Preparing Hand Saws For Operation
Preparing saw teeth for work.
Preparing tungsten carbide circular saws.
The preparation of the saws during work includes notching teeth, measuring the gear rim, sharpening and planing the teeth.
The notching of teeth is performed on manual (PSh) or mechanical (PShP-2) saw dies, when it is required to change the tooth profile if 3 (total) or 2 teeth in a row are broken on the saw. The final shape of the teeth is achieved on grinding machines.
Widening of the ring gear (on the side) depends on the species and condition of the wood being cut and lies in the range from 0.3 mm for hardwoods to 1.0. 1.3 mm for softwoods at high humidity. With planer saws, widening of the kerf is not required due to the shape of the disc, which tapers from the periphery to the center. With carbide saws, the cut is widened by overhanging the carbide blade. All other saws require periodic widening of the ring gear by spreading or flattening.
Tooth set. the most versatile method used for ripping and cross-cutting saws with straight and oblique sharpening. The divorce consists in alternately bending the teeth to the left and right sides by 1/3. 1/2 of the height of the tooth from its size. Saw teeth can be adjusted both before and after sharpening.
To set the teeth, use the RPK8, RP8 machines (for Æ saws up to 800 mm), manual wiring PI-39, a vice for clamping saws during divorcing, indicator divider and templates for controlling the accuracy of the divorce. The advantages of setting saw teeth are relative simplicity and versatility. The disadvantages are that each kerf is formed by only half of the teeth and that an unbalanced force acts on each tooth, which reduces the stability of the saw in the kerf.
Flattening of teeth used to widen the ring gear of saws for longitudinal sawing with straight sharpening. The crimping roller 3 is pressed to the tip of tooth 1 from the front facet, and an anvil stop is pressed from the rear facet.
When the crimping roller is turned, it penetrates into the material of the saw tooth due to a smooth increase in the radius of its working area. The tip of the tooth rests on both sides (I). Then it is given the correct shape by molding, crimping it with dies (II) and tightening it (III). Double-sided widening of the tooth provides a symmetrical action of forces during the operation of the saw, and the cut surfaces are formed by each tooth. The quality of the cut is higher, the stability of the saw is great. Crimped teeth retain sufficient broadening for 3. 4 regrinds. Due to the greater stability, saws with crimped teeth can be 0.2. 0.4 mm thinner, allow 15. 20% greater feed per tooth and 0.1 mm less widening of the gear rim than saws with set teeth. To crimp the teeth, a semi-automatic machine for cold crimping and forming of teeth PCFK8 (PCFD) for saw diameters up to 800 mm is used, a PKTs manual conditioner, a FKTs manual molding, a device for installing a saw during pressing and forming. In the presence of a large number of saws for longitudinal sawing, it is rational to use machines for flattening and forming teeth in cold and hot (heating up to 800. 600 о С in the field of HFC).
Sharpening teeth saws with an abrasive wheel consists in grinding off the edges of the teeth a layer of metal, the thickness of which is sufficient to restore their sharpness and correct shape. In one pass, a layer with a thickness of 0.02. 0.05 mm is ground, therefore the saws are sharpened in several passes. Wherein:
All teeth after sharpening must have the same profile, pitch, height, angles, etc.
The tops of all teeth must be on the same straight line (frame and band saws) or a circle (circular saws).
In order to avoid the formation of a crack in the plane and breakage of the teeth, the bottom of the depressions should have a smooth rounding.
Saw teeth should not have twists, bluing tips and other defects.
Sharpened teeth should not shine at intersecting corners. Gloss indicates insufficient sharpness of the tooth.
Distinguish sharpening methods on the front, on the back, on the front and back edges. Sharpening on the front face allows the maximum number of regrinds, but takes more time. Rear edge sharpening is uneconomical in terms of saw consumption. Therefore, steel saws are sharpened along the front and back edges. There are sharpening machines for frame, round, band and disk saws with carbide plates: TchPR, TchPK (TchPD), TchL and TchPT and others.
Tooth planing saws are the process of grinding metal from the tips of the most protruding teeth to align the ring gear in height and width. This allows you to reduce the depth of kinematic irregularities and ensure the participation of all teeth in the formation of the cut. Jointing can be lateral and radial and is carried out with the help of jointing bars manually and on a sharpening machine (static) or on the shaft of a circular saw (dynamic). As a result, planer areas are formed at the tips of the teeth. Within their limits, the clearance angle is 0, therefore, their size should not be more than 0.3 mm in order to exclude large friction forces. Diamond sharpening and finishing increases the tool life by 2.3 times and reduces the consumption of hard alloys by 1.5. 2 times.
Basic operations for preparing circular saw blades with carbide inserts: milling of cavities for carbide plates, soldering of carbide plates, sharpening and finishing of teeth. Silver or copper-zinc solders are used in the form of a thin wire and a calcined dehydrated borax flux in the form of a fine powder. Soldering heating. electrical contact; in the HDTV field; gas burner; oxygen acetylene flame. Sharpening and finishing is performed with abrasive (carborundum) or diamond wheels; as well as combined coarse sharpening. with abrasive wheels, and final sharpening and lapping. with diamond.
The main sharpening is carried out along the rear edge 4, auxiliary. along the front edge 3.Rear edge sharpening includes sharpening on the steel part of 1 tooth at an angle of a6 о. finishing sharpening on plate 2 at an angle a2 o and finishing the plate (part) at an angle a. Front edge sharpening (if necessary) consists of preliminary sharpening along the entire face at an angle g. Sharpening is carried out only on the plate (a2 o) with an allowance of 4 567
Date added: 2017-04-05; views: 1862; ORDER WRITING WORK
Preparing hand saws for work.
Planing the tops of the teeth. Tooth set. Sharpening saws with a file.
Saw preparation consists of the process of planing, setting and sharpening the saws.
First, the saws must be thoroughly cleaned of resin, adhering sawdust, rust, rinsed in kerosene. If the surfaces of the blades have irregularities, they are straightened with a hammer on a flat metal plate. Then they proceed to jointing. alignment of the sawtooth tips, as they must be at the same height. A file 1 is inserted into a wooden block (Fig. 11, a), after which the block with a file is put on the saw 3 and moved along the blade, while aligning the tops of the teeth.
You can also align the tops of the saw teeth in another way. In the workbench 4, a board is strengthened (Fig. 11, b), into the slot of which a file is inserted, after which the saw blade is inserted into this slot with the teeth down and, moving the saw along the file, align the tops of the teeth. It is necessary to align the tops of the teeth periodically, otherwise they will unevenly participate in the sawing. The quality of the planing is checked by applying a ruler to the tops of the teeth. If the tops of the teeth fit snugly against the edge of the ruler, the planer is correct.
During the sawing process, the saw blade rubs against the walls of the board being sawn and is clamped in the cut. To avoid jamming the saw blade in the cut, the teeth must be set.
The spread of saw teeth is that they are bent in turn: even teeth in one direction, and odd ones. to another. When spreading the teeth, it is necessary to bend to the side not the entire tooth, but only its upper part approximately at a height of up to 2/3 of the base. When sawing hardwood, the teeth are set at 0.25. 0.5 mm per side, but soft rocks. 0.5. 0.7 mm.
The teeth of the hand saws are bred using the wiring (Fig. 12, a) as follows. The saw blade is tightly clamped in a vice, and then the teeth are bent alternately in one direction or the other. It is necessary to spread the saw teeth evenly, without applying great efforts and sudden movements, since otherwise you can break the tooth.
In addition to the usual one, a universal wiring is used (Fig. 12, c), consisting of a lever 3 designed to bend the saw tooth, plate 4, which regulates the width of the gap for the saw passage, and adjusting screws 5. In the upper part of the wiring there is a scale 7 showing the amount of divorce. and a screw 8 with a stop, which regulates the height of the bent tooth. Spring 9 serves to return the lever 3 to its original position after compression of the wiring.
and. simple wiring with stops, b. template for checking the correct setting of the saw teeth, c. universal wiring, g. indicator divider, type RI; 1.saw, 2. template, 3. lever, 4. plate, 5. adjusting screws, 6. swivel adjuster, 7. scale, 8. screw with stop, 9. spring, 10. bearing surface, 11. indicator
The correctness of the spread of the saw teeth is checked with a template 2 (Fig. 12, b), applying it to the saw blade 1, clamped in a vice. The even teeth are checked first, and then the odd ones. Incorrectly bent teeth need to be corrected.
The correctness of the saws divorce can be checked more accurately with an indicator divider of the RI type (Fig. 12, d). When measuring, the water meter is pressed tightly against the saw blade with the supporting surface, and the indicator tip is placed opposite the top of the monitored tooth. The deviation of the indicator arrow determines the amount of divorce.
Next operation. sharpening saw teeth with double and single cut files. Files are distinguished by shape, triangular, rhombic and flat. Hand saws are usually sharpened with triangular or rhombic files.
When sharpening, the saw blade is clamped in a vice, fixed on a workbench. The file is pressed against the tooth as it moves away from you, and when it is returned it is slightly raised so that it does not touch the saw. Do not press the file strongly against the tooth, as this will heat up, which will lead to a decrease in the strength of the saw teeth. Straight-cut teeth for ripping saws are sharpened on one side, with the file held perpendicular to the saw blade.
Saws for cross-cutting wood have an oblique sharpening, so their teeth are sharpened with a file, which is held at an angle of 60.70 °. These saws sharpen their teeth after one. Having sharpened the teeth on one side, the saw is turned towards itself with the other side and, having strengthened in a vice, the remaining teeth are sharpened.
Bow saws are sharpened with triangular files, which are selected according to the size of the saw teeth. Sharpened saws should be free of burrs, stains and other defects. Manual saw sharpening techniques are shown in Fig. thirteen.
and. location of the pilot hole with direct sharpening, b. the location of the pilot when sharpening obliquely, c. sharpening a bow saw fixed in a vice, d. sharpening a bow saw in a wooden block
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The blade of an undisturbed saw will be pinched by the sides of the cut, or the saw is said to bite. As a result, a large expenditure of effort will be required for sawing, the saw blade will be very hot, and the quality of the cut will deteriorate. To avoid this, the saws are bred.
The saw divorce consists in alternately bending its teeth in different directions: even teeth in one direction, odd teeth in the other (Fig. 1).
When divorcing, the upper part of each tooth is folded back by no more than half its height. Bending teeth to their full height leads to curvature of the blade, the appearance of cracks in it, breakage of the teeth.
The amount of divorce is 0.5 mm, but not more than half the thickness of the web on each side. With a large divorce, the cleanliness of the cut deteriorates and the loss of wood in sawdust increases, in addition, the effort spent on sawing increases. With regard to saws for rip sawing, this is due to the fact that with a very large set of teeth, the load on their lateral edges, sharpened at right angles, increases.
When cross-cutting with a saw with a large spread, the length of the sawdust increases and more efforts are required to chip them from the bottom of the cut.
The spread of all teeth of each saw must be the same. With an unequal setting, less bent teeth will not participate in sawing, and more bent teeth will work with overload and therefore fail faster.
To set the teeth, the saw blade is clamped in a wooden vice near the mowing line of the tooth bases (Fig. 2). If the canvas is clamped in a metal vice, then wooden blocks are placed on both sides of the canvas.
The teeth can be spread with pliers, but it is better to do this with a special setting. There are layouts of various designs (Fig. 3). There are setups with an emphasis that provide the same amount of setback for all teeth. The universal wiring shown in fig. four.
The correctness of the divorce is checked by the template shown in fig. 3, e. An unevenly spread saw can be straightened by stretching its gear ring between the jaws of a metal vise, spread apart by an amount equal to the thickness of the saw blade with a set.
Tooth set is done before sharpening.
Recently, more and more began to produce saw blades of unequal thickness: thicker to the ring gear, and thinner to the butt. These canvases do not have a set of teeth.
Hand saws are sharpened with finely cut triangular files. With straight sharpening (Fig. 5, a), the file is held perpendicular to the blade, and with oblique (Fig. 15.6). at an angle of 45. 80 °.
The file pressure should be even and not very strong. With strong pressure, large burrs are formed and sharpening becomes heavier. With a return movement (towards yourself), the file is raised.
For sharpening, the blade is clamped in a vice the same way as when the teeth are set. When clamping the bow saw for sharpening, the bow is thrown away from you.
For every saw, the height of the teeth must be the same, and the pitch along the entire ring gear must be the same. The saw teeth work unevenly: some are larger, others are smaller, so they are leveled in height before sharpening. the saw, as they say, is fugue. The tool for planing saws is a file inserted into a wooden block (Fig. 6, a). An even simpler device is shown in Fig. 6.6.
Before starting to work with a bow saw, unscrew the bow to the right of the plane of the blade: for sawing along. by the width of the sawn bars, for sawing across. by 30. 35 °. At the spreading saw, the beam is set at right angles to the blade.
The saw blade should be in the same plane along its entire length, that is, it should not have distortions. This is checked by eye. The saw tension should be quite strong. A correctly tensioned blade can hardly be pulled out of the tension plane with your fingers. The twist should not protrude beyond the spacer.
The quality of the saw blade can be determined by the joiner by bending the saw blade, hanging it by the eyelet, and also by sound. The canvas, bent and clamped at the ends, should form a regular circle; the canvas, freely suspended by the eyelet, should not have noticeable distortions. A good quality suspended canvas makes a clear, even sound when struck with a fingernail. A rattling sound indicates cracks in the web.
The surface of the canvas should be smooth, without shells. There should be no rust on it.
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Preparing hand saws for work.
A well-prepared and sharpened tool greatly facilitates work, helps to increase labor productivity and ensure high quality products.
Therefore, the condition of the instrument must be systematically monitored.
The first thing to do before setting up the saw is to clean the saw blade of rust and layering. After aligning the teeth in height, you need to make sure that all the saw teeth have the same shape, and if the teeth are very sharpened, then they are sharpened by sawing the depressions between them.
Then the teeth are sharpened and set. Both of these operations are carried out in a special device such as a vise, which can be replaced with a suitable rip-cut board. The saw blade is inserted into the groove of the device so that only the saw teeth protrude from it, and in the latter it would be possible to cut cavities between the teeth.
After cutting depressions (if necessary), the teeth are set apart and the saw is sharpened using triangular or rhombic files with a fine notch.
When forming teeth in rip saws, in which the teeth are in the form of oblique triangles, the file is inserted into the cavity between the teeth and with gentle uniform movements grind the front part of the back tooth and the back face of the next one until the front face is completely sharpened (Fig.a).
When sharpening, make sure that the file is oriented strictly perpendicular to the plane of the blade. Rip saw teeth are straight sharpened.
Sharpening of saws for cross-cutting is carried out along the edges of the teeth, chamfering at an angle of 30-40 degrees so that the top of the tooth becomes in the form of a triangular point (Fig. B).
Of course, for divorced (bent) teeth, the chamfers are removed from the inside of the tooth, that is, if the tooth is bent to the right, then the chamfers are removed from the left side of the tooth.
In this case, it is necessary to carefully monitor the shape of the cavity between the teeth, so that when sharpening the tooth, the chamfers coincide exactly, there are no steps and their unnecessary deepening.
The tops of the teeth along the entire length of the blade must also be at the same level.
Sharpening longitudinal (a) and transverse (b) saws
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Preparing hand saws for work
Preparation of hand saws for work consists in jointing, setting and sharpening the saws. First, the saws must be thoroughly cleaned of resin, adhering sawdust, rust, rinsed in kerosene. If the surfaces of the blades have irregularities, they are straightened with a hammer on a flat metal plate. Then they proceed to jointing. aligning the tops of the saw teeth, since they must be at the same height. A file is inserted into a wooden block (Fig. 9, a), after which the block with a file is put on the saw and moved along the blade, while aligning the tops of the teeth.
You can also align the tops of the saw teeth in another way. A board is strengthened in the workbench (Fig. 9, b), into the slot of which the file is inserted first, and then the saw blade with the teeth down and, moving the saw along the file, align the tops of the teeth. It is necessary to align the tops of the teeth periodically, otherwise they will unevenly participate in the sawing. The quality of the planing is checked by applying a ruler to the tops of the teeth. If the tops of the teeth fit snugly against the edge of the ruler, the planer is correct.
During the sawing process, the saw blade rubs against the walls of the board being sawn and is clamped in the cut. To avoid jamming the saw blade in the cut, the teeth must be set apart. The divorce of saw teeth is that they are bent one by one: even teeth. in one direction, and odd. in the other. When separating the teeth, it is necessary to bend to the side not the entire tooth, but only its upper part approximately at a height of up to 2/3 from the top.
When sawing hardwood, the teeth are set at 0.25. 0.5 mm to the side, and soft rocks. by 0.5. 0.7 mm. It is necessary to strictly observe the size of the divorce, since with a wide divorce, the cut turns out to be large and uneven.
The teeth of the hand saws are set in the following way (fig. 10, and). The saw blade is tightly clamped in a vice, and then the teeth are bent alternately in one direction or the other. It is necessary to spread the saw teeth evenly, without applying great efforts and sudden movements, as otherwise the tooth can be broken. In addition to the usual, universal wiring is used (Fig. 10, in).
The correct spread of the saw teeth is checked with a template (Fig. 10, b), applying it to the saw blade, clamped in a vice. The even teeth are checked first, and then the odd ones. Incorrectly bent teeth need to be corrected.
The correctness of the set of saws can be checked more accurately with an indicator divider of the RI type (Fig. 10, r). When measuring, the water meter is pressed tightly against the saw blade with the supporting surface, and the indicator tip is placed opposite the top of the monitored tooth. By the deviation of the indicator arrow, the amount of divorce is determined.
The next operation is to sharpen the saw teeth with double and single cut files. Files are distinguished by their shape as triangular, rhombic and flat. Hand saws are usually sharpened with triangular or rhombic files.
When sharpening, the saw blade is clamped in a vice, fixed on a workbench. The file is pressed against the tooth when moving away from you, and when it is returned, it is slightly raised so that it does not touch the saw. Do not press the file strongly against the tooth, as this will heat up, which will lead to a decrease in the strength of the saw teeth. Straight-cut teeth for ripping saws are sharpened on one side, with the file held perpendicular to the saw blade.
Saws for cross-cutting wood have an oblique sharpening, so their teeth are sharpened with a triangular file, which is held at an angle of 60. 70 °. These saws sharpen their teeth after one. Having sharpened the teeth on one side, the saw is turned towards itself with the other side and, having strengthened in a vice, the remaining teeth are sharpened.
Bow saws are sharpened with triangular files, which are selected according to the size of the saw teeth. Sharpened saws should be free of burrs, stains and other defects. Burrs are removed with a file with a fine notch (velvet). Manual saw sharpening techniques are shown in Fig. eleven.
Techniques for working with hand saws are as follows. For operation, the saw blade in relation to the machine (beam) is set at an angle of 30 °, while the saw blade should be straight, without distortions and well tensioned. The correctness of the installation of the saw is checked as follows: with the left hand, hold the mullion, and with the right hand, the handle and look with one eye at the saw blade. If the saw blade is installed correctly, it will look like a taut thread (fig. 12, and), and if not, the twisted end will be thicker (fig. 12, b). Correct the position of the saw blade by turning the handle.
When longitudinal sawing, a board or block is placed on a workbench or on a table so that the sawn-off part protrudes outward, that is, hangs over the workbench, and is strengthened with a clamp. Then mark the cutting line with a pencil with a ruler or thickness gauge. the cutting line can be marked with a sharp chisel blade, while a cut is formed in the form of a risk, clearly visible on the surface of the wood.
When sawing wood, the saw is guided in such a way that it does not come off the intended mowing line of the cut and does not get clamped in the cut, it goes freely and easily, does not skew in the cut, but goes smoothly, without swinging. If the saw blade is skewed, it will jam in the cut or it will be difficult to advance from friction, it will heat up and lose its strength properties.
During the sawing process, hold the saw with the right hand by the stand, and with the left hand support the board being cut. In this case, the foot of the left leg should be parallel to the workbench, and the right. at an angle of 70.80 ° to the foot of the left leg.
When sawing (fig. 13, and) make sweeping movements, press the saw to the bottom of the cut when moving down and slightly take it to the side when moving up (idle). You need to cut straight, without sudden movements, strong pressure and without distortions. When longitudinal sawing, short boards with markings are fixed in a vice in a vertical position so that the risk is visible to the worker (Fig. 13, in). The saw is placed on the line of the markings and a shallow cut is made with a slow movement towards themselves, after which you can saw in full swing of the saw. Sawing can also be done on a block (fig. 13, r).
When sawing, the quality of the surface to be sawn must be monitored. A rough, rough surface is obtained when sawing wood with a saw with large and incorrectly set teeth, as well as when working with a poorly sharpened saw. Incorrect cutting of wood is also obtained with strong pressure with the saw and when deviating from the risk.
When cross-sawing boards and bars, the material is placed on a workbench or table so that the cut to be sawn hangs from it, and at the risk made in advance, they make a saw, holding the bow saw with the right hand for the rack above the handle, and with the left hand support the material (Fig. 14).
For precise transverse cutting of a board or a bar at a certain angle without marking, a saw box is used (Fig. 15), in the side walls of which there are cuts made at a certain angle (45, 90 °). When sawing, the material is supported with the left hand, and the right hand is taken by the saw stand and, guiding it to the desired cut, the material is cut.
Date added: 2020-07-18; views: 142; ORDER WRITING WORK
Preparing hand saws for work
The blade of an undisturbed saw will be pinched by the sides of the cut, or the saw is said to jam. As a result, a large expenditure of effort will be required for sawing, the saw blade will be very hot, and the quality of the cut will deteriorate. To avoid this, the saws are bred.
The saw divorce consists in alternately bending its teeth in different directions: even teeth in one direction, odd teeth in the other (Fig.I).
When divorcing, the upper part of each tooth is folded back by no more than half its height. Bending of the teeth to their full height leads to curvature of the blade, the appearance of cracks in it, and breakage of the teeth.
Divorce rate 0.5 mm, but not more than half the thickness of the web on each side. With a large divorce, the cleanliness of the cut deteriorates and the loss of wood in sawdust increases, in addition, the effort spent on sawing increases. With regard to rip saws, this is due to the fact that with a very large set of teeth, the load on their lateral edges sharpened at right angles increases.
When cross-cutting with a saw with a large spread, the length of the sawdust increases and more efforts are required to chip them from the bottom of the cut.
The spread of all teeth of each saw must be the same. With an unequal setting, less bent teeth will not participate in sawing, and more bent teeth will work with overload and therefore fail faster.
To set the teeth, the saw blade is clamped in a wooden vice near the mowing line of the bases of the teeth (Fig. 12). If the canvas is clamped in a metal vice, then wooden blocks are placed on both sides of the canvas.
The teeth can be spread with pliers, but it is better to do this with a special setting. There are layouts of various designs (Fig. 13). There are emphasized layouts that provide one-
A. simple (die); b. die with stops; c. disc one-sided with emphasis; d. double-sided disc with stops; d. gable; e. a template for checking the correctness of a divorce; /. regulators of the amount of divorce; 2.- Bending tooth; 3. stops
The same amount of spread of all teeth. The universal wiring shown in fig. 14.
The correctness of the divorce is checked by the template shown in fig. thirteen, e. An unevenly spread saw can be straightened by extending its ring gear between the jaws of the metal vise, spread apart by an amount equal to the thickness of the saw blade with a set.
Tooth set is done before sharpening.
A. performing straight sharpening; b. performing oblique zatdaki; c. the view of the sharpened teeth at the saw for transverse stitching
Recently, more and more began to produce saw blades of unequal thickness: thicker to the ring gear, and thinner to the butt. These canvases do not have a set of teeth.
Hand saws are sharpened with finely cut triangular files. With straight sharpening (Fig. 15, a), the file is held perpendicular to the blade, and with oblique (Fig. 15.6). at an angle of 45-80 °.
The file pressure should be even and not very strong. With strong pressure, large burrs are formed and sharpening becomes heavier. With a return movement (towards yourself), the file is raised.
For sharpening, the blade is clamped in a vice the same way as when the teeth are set. When clamping the bow saw for sharpening, the bow is thrown away from you.
For every saw, the height of the teeth must be the same, and the pitch along the entire ring gear must be the same. The saw teeth work unevenly: some are larger, others are smaller, according to
this, before sharpening, they are leveled in height. the saw, as they say, is fugue. The tool for planing saws is a file inserted into a wooden block (Fig. 16, a). An even simpler device is shown in Fig. 16, b.
Before starting to work with a bow saw, unscrew the bow to the right of the plane of the blade: for sawing along. by the width of the sawn-off bars, for sawing across. at 30-35 °. At the spreading saw, the beam is set at right angles to the blade.
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The saw blade should be in the same plane along its entire length, that is, it should not have distortions. This is checked by eye. The saw tension should be quite strong. A correctly tensioned blade can hardly be pulled out of the tension plane with your fingers. The twist should not protrude beyond the spacer.
The quality of the saw blade can be determined by the joiner by bending the saw blade, hanging it by the eyelet, and also by sound. The canvas, bent and clamped at the ends, should form a regular circle; the canvas, freely suspended by the eyelet, should not have noticeable distortions. A good quality suspended canvas makes a clear, even sound when struck with a fingernail. A rattling sound indicates cracks in the web.
The surface of the canvas should be smooth, without shells. There should be no rust on it.
Saw rolling
The circular saw does not heat up evenly during cutting, and its operating temperature can reach 60–70 ° C. It heats up most of all at the ring gear. The temperature drop along the radius of the saw body causes the appearance of compressive stresses at the saw periphery. The tool becomes unstable in the kerf, and even small shear cutting forces cause the blade to lose its flat shape. The saw cuts (“wanders” in the kerf). The main purpose of forging or rolling is to create tensile stresses to compensate for thermal stresses. This is especially important for thin saws (less than 2 mm thick) and large diameter saws (over 800 mm).
Saw rolling is performed in order to create the initial stresses necessary to compensate for the temperature stresses arising from uneven heating of the saw blade (in the wedding and central zones) during the sawing process, and to reduce the risk of resonance states of the tool. The essence of rolling lies in the weakening of the middle part of the saw due to the lengthening of its toothed (wedding) zone as a result of rolling under pressure between the two working rollers of the rolling machine. The grooved saw acquires the lateral stability of the ring gear during operation, that is, the ability to withstand unbalanced lateral forces acting on the saw body during sawing, and thereby ensure the straightness of the cut.
It is sufficient to roll saws with a diameter of up to 300 mm along one circle with a radius of 0.8 R (R is the radius of the saw without teeth) for one to three saw revolutions under the action of the rollers (depending on the quality of the steel of the saw body). For saws with a diameter of up to 450 mm. in two circles with a step of 30-40 mm, for saws with a diameter of up to 630 mm. in three circles, for saws with a diameter of up to 800 mm. in four, for saws with a diameter of up to 1000 mm. in five circles.
For saws made of conventional tool steels, the pressure on the drums should be in the range of 10-30 N; for saws made of especially high-alloy steels operating at feed speeds of more than 50 m / min. up to 60–80 N, and it is advisable to use rollers with a radius of the working area within 30 mm.
It is strictly forbidden to use rollers with defects (dents, notches, etc.) on the working surfaces when rolling saws, which can lead to deformation of various zones of the saw body, the appearance of cracks and the rejection of this saw, if it cannot be corrected by local forging manually.
It should be borne in mind that it is necessary to start work on the rolling machine with a small (from 10 N) pressure on the rollers. Having worked out the technique on one saw, it is advisable to extend it to the preparation of all saws of this manufacturer, simultaneously correcting all local defects and remembering that there are no absolutely identical saws.
As a rule, saws that have undergone five to six sharpenings in production conditions must be re-rolled, if necessary, all local defects (slack, tight spots, burn zones on the saw body) must be corrected. For saws working at 50 m / min. and higher, these operations must be performed every time after removing the saws from the machines.
It is possible to start rolling saws after operation following the factory traces of rolling, usually 15-20 mm from the interdental cavities. If there are no marks, new ones should be made. at the same distance from the cavities between the saw teeth. If there are multiplexes and temperature slots on the saws in the rolling zone, rolling of 15–20 mm must not be allowed before and after multiplexes and slots.
Sharpening saw teeth
The sharpening of the teeth provides the specified angular parameters of the teeth and the sharpness of the cutting edges. For sharpening circular saws brazed with carbide plates, experts recommend using diamond grinding wheels with the use of coolant (coolant), and better. oil. The feed per wheel stroke should not exceed 0.06 mm. The teeth are ground to reduce the surface roughness with the same circles, but without feed per stroke (the so-called aging) or with a finer-grained wheel. In this case, two or three light passes are made with a feed (cut) value per wheel stroke of no more than 0.02 mm. Burrs from the cutting edge and lateral edges of the teeth are removed with a fine-grained abrasive bar.
The saw is considered to be correctly sharpened if provided: a given standard profile of the teeth, the required sharpness of the cutting edges, the location of the tops of the teeth on one circle (if there is no other profile and parameters of the teeth), the absence of twists, breaks and burrs, smooth rounding of the profile of the interdental cavities (when they are modified ) without visible scratches on the edge of the grinding wheel. Saw saws are sharpened only along the front edge so that they can be re-soldered in the future (some saws 5-6 times with correct operation) without further refinement of the sinus of the tooth and the bed for a hard alloy plate.
Some manufacturers, in order to achieve the location of the tops and side faces of the teeth on the same circle and in the same plane, join the teeth. Pre-jointing is performed according to the height of the teeth and the width of the cutting edge (from the sides) with jointing devices, which are installed on saw machines (this is typical for saws with a diameter of 1.5 m), as well as on sharpening machines. Pre-jointing on the machine shaft is carried out with a fine-grained whetstone (grain size 5–10 microns) when the saw rotates in the direction opposite to the working one and at a low rotation frequency. The size of the jointing surface (chamfer) should be no more than 0.1-0.3 mm. From the sides, the teeth are planed with a minimum feed of the donkey. The operation should be considered complete if 1/3 of the teeth have traces of jointing.
If you have high-quality sharpening machines and sharpening circular saws on the sharpening (and not on the saw) equipment, pre-jointing may not be necessary.
The sharpening area should also contain:
protractors and templates for checking the angular elements of the teeth and the profile of the grinding wheel;
a device based on a dial indicator for measuring the lateral widening of saw teeth;
attachment for teeth jointing (option).
Rules for checking the quality of saw rolling
Correctly rolled saw, laid in a horizontal plane on three supports evenly spaced from each other (some experts recommend laying on two supports, which is also possible), located below the circle of the tooth cavities relative to the center of the saw at a distance of 3-5 mm from this circle, with a free sagging of the middle part should acquire a uniform concavity (poppet).
If the required weakening of the middle part of the saw is not achieved, the saw is turned over and re-rolled with the same pressure of the rollers. This operation contributes to some reduction of the bending of the web by the rollers. If the middle part of the saw has not received the required weakening, the rolling process continues along the same circle with an increased pressure of the rollers. Excessive weakening of the middle part of the saw during rolling is corrected by rolling along a circle spaced 3-5 mm from the circumference of the tooth cavities. In this case, the clamping force of the rollers is taken from 10 to 30 N, depending on the initial stress state of the tool.
Until now, there is no single scale for the preparation of circular saws equipped with carbide inserts, and methods for determining the amount of rolling for each standard size of circular saws. The problem is that one of the few non-destructive methods for assessing hammering is to measure the deflection of a saw blade placed on three (two) points located directly at the interdental cavities at an angle of 120 ° (180 °). However, the value of the optimal blade deflection boom depends on the steel grade, the diameter and thickness of the saw, the size and dimensions of the saw washers or spacer rings, the design of the circular saw itself and its operating conditions. It is individual for each standard size of circular saws and is only an indirect indicator of the correctness of its rolling.
Information about the process of preparing saws by each saw manufacturer is fairly well “classified” and does not lend itself to instrumental assessment methods. Some manufacturers may give recommendations on the operation of certain models (types) of their saws, but such units.
When rolling, the metal of the saw body is capable of some increase in its size due to the appearance of internal stresses, while the saw body remains flat in a vertical position (namely, the vertical position, with rare exceptions, is occupied by a working circular saw). This process is called plastic deformation.
At a certain moment, the metal of the saw blade can no longer deform linearly from the compressive stress of the central part and the stretching of the wedding zone. The un-rolled central part of the saw and the stretched bridal zone compress the saw blade with a ring, and it can no longer remain flat and takes a bowl-like shape in a horizontal position. over, from the application of a small force, the bowl shape easily passes from one side of the disc to the other and is fixed in this position, that is, the disc acquires two stable states in an upright position. For such states of an object in technology there is a clear definition given by V. V. Kucherov: “The trigger state of an object is when the object has the ability to stay in one of two stable states for a long time and alternate them under the influence of external efforts or impulses.”.
A visual assessment of the rolling quality of a circular saw can be done by tilting it to the right and left of the vertical. In the case of correct rolling, when the saw is tilted to the right and to the left, the center of the saw blade falls through, forming a bowl of varying degrees of depth. You can estimate its value by placing a large saw-blade ruler in the area of the center hole vertically to the saw, and then deflect the ruler together with the saw at an angle of 30-60 degrees from the vertical. For example, the value of the resulting light gap on a circular saw with a diameter of 1000 mm will be from 0.1 mm on an unrolled saw to 2 mm on an absolutely correctly rolled saw made of ordinary low-alloy chrome vanadium tool steel and 0.5–0.8 mm for high-alloy tool steel. The size of the gap is measured with a special probe of the automotive type for measuring the gap between the electrodes of the spark plugs. For different equipment and circular saws from different manufacturers, these values are very conditional and can be very different, therefore it is advisable in each case to consult both the saw manufacturer and the equipment supplier.
Another way to visually assess the rolling of circular saws: the ruler is applied to the vertically inclined saw in the area of the center bore.
With an increase in the rolling force, the center of the saw falls more and more when it is tilted relative to the vertical position. This is noticeable when looking at the saw from above and from the side. If the operation of rolling the saw is done correctly, the gap between the saw and the ruler will be approximately the same for both measuring methods.
Together, both of these methods give a cross check, that is, when a large saw blade is applied to an inclined saw alternately vertically and horizontally.
Even more accurate is a method for determining the degree of saw rolling using a tool for measuring the end runout and saw stiffness, equipped with dial indicators and two pneumatic cylinders located at an angle of 90 ° to the saw body. These installations are produced by several German companies engaged in the production of equipment for the preparation of saws.
Cut metal easily! DIY Power hacksaw
It is advisable to have at the sharpening area:
a set of saw-blade tools, including an anvil, a set of hammers, a set of correct rulers;
a device for checking the beating of saws;
semi-automatic device for checking the rigidity of saws or a set of pilot points.
Saw flatness and stress state control
After the end of rolling, the flatness and stress state of the saw is assessed. If local defects are found using a short ruler (for example, if the deviation from flatness exceeds 0.15 mm), then additional straightening is carried out. If the stress state of the saw does not correspond to the norm, then additional rolling is carried out along the existing traces. In this case, the total number of tracks for new saws should not exceed five. Flatness and stress state control is carried out every five to six changes of tool operation.
About forging and straightening saws
Rolling (if a rolling machine is available in the production) can replace the forging of saws, which can only be done correctly with a well-prepared pilot. True, it is impossible to replace the dressing and forging of individual defective spots on the saws by rolling. There is positive and negative forging.
Defective places should be straightened and forged on a special convex saw-blade anvil with special saw-blade hammers. Such equipment and devices can be purchased from both domestic and foreign manufacturers. This operation can only be worked out with specialists who know how to perform forging, therefore it is advisable to send your pilots to special courses or to factories where such a tool is made; as an option, to the factories. manufacturers of circular saws. Self-education is a good thing, but each manufacturer has nuances in technologies and materials.
Preparing carbide circular saws for work
Saw repair
In some sawmills in our country, in cases of partial breakage of the tips of the saw teeth, welding or surfacing of the tips of the saw teeth and the formation of the profile and the soldering zone of the hard alloy plate are performed. This makes it possible not to reject the saws, but to continue to use them in production, which provides significant savings, especially when repairing special saws.
What you need to know when, for example, teeth break off 1/3 of the tooth height or break off completely?
It is known that the main European manufacturers of saws use special alloys as a material for the manufacture of the saw body, and the Russian ones use domestic steel 9HF, typical tool steel Uddeholm (Sweden) or running German tool steel.
As a rule, the hardness of the bodies of circular saws equipped with carbide plates is 40–46 HRC, and the ring gear during heat treatment before brazing the saw teeth is released to 35–45 HRC. If the tip of a tooth breaks off on the saw, it means that the saw ring gear is overheated and its hardness exceeds 45 HRC, and if the saw teeth break off at the base, then vice versa: less than 35 HRC. It should be remembered that saws with teeth completely cut off at the base are almost beyond repair.
When small cracks appear in the interdental cavities, it is advisable to close them on both sides or drill with a drill up to 2 mm in diameter, and for saws working in difficult cutting conditions at a large cutting depth (over 100 mm), this operation is impractical, it is necessary to discard the saws or use them on other equipment. with lighter working conditions.
The list of measures for the repair of saws also includes re-soldering of hard alloy plates that have become unusable after operation and their failure during emergency wear (if a foreign solid object gets into the cut).