Why Saw Teeth Bred
The main cutting element of any hand saw. A series of teeth cut on the blade and representing cutters in the form of wedges. Wood, in the manufacture of all kinds of products from it, is sawed lengthwise, crosswise and at an angle Θ to its fibers, in this regard, transverse, longitudinal sawing and sawing are distinguished at an angle to its fibers and in each case they use the corresponding type of saw different from other forms teeth.
For transverse sawing, transverse saws are used, the cutting edges of the teeth of which, when moving in the wood, cut its fibers like a knife and form a cut. Longitudinal sawing differs from transverse in that the direction of movement of the saw is parallel to the wood fibers. The leading edges of the teeth of the longitudinal saws plan the wood, like knives in planers, and, deepening, form a cut. When sawing wood at an angle Θ, universal (mixed) saws with teeth are used to its fibers, which are an intermediate form of teeth of transverse and longitudinal saws.
Sharpening a saw
Sharpening teeth saws. A kind of art, requiring fidelity of hands, a good eye, attention. It is not difficult to learn this business, you must have a desire and clearly adhere to the following rules:
- The saw blade must be rigidly fixed in a special device made of wood, which is also stably installed on a well-lit work table. Sharpening saw teeth on stools or on the knees does not give a satisfactory result.
- You should use a personal file with the subsequent cleaning of the sharpened edges of the teeth with velvet (with a small notch) or file. It is advisable that the file is new, sharp and with a mounted handle. If at the right time it wasn’t, then you can use a used, but always brushed with steel brush and rubbed with charcoal so that the file does not clog and dull. When sharpening a tooth, the file should cling to its metal and remove its layer, depending on the pressure. And if it slides along the tooth without removing the metal, then the saw teeth are overheated or the file is worn out. In this case, it is necessary to repeat the sharpening with a new file. If in this case it slides along the tooth, it remains to take another saw.
- The file handle is clamped with the right hand, and the end is held with the left hand and the file is sent to the saw teeth. The file operation is described below, depending on the type of saw.
- The file pressure on the teeth should be smooth and uniform and only one way away from you. When the file returns to its original position, it should not touch the teeth.
- It is necessary to try to grind metal from the edges of the teeth of at least the same thickness, driving the file the same number of times with the same pressure, which allows you to save the angles, pitch and height of the teeth after sharpening.
- Burrs are formed on the sides of the tooth on the file exit side, which reduce the sharpness of the tooth, and if they are not removed, then during the operation of the saw they become chipped, and the teeth become significantly dull. To remove the burrs, the edges of the teeth are ground with a file with a velvet notch and the burrs are removed from the side faces with a wet donkey.
- After sharpening the teeth, check their sharpness. Look at the point of the needle and the edge of the razor blade: they, sharpened, do not shine in the light. And if you dull them, then rounded surfaces appear on the tip of the needle and on the edge of the blade, which reflect light well and shine. This principle is based on the quality control of sharpening the teeth of saws. To do this, put a saw in front of the eyes and examine its teeth along the blade. If their cutting edges and tops do not shine, then the saw teeth are sharpened satisfactorily, and if some of the teeth are glossy (this often happens), they must be ground with a velvet file, remove burrs and again check the reflection of light with their edges and tops.
Cross saws. The teeth of the transverse saws are sharpened using a trihedral file with a fine notch with an angle at the apex of 60 °.
To sharpen the teeth, the saw is clamped in a special device that allows you to set its blade at an angle of 45-50 ° to the plane of the working table. The file is led parallel to the work table at an angle of 60-75 ° to the saw blade and thus the left edge A is sharpened in the first tooth1A2IN2IN1.
Sharpen the saw teeth in several steps. First, a file passes along the left sides of the odd teeth located in the far row, adjusting the hands to the same movement. Then they pass a file along the right sides of the same odd teeth, completing the sharpening of the main cutting edges with very sharp peaks. After the sharpening of the odd teeth, the saw blade in the grinding device is turned over and thus the even teeth that are in the far row are sharpened. When sharpening the teeth of the transverse saws, it is necessary to carefully monitor that in each tooth sharp main cutting edges with a dihedral angle of φ = 60-75 °, a short cutting edge and a sharp top are obtained.
To sharpen the teeth, the saw blade is mounted vertically in a clamping device, which, in turn, is fixed to the work table. Below are two ways of sharpening the teeth of longitudinal saws, differing from each other only in the value of the angle of sharpening φ, i.E., the file directions with respect to the saw blade.
The first way. A straight line in which the file or file is directed horizontally at an angle φ = 90 ° to the saw blade and a small metal layer is removed from the front and rear faces of the tooth, sharpening the cutting edges.
Thus, all teeth located in the far row are sharpened. Then the saw blade in the clamping device is turned over and the teeth of the other row are turned in, which are in the far row. This method is used by most modern joiners and hobbyists when sharpening the teeth of longitudinal saws.
The second way. Oblique, differing from the first only in the direction of the file with respect to the saw blade, that is, the sharpening angle, which is selected within the range of φ = 75-80 °.
Also sharpen the front and rear edges of the teeth, first one row, and then. Of another. With this method of sharpening teeth, side edges are obtained, and it is used by cabinetmakers when sharpening on-beam swing saws.
Saws for mixed sawing. To restore the cutting qualities of the teeth, they are sharpened like the teeth of longitudinal saws, using rhombic files with fine or files with a coarser notch. As when sharpening longitudinal saws, two methods are used: straight and oblique, differing from each other by the value of the angle of sharpening φ, which are 90 ° and 75-80 °.
Sharpening angle φ = 75-80 ° is used by cabinetmakers when sharpening the teeth of tenon and fine-tooth bow saws. After sharpening the teeth, the burrs are removed from the cutting edges and the sharpness of the teeth in the light is checked.
Sharpening devices. To sharpen the teeth, the saw blade is installed in a clamping device, which, in turn, is fixed to the desktop. The figure below shows the clamping device used when sharpening the teeth of hacksaws and hacksaws and allows you to set them at an angle of 45 ° and 90 ° relative to the desktop.
The device consists of a base with dimensions of 550×200 mm, made of plywood with a thickness of about 20 mm. On the basis of two guides of rectangular triangles with equal legs, welded from a steel strip with a section of 20×3 mm. To install the guide triangles at the base of the device, four M6 studs are screwed on with PVA glue. In turn, the supporting triangles with the help of M6 bolts with wing nuts, fasten the support and pressure strips, interconnected on loops with dimensions of 400×150 mm, made of plywood 15 mm thick. A sharpening saw is placed between the planks with the teeth facing up. Its blade is set so that the teeth protrude 15-20 mm above the clamping bar. This clamping device allows you to set the sharpened saws at an angle of 45 ° (the figure shows this position) and at an angle of 90 °. To do this, you need to change the position of the guide triangles on the basis of the device, which is clearly visible in the figure. When sharpening the teeth of the transverse saws, the support and clamping bars are set at an angle of 45 °, and when sharpening the teeth of longitudinal and mixed saws. At an angle of 90 °.
The device in the position of the strips at an angle of 90 ° can be used to align the height of the teeth, and for their divorce.
The figure below shows the clamping device for sharpening the teeth of two-handed saws and large-sized hacksaws.
The device consists of two posts with a length of 1100 mm and a section of 60×40 mm, two transverse bars with a length of about 550 mm and a section of 40×30 mm and two clamping bars with dimensions of 450×150 mm and made of plywood 15 mm thick. The racks and the crossbar are interconnected on the screws. The assembly of the device is carried out in the following sequence: the lower crossbar is screwed to the uprights at a small height from the floor, then the right foot is placed on it and the attachment point of the second crossbar is marked so that the knee of the right foot rests on the second crossbar. This ensures the rigidity of the rack, leaning against a table or workbench. Sharpening saws are placed between the clamping bars with the teeth up and clamped with M8 bolts with wing nuts. Having finished sharpening on one side, without removing the saw from the clamping bars, turn the device over and continue sharpening on the other side.
The wider the tooth bore, the wider the cut and, accordingly, the less likelihood of jamming the saw in it. However, too wide a cut due to the large amount of tooth divorce requires great effort to advance the saw in the wood.
When using an undiluted or slightly diluted saw, which occurs after its repair or long work, when the tooth bite is greatly reduced, the width of the cut is close to the thickness of its blade, and the friction that occurs between the walls of the cut and the blade causes it to heat and expand, and ultimately account, jamming the saw in the cut, for the promotion of which it will require tremendous effort. Probably, each of us experienced this trouble when sawing raw wood with a sparse saw. And yet, if there is no free gap in the cut for the saw blade, then it is difficult to control and it leads away from the intended direction.
The teeth are cut apart using a special tool called wiring. Some of its designs allow you to choose the magnitude of the divorce on one side with the help of an adjusting screw, which ensures the same bending of the teeth.
The saw teeth are separated in a special wooden clamping device, in which the saw blade is set so that only the teeth protrude slightly from it, and the device itself is mounted on the desktop. Tooth divorce is formed by alternately bending them in different directions along the withdrawal line, located at about half their height, and the whole tooth cannot be retracted. It will break at the base. It may turn out that during bending, some teeth protrude to the side more than others, and they will slow down when sawing, reduce the quality of the cut surface and quickly become dull. To avoid this, the teeth are leveled by pulling between the jaws of a manual vice, disclosed by the amount of divorce. As a result, all the teeth are aligned, and their divorce becomes uniform.
The magnitude of the divorce of the teeth of the saws is determined by the elastic recovery of wood in the cut, which is greater, the softer and wetter it is. Therefore, for such wood, the divorce should be greater than for hard and dry. The magnitude of the divorce of the teeth on one side and the amount of cut in the wood is determined by the formulas:
Where a. Saw blade thickness (mm), k. A coefficient depending on the state of the wood, k = 0.25-0.4. For hard and dry and k 0.5. For soft and wet, b. Cut width.
Example. Determine the amount of divorce on one side for the hacksaw and hacksaw with blade thicknesses of 0.6 and 0.9. Sawn wood: dry and hard for a hole saw and wet. For a hacksaw. We select the coefficient for the hacksaw k = 0.35 and k = 0.5 for the hacksaw. Then, for a bow saw, the amount of divorce on one side and the amount of cut are equal to:
Δ = 0.350.6≈0.2;b = 0.620.2 = 1 mm;and, accordingly, for a hacksaw:Δ = 0.50.6 = 0.3;b = 0.920.3 = 1.5 mm.
You should not choose any amount of divorce for the saw teeth, not taking into account the state of the sawn wood, as this affects the quality of the cut and the effort to advance the saw. It is difficult to saw hardwood with a high divorce saw. It turns out a wide, uneven ragged cut of low quality, the saw travel is heavy, you have to put a lot of pressure on it, and as a result, its teeth quickly become dull. Therefore, the master should have in his household several saws with different sizes of divorce: for dry and wet wood. And if he has one saw with a small stain and it is necessary to saw wet wood along the fibers, then in the process of sawing, a wooden wedge is inserted into the cut, which is moved behind the saw so that it does not pinch, and additionally lubricate its surface with laundry soap.
Sawing arrangements. Sawing is performed using a special tool called wiring. The figure shows the general types of simple wiring and wiring with emphasis.
Simple wiring is made in the form of a small steel die of arbitrary shape with a wooden or metal handle. In the die, several slots of different widths are made.
The use of such a wiring is very simple: a slot corresponding to the thickness of the saw blade is selected in the wiring, and, having grasped half of the saw tooth with it, carefully bend it in one direction or another. When bending the teeth, one must strive to ensure that their inclination is the same along the entire length of the saw.
Significantly facilitates the process of tooth biting saws using wiring with emphasis, which provides the same bending of the teeth. Before starting work, the tool is adjusted to a certain amount of divorce, and then the emphasis is fixed in position by the wing nut and screw. Saw teeth are bred in wooden (carpentry) and bench vices or in special clamping devices in which the teeth are ground. When using a bench vise, plywood strips corresponding to the dimensions of the saw blade are laid between their jaws. The saw is clamped in a vice so that its teeth are very close to their lips.
Tooth alignment in height
Saw tooth shape
Each tooth can be imagined as an acute-angled knife with an angle at the apex β, sharpened laterally by one-sided sharpening with a sharpening angle φ = 60-75 ° (the sharpening is shaded), and each of them contains two front and two side faces.
For example, in the drawn tooth, the front faces. A1IN1IN2A2 and A1IN3IN4A2, side. A1IN1IN3 and A2IN2IN4. Ribs A1IN1 and A1IN3. Main cutting edges and rib A1A2, resulting from sharpening two front edges is called a short cutting edge. Each tooth having the above cutting edges, saws wood when moving it in both directions, that is, from itself and onto itself. For example, in a drawn tooth, cutting edge A1IN1 cuts wood fibers when the saw moves to the left, and cutting edge A1IN3. When the saw moves to the right, and the short cutting edge A1A2 delaminates the cut fibers and removes them in the form of sawdust from the resulting cut.
The teeth of the transverse saws, which are isosceles triangles, are characterized by a sharpening angle β, a rake angle γ, a cutting angle δ, a pitch t, and a height h. Point A1, A4, A5 are the tops of the teeth. Point angle β characterizes the saw’s ability to saw one or another wood. Typically, in the transverse saws for soft and raw wood, the angle β is taken equal to 40 °, and for dry and hard wood. 50-60 °. The angles in the tooth triangle are interdependent:
Longitudinal saws. In longitudinal saws, the teeth are incisors in the form of inclined wedges. The figure below shows two types of teeth, the first. Most common in saws, and the second. With a deepened depression, used in saws for sawing soft tree species (linden, aspen, alder), which abundantly excrete sawdust.
Ribs A1A2, A3A4. Main cutting edges and ribs A1IN1, A2IN2, A3IN3, A4IN4. Side cutting edges. The teeth in longitudinal saws, like cutters on planing machines, saw wood when moving only in the direction of the inclination of the teeth, in which the main cutting edges, when cutting, form the bottom of the cut, and the side edges. Its walls, and during the reverse movement they idle, sliding along the cut and not sawing wood.
The positions of the cutting edges of the tooth between themselves form the angles: α. A rear angle formed between the rear face and the cutting plane; β. Point angle between the front and rear faces; γ. Rake angle between the front face and the perpendicular to the cutting plane; δ. Cutting angle; π. The angle between the front and rear faces of adjacent teeth. Looking at the tooth triangle of a longitudinal saw, we find the relationship between the angles:
Α β γ = 90 °; α β = δ; π 60 °
The quality of the cut surface and the performance of the sawing process depend on the correct choice of the angular values of the cutting tooth of the saw. The most important of all angles. This is the angle of sharpening β, when its value is small, sawing of wood occurs with less effort, but the tooth’s strength decreases, it crumbles, dulls quickly, and it has to be sharpened often. With a large value of this angle, the tooth strength increases, but the sawing force increases. Typically, the point angle should be at least 20 °.
With an increase in the cutting angle δ, the quality of the cut surface increases, but the cutting force increases, the cutting angle can be reduced due to the back angle, but the friction between the tooth and wood increases and the tooth unnecessarily heats up, loosens, and its strength decreases, so the cutting angle δ is taken within 40-75 °.
The angle γ determines the inclination of the tooth, its value is taken in the range of 10-20 °.
Thus, the values of the angles α, β, γ for the teeth of the longitudinal saws are interconnected, and they are determined by practice. For example, the teeth of the longitudinal (swinging) saw blades are determined by the angles α = 20-30 °, β = 50-60 °, γ = 8-10 °, and the teeth of the hacksaws of longitudinal sawing. Angles α = 20-40 °, β = 40-50 °, γ = 10-20 °.
Saws for mixed sawing. In hand saws, tooth designs are widely used, which can be used for both longitudinal and transverse sawing of wood. The figure below shows some tooth shapes used in mixed sawing.
If the teeth of longitudinal saws can be characterized as acute-angle wedges, then the teeth of saws for mixed sawing can be represented as rectangular or obtuse-angled wedges with a cutting angle δ = 90 ° γ. Angle γ. Front, equal to zero or a negative value in the range of 10-15 °. They are sawing wood with these saws in the same way as longitudinal ones, when moving only from themselves, and when moving towards themselves they idle.
Ribs A1A2, A3A4. Main cutting edges and ribs A1IN1, A2IN2, A3IN3, A4IN4. Side cutting edges. When sawing wood along the fibers, the main cutting edges form the bottom of the cut, and the side edges. Its wall, and when sawing wood across the fibers, the side edges A2IN2, A3IN3, A6IN6 wood fibers are cut from the sides, and the main cutting edges A1A2, A3A4 layered cut fibers and remove them in the form of sawdust from propyl.
The saw teeth for mixed sawing are determined by the angle of sharpening β, the cutting angle δ and the rake angle γ. The angles δ and γ are related by the dependence δ = 90 ° γ. The quality of the cut surface and the performance of the sawing process depend on the correct choice of the angular values of the teeth. In practice, the following angles are chosen: in beam saws β = 60 °, γ =.10 °, hacksaws β = 45-50 °, γ = 0 ° or. (10-15 °). Saws with teeth with a rake angle of γ =.10 ° are widely used in beam saws (tenon, circular) as universal for sawing wood in any direction.