainless steels have a more massive (thick) core.
Grooves are recesses between the cutting teeth (feathers), obtained by removing a part of the metal. These grooves are used to form cutting edges and to accommodate chips in threading.
Taps have a different design, depending on which they are cylindrical and conical. The set, consisting of three taps, includes rough, medium and finishing taps, which have different diameters and remove different amounts of metal (chips). Draft - up to 60% of metal; medium tap up to 30% metal; the finishing tap is still up to 10%, after which the thread has a full profile.
According to the accuracy of the thread being cut, taps are divided into four groups - C, D, E and H. Group C taps are the most accurate, groups E and H are less accurate with an unpolished tooth profile. Group C and D - with a ground tooth profile; they cut high quality threads.
Machine-manual taps are used for cutting metric, inch and pipe cylindrical and conical threads in through and blind holes of all sizes.
Machine taps are used for cutting machine threads in through and blind holes. They are cylindrical and conical.
Nut taps are used to cut metric threads in nuts in one stroke by hand or machine. They are made in one set, have a long cutting part and shank.
There are also die taps, master taps, special taps, grooveless taps, combined taps, screw-fluted taps, they all differ from each other in shape and place of application.
Collars. When cutting threads by hand, the cutting tool is rotated with the help of knobs mounted on the squares of the shanks.
Non-adjustable collars have one or three holes; in adjustable knobs there is an adjustable hole for turning the tap when cutting threads in hard-to-reach places.
The calibrated wrench consists of a body, a spring and a bushing and is used for threading in deep and blind places.
The universal wrench is designed for fixing dies with an outer diameter of 20 mm, all types of taps and reamers with square shanks with sides up to 8 mm. To fix the dies in the body of the universal wrench there is a socket. The plate is fixed with screws.
Cutting of internal and external threads.
For cutting internal threads, various types of taps are used, and for external threads, various types of dies are used.
Selection of drills for drilling holes for threads. When threading, the material is partially "extruded", so the diameter of the drill should be slightly larger than the inner diameter of the thread.
The diameter of the drill for drilling holes for metric and pipe threads is determined from the reference tables and calculated by the formula
dc=d-KcP, where dc - drill diameter, mm; Kc - coefficient depending on the breakdown of the hole, taken from the tables; d - nominal thread diameter, mm; usually Kc=1…1.08; P - thread pitch, mm.
Driver dimensions for internal thread. The total length and diameter of the crank handle is determined according to the formulas established by practice: L=20D+100; d=0.5D+5, L - collar length, mm; D - tap diameter, mm; d - diameter of the crank handle, mm.
Lubrication of thread-cutting tools. The lubricant proposed by G.D. Petrov, makes it possible to obtain high-quality threads with the lowest labor costs. It has the following composition (%): oleic acid - 78, stearic acid - 17, fine sulfur - 5. A tool lubricated with this paste easily cuts threads in the holes of parts hardened to HRCE 38 ... 42.
External threads are cut with dies manually and on machines. Depending on the design, the dies are divided into round, rolling, sliding (pri-zmatic).
Defects. The most common defects in thread cutting are of various types (torn, tight, weakened, dull, thread failure, etc.).
How to remove broken taps
In the event of a breakage, the tap is removed from the hole in several ways.
If a piece of a tap sticks out of the hole, then the protruding part is grasped with pliers or hand vise and the piece is turned out of the hole.
When a HSS tap is broken, the piece with the broken tap is heated in a muffle or oil furnace and allowed to cool with the furnace.
If the part is very large and its heating is associated with significant difficulties, the following methods are used:
- 1) with the help of a special mandrel having three protrusions (horns) at the end;
- 2) using a special countersink;
- 3) by welding with an electrode a bar onto a piece of a tap broken into a part made of silumin;
- 4) using a key put on the square end of a special mandrel welded to a broken tap;
- 5) by etching the tap broken into aluminum alloy parts.
Safety. When cutting threads with a tap on the machine, you should be guided by the safety requirements for drilling machines. When cutting threads with taps and dies by hand in parts with strongly protruding sharp parts, make sure that when turning the funnel, do not injure your hands.
Riveting is the process of connecting two or more parts with rivets. This type of connection belongs to the group of non-detachable ones, since the separation of riveted parts is possible only by destroying the rivet.
Riveted joints are used in the manufacture of metal structures of bridges, trusses, frames, beams, as well as in aircraft construction, boiler construction, shipbuilding, etc.
The riveting process consists of the main operations:
the formation of a hole for a rivet in the parts to be joined by drilling or punching;
countersinking of the nest for the embedded head of the rivet (when riveting with countersunk head rivets);
inserting a rivet into a hole;
the formation of the closing head of the rivet, i.e. the rivet itself.
Riveting is divided into cold, performed without heating the rivets, and hot,
in which the rivet rod is heated to 1000 ... 1100 degrees before setting.
Cold or hot riveting is performed depending on the diameter of the rivet:
up to d = 8mm - only cold;
at d = 8…12mm - both hot and cold;
with d > 12mm - only hot.
Depending on the tool and equipment, as well as the impact or pressure on the rivet, there are three types of riveting - percussion with hand tools; shock with the help of riveting pneumatic trays; pressing with the help of riveting presses or staples.
Riveted joints have a number of disadvantages: an increase in the mass of riveted structures; weakening of the riveted material in the places where holes for rivets are formed; increase in technological operations.
Riveting is divided into manual, mechanized and machine.
Rivet types
A rivet is a cylindrical metal rod with a head of a certain shape. The rivet head, planted in advance, i.e., made together with the rod, is called a mortgage, and formed during riveting from a part of the rod that protrudes above the surface of the parts to be riveted, it is called a closing head.
According to the shape of the heads, rivets are distinguished: (a) - with a semicircular high head with a rod with a diameter of 1 ... 36 mm and a length of 2 ... 180 mm; (b) - with a semicircular low head with a rod with a diameter of 1 ... 10 mm and a length of 4 ... 80 mm; (c) - a flat head with a rod 2…36 mm in diameter and 4…180 mm long; (d) - with a countersunk head with a rod with a diameter of 1 ... 36 mm and a length of 2 ... 180 mm; (e) - with a semi-secret head with a shaft with a diameter of 2 ... 36 mm and a length of 3 ... 210 mm.
Rivets are made from materials with good ductility - steels (St2, St3, steel 10 and 15), copper (MZ, MT), brass (L63), aluminum alloys (AM-5P, D18, AD1), stainless steel (Kh18N9T), alloyed steel (09G2).
Rivets are made from the same material as the parts to be joined.
Explosive rivets have a recess (chamber) in the free end of the rod, filled with explosive, protected from moisture by a layer of varnish.
Riveting with explosive rivets is carried out in cases where it is impossible to make a closing head.
Riveting with tubular rivets consists in installing a rivet with a hollow rod into the hole, then the rivet is upset with a piston, thereby pulling the parts to each other and riveting.
Rivets with cores have a hollow core (piston), in which a core with a thickened part at the end is placed. The riveting process is carried out using tongs or a hand press by pulling the core through the piston and pressing it into the hole walls, and with further pulling, the closing head enters the piston and expands it.
TsAGI rivets consist of two parts - a piston and a core (made of 30KhMA steel), which is hardened.
Types of rivet seams
The place where parts are connected with rivets is called a rivet seam, which are divided into three types.
A strong seam has several rows of rivets and is used when riveting beams, columns, bridges, etc.
A tight seam is used for hermetic structures (tanks not subjected to high pressures) at light loads. For the tightness of the seam, gaskets made of paper or fabric impregnated with drying oil are used. Perform riveting in a cold way.
A strong-tight seam is made with hot riveting using riveting machines, followed by caulking of the rivet heads and the edge of the sheets. Rivet joints are divided into single-row, double-row and multi-row, and depending on the location of the rivets - into parallel and staggered.
For manual riveting, locksmith hammers with a square striker, supports, crimps, tensions and chases are used.
Choice of rivets. Regardless of the tools and fixtures used, the parts to be riveted are positioned in such a way that the embedded rivet heads are on top. This allows you to insert rivets in advance.
The required number, diameter and length of rivets are determined by calculation.
The length l(mm) of the rivet rod for the formation of a closing countersunk head is determined by the formula l=S+(0.8…1.2)d, where S is the thickness of the sheets to be riveted, mm; d - rivet diameter, mm.
For the formation of a semicircular closing head l=S+(1.2…1.5)d.
According to the calculated value, the nearest larger value is selected from among the lengths of the rivets provided for by the standard.
The distance from the center to the edge of the sheets to be riveted should be 1.5d.
The hole diameter must be larger than the rivet diameter.
Rivet diameter, mm…. 2 2.3 2.6 3 3.5 4 5 6 7 8
Hole diameter, mm…2.1 2.4 2.7 3.1 3.6 4.1 5.2 6.2 7.2 8.2
Types and methods of riveting. There are two types of riveting - with a two-sided approach, when there is free access to the closing and mortgage head, and with a one-sided approach, when access to the closing head is impossible.
There are two methods of riveting: direct, when hammer blows are applied to the rod from the side of the newly formed closing head; the reverse, when hammer blows are applied to the mortgage head. This method is used when access to the closing head is difficult.
Thaumel riveting method. The Thaumel head, in which the crimp is placed, rotates around the axis of the rivet rod, forming a closing head by gradual deformation of the material.
Riveting of large parts is carried out mechanized or machine, using pneumatic hammers or riveting machines, presses, both manual and stationary.
The method of processing metal by pressure, in which a shallow relief is applied to the workpiece by strongly pressing the tool (chasing), is called chasing. Chasing is used to seal seams during riveting using liners made of canvas impregnated with liquid minium or a thin steel mesh coated with a special putty (shellac and whitewash on wood alcohol).
The strikers have a different shape of the striker, flat, rounded, sharp-edged and dull-edged.
scraping
General information. Scraping.
Scraping is the operation of removing (scraping off) very thin metal particles from the surfaces of parts with a special cutting tool - a scraper. The purpose of scraping is to ensure a snug fit of the mating surfaces and the tightness of the connection. Scraping process rectilinear and curved surfaces manually and on machines.
In one working stroke, a layer of metal with a thickness of 0.005 ... 0.007 mm is removed with a scraper. Scraping achieves high accuracy (up to 30 bearing spots in a square of 25x25mm) and surface roughness of not more than Ra 0.32.
It is widely used in tool making as a finishing process for non-hardened surfaces.
Scrapers - metal rods of various shapes with cutting edges. They are made from tool carbon steels U10 and U12A. The cutting end of the scraper is hardened without tempering to a hardness of HRC 64 ... 66.
According to the shape of the cutting part, the scrapers are divided into flat, trihedral, shaped; by the number of cutting ends (edges) - into one-sided and two-sided; by design - on solid and with plug-in plates.
Flat scrapers are used for scraping flat surfaces - open grooves, grooves, etc. The length of flat double-sided scrapers is 350 ... 400 mm. The width of the scraper for coarse scraping is assumed to be 20…25mm, for fine scraping - 5…10mm. The thickness of the end of the cutting part ranges from 2 to 4 mm. The sharpening angle of scrapers for rough scraping is taken equal to 70 ... 75 degrees, for finishing 90 degrees.
Double-sided flat scraper due to the presence of two cutting ends has a long service life.
Three- and four-sided scrapers are used for scraping concave and cylindrical surfaces. Triangular scrapers are 190, 280, 380 and 510mm long.
The universal scraper with interchangeable blades consists of a body, a holder, a handle, a clamping screw, an interchangeable blade made of high speed steel or carbide.
A disk scraper is used for scraping wide planes. A disk with a diameter of 50 ... 60 mm and a thickness of 3 ... 4 mm is sharpened on a circular grinding machine. Thus, the entire scraper disk is used, which increases labor productivity.
Sharpening. Often the angle of sharpening of the cutting part of the scraper for steel is taken equal to 75 ... 90 degrees. The sharpening angles of the scraper for processing cast iron and bronze are 75 ... 100 degrees, for rough scraping of soft metals 35 ... 40 degrees.
After sharpening, burrs and irregularities form on the blade of the scraper, so the blade is adjusted by carrying out on abrasive bars with a grain size of 90 and below. For precise scraping and final finishing of the cutting part of the scraper, GOI pastes are used. On average, for 7 hours of work, the scraper is adjusted 4 ... 6 times, depending on the nature of the scraping and the material being processed.
Before scraping, surface irregularities are revealed by staining them with a mixture of machine oil and azure. Azure can be replaced with soot mixed with a mixture of autol and kerosene.
The paint is applied to the surface of the plate with a swab of clean linen rags folded in several layers. It is convenient to carry out staining with a bag made of clean linen (canvas) into which paint is applied.
In small recesses, the paint will accumulate, and in more recessed places it will not. This is how white spots appear - the most in-depth places that are not covered with paint; dark spots - less deep places in which paint has accumulated; gray spots are the most prominent places on which the paint lies in a thin layer.
Safety. When scraping, the following safety requirements must be met:
the workpiece must be securely installed and firmly fixed;
it is not allowed to work with defective scrapers (without handles or with cracked handles);
when performing work with grinding heads, observe the rules of electrical safety.
Cutting is a plumbing operation in which a layer of metal is removed from a part with a cutting and impact tool. The cutting tool for chopping is a chisel or cross-cutting tool, and the percussion tool is a hammer.
The chisel and crosshead are made of carbon tool steel, then the working and impact parts are hardened and subjected to low tempering.
A chisel cuts metal and cuts off burrs. Its cutting part has the shape of a wedge, which, depending on the hardness of the metal being processed, is sharpened at different angles: for cast iron and bronze 70 °, for steel 60 °, for copper and brass 45 °. The impact part of the chisel (head) is machined into a cone and rounded to center the impact. Key holes and narrow grooves are cut out with a crosscut.
Locksmith hammers have a round or square impact part - a striker. A hammer with a square-shaped striker leaves dents on the work surface with sharp corners during oblique blows.
The end of the hammer opposite the striker, which has the shape of a rounded wedge, is called the toe. The hammer is selected by weight, for each millimeter of the length of the cutting edge of the chisel, 40 g of the mass of the hammer is required.
Hammers are made of steel grades 50, 40X, U7 and U8. The working parts of the hammer - the striker and the toe are subjected to hardening and tempering.
Cutting is done in a vice, on a plate or on an anvil, large parts are processed on the floor. Cutting is recommended to be done in a chair vice, installed in accordance with the height of the worker. When felling, stand at the vise straight and steady so that the body is to the left of the axis of the vise. The left leg is put on the floor, one step forward, and the right one, which serves as a support, is set aside slightly back. The chisel is held in the left hand without excessive clamping, the distance from the hand to its impact part should be 20-25 mm.
Depending on the thickness of the metal, cutting is carried out with a carpal, elbow or shoulder swing. The wrist swing is performed by the movement of the hand, the elbow swing is made by the elbow movement of the arm, and the shoulder swing is the swing of the whole arm. Usually, cutting is done with an elbow swing; with such a blow, you can cut for quite a long time without getting tired.
During work, they look at the felling site. Cutting in a vice is carried out according to the level of the vise jaws or according to the intended risks. According to the level of the vise jaws, thin strip or sheet metal is cut, and the wide surfaces of the workpieces are cut according to the intended risks. Metal (sheet, strip and round) of considerable thickness is chopped on a plate or on an anvil with a strong vertical blow. To facilitate the cutting process and increase labor productivity, this process is currently mechanized using pneumatic hammers.
Another fairly common plumbing operation is metal cutting (cutting holes in a workpiece, cutting oil grooves, or simply cutting off an excess metal layer from a workpiece). Cutting is carried out on an anvil or on a massive metal plate. Smaller parts for cutting are clamped in a vice.
It should be noted that when cutting it is impossible to achieve high machining accuracy, it is used either for roughing the workpiece, or in cases where machining accuracy is not required.
When working with a chisel (the main cutting tool) and a hammer, depending on the purpose of the work, three types of blows are used:
- a brush stroke is used to remove a thin layer of metal, minor irregularities, and also in cases where it is necessary to cut a sheet of thin steel. Wrist strikes should be performed at a pace of 50-60 beats per minute; only the hand moves. When swinging, it is recommended to unclench the fingers of the hand, holding the hammer handle only with the index and thumb, and when striking, squeeze the brush;
- the elbow strike has a greater force compared to the wrist strike. The pace of beats is slightly slow - 40-50 beats per minute. When swinging, it is recommended to bend the arm at the elbow to failure, slightly unclench the ring and middle fingers. Elbow strikes are used to cut grooves and grooves, as well as to remove a layer of metal of medium thickness;
- The shoulder strike is the most powerful. The impact force is achieved by a large swing, in which the arm moves in the shoulder joint. Fingers, hand and elbow should work, as in the case of wrist and elbow strikes, but when swinging, the arm that is maximally bent at the elbow joint should be raised so that the hand is at ear level. The rate of beats should be even slower - 30-40 beats per minute. Such impacts are used for processing large surfaces, cutting thick metal, and also in cases where it is required to remove a large allowance in one pass of the chisel.
The quality of the cutting and the safety of the locksmith who produces it also depend on how the tool is held. The fingers on the hammer handle should be located at a distance of 15–30 mm from its end, with the thumb placed on the index finger. The chisel should be kept at a distance of 20-30 mm from its head, fingers should not be squeezed tightly. The probability of the hammer jumping off the chisel head is significantly reduced if a rubber washer with a diameter of 50 mm and a thickness of about 10 mm is put on its upper part.
When performing this type of locksmith work, it is also important to observe the correct setting of the chisel relative to the workpiece being processed (Fig. 23):
- when cutting is directed along the plane of the vise jaws, the angle between the axis of the chisel and the plane of the jaws should be approximately 45 °;
- when cutting is directed perpendicular to the plane of the jaws of the vise, the angle of inclination of the chisel relative to the workpiece should be 30–35 °: if the angle of inclination is large, then the chisel will go deep into the metal upon impact, creating a significant unevenness of the machined surface; with a smaller angle, the chisel will slide over the surface of the metal, and not chop it.
Rice. 23. The position of the chisel when cutting the workpiece in a vice.
An important note: inexperienced locksmiths, when hitting a chisel with a hammer, look, as a rule, at the head of the latter, on which the hammer strikes. This is a gross mistake that leads to a decrease in the quality of work: you need to look at the cutting edge of the chisel in order to control the angle of inclination and see the result of each blow.
When placing the workpiece in a vise, it is necessary to ensure that the marking marks are exactly at the level of the jaws and are not skewed.
The entire cut part of the metal (shavings) must be located above the level of the vise jaws.
Cutting a layer of metal on a wide flat surface
In cases where metal is to be cut on a wide flat surface, the workpiece should be positioned in such a way that the marking risks protrude 5-10 mm above the plane of the vise jaws. In this case, the felling operation should begin with cutting grooves 8–10 mm wide using a cross cutter (see Fig. 4, b). It should remove chips with a thickness of 0.5 to 1 mm in one pass.
The grooves should be arranged in such a way that there are gaps between them 4/5 of the length of the cutting edge of the chisel.
After cutting the grooves, the gaps between them are cut with a chisel. The chip thickness should be between 1.5 and 2 mm.
Caution is required when cutting brittle metals - such as cast iron, bronze, etc. Cutting should not be brought to the edge of the workpiece, as a chip will occur if the blow is directed from the center of the workpiece to its edge. There are two ways to avoid such a defect: firstly, the unfinished place is cut from the opposite side, directing the chisel with the tip towards the workpiece, and the head towards you, and secondly, having processed the edges in advance and made a bevel at an angle of 45 °. When cutting viscous metals (mild steel, copper, brass), it is recommended to lubricate the cutting edge of the chisel with soapy emulsion or machine oil.
Punching of curved grooves
Grooves and curved lubrication grooves must be cut through pre-marked marks. To do this, use a cross-cutting machine, which is used to cut down 1.5–2 mm of metal for each pass. Irregularities left after working with a crosscut can be removed with a groover, giving the grooves the same width and depth.
Some features have work when cutting metal along a curved contour. It is better to use a crosscut or a chisel with a rounded blade for this type of work.
First of all, it is necessary to cut the contour with light blows, deviating from the marking marks by 2–3 mm, and then remove the metal within the contour with strong blows. If the thickness of the sheet allows, then after a while the workpiece can be turned over and chopped from the opposite side, focusing on the contour indicated by the first blows.
From the book: Korshever N. G. Metalwork
Cutting is called an operation for removing a layer of material from the workpiece, as well as cutting metal (sheet, strip, profile) into pieces with cutting tools (chisel, cross-meisel or groover with a hammer). Processing accuracy during felling does not exceed 0.7 mm. In modern mechanical engineering, metal cutting is resorted to only in those cases when the workpiece, for one reason or another, cannot be processed on metal-cutting machines. Cutting perform the following work: removal of excess layers of material from the surfaces of workpieces (cutting off castings, welds, cutting edges for welding, etc.); trimming edges and burrs on forged and cast blanks; cutting into pieces of sheet material; punching holes in sheet material; cutting oil grooves, etc.
Cutting is carried out in a vise on a plate or on an anvil. Large workpieces are fixed in a chair vice during cutting. The trimming of castings, welds and bosses in large parts is carried out on site. Manual cutting is a very difficult and time-consuming operation, so it is necessary to strive to mechanize it as much as possible.
Cutting tools
The tools used in cutting are cutting tools; they are made of carbon tool steel grades U7, U8, U8A. The hardness of the working part of the cutting tools after heat treatment should be at least HRC 53 ... 56 for a length of 30 mm, and the impact part - HRC 30 ... 35 for a length of 15 mm. The dimensions of cutting tools for cutting depend on the nature of the work performed and are selected from the standard range. Hammers of various sizes and designs are used as a percussion tool when cutting. Most often, when cutting, metalwork hammers with a round head of various weights are used.
The locksmith's chisel (fig. 2.20) consists of three parts: working, middle, shock. As with any cutting, the cutting part of the tool is a wedge (Fig. 2.20, a).
The effect of a wedge-shaped tool on the metal being processed varies depending on the position of the wedge and the direction of the force applied to its base. There are two main types of wedge operation during cutting:
The axis of the wedge and the direction of the force applied to it are perpendicular to the surface of the workpiece. In this case, the workpiece is cut into pieces (Fig. 2.20, b);
The axis of the wedge and the direction of the force applied to its base form an angle less than 90° with the workpiece surface. In this case, chips are removed from the workpiece (Fig. 2.20, c).
The planes that limit the cutting part of the tool (see Fig. 2.20, c) are called surfaces. The surface along which the chips come off during the cutting process is called the front, and the surface opposite to it, facing the workpiece surface to be machined, is called the back. Their intersection forms the cutting edge of the tool. The angle between the surfaces that form the working part of the tool is called the angle of sharpening and is denoted by the Greek letter b (beta). The angle between the front and machined surfaces is called the cutting angle and is denoted by the letter 8 (delta). The angle between the front surface and the plane drawn through the cutting edge perpendicular to the cutting surface is called the front angle and is denoted by the letter y (gamma).
The angle formed by the back and machined surfaces is called the back angle and is denoted by the letter a (alpha).
The smaller the angle of sharpening of the cutting wedge, the less force must be applied when cutting. However, with a decrease in the cutting angle, the cross section of the cutting part of the tool also decreases, and hence its strength. In this regard, the value of the taper angle must be chosen taking into account the hardness of the material being processed, which determines the cutting force required to separate the metal layer from the surface of the workpiece, and the impact force on the tool necessary to create a cutting force.
With an increase in the hardness of the material, it is also necessary to increase the angle of sharpening of the cutting wedge, since the force of impact on the tool is large enough and its cross section must provide the cross-sectional area necessary to absorb this force. The values of this angle for various materials are approximately: cast iron and bronze - 70 °; steel of medium hardness - 60 °; brass, copper - 45 °; aluminum alloys - 35 °.
Relief angle a determines the amount of friction between the rear surface of the tool and the surface of the workpiece being machined, its value ranges from 3 to 8. The value of the back angle is adjusted by changing the inclination of the chisel relative to the surface to be machined.
Kreutzmeisel(Fig. 2.21) differs from a chisel in a narrower cutting edge. Kreuzmeysel is used for cutting grooves, cutting keyways and similar work. In order to prevent jamming of the crosscut during operation, its working part has a gradual narrowing from the cutting edge to the handle. The heat treatment of the working and impact parts, as well as the geometric parameters of the cutting part and the procedure for determining the sharpening angles of the cutting part for crosscuts are exactly the same as for the chisel.
ditcher(Fig. 2.22) is used for cutting lubrication grooves in bushings and bushings of plain bearings and profile grooves for special purposes. The cutting edges of the groover can have a straight or semicircular shape, which is selected depending on the profile of the groove being cut. The ditcher differs from the chisel and the crosscut only in the shape of the working part. The requirements for heat treatment and the choice of sharpening angles for groovers are the same as for chisels and crosscuts.
Locksmith hammers(Fig. 2.23) are used when cutting as a percussion tool to create a cutting force and are of two types - with a round (Fig. 2.23, a) and square (Fig. 2.23, b) striker. The end of the hammer opposite the striker is called the toe; it has a wedge-shaped shape and is rounded at the end. The hammer is fixed on the handle, which is held in the hand during operation, striking the tool (chisel, cross cutter, groover). To securely hold the hammer on the handle and prevent it from jumping off during operation, wooden or metal wedges (usually one or two wedges) are used, which are hammered into the handle (Fig. 2.23, c) where it enters the hammer hole.
Cutting of small pieces(up to 150 mm) from sheet material, wide surfaces of steel and cast iron blanks of small sizes, as well as cutting grooves in bearing shells, are performed in a vice.
On a plate or anvil, workpieces are chopped into pieces or cut out along the contour of workpieces from sheet material. Cutting on a plate is used in cases where it is impossible or difficult to fix the workpiece in a vice.
In order to give the working part of a chisel, crosscut or groover the necessary sharpening angle, it is necessary to sharpen it.
Sharpening of the cutting tool is carried out on grinding machines (Fig. 2.24, a). The tool to be sharpened is placed on the handpiece 3 and with a slight pressure slowly move it across the entire width of the grinding wheel. During the sharpening process, the tool is periodically cooled in water.
Sharpening the surfaces of the cutting wedge lead alternately - first one side, then the other, which ensures uniform sharpening and obtaining the correct angle of sharpening of the working part of the tool. The grinding wheel during operation must be closed with a casing 2. Protection of the eyes from the ingress of abrasive dust is carried out using a special protective screen 1 or goggles. The control of the sharpening angle of the cutting tool during the sharpening process is carried out using a special template (Fig. 2.24, b).
Cutting is an operation in which, with the help of a chisel and a metalwork hammer, layers of metal are removed from the workpiece or the workpiece is cut.
The physical basis of cutting is the action of a wedge, the shape of which is the working (cutting) part of the chisel. Cutting is used in cases where the machining of workpieces is difficult or irrational.
With the help of cutting, metal irregularities are removed (cut down) from the workpiece, hard crust, scale, sharp edges of the part are removed, grooves and grooves are cut, and sheet metal is cut into pieces.
Cutting is usually done in a vise. Cutting sheet material into parts - can be performed on a plate.
The main working (cutting) tool during cutting is a chisel, and a hammer is a percussion tool.
The bench chisel (11) is made of tool carbon steel. It consists of three parts: shock, middle and working. The shock part / is made tapering upwards, and its top (the striker) is rounded; for the middle part 2, the chisel is held during cutting; working (cutting) part 3 has a wedge shape. The angle of sharpening is selected depending on the hardness of the material being processed.
For the most common materials, the following taper angles are recommended: for hard materials (hard steel, cast iron) - 70°; for materials of medium hardness (steel) ~ 60°; for soft materials (copper, brass) "- 45 °; for aluminum alloys - 35 °.
The working and impact parts of the chisel are subjected to heat treatment (hardening and tempering). The degree of hardening of the chisel can be determined by running a file over the hardened part of the chisel: if the file does not remove chips, but slides over the surface, the hardening is done well.
To cut out narrow grooves and grooves, a chisel with a narrow cutting edge is used - a cross-cutting tool. Such a chisel can also be used to remove wide layers of metal: first, grooves are cut with a narrow chisel, and the remaining protrusions are cut down with a wide chisel.
For cutting out profile grooves (semicircular, dihedral, etc.), special crosscut groovers are used, which differ only in the shape of the cutting edge.
Bench hammers used in cutting metals are of two types: with a round and with a square head. The main characteristic of a hammer is its mass. For cutting metals, hammers weighing from 400 to 600 g are used.
The cutting of metals is a very labor-intensive operation. To facilitate labor and increase its productivity, mechanized tools are used. Among them, the most common is a pneumatic chipping hammer (12). It is driven by compressed air, which is supplied through hose 3 from a permanent pneumatic network or a mobile compressor. When chopping metal, the trigger 2 is pressed, squeezing the spool 4. Air, entering through the air channels, moves the striker 6, which strikes the shank of the chisel 7 inserted into the barrel 5. During cutting, the pneumatic chipping hammer is held with both hands: with the right - by the handle of the left - behind the end of the trunk, and guide the chisel along the cutting line.
