Sawing wood. Saws and Sawing

14.07.2019 -

Classification of types of sawing

Characteristics of the sawing process

Sawing is the process of dividing wood with a saw into volumetric, undeformed parts by turning the volume of wood between these parts into chips.

A saw is a multi-blade cutting tool that works in a closed cut. A kerf is a gap formed in wood when teeth cut narrow shavings (sawdust). The cut has side walls and a bottom with which the blades (teeth) interact.

Sawing wood is classified according to several criteria.

Depending on the position of the saw plane in relation to the wood fibers, longitudinal, transverse and mixed sawing is distinguished.

For longitudinal sawing The plane of the saw is parallel or approximately parallel to the grain of the wood. Saw frames, circular saws and band saws operate on the principle of longitudinal sawing, on which logs and beams are sawed into boards, lumber is cut to width or thickness in the longitudinal direction.

When cross cutting the plane of the saw is perpendicular or approximately perpendicular to the grain of the wood. Sawing is performed manually with cross-cut saws, hacksaws or on cross-cutting machines used for cutting logs into round logs, removing wood defects and wane areas from the ends of the lumber, as well as giving the lumber a given length and quality.

For mixed sawing the saw plane is located at an acute angle (10˚...80˚) to the direction of the fibers.

Depending on the type of saws used, there are different the following types sawing:

– longitudinal frame sawing, sawing with band, circular and jigsaws;

– cross-cutting with circular, chain and jigsaws;

– mixed sawing circular, band and jigsaws.

Depending on the number of simultaneously working saws in the machine, a distinction is made between individual and group cutting methods. Cutting logs and lumber with one saw is called individual cutting, and cutting with several saws is called group cutting.

For individual sawing logs are sawn into lumber with separate cuts on circular saws, band saws, vertical or horizontal machines. The cutting is carried out taking into account individual characteristics quality zones of each log. This cutting method is effective when sawing valuable wood, cutting large-diameter logs and logs with significant defects.

For group sawing sawmill frames, multi-saw circular saws and band saws, as well as milling and sawing machines are used.

Depending on the position of the workpiece relative to the center of the circular saw, sawing with the peripheral zone of the saw, the middle zone and the central zone of the saw, as well as sawing with the upper and lower zone of the saw are distinguished.

When working in the peripheral zone saws, the teeth of the saw protrude above the surface of the workpiece by an amount approximately equal to the height of the tooth.

When working in the middle zone saw teeth protrude above the surface of the workpiece by an amount equal to approximately one third of the radius of the saw.

When working in the central zone The center of the saw is located at the middle of the cutting height. This type of sawing is used in milling and sawing machines.

The peripheral and middle working zones of the saw can be located on the upper or lower sections of the saw, which is observed in circular saws with a lower and upper saw shaft.

At divorce (Fig. 2, A) the tips of the teeth with a length of 0.3...0.5 of the tooth height are bent alternately in different directions. At flattening (Fig. 2, b) the tips of the teeth are flattened and shaped, giving them the shape of blades located symmetrically relative to the saw body.

The sawing rule can be formulated as follows: when inserting a tooth into wood, you first need to cut the fibers, and then, with the least resistance, separate them from the massif and remove the chips from the cut.

Lecture 11

Sawing wood. General information

1. Characteristics of the sawing process

Sawing is the process of dividing wood with a saw into volumetric, undeformed parts by turning the volume of wood between these parts into chips.

2. Classification of types of sawing

Sawing wood is classified according to several criteria.

Depending on the position of the saw plane in relation to the wood fibers, longitudinal, transverse and mixed sawing is distinguished.

For mixed sawing the saw plane is located at an acute angle (10˚...80˚) to the direction of the fibers.

Depending on the type of saws used, the following types of sawing are distinguished:

– longitudinal frame sawing, sawing with band, circular and jigsaws;

– cross-cutting with circular, chain and jigsaws;

– mixed sawing with circular, band and jigsaws.

For individual sawing logs are sawn into lumber with separate cuts on circular saws, band saws, vertical or horizontal machines. Cutting is carried out taking into account the individual characteristics of the quality zones of each log. This cutting method is effective when sawing valuable wood, cutting large-diameter logs and logs with significant defects.

For group sawing sawmill frames, multi-saw circular saws and band saws, as well as milling and sawing machines are used.

When working in the peripheral zone saws, the teeth of the saw protrude above the surface of the workpiece by an amount approximately equal to the height of the tooth.

When working in the middle zone saw teeth protrude above the surface of the workpiece by an amount equal to approximately one third of the radius of the saw.

When working in the central zone The center of the saw is located at the middle of the cutting height. This type of sawing is used in milling and sawing machines.

The peripheral and middle working zones of the saw can be located on the upper or lower sections of the saw, which is observed in circular saws with a lower and upper saw shaft.

When cutting logs into lumber, the following methods are used (Fig. 1):

– log collapse;

– beam collapse;

– sawing with beams into one or two beams;

– cutting out asymmetrical timber (sleepers);

– camber-segment and beam-segment;

– circular;

– sectoral.

When sawing logs waddle On sawmill frames or multi-rip circular saws, unedged boards and slabs are formed in one pass. This sawing method is often used when cutting hardwood logs.

When sawing with lumber The log is sawn in two passes. On the first pass, one or two double-edged beams, unedged boards and two slabs are obtained from the log. On the second pass, the beam is collapsed and edged boards with a width equal to the thickness of the beam, unedged boards and two slabs are obtained. In this case, the boards cut from the middle part of the timber are radial. Boards cut from the peripheral zones of the timber are tangential. The remaining boards occupy an intermediate position.

With the split-segment cutting method, on the first pass from middle zone The logs are cut into several unedged boards, and two segments are obtained from the side zone.

With the circular method of sawing logs, each subsequent cut can be directed parallel, perpendicular or at any angle to the previous one. This makes it possible to obtain radial and tangential sawn timber. The log can be sawed parallel to its longitudinal axis or parallel to its generatrix. The circular method is especially effective when cutting large-sized raw materials.

With the sector sawing method, the log is first sawed along the axis of the log into parts that have the shape of sectors in cross section. Then one block is cut from each sector, the face of which is parallel or perpendicular to the radius of the log. If the annual layers of wood are located to the face at an angle of less than 45˚, then tangential sawing lumber is obtained; at an angle of more than 45˚, but less than 60˚, mixed sawing lumber is obtained, and at an angle of more than 60˚, radial sawing is obtained.

3. Widening the cut

When sawing, the side cutting edges of the teeth deform the walls of the cut. After the teeth pass, the walls of the cut are elastically restored, the distance between them is reduced, and the saw blade can be clamped. Due to friction, the saw becomes so hot that it becomes impossible to work with it, it loses stability.

To prevent the saw from clamping, its serrated edge is widened. The width of the cut should always be greater than the thickness of the saw blade. If this condition is not met, then the walls of the cut clamp the saw.

The widening of the cut is carried out by setting or flattening the teeth, or using saws with a lateral undercut, or the saws are equipped with plates made of hard alloys, the teeth of which are sharpened with a lateral undercut.

Round planing saws (Fig. 2, V), have a lateral undercut at an angle of 15¢ and 25¢.

Saw teeth with carbide inserts (Fig. 2, G) have the shape of spatulas with a lateral undercut.

The width of the cut in this case is found as follows:

Where b– cutting width, mm;

S– saw blade thickness, mm;

S’ – widening of teeth on each side, mm.

Values S’ it is recommended to use the reference book in the range of 0.2...1.1 mm. Its value depends on the type of wood (density), humidity and working conditions.

4. Specific friction force

A kerf is a narrow gap formed by a saw. Cutting chip width b falls into the cut width b p.

Due to the elasticity of wood, the walls of the cut are partially restored after the passage of the tooth. Kerf width b n< b. Thus, the chips are clamped from the sides by the walls of the cut (Fig. 3).

With further movement of the tooth, the chips overcome frictional forces F t along the walls of the cut and the front surface of the tooth, is pressed into the interdental cavity, gradually filling it. The longer the path of the tooth in the wood, the more chips accumulate in the cavity, the more it is compressed and rubs against the walls of the cut.

Average friction force per tooth passage in the workpiece

where a is the tangential pressure on the tooth from the friction of the chips in the cut (specific friction force of the chips on the walls of the cut), MPa.

The specific friction force of the chips in the cut is equal to the ratio of the average friction force to the cross section of the cut layer:

. (2)

The values of a for saws with set teeth al and flattened teeth aD are found from (Table 1).

Table 1

Tangential pressure a on the saw tooth due to chip friction in the cut


	tape

The specific friction force is the tangential pressure of the chips on the tooth, created by the friction forces in the cut.

5. Saw performance in terms of cavity capacity

Sawing performance is characterized by the amount of feed per tooth, determined by the capacity of the interdental cavity.

The sawdust formed during sawing is placed between the teeth and removed from the cut.

Based on numerous studies of cutting theory, the following formulas are recommended for calculating the feed per tooth based on filling the cavities with sawdust:

when sawing with frame saws

; (3)

when sawing with band saws

when sawing with circular saws

Where t max – maximum cutting height.

6. Thickness of the cut layer when working with flattened and set teeth

In Fig. 4 shows three cuts of the same width b, in which layers of wood are cut at the same feed per tooth S z. The first cut shows the set teeth of the saw, and the second cut shows the shapes of the layers cut by these teeth. The third cut shows the shape of the layers being cut by flattened teeth. The areas of the layers cut by set and flattened teeth are the same and equal bS z. Average feed per tooth along the length of the cutting edge found by dividing the cut area by the length of the cutting edge bl:

Usually taken

, (6)

where m is the feed angle (the angle between the directions of the feed and main movement speeds).

7. Saw tooth shape for longitudinal and cross cutting

For longitudinal sawing (Fig. 5, A) the tooth with its main cutting edge cuts into the wood and cuts its fibers. The wedge of the tooth penetrates the wood and the front edge tends to press the cut chips away from the wood. Since the strength of the wood in the plane of the fibers is weak, the cut part of the chips breaks off and falls into the interdental cavity.

The saw tooth must have a cutting angle at the main cutting edge that is always less than 90°. The side cutting edges are not sharpened and are left with a cutting angle of 90°.

When cross cutting (Fig. 5, b) the work of cutting wood fibers is performed by the side cutting edges. For this purpose, the teeth are made with side sharpening. When teeth are inserted into wood to a depth of 0.8 mm, stresses at the bottom of the cut created by the beveled front edges of the teeth (Fig. 5, V), reach the limit of shear strength along the fibers and the cut fibers split either to the left or to the right along the fibers.

When cross-cutting wood, the main work is performed by the side cutting edges of the teeth, inclined forward and having beveled front edges. To ensure these conditions, the saw teeth are sharpened as follows: cutting angle at the main cutting edge d > 90 ° , and the side cutting edge is made with an oblique sharpening anglej = 40...45 ° .

Test questions and assignments

Please indicate the number of the correct answer.

1. When sawing wood with a circular saw whose blade thickness is 2 mm and the widening of the teeth on the side is 0.6 mm, the cutting width is equal to, mm

2. Widening of saw teeth is achieved by

1) divorce,

2) flattening,

3) use of saws with side undercut,

4) soldering of plates followed by oblique sharpening,

5) increasing the thickness of the saw.

3. What is the difference between rip saws and cross cutting?

4. How to take into account the friction of the saw in the cut in the calculations?

5. What cutting methods do you know?

Sawing is the process of dividing a processed wood sample into two or more parts using repeated movement of the cutters in a given section.

For this purpose, tools are used that have several cutters and are called saws.

Sawing wood is much more difficult than cutting with a basic cutter. Each saw tooth has several cutting edges (essentially several incisors) that perform cutting in different directions in relation to wood fibers. In addition, when cutting, the saw teeth work in a closed space called cut, which creates specific conditions compared to the work of an elementary cutter.

Depending on how the cutting plane is located relative to the fibers, the following main types of sawing are distinguished:

· transverse- the cutting plane is perpendicular to the direction of the fibers (Figure 1.2, A);

· longitudinal- the cutting plane is parallel to the direction of the fibers (Figure 1.2, b);

· mixed– the cutting plane is located at an angle to the direction of the fibers.

A– cross cutting; b– longitudinal sawing

Figure 1.2 – Types of wood cutting

In logging, the most common is cross-cutting with chain and circular saws. It is used for felling trees, bucking logs and long assortments into short ones. Longitudinal sawing is used for sawing lumber: boards, beams, sleepers, trimming edges of boards, etc., and mixed sawing is used for sawing trees to be felled and trimming branches from fallen trees.

Saws used in timber yards are divided into the following types:

· round– the teeth are located around the circumference of a steel disk, continuously rotating in one direction; saws of this type are used for both transverse and longitudinal cutting;

· tape– the teeth are located on a steel belt moving continuously in one direction; used for longitudinal sawing;

· straight (frame)– the teeth are located on a steel strip performing reciprocating motion; used for longitudinal sawing on sawmill frames.

· chain– consist of individual teeth, hingedly connected to each other with rivets. The saw chain moves continuously along the guide bar in one direction; used for all types of sawing.

An important parameter the sawing process is clean sawing performance S- area of cut that can be made by a saw in 1 s. It is measured in m 2 /s.

The productivity of clean sawing depends mainly on the engine power and the type of cutting tool and averages 0.006–0.025 m 2 /s when sawing with saw chains, and 0.03–0.05 m 2 /s with circular saws.

Sawing is one of the main and initial methods of wood processing using multi-cutting tools of various designs.

Preparing hand saws for work

The preparation of saws for work includes the following operations: checking the quality of the tool, sharpening, planing and setting saw teeth.

Saw quality check includes an assessment of their technical condition - the strength and integrity of the handles, the reliability of the blades and their fastening, the sharpness of the teeth and the quality of the setting. The effort spent on sawing largely depends on the quality of sharpening and the correct alignment of the saw teeth.

During the sawing process, the saw teeth become dull, and in order to restore their cutting ability, sharpening. Hand saws are usually sharpened with triangular or diamond files.

The teeth of saws for cross-cutting wood have an oblique sharpening; they are sharpened at an angle of 60...70° to the saw blade (Fig. 1.9, A). These saws have teeth that are sharpened one at a time and, when sharpening, the metal is removed from the beveled surface of the tooth. Having sharpened the teeth on one side, turn the saw towards you with the other side and, having secured it in a vice, sharpen the remaining teeth at the same angle.

The teeth of saws for longitudinal sawing are straight sharpened, so they are sharpened on one side at an angle of 90° to the saw blade (Fig. 1.9, b).

The teeth of rip saws, in which the angle between the front and rear edges of adjacent teeth is less than 60°, are sharpened with a diamond file.

The teeth of saws for universal sawing are sharpened with a triangular file using direct sharpening, removing metal simultaneously from the front and rear surfaces of the teeth (Fig. 1.9, V).

When sharpening teeth, for each working pass of the file, you need to remove a layer of metal of the same thickness. To do this, the file pressure must be uniform and only when moving forward. You need to move the file in the opposite direction freely, without pressure, tearing it off or without tearing it off the surface to be sharpened. The final finishing is done with a finely cut (velvet) file. After filing, the burrs from the side edges of the teeth are removed with a wet whetstone. For ease of sharpening, the saw blade is clamped in a wooden vice of various designs.

To prevent the protrusion of individual saw teeth and straighten their position along one line, they resort to jointing with a whetstone or a triangular file. If the deviations of the tops of the saw teeth from a straight line are significant, then all the teeth are planed with a file inserted into a wooden block (Fig. 1.10). The saw blade must be secured in a wooden vice. The saw teeth are planed with a file before sharpening or, as a rule, after setting.

During the sawing process, the saw blade rubs against the walls of the material being cut and is clamped in the cut. To avoid this, the teeth must be set apart.

The alignment of the saw teeth is that they are alternately bent in one direction (even teeth) and then in the other (odd numbered) direction. When setting, the tooth is bent not entirely in height, but halfway. When sawing hardwood, the teeth are set apart by 0.25...0.5 mm per side, and softwood - by 0.5...0.7 mm. The total tooth set should not be greater than the thickness of the blade.

When setting teeth, it is important to ensure that the teeth bend equally on each side. If this condition is not met, the cutting quality will decrease. The teeth are set manually using settings of various designs - from simple to universal (Fig. 1.11). The saw blade is tightly clamped in a vice, and then the teeth are bent alternately, in one direction or the other. You need to spread the saw teeth evenly with a simple set, without much effort, otherwise the tooth can be broken. In addition to the simple setting, a universal setting is used, which makes it possible to obtain the correct amount of saw tooth set. The amount of tooth set is checked with a template. You can set the teeth before and after sharpening, depending on their wear. If the saw is significantly distorted, it is better to first loosen and then sharpen the saw. Requirements for sawing quality

The quality of sawing is characterized by the roughness of the resulting surfaces and accuracy

processing the workpiece. A rougher surface is obtained when working with a dull and poorly set saw, so before work the saw should be sharpened and set well. Inaccurate cutting of wood occurs when the saw presses hard and when it deviates from the marking line. Sawing of tenons and eyes should only begin after gaining sufficient experience in the work. hand saws and practicing sawing techniques. When sawing, the marking line is preserved. The cutting line should pass next to the mark, and the cutting accuracy is determined along this line. During further processing by planing, the processing allowance is removed.

To avoid flakes and broken edges when cross-sawing parts, their ends should be supported with your left hand when finishing sawing. Sawing of tenons and eyes must be done with sufficient precision.

Useful tips carpenter

The thinner the part, the smaller the saw teeth should be. Therefore, to file small glazing beads or strips, you can use a slotted metal file, but you should work with it in a miter box.

When cutting across the jacket layer, the edges of plywood will not chip if the cut area is pre-moistened with water.

To prevent a saw with a narrow tooth spread from getting stuck in wood (especially damp wood), just rub it with soap and the work will go faster.

6. Plane planing.

Sherhebel used for initial rough planing of boards and blanks, especially when it is necessary to remove a thick layer of wood by planing. The piece of iron in the sherhebel is released beyond the plane of the sole up to 3 mm; it has an oval cutting edge, removes thick chips, and leaves quite deep grooves on the processed surface. The ovality of the cutting edge allows you to plan with scherhebel across the fibers and at different angles to them without breaking them longitudinally.

Single planer used for leveling the surface after sawing or planing with Sherhebel. The blade of the iron is straight.

Double planer It differs from the single one in that it has a counter piece (chip breaker). The edge of the counter iron is parallel to the cutting edge; install it as close to the cutting edge as possible. The closer the edge of the counter iron is to the cutting edge, the cleaner the planing. A double plane is used for clean planing, for touching the ends, and for cleaning out burrs and strands.

Sander- this is a shortened double plane with a reduced span and increased angle of attachment. Serves for cleaning burrs, strands, and ends. Removes very thin chips. The sander is suitable for processing hard pressed wood.

Jointer used for planing large surfaces for a ruler and for aligning the length (sharpening) of edges, in particular for gluing them. A jointer differs from a plane in the size of the block and piece of iron. The long block of the jointer helps to level the surface being planed. The iron on the jointer is often double. A low cylindrical insert - an impact button - is glued into the front part of the jointer block. By hitting the button with a hammer they knock out piece of iron from the tap hole.

Zinubel- a special single plane with fine teeth on the blade. The teeth are formed by longitudinal corrugation of the front edge of the iron. Tsinubel serves to create a roughness on the surface of the wood before gluing facing plywood onto it during veneering in order to prevent strong squeezing of the glue in certain places and to avoid weak gluing in these places. Some carpenters insert a sharpened piece of a single or double plane into the tsinubel block and plan the twisted hardwood with it. Since the additive angle of the zinubel is 80 degrees, the planing is clean.

End a plane with a piece of iron installed at an acute angle to the side of the block serves to touch the ends.

Planing tools also include cycle. The cycle is a steel plate 100-150 long mm, width about 60 mm and thickness up to 1 mm. It is often made from used band and bow saw blades. The purpose of the scraper is to clean hardwood after it has been processed with a double plane or sander. The cutting part of the cycle is a burr (sting) on the machined edge. When scraping, the tip is located almost perpendicular to the surface being processed and removes very thin (openwork) chips. Sometimes the cycle is inserted into a block with handles.

Irons with a straight or oval cutting edge are sharpened on a small sharpener, on a fine-grained whetstone; The final adjustment (editing) is done on the touchstone. After sharpening and straightening, you should press the piece of iron with the tip of the blade along hard wood or along a knot. After this, finishing is done on the whetstone. This prevents the formation of a so-called “false sting” on the sharpened piece of iron, which causes the blade to become dull at the very beginning of working with the tool. The ends of a straight blade should be slightly curved so that when planing they do not tear up the wood and leave marks on its surface.

7.Profile planing.

humpbacks used for processing concave and convex surfaces. Pad length 250 mm, width 60 mm. The iron is an ordinary plane, double. The curvature of the humpback sole should correspond to the curvature of the surface being treated. The sole of the wooden humpback has a constant curvature. The humpback sole with a metal block is an elastic steel plate capable of bending in both directions; its curvature can be changed using special set screws.

Zenzubel used for picking at the edges of folded parts. Zenzubel block length 250 mm, height 80 mm, width 20 mm. The sole is straight. On the side of the block there is a sink for chips to fly out. The gland of the zenzubel has the shape of a spatula 20 mm in the blade and 7 mm in the shank. The piece of iron is inserted into the block from below and secured with a wedge inserted from above. The blade can be straight and form a right angle with the side edge; it may also be beveled. A piece of iron with an oblique blade is installed at an acute angle to the side of the block. A zenzubel with an oblique iron gives a cleaner planing; in addition, it is more convenient to use: thanks to the sharp angle of the piece of iron, the block is pressed better to the side of the fold being cut out.

Falzgobel serves the same purpose as the zenzubel, but it produces a recess of a certain size - a quarter. Unlike the zenzubel, the folded gobel has a block with a width of 30 mm and a stepped sole. The cheek of the sole serves as a planing width limiter, and the ledge serves as a depth limiter. The folding iron is always single. The sink is one-sided, the chips fly out to the left of the block.

Staffgobel- a tool that gives a predominantly rounded shape to the front edges of some parts (shields, bars), as well as the front side of the posts. Stab tapestries have pads of different widths. The cutting edge of the piece of iron and the sole of the block are usually concave; letok - one-sided shell.

Mold, or selector, is used for shaped processing of the front edges of parts. The sole of the block and the cutting edge of the piece of iron have a shape opposite to the selection profile. The entrance is a one-sided shell.

Figarei serves for cutting a wide chamfer or a wide profile on the edges of a board panel. Accordingly, the figari has a wide sole inclined to the horizontal or a shaped one, an oblique or profile piece of iron with a width of up to 90 mm.

Eaves- a tool for processing cornice bars and platbands with complex profile.

Fillet used for cutting grooves of various widths and depths with different radii of curvature. In this regard, there are fillets with iron of different widths. The cutting edge of the piece of iron is rounded, the taphole is through. Tapholes in the form of a side shell are made only in very narrow blocks.

tongue and groove- a plow of a rather complex design, consists of three main parts: a block with a piece of iron, a guide bar and two screws with nuts and locknuts. The tongue and groove is designed for cutting out a rectangular groove on the edge or face of parts, at a given distance from the edge. The sole of the tongue and groove is formed by inserting a metal plate 3 thick into the block from below. mm with a slot for a piece of iron. Using thumbscrews, you can move the plate out of the block to a greater or lesser distance, depending on the depth of the selected groove. The width of the groove depends on the width of the piece of iron. The tongue and groove pile has a set of pieces of iron with a width of 3 mm up to 15 mm. The distance between the piece of iron and the edge of the workpiece is adjusted by a guide bar located on the side of the block with two screws.

Federgobel serves for sampling on the edge of the ridge inserted into the groove. This tool consists of a block with a piece of iron different shapes.

Gruntubel used for cutting out a groove of a trapezoidal cross-section across the fibers after the groove has been cut along the sides (edges) with a reinforcement. The primer consists of a block and a cutter inserted on the side in the form of a pointed hook. The cutter is secured in the block with a wedge or a thumbscrew. Wood from a sawn groove is often removed with a chisel or chisel, and only the bottom of the groove is cleaned with a primer.

The iron of tools for profile planing, if the shape of their cutting edge allows, is sharpened on a whetstone and whetstone. In other cases, sharpening is done with files of various shapes with a fine notch, and straightening is done with a shaped block of hard wood, soaked in oil and sprinkled with emery powder.

Sawing- this is the operation of dividing wood into parts using a multi-cutting tool - a saw. The saw is a steel blade with teeth cut along the edge. When sawing wood with hand saws, the blade reciprocates straight motion when the workpiece is stationary, and the teeth cut off chips (sawdust) and move them out of the closed cut. As a result of sawing, flat or curved side surfaces and bottom are formed.

Teeth- the main part of the saw. The teeth have front edges, back edges and side edges. The front main cutting edges form the bottom of the cut during the cutting process, and the side edges form the side surfaces of the cut.

The shortest distance between the peak and the valley (base) is called the height of the tooth.
The distance between the front main cutting edges of adjacent teeth is called the pitch of the saw.

Depending on the installation of the material to be sawn relative to the workbench cover and the direction of cutting the wood, four types of sawing are distinguished: 1 - along the fibers when securing the material horizontally, 2 - along the fibers when securing the material vertically, 3 - across the fibers when securing the material horizontally (trimming), 4 - mixed - sawing at an angle and along curved lines (curly).

The geometry of the tooth is determined by the clearance angle, sharpening angle (pointing), rake angle and cutting angle.
The entire row of teeth is usually called a ring gear. The edge of the saw blade opposite the toothed ring is called the back or butt. The depressions between the teeth are called sinuses.

Depending on the purpose and type of sawing, the teeth are made according to the shape isosceles triangle- for cross cutting, oblique triangle - for longitudinal cutting, rectangular and inclined triangle - for mixed (transverse and longitudinal) sawing.

In addition to these types, two-handed saws have M-shaped sawdust ejectors, which are placed in a gear rim through four teeth of an isosceles triangle. Hacksaws for cross-cutting have two paired teeth with one beveled cutting edge and an enlarged groove between them.

In rip sawing, the front main cutting edge of the tooth produces the end cut where the wood offers the greatest cutting resistance. In this case, the cutting angle is 60-80 degrees.

When sawing, the front edge of the cutter, when moving forward, presses on the cutting chips, separates them from the bottom of the cut and inserts them into the cavity (sinus) between the teeth, facilitating the sawing process. To ensure that the cavity capacity is sufficient, the sharpening angle is made no more than 50 degrees.

In cross sawing, the main edge of the tooth cuts the wood across the grain, that is, the grain of the wood is cut by the outer side cutting edges.

The short cutting edge breaks off the chips inside the cut and removes them. The tooth sharpening angle is 40-50 degrees, the sharpening angle is 60-75 degrees.

The saw pitch is 2.5-6.5 mm depending on the purpose and shape of the tooth. It is recommended to set the teeth in increments of up to 3 mm, 0.1-0.6 mm on one side, for teeth with a pitch of 3 mm or more - 0.3-0.6 mm on one side.

According to their design, saws are divided into bow saws with a tensioned blade and non-tensioned ones - hacksaws, two-handed saws.

Bow saws consist of a wooden or metal (yoke) beam (machine) and a saw blade stretched in it. The wooden machine consists of two handles (shakhovok), a bowstring and two struts and a twist. The bowstring is usually made from twisted linen or hemp cord with a diameter of 3-4 mm. Sometimes the bowstring is replaced with a metal rod, which is tensioned using a thumbscrew.

The posts and shanks are made from hardwood, the spacer and twist can be made from softwood.

A bow (yoke) saw consists of a blade, an arc-shaped frame made of an oval-section metal pipe, an eccentric tensioning device, a clamp, screws, and blade fastening.

A hacksaw usually consists of a saw blade fastened at one end in a handle. There are universal hacksaws with interchangeable blades of various cuts.

The length of hacksaw blades is made from 250 to 600 mm.

Handles can be made of phenolic plastic, high-density polyethylene, 1st grade hardwood lumber, aluminum alloys, steel of any grade. The blades are made from steel grades 7xF, 8xF, Ekhf, EkhE or from steel 65G, etc.

Preparing saws for work. Sharpening saws.

The quality of the sawing surface and the effort spent on sawing largely depend on the correct sharpening and setting of the saw teeth. During the sawing process, the teeth become blunt, that is, the front and side edges of the tooth become rounded. To restore the cutting ability of the teeth, they are sharpened with files. In this case, the profile, pitch and height of the teeth must remain unchanged. For teeth with straight sharpening, metal is removed simultaneously from the front and rear edges. This is how teeth are sharpened for longitudinal sawing when the angle between the front and rear edges of adjacent teeth is approximately 60 degrees, which corresponds to the angle of the cross-sectional profile of a triangular file. Teeth for longitudinal sawing, in which the angle between the front and rear edges of adjacent teeth is less than 60 degrees, are sharpened with a diamond file from the rear edge.

For teeth with oblique sharpening for cross-cutting, the metal is removed as a chamfer from the front and rear edges at an angle D1 = 60-70 degrees to the blade. In this case, more metal is ground off from the top of the tooth than from the base.

When sharpening one cutting edge, it is recommended to point the file upward, that is, make movements at an angle of 20-30 degrees to the horizontal plane if the blade is fixed vertically.
In this case, sharpening is carried out through a tooth, first on one side of the blade, then on the other. You can sharpen teeth on two edges at the same time. The front face of one and the back face are processed simultaneously adjacent tooth. In these cases, the groove must correspond to the size of the file and good sharpening skills are required.

To sharpen the teeth, the saw blade is clamped in a wooden vice of various designs.
When sharpening teeth, you need to remove a layer of metal of the same thickness for each working pass of the file. To do this, the file pressure must be applied evenly and only when moving forward. You need to move the file in the opposite direction freely, without pressure, tearing it off or not tearing it off the surface to be sharpened. Final finishing is done with velvet files. For precise work, after using a velvet file, the burrs are removed with a wet donkey from the side edges of the tooth.

Tooth set

To ensure free movement of the saw blade in the cut, the teeth are set using devices, that is, adjacent teeth are alternately bent in different directions of the blade by the same amount. For soft and damp wood, the spread should be greater than for hard and dry wood, but not more than the thickness of the blade on both sides. When setting the teeth, it is necessary to make the same bend of the teeth on each side and at the same height. It is recommended to bend the tooth at half the height of the tooth using sets. You can set the teeth before and after sharpening, depending on the wear of the teeth. If the saw teeth are significantly distorted, it is better to first set them apart and then sharpen them.

To set the teeth, settings of various designs are used: simple, with a stop, universal.
If the deviations of the tops of the teeth from a straight line are significant, all teeth are planed (aligned) with a file inserted into a wooden block. The saw blade must be secured in a wooden vice. The teeth are planed before sharpening and, as a rule, after setting.

Cutting saw teeth

During operation, the teeth wear out and change their shape, and also break when set. In addition, the industry produces large number saw with large teeth.
If necessary, various tools can be used to cut saw teeth.
Devices can be lever, screw and impact, which are called stamps.

Sawing techniques

Longitudinal sawing when securing material horizontally. The board to be cut is placed on the lid of the workbench and secured with a clamp so that the sawn part hangs over the edge of the lid. The saw blade is set at an angle of 90-110 degrees in relation to the axes of the machine posts.
Cutting begins from the top edge of the end edge of the board, making the first movement of the saw towards you from the bottom up. During the sawing process, the saw blade should be at an angle of 80-90 degrees to the plane of the board. The carpenter's body is slightly tilted forward, the feet are turned at approximately 90 degrees in relation to one another. Hold the saw while sawing right hand for the shakhovka (handle), with the left - for the counter. The saw is advanced onto the board being cut by lightly pressing the teeth while moving downwards. When the saw moves upward, the blade is moved slightly away from the bottom of the cut.

Longitudinal sawing when securing material vertically. To secure a piece of board, the lumen of the rear clamping box is opened 1-2 cm larger than the size of the workpiece. Then the right edge blank is installed vertically into a fixed clearance angle. In this case, the protruding part of the workpiece (end) should be above the workbench lid at elbow level, but so that the protruding end does not bend when sawing. Place the saw with its teeth on the edge of the workpiece at an angle of 15-20 degrees to the end and exactly according to the markings. Guide the saw blade when cutting along the block, but you can use your fingernail or knuckle thumb left hand. The cut is made by smoothly moving the saw towards you, without pressing, until the blade is deepened 1-1.5 cm into the wood or the opposite edge of the end is cut. Do not start sawing with a jerk.
To saw, stand with your right side to the workbench opposite the workpiece, place the foot of your left foot parallel to the lid of the workbench, take half a step back with your right foot and place your foot at an angle of 70-80 degrees to your left. When working, the saw is held firmly by the handle with the whole hand of the right hand, and the material being cut is supported with the left hand, first by the end and then by the edge. Using working movements, the saw is gradually transferred to horizontal position. As the cut deepens, the section of the board is raised up so that the bottom of the cut is at the height of the elbow of the right hand, but not higher than the shoulder. Sawing evenly, without making strong pressure, first with a movement of 40-50, and then 60-80 cuts per minute. Full swing over the entire length of the blade with light pressure when moving away from you. Sawing is done with the movement of the right hand, while the body is motionless and slightly tilted forward.
At the end of sawing, the section to be sawn is set obliquely, in left side so that the risk remains unclamped and is visible until the very end. The unfinished part of the board cannot be chipped, as this can lead to defects, and in cross-laminated wood, defects are inevitable when chipped. If you are sawing short sections of boards, you can place the lower end of the workpiece up above the workbench lid and make a cut again, and then continue sawing until you meet the initial cut.

Sawing across the grain of the wood. Place the board flat on the workbench so that the end to be sawn protrudes beyond the back bar of the lid, and the cut line should be 3-5 mm from the folding stop. With your left hand, press the edge of the board against the stop, and with your right hand, hold the saw by the handle with a slight inclination to the surface (20-30 degrees). Place the saw blade with its teeth at the handle on the cutting line and hold it perpendicular to the face of the board, exactly according to the markings. The foot of the left foot is perpendicular to the lid of the workbench, approximately at the lower base of the bench, the right foot is turned 70-80 degrees in relation to the left, the body is slightly tilted forward.
The beginning of sawing (cut) is done by moving the tool towards you, while the saw blade is directed along the line using the nail or the second joint of the thumb of the left hand. Keep the nail and joint above the teeth. It is not recommended to make cuts by jerking the saw forward.

The saw movements should be uniform (60-80 cuts per minute) with light pressure on the material.

When finishing sawing, you need to hold the part being sawn with your left hand, and reduce the pace of work by about 2 times. When sawing, you can use various devices. A miter box is widely used, which consists of two side walls, fastened with nails or dowels with glue on the bottom board. Cuts are made along the walls, reaching to the very bottom. One cut is made at a right angle, the other two - at an angle of 45 degrees.