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Metal cutting
Chopping divide the workpiece into parts, remove excess metal ( allowance), make lubrication grooves in parts, etc. This operation is carried out using chisels (picture on the right) and a hammer.
Cutting part chisels, like any other cutting tool, have the shape wedge .
Point angle (sharpening) depends on the hardness of the metal being processed: the harder the metal, the larger the sharpening angle should be. For processing steel, an angle of 60° is recommended, for non-ferrous metals - 35° ... 40°.
A special chisel is used to cut grooves - kreutzmeisel(picture on the right).
When chopping, hammers weighing 400 or 500 g are used.
Before chopping, the workpiece is secured in a vice slightly to the left of the right edge of the jaws so that there is room for installing the chisel (Fig. on the left). The hammer is placed with the striker to the left on the workbench to the right of the vice, and the chisel is placed on the left, with the cutting part towards itself. A protective mesh (or screen) must be installed at the cutting workplace to protect others from metal fragments.
When chopping, it is very important to adopt the correct working posture (picture on the right). You should stand straight, your body should be turned towards the vice, your right shoulder should be against the head of the chisel. For stability, the left leg should be pushed forward, the body rests on the right leg.
The chisel and hammer are held so that the striking part and the edge of the handle protrude 15...30 mm (Fig. on the left).
Chopping in a vice can be done according to the marking marks and according to the level of the vice jaws. In the first case, the workpiece is installed so that the marking mark is 1.5... 2 mm above the jaws of the vice. The chisel is placed at an angle of 30... 40° (fig. on the right) to the surface to be processed. After each blow, return the chisel to its original position.
In the second case, the marking marks are lowered below the level of the jaws in such a way that after processing, an allowance of 1... 1.5 mm remains on the surface of the workpiece.
Depending on the hardness of the material being processed and its thickness, blows of varying strength are applied to the chisel with a hammer.
Distinguish carpal
, ulnar
And shoulder blows(
see fig. below).
Kistev
(rice. A) remove small irregularities and thin chips with a blow, elbow
(rice. b) - cut off excess metal and cut into pieces a workpiece of small thickness. At carpal
When struck, the hammer moves due to the movement of the hand.
At elbow
When hitting, the arm bends at the elbow and the blow becomes stronger (Fig. b). Elbow
the excess metal is cut off with a blow and the workpieces are divided into parts.
Shoulder
blow (Fig. V) - cut down thick shavings, cut rods, strips of large thickness.
In cases where the workpiece cannot be secured in a vice, it is processed on stove(picture on the left). The chisel is placed vertically on the marking line and blows are struck.
After each blow, the chisel is moved halfway along the cutting edge. This makes it easier to install the chisel in correct position and a continuous cut is formed. In workpieces of large thickness, marking marks are applied on opposite sides. First, cut to about half the thickness of the sheet on one side, then on the other.
When cutting a workpiece complex shape The cutting edge is placed at a distance of 1 ... 1.5 mm from the marking line and the workpiece is cut with light blows along the entire contour. After this, they chop along the entire contour with stronger blows. Then the workpiece is turned over and cutting is completed along the designated contour.
You can only work with a working tool. Impact part chisels and hammers should be free of cracks and burrs.
The hammer handle should be firmly seated and free of cracks.
Do not check the cutting quality by touch.
At the end of the cut, ease the force of the blow.
To avoid injury, place a rubber washer on the top end of the chisel.
Felling can only be done if there is protective screen and safety glasses.
You cannot stand behind someone working.
Manual cutting is a labor-intensive operation. IN industrial production it is replaced by other processing methods. Where it is impossible to do without felling, it is carried out locksmiths by using pneumatic or electric chipping hammers. Most often, blanks from sheet metal are cut out on presses using special dies. Among the high-performance methods that are used in lately, it should be noted oxygen, laser, etc. These installations serve metal cutters.
The variety of chisels and crosscuts is shown in the figure below.
Chopping is an operation in which, using a chisel and plumber's hammer layers of metal are removed from the workpiece or the workpiece is cut.
A chisel is the simplest cutting tool in which the wedge shape is particularly clearly expressed. A bench chisel is a steel rod made of tool carbon steel (U7, U8, 7HF, 8HF). The chisel consists of three parts - working, middle and impact.
The working part 2 of the chisel is a rod with a wedge-shaped cutting part (blade 1 at the end), sharpened at a certain angle.
The striking part (striker) 4 is made tapering upward, its apex is rounded.
For middle part 3 chisels are held when chopping. The sharpening angle is selected depending on the hardness of the metal being processed. Recommended chisel sharpening angles (degrees) for cutting some materials are given below.
Hard materials (hard steel, bronze, cast iron) - 70
Medium hard materials (steel) - 60
Soft materials(brass, copper, titanium alloys) - 45
Aluminum alloys - 35
The chisel is made in lengths 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 03-0.5 is hardened and tempered. After heat treatment cutting edge should have a hardness of HRSE 53...59, and the striker should have a hardness of HRSE 35...45.
When testing a chisel for strength and durability, it is used to cut off a strip of steel grade St6, 3 mm thick and 50 mm wide, clamped in a vice. After the test, the chisel blade should be free of dents, chipped areas and noticeable signs of dullness.
The degree of hardening of the chisel can be determined by using an old file, which is used to pass along the hardened part. If the file does not remove chips from the hardened part of the chisel (only barely noticeable marks remain on it), the hardening is done well.
Hammer swing when chopping:
Chopping tools:
a - chisel; b - crossmeisel; c - groover.
Kreuzmeisel is a type of chisel. The crosspiece is designed for cutting keyways, narrow grooves and recesses in hard materials. You can also use a cross-cutting machine to cut grooves when cutting large metal surfaces.
The groover is used for cutting out profile grooves: semicircular, dihedral, etc. It differs from the crossmeisel only in the shape of the cutting edge.
Mechanized cutting is carried out using pneumatic or electric chisels equipped with a set of wide and narrow chisels. For chopping, pneumatic chipping hammers are used, operating compressed air under a pressure of 5 atm with a number of blows from 1000 to 2400 per minute.
When cutting it is necessary to carry out following rules safety precautions:
1. Use only working tools:
hammers, chisels, crosspieces should not have knocked down places, rivets (hats) and cracks;
the hammer handle must be intact (without cracks or knots), made of hard and tough wood and wedged with a polished metal wedge;
The chisel and crosspiece must be sharpened to the required angle depending on the metal being processed.
2. Wear safety glasses. The cutting area should be protected with screens and shields.
To make work easier and increase productivity, mechanized tools are used. Among them, the most common is the pneumatic chipping hammer.
The most common operation associated with metal processing is its cutting. The simplest and most productive method of performing it is cutting metal using a guillotine. This equipment can be used to cut:
- sheet metal;
- fittings;
- rolled metal, etc.
This method allows you to accurately cut thick metal in the longitudinal or transverse direction. At the same time, the strength characteristics of the resulting products are not lost. In addition, cutting with a guillotine is a significantly cheaper operation compared to other popular cutting methods: laser or plasma.
Definition
Metal cutting is an operation that involves separating any part of a metal workpiece according to pre-applied markings. This method of processing metal workpieces is very economical, as it significantly reduces the cost of additional processing. This leads to a reduction in the cost of finished products.
Metal cutting methods
There are two ways to cut metal:
- manual;
- using a guillotine.
Manual method of cutting metal
This method involves the use of a chisel, a crosspiece and a hammer. The operation is performed on a steel plate or using a bench vice. Used in single production in the absence of specialized equipment. Characterized by low quality and productivity and high labor intensity.
Cutting metal with a guillotine
Cutting metal with a guillotine is a very popular manufacturing operation. Using a guillotine, cuts are made in transverse and longitudinal sections and parts of simple geometric shapes, bounded by straight lines. The use of this equipment allows you to make clear and precise cuts. The parts will not have any edge damage: chips, nicks or other defects along the cut line.
Equipment used
Used in industry the following types guillotine:
- manual:
- pneumatic;
- hydraulic;
- electromechanical.
The operating principle of the equipment is as follows. The roller conveyor feeds the metal intended for processing, which is fixed by a clamping device. A massive knife, the length of which exceeds the width of the sheet being processed, is lowered to the cutting site. He creates high blood pressure and, thanks to this, cuts the rolled steel as evenly as possible. With this processing method, the metal does not form burrs and does not wrinkle. The equipment is equipped with a mechanical, hydraulic or pneumatic drive. During operation, preference is given to an automatic guillotine, since it has different functional settings.
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Russian Federation
Ministry of Agriculture
FSBEI HPE "Oryol State Agrarian University"
Abstract
on the topic:" Metal cutting"
Completed:
Popryadukhin Alexander Vladimirovich
Checked:
Goncharenko Vladimir Vladimirovich
1. Metal cutting
2. Modern instrument
3. Rules and techniques for cutting metal
4. Safety rules
1. Metal cutting
Metal chopping is used to divide a workpiece into parts, remove excess metal, cut out grooves, grooves, etc. in parts. Chopping is carried out using a chisel, a cross-cutting tool and a hammer.
The chisel is a steel rod with a wedge-shaped cutting edge (Fig. 71). Angle of sharpening of the chisel when cutting steel billets should be equal to 60°, and when cutting non-ferrous metals - 35...45°.
A crosspiece is a narrow chisel designed for cutting out narrow grooves, grooves, etc. (Fig. 71, b).
When cutting workpieces, you need to stand straight, slightly turning your body relative to the vice, your right shoulder should be against the chisel striker. The chisel is held so that the striking part protrudes from the left hand by 15 ... 30 mm.
Depending on the hardness and thickness of the workpiece being processed, the force of the hammer hitting the chisel should be different.
A brush blow is used to remove small irregularities and thin chips. During a wrist strike, the hammer moves due to the movement of the hand (Fig. 72, a).
With an elbow strike, the arm bends at the elbow and the blow becomes stronger (Fig. 72, b). Using an elbow blow, excess metal is cut off and the workpieces are divided into parts.
The shoulder blow is used for cutting thick shavings, cutting rods and strips of large thickness (Fig. 72, c).
The workpieces are cut in a vice and on a stove. When cutting in a vice, the workpiece is secured in such a way that the marking mark is 1.5...2 mm below the level of the jaws. In this case, after processing, an allowance remains on the workpiece for filing the edges. The cutting edge of the chisel is placed on the surface of the jaws at an angle of 30...40° to the cutting plane (Fig. 72, d). The angle of inclination of the chisel to the edges of the jaws should be 45...60°.
When cutting on a slab, the chisel is placed vertically (Fig. 72, c) on the marking line and blows are applied. After delivering the first blow, the chisel is positioned so that half of its cutting edge is in the already cut hole, and half is on the marking line, and the second blow is applied. By moving the chisel along the marking mark in this way, it is easier to install it in the correct position and ensures a continuous cut.
If the thickness of the workpiece is no more than 2 mm, then the metal is cut on one side, and a mild steel plate is placed on the other side so as not to dull the chisel on the plate. If the thickness of the workpiece is more than 2 mm, then the marking line is applied on both sides. First, they cut through the sheet on one side, about half its thickness, and then turn it over and cut it completely.
When cutting out blanks of complex shapes from sheet metal, initially, at a distance of 1...2 mm from the marking lines, a shallow groove is cut with light hand blows on the chisel. Then, with powerful elbow blows, they chop the workpiece along the intended groove until the contour to be cut appears on its opposite side. After this, the sheet is turned over and the workpiece is finally cut out.
At enterprises, cutting is carried out by mechanics using pneumatic and electric hammers. Sheet metal blanks are cut out by stampers using presses and special dies. To process workpieces made of high-strength steels, plasma and laser cutting. metal cutting chisel crossmeisel
Metal cutting is carried out in a vice, on a plate and on an anvil using a metalworker's hammer, a chisel, a cross-cutting tool, a blacksmith's chisel and a sledgehammer.
Metal cutting can be horizontal or vertical depending on the location of the chisel during the operation. Horizontal cutting is done in a vice. In this case, the rear edge of the chisel is installed to the plane of the vise jaws almost horizontally, at an angle of no more than 5°. Vertical cutting is done on a slab or anvil. The chisel is installed vertically, and the material to be cut is laid horizontally on the slab.
2. Modern instrument
For metal cutting, hammers weighing 400, 500, 600 and 800 g are used. Hammers are mounted on handles made of hard and tough wood (birch, maple, oak, rowan). Handles should be oval in shape, with a smooth and clean surface, without knots or cracks. The length of the handle of a hammer weighing 400-600 g is 350 mm, and that of a hammer weighing 800 g is 380-450 mm. To prevent the hammer from jumping off during operation, the end of the handle on which the hammer is mounted is wedged with wooden or metal wedges 1-3 mm thick. The wedges are placed along the major axis of the handle section. Wooden wedges are placed on glue, and metal ones are roughed up so that they do not fall out.
The working part of the chisel and the crosspiece - (5, c, d) is hardened to a length of at least 30 mm, and the head is hardened weaker than the blade (to a length of about 15-25 mm) so that when hit with a hammer it does not crumble or crack.
The rest of the chisel and crosspiece should remain soft. Chisels and crosspieces should not have cracks, caps or other defects.
The most commonly used chisels are 175 and 200 mm long with blades 20 and 25 mm wide. To cut grooves in steel and cast iron, cross-cutting tools 150-175 mm long with a blade 5-10 mm wide are used. The heads of the chisel and crosspiece are forged onto a cone, which ensures right direction impact with a hammer and reduces the possibility of mushroom cap formation on the head.
The sharpening angle of chisels and crossbars depends on the hardness of the metal being processed. For chopping cast iron, hard steel and hard bronze, the sharpening angle of the tool is 70°, for chopping medium and soft steel - 60°, for chopping brass, copper and zinc -45°, for chopping very soft metals (aluminum, lead) - 35- 45°.
Tools are sharpened on sharpening machines with abrasive wheels. During sharpening, the working part of the tool (blade) becomes very hot and may become tempered. During tempering, the hardness of the hardening is lost and the tool becomes unsuitable for further work. To avoid this, the working part of the tool is cooled with water during sharpening. Figure 6 shows how to hold the chisel when sharpening and how to check that the angle is sharpened correctly.
3. Rules and techniques for cutting metal
The productivity and cleanliness of metal cutting depend on correct techniques work. When chopping, you need to stand steadily and straight, half-turned towards the vice. The hammer is supposed to be held by the handle at a distance of 15-20 mm from the end and applied strong blows to the center of the chisel head. You should look at the chisel blade, not at its head, otherwise the chisel blade will not go properly. The chisel should be kept at a distance of 20-25 mm from the head.
4. Safety rules
1. Carry out cutting only with safety glasses and a protective screen installed.
2. Securely secure the workpiece in a vice.
3. Use a working tool.
4. You cannot stand behind a working comrade.
5. When finishing work, reduce the impact force.
3. Tools and devices for cutting metal
Chopping is a metalworking operation in which, using a cutting tool (chisel), excess layers of metal are removed from a workpiece or part or the workpiece is cut into pieces.
With modern methods of processing material or workpieces, metal cutting is an auxiliary operation.
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TO category:
Metal cutting
General concepts about logging in plumbing
Felling is the processing of metal with cutting and impact tools, as a result of which excess layers of metal are removed (cut down, cut down) or metal intended for further processing and use is cut into pieces. A chisel or kreidmeisel is usually used as a cutting tool in plumbing, and as a percussion instrument- simple or pneumatic hammers.
Using chopping you can do:
— removal (cutting down) of excess metal layers from the surfaces of workpieces;
— leveling uneven and rough surfaces;
— removal of hard crust and scale;
— cutting off edges and burrs on forged and cast workpieces;
— chopping off the protruding edges of sheet material, ends of strips and corners after assembly;
— cutting into pieces sheet and varietal material;
- cutting out holes in sheet material along the intended contours;
— cutting edges into a joint for welding;
— cutting off the heads of rivets when removing them;
— cutting out lubrication grooves and keyways.
The cutting is done in a vice, on a plate or on an anvil; Bulky parts can be processed by cutting at their location. A chair vice is best for chopping; It is not recommended to cut on a parallel vice, since their main parts - jaws made of gray cast iron - often cannot withstand strong impacts and break.
The part being processed by cutting must be motionless. Therefore, small parts are clamped in a vice, and large parts are placed on a workbench, plate or anvil, or placed on the floor and well strengthened. Regardless of where the cutting is done, the height of the parts must be installed in accordance with the height of the worker.
When starting to cut, the mechanic first of all prepares his workplace. Taking the chisel and hammer out of the workbench box, he places the chisel on the workbench on the left side of the vice with the cutting edge facing him, and the hammer on the right side of the vice with the striker pointing towards the vice.
When chopping, you must stand straight and steady at the vice, so that the body is to the left of the axis of the vice.
Rice. 1. Chopping technique: a - elbow swing, b - shoulder swing, c - correct position of the legs of the person working when chopping, d - holding the chisel
The left leg is placed half a step forward, and the right leg, which serves as the main support, is slightly set back, spreading the feet at an angle approximately as shown in Fig. 1, c.
Hold the chisel in your hands as shown in Fig. 1, g, freely, without excessive clamping. During chopping, they look at the working part of the chisel, more precisely, at the place of chopping, and not at the striking part, which is hit with a hammer. You only need to chop with a sharply sharpened chisel; a blunt chisel slips from the surface being cut, the hand quickly gets tired of this, and as a result the correctness of the blow is lost.
The depth and width of the metal layer (chips) removed by a chisel depends on physical strength working, the size of the chisel, the weight of the hammer and the hardness of the metal being processed. The hammer is selected by weight, the size of the chisel is selected by the length of its cutting edge. For every millimeter of chisel cutting edge length, 40 g of hammer weight is required. Hammers weighing 600 g are usually used for chopping.
Depending on the order of operations, felling can be roughing or finishing. When roughing, with strong blows of a hammer, a layer of metal with a thickness of 1.5 to 2 mm is removed in one pass. When finishing cutting, a layer of metal with a thickness of 0.5 to 1.0 mm is removed per pass, applying lighter blows.
To obtain a clean and smooth surface, when cutting steel and copper, it is recommended to moisten the chisel with machine oil or soapy water; Cast iron should be cut without lubrication. Brittle metals (cast iron, bronze) must be cut from the edge to the middle. In all cases, when approaching the edge of a part, you should not cut the surface to the end; you should leave 15-20 mm to continue cutting with opposite side. This prevents chipping and chipping of the corners and edges of the workpiece. At the end of chopping metal, as a rule, you need to release the hammer blow on the chisel.
Chopping in a vice is done either at the level of the jaws of the vice, or above this level - at the intended risks. According to the level of the vice, thin strip or sheet metal, above the level of the vice (by risks) - wide surfaces of the workpieces.
When chopping wide surfaces To speed up the work, use a crosscut tool and a chisel. First, cut grooves of the required depth with a cross-section, and the distance between them should be equal to 1D of the length of the cutting edge of the chisel. The resulting protrusions are cut off with a chisel.
To properly chop, you need to be good at using a chisel and a hammer: this means holding the chisel and hammer correctly, moving your hand, elbow and shoulder correctly, and hitting the chisel with the hammer accurately, without missing a beat.
division of metal shavings, which represents the essence of the cutting process.
The tool used for chopping, the chisel, is the simplest cutting tool in which the wedge is especially clearly defined. The wedge, as the basis of any cutting tool, must be strong and correct in shape - it must have front and back edges, a cutting edge and a sharpening angle.
The front and rear faces of the wedge are two generatrix planes that intersect each other at a certain angle. The edge that faces outward during operation and along which the chips flow is called the front; the edge facing the object being processed is the rear.
The cutting edge is the sharp edge of the tool formed by the intersection of the front and rear edges. The surface that is formed on the workpiece directly by the cutting edge of the tool is called the cutting surface.
Normal cutting conditions are ensured by the presence of rake and back angles on the cutting tool.
In Fig. Figure 2 shows the angles of the cutting tool.
The rake angle is the angle that is between the front edge of the wedge and the plane perpendicular to the cutting surface; denoted by the letter g (gamma).
Rear angle - the angle formed by the rear edge of the wedge and the cutting surface; denoted by the letter a (alpha).
Point angle - the angle between the front and rear edges of the wedge; denoted by the letter p (beta). The division of the metal layer from the rest of its mass occurs as follows. The wedge-shaped steel body of the cutting tool, under the influence of a certain force, presses on the metal and, compressing it, first displaces and then chips off metal particles. Previously broken off particles are replaced by new ones and move up along the front edge of the wedge, forming chips.
Rice. 2. Cutting patterns and cutting tool angles
Chip particles are sheared along the shear plane MN, located at an angle to the front edge of the wedge. The angle between the shearing plane and the direction of movement of the tool is called the shearing angle.
Let's consider the effect of a wedge when operating a simple planing cutter (Fig. 3). Let's assume that a certain layer of metal needs to be removed from workpiece A using a cutter. To do this, install a cutter on the machine so that it cuts the metal to given depth, and by the action of a certain force P impart to it continuous movement in the direction shown by the arrow.
A cutter made of a rectangular bar, devoid of wedge corners, does not separate the chips from the metal. It crushes and crushes the layer being removed, tears and damages the treated surface. It is clear that such a tool cannot be used.
In Fig. 54 shows a cutter with a working part sharpened in the shape of a wedge. The cutter easily separates the chips from the rest of the metal, and the chips flow freely along the cutter, leaving a smooth machined surface.
Chisel. The mechanic's chisel is an impact chisel cutting tool, used in cutting metals. In Fig. 55, and a drawing of a chisel is given. The end of the working part of the chisel has a wedge-shaped shape, which is created by sharpening two symmetrical surfaces at a certain angle. These surfaces of the working part are called the faces of the chisel. The edges at the intersection form a sharp edge called the cutting edge of the chisel.
The edge along which the chips flow when cutting is called the front, and the edge facing the processed surface, - back. The angle a formed by the edges of the chisel is called the sharpening angle. The sharpening angle of the chisel is selected depending on the hardness of the metal being processed. For hard and brittle metals, angle a should be greater than for soft and viscous metals: for cast iron and bronze, angle a is taken to be 70°, for steel - 60°, copper and brass - 45°, aluminum and zinc - 35°, medium shape The part of the chisel is such that it allows you to hold it comfortably and firmly in your hand while chopping. The sides of the chisel should have rounded and smooth edges.
Rice. 3. Cutter during the cutting process: L - product, 1 - cutter, 2 - depth of the layer being removed, P - force acting during cutting
The striking part of the chisel has the shape of a truncated cone irregular shape with a semicircular upper base. With this shape of the striking part, the force of hitting the chisel with a hammer is used with the best result, since the blow always falls in the center of the striking part.
Rice. 4. Chisel (a) and cross-section (b) Dimensions of chisels in mm
When chopping metal, the chisel is held in the left hand by the middle part, loosely clasping it with all fingers so that the thumb lies on the index finger (Fig. 56) or on the middle one, if index finger is in an extended position. The distance from the hand to the striking part of the chisel must be at least 25 mm.
Rice. 5. Position of the chisel when cutting: a - cutting at the level of the vice, 6 - cutting at the risk
Rice. 6. Installing the chisel on the workpiece in relation to the jaws of the vice
For chopping, the chisel is placed on the workpiece, as a rule, with the back edge inclined to the workpiece surface at an angle, but not more than 5°. With such an inclination of the rear face, the angle of inclination of the chisel (its axis) will be the sum of the rear angle and half the sharpening angle. For example, with a sharpening angle of 70°, the tilt angle will be 5 + 35°, i.e. 40°. In relation to the line of the jaws of the vice, the chisel is set at an angle of 45°.
Correct installation chisel contributes complete transformation impact force with a hammer into cutting work with minimal fatigue of the worker. In practice, the angle of the chisel is not measured, but the correct angle is felt to work, especially with proper skill. If the angle of inclination is too great, the chisel cuts deep into the metal and moves forward slowly; if the angle of inclination is small, the chisel tends to break out of the metal and slide off its surface.
The inclination of the chisel to the surface being processed and relative to the jaws of the vice is directed by the movement of the left hand during chopping.
Kreuzmeisel. The Kreutzmeisel is essentially a chisel that has a narrow blade. It is used for cutting narrow grooves and keyways. The sharpening angles of the crossmeissel are the same as those of a chisel. Sometimes the crossmeisel is used instead of a chisel, for example, when the chisel is too wide for the cutting edge or when the working conditions make it inconvenient to use.
Rice. 7. Sharpening the chisel (crossmeissel) on sharpening machine and a template for checking the correct sharpening
Cross-cutting tools are used to cut semicircular, sharp and other grooves special form, called ditchers.
Sharpening chisels and crosspieces. During the operation of the chisel and the cross-section, abrasion of their edges occurs, a small break in the cutting edge and a rounding of the tip of the sharpening angle. The cutting edge loses its sharpness and further work tool becomes ineffective and sometimes impossible. The performance of a dull tool is restored by sharpening.
The chisel is sharpened on a grinding wheel - on a sharpening machine. Taking the chisel in your hands, as shown in Fig. 7, place it on the rotating circle and, with light pressure, slowly move it left and right across the entire width of the circle. During sharpening, the chisel is rotated first with one edge and then with the other, sharpening them alternately. You cannot press the chisel hard on the wheel, as this can lead to severe overheating of the tool and its working part losing its original hardness.
At the end of sharpening, remove burrs from the cutting edge of the chisel, carefully and alternately placing the edges on the rotating grinding wheel. After sharpening, the cutting edge of the chisel is set on an abrasive stone.
The chisel can be sharpened with a supply of coolant and on a dry wheel. In this case, it is necessary to cool the chisel being sharpened by lifting it from the wheel and lowering it into water.
When sharpening a chisel, you need to carefully ensure that the cutting edge is straight and the edges are flat, with equal angles of inclination; The sharpening angle must correspond to the hardness of the metal being processed. The sharpening angle during sharpening is checked with a template.
The Kreuzmeisel is sharpened in the same way as a chisel.
Locksmith's hammers. It was already indicated earlier that in plumbing two types of hammers are used - with a round and square striker. The end of the hammer opposite the striker is called the toe. The toe is wedge-shaped and rounded at the end. It is used for riveting, straightening and drawing out metal. During chopping, the chisel or cross-meisel is hit only with the hammer head.
Ways to hold a hammer. The hammer is held by the handle in the right hand at a distance of 15-30 mm from the end of the handle. The latter is grasped with four fingers and pressed against the palm; The thumb is placed on the index finger, all fingers are squeezed tightly. They remain in this position both during the swing and during the impact. This method is called “holding the hammer without unclenching your fingers” (Fig. 9, a).
Rice. 8. Bench hammers: a - with a round striker, b - with a square striker, c - jamming of the hammer on the handle
There is another method that involves two steps. With this method, at the beginning of the swing, when the hand moves upward, the hammer handle is clasped with all fingers. Subsequently, as the hand rises up, the clenched little finger, ring finger and middle fingers gradually unclench and support the hammer tilted back (Fig. 9, b). The hammer is then given a push. To do this, first clench the unclenched fingers, then accelerate the movement of the entire arm and hand. The result is a strong hammer blow.
Rice. 9. Methods of holding a hammer when chopping: a - without unclenching your fingers, b - with unclenching your fingers
Hammer blows. When chopping, hammer blows can be made with a wrist, elbow or shoulder swing.
The wrist swing is carried out by moving only the hand.
The elbow swing is made by the elbow movement of the arm - bending it and then quickly extending it. During an elbow swing, the fingers of the hand operate, which open and close, the hand (moving it up and then down) and the forearm. To receive a strong blow, the extension movement of the arms must be done quickly enough. Exercises in the elbow swing develop well the elbow joint along with the hand and fingers.
The shoulder swing is a full arm swing that involves the shoulder, forearm and hand.
The use of this or that swing is determined by the nature of the work. The thicker layers of metal are removed from the surface being processed, the greater the need to increase the impact force, and therefore, to increase the swing; However, if you use a wide swing incorrectly, you can damage the workpiece and tool and tire unnecessarily quickly. You need to learn to accurately proportion the impact force according to the nature of the work being performed.
The hammer should strike the chisel with an elbow swing with the fingers unclenched; with such a blow you can chop for quite a long time without getting tired. The blows must be measured, well-aimed and strong.
The productivity of the cutting depends on the force of the hammer applied to the chisel and on the number of blows per minute. When chopping in a vice, make from 30 to 60 strokes per minute.
The impact force is determined by the weight of the hammer (the heavier the hammer, the hit harder), hammer handle length (than longer handle, the stronger the blow), the length of the worker’s arm and the size of the hammer swing (the longer the arm and the higher the swing, the stronger the blow).
When chopping, you must use both hands in concert. Right hand you need to accurately and accurately hit the chisel with a hammer, and with your left hand, in the intervals between blows, move the chisel along the metal.
