Home Removal Mixed sawing. Sawing wood, preparing for work

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Mixed sawing. Sawing wood, preparing for work

Position the log so that when sawing, minor defects in the material will be inside the lumber (of course, if these defects are not so serious as to affect the strength of the final product). If possible, cut so that all knots and imperfections are on one side of the lumber, while leaving the other side clean. True, in the case of building materials, a clean surface does not affect the final price of the product.

Sawing quality

Let us discuss the following criteria, which are the technical basis of the sawing operation.

The purest, knot-free, most valuable wood is found in the outer part of the log. The quality decreases as you start cutting closer to the center of the log.

The most valuable are wide, long, clean boards. Best variety lumber ensures that the boards at a minimum have a clean, smooth surface.

There are several techniques. To perform each of them, a certain set of tools and knowledge is required. Wood processing techniques

* Wood planing - separation of bark from solid wood. The main tool is an axe. All actions are directed from the top to the base along the circle of the trunk. In this case, the ax blade should not penetrate deep into the bark layer, so as not to damage the wood itself. As work progresses, protruding knots should also be cut off along with the bark.

* Planing of wood involves leveling the surface after sawing. The part prepared for finishing must be placed on the workbench and secured. First of all, they start with rough leveling, for which sherhebel is used. In this case, all movements are directed across the grain so as not to remove too much wood. After treating the surface of small parts with Sherhebel, it must be cleaned with a single plane and then a double one. The plane should be moved along the surface along the fibers. When planing the ends of boards and bars, several movements are made with the plane from one edge to the center, and then several movements from the other edge to the center.

* Sandpaper is used for the surface. Sanding should be done in the direction of the grain or obliquely. Types of skins

* Soft, fine-grained sandpaper is used for final sanding. Does not leave grain marks on the surface. There are several wood processing techniques. To perform each of them, a certain set of tools and knowledge is required. Wood processing techniques

* Sawing wood. When cutting, several movements are made with the hacksaw blade along the already marked line, thereby strengthening the blade in the solid wood. During further work, you will only need to adjust the movement of the hacksaw if its blade tries to get around a knot or difficult area. During this operation, it is best to position the workpiece so that the piece to be sawn is on the left side. When cutting is completed, free left hand It will be easier to hold an unnecessary piece and prevent it from falling. All movements when cutting out a part are made in a sweeping manner.

* Drilling wood is done to make various holes. Before you start drilling, you need to select a drill of the appropriate size, then use an awl to make a mark on the wood, secure the drill in the chuck and set the drill exactly to the mark.

* When chiseling wood, before starting work, you should secure the workpiece well in a vice. Then apply markings to the surface of the wood, first with a simple hard pencil and then with a knife. If it is necessary to make a sufficiently deep and large hole, then first knock out the wood with a chisel, and then begin to clean the surface with a chisel.

* Cutting is done either with chisels or a jamb knife. Wood cutting is carried out as follows: a chisel blade is placed on the marking with a chamfer inside the future recess. Then cut the chisel 2-3 mm deep into the wood. After the first cut, place a chisel 1-2 mm deep into the intended socket and make the same cut. In the middle of the recess, the cut can be made to a depth of approximately 5-6 mm, but near the edges, so as not to damage the sides, only 2-3 mm, no more.

* Wood scraping is a processing that allows you to use a knife to clean the surface of the wood as smoothly as possible. In this case, the process itself is more like scraping. The movements of the cycle are directed towards themselves, and the knife itself is installed with the chamfer facing up. After all the work is completed, all that remains is to level and clean the treated surface after the plane.

* Emery cloth is used to sand the surface. Sanding should be done in the direction of the grain or obliquely. Types of skins

* Rough, coarse-grained sandpaper is used for rough surface treatment

* Soft, fine-grained sandpaper is used for final sanding. Does not leave grain marks on the surface. Methods of joining (gluing) wood Gluing. Bonding is used for various tenon and miter joints.

* By lapping, mainly thin parts are connected, which, after slightly setting, are adjusted to each other and left until the glue has completely dried. Bonding spacers are used for maximum uniform distribution forces during compression and protect surfaces from the formation of dents when clamped with clamps. The gasket is always done slightly more sizes glued parts. Most often, gaskets are made from sheets of plywood.

* Gluing is used only in facing works (in the manufacture of plywood, when finishing the surface with veneer, etc.). This is a fairly simple way to imitate solid wood using only veneer and a wooden base. In addition, this technique will also help in making mosaics. Veneer should only be glued onto a very flat surface, slightly rough, but without visible notches. The veneer must be glued across the direction of the base grain, otherwise cracks may appear. They arise due to different shrinkage of the veneer and the base. If expensive veneer is used and glued to a particle board, then an intermediate layer of cheap veneer or cotton fabric must be glued.

Step 1. Position so that when sawing, minor defects in the material will be inside the lumber (of course, if these defects are not so serious as to affect the strength of the final product). If possible, cut so that all knots and imperfections are on one side of the lumber, while leaving the other side clean. True, in the case of building materials, a clean surface does not affect the final price of the product. But large branches or defects can affect the strength of the structure.

Step 2. Select the worst side of the log and start sawing from there, producing short lumber. Forget about compensating for the log's taper while you're working on that bad edge. The first lumber will be the worst and therefore must be short to be salable.

Step 3. Once the log has been cut from the bad edge along the entire length of the log, move to the opposite edge, sawing parallel to the bark. From a good edge, the width of the board being cut should be at least 15 cm. On smaller logs (less than 30 cm in diameter), the first board should be 10 cm wide. Huge logs will have fewer defects inside and, therefore, there is no need to transfer them to large building structures; it is better to saw them into lumber, which is more expensive on the market.

Step 4. Always turn the log from one side to another if you see that the lumber from the new side will best quality than from the one you just sawed.

Step 5: Waste logs. Saw the “ears” in one pass of the saw, then turn the log over onto its “belly”, perhaps you can make at least a few short boards out of it. In general, as I already said, sawing such logs is a waste of money. for furniture production Sawing operations are the same as in the case of construction materials, excluding the first cut. From a good edge, the log should be sawn so as to obtain boards 15-1 cm wide and along the entire length of the log. On logs with a diameter of less than 30 cm, you need to make boards 10-1 cm wide.

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 multiple cutting edges (essentially multiple cutters) that cut in different directions relative to the grain of the wood. 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 of 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.

Introduction

Wood processing is one of the most ancient crafts. Wood processing tools and techniques are widely known.

Wood processing techniques for building aircraft models are very diverse: splitting, turning, planing, veneering, chiselling, drilling, bending, gluing, etc.

Ignorance of basic techniques for processing and setting up tools causes unnecessary difficulties in work and sometimes even discourages the desire to work. You can see how a novice modeler, using a dull saw, works for a long time and, without receiving desired results, splits the board along the layer with an ax or knife. This often leads to damage to the part. The resulting material residues, as a rule, cannot be used, and they lose their value. Working with a sharp, serviceable tool that suits its purpose is always effective and does not require much physical effort.

Wood can be processed manually, using mechanized tools and on machines.

Carpentry and special modeling tools are used to process wooden parts.

Every modeler needs to have a set of carpentry tools, and in model workshops, in addition, there should be small woodworking machines

Marking and marking tool

Before you start processing the part, you need to mark the workpiece. The quality of the part largely depends on the correctness and accuracy of the markings. Even small errors in drawing marking lines can lead to irreparable defects. Despite the apparent simplicity of this work and the simplicity of the tool used, you need to be very careful, and after marking is completed, carefully check the constructions made.

To draw lines in carpentry, a surface gauge, a scriber and a compass with sharpened legs are used. In the manufacture of flying models, these tools are used less frequently, since they deeply cut the surface of the parts, significantly reducing their strength. It should be borne in mind that on smooth surfaces intended for polishing or coating with nitro varnishes, these tools leave deep marks that are difficult to remove.

To draw lines when marking, it is best to use a simple graphite pencil. To mark parts made of hard wood, TM, T, 2T and ZT pencils are used; for soft wood, for example, linden or spruce, M pencils are used.

The following tool is used for marking.

A metal or wooden ruler with millimeter divisions is used for measuring and marking dimensions. When marking, you can also use a folding meter or a steel tape measure, for sizes less than 100 mm - a caliper.

A metal square is used for marking right angles and checking them. The correctness of such squares is checked by comparing them with a control square. If there is no control square, then on a flat board with a straight edge a line is drawn along the square, then the square is turned to the other side and a second line is drawn next to the first line.

If the lines turn out to be parallel, the square is correct.

The malka is used for setting aside corners and checking them. Set the grinder to the desired angle using a protractor or protractor.

The marking tool is used to draw lines parallel to the edge.

Thin plywood, cardboard and celluloid can not only be marked with a marking tool, but also cut. To do this, the surface scriber needs to be sharpened in the form of a cutter.

SAWING OF WOOD and wood MATERIALS.

The task is not just to divide the wood, but to perform a dimensional operation for processing transverse, longitudinal, oblique, inclined planes using a saw. Ideally, the plane obtained by sawing is not subject to any further processing and is geometrically and dimensionally accurate.

Today, the best tool for hand sawing at home is a hacksaw with a universal tooth with a pitch of 2.5 ... 4.5 mm. This hacksaw allows for precise sawing in any direction and is universal in the household. She is also good at professional things. With a hacksaw you can make cuts in wood in any direction with a cut width the size of the thickness of the hacksaw or more, i.e. With just one hacksaw you can make a groove with a width ranging from the width of the hacksaw set (1.5 - 2 mm) to 4 - 5 mm or more. Wider grooves are made using a hacksaw and chisel. A hacksaw can be used to very accurately and better than a file to correct the side surfaces of a tenon.

The universal sharpening of the tooth is shaped closer to the tooth for longitudinal sawing and therefore it is the starting point for sharpening. Several types of sharpening have been tested in practice (see appendix). With different labor intensity, they give comparable results. Therefore, you can choose the sharpening method according to the shape of the saw tooth, file, equipment and your skill in sharpening saws. A hacksaw, like any cutting tool, must always be sharpened, be straight, have an appropriate spread, and have a comfortable handle.

Now, actually, about sawing. First of all, you need to choose a comfortable position. The legs are apart, the back is straight, the torso is tilted in hip joints, emphasis on the left (for right-handed) hand. The position is balanced, stable, comfortable.

Sawing is carried out along the marking line, cutting off half of it from the side of the material being removed, i.e. always the marking line (half of it) remains in the part (in the body of the part). It is more convenient when you observe the marking line to the left of the hacksaw. This is achieved by positioning the workpiece. Once a certain skill is achieved, cutting is also easy to do to the left of the line.

When sawing, the workpiece itself must be secured, fixed in a vice, or on special stops with pressure with a non-working hand. Dimensional sawing is always (in most cases) carried out from the front side of the workpiece with a horizontal movement of the hacksaw. We pay special attention to the straightness of the hacksaw’s movement in both horizontal and vertical planes. The whole body, legs, back, neck, supporting arm are relaxed. The working hand holds the hacksaw without tension; the muscles used are only those necessary to hold the hacksaw and move it. Check to see if opposing muscles are engaged (flexor-extensor and vice versa).

The cut (start of sawing) is made with an inclined hacksaw, moving away from you far edge marking line. Holding the hacksaw in a canopy, we make one or two smooth movements of the hacksaw over the marking line. We observe the passage of the edges of the hacksaw teeth relative to the line, adjust its position and, while moving away from us, lightly touch the workpiece with the hacksaw. The main thing is not to cut the line. If the cut has moved away from the line towards the material being removed, this can be easily corrected. The hacksaw is tilted at an angle of approximately 10° to the horizon (practically rests on the workpiece) with its teeth in the direction of the desired offset of the cut, and several light longitudinal movements of the hacksaw are made with virtually no pressure until the hacksaw teeth reach the marking line. Without stopping the longitudinal movements of the hacksaw, it turns to a vertical (or other necessary) position and continues cutting. When the hacksaw is immersed in the material to a depth of ~ 2 mm, the hacksaw is transferred from an inclined position to a horizontal position without stopping its longitudinal movements. While sawing, you should not put pressure on the hacksaw - it seems to be sawing itself and selecting the optimal cutting depth required for it (the thickness of the chips removed).

How should you direct the hacksaw to the marking line? There is a rule: a block of wood with a flat end is taken in the left (non-working) hand, placed on the cutting line, through this block the workpiece is fixed on the stop, and along the end of this block the hacksaw is directed to the line by pressing it against the end of the block during the filing motion of the hacksaw . The fingers of the left hand are kept at a safe distance to prevent injury from the hacksaw. But in this way it is more than difficult to make an accurate cut with a hacksaw, especially when making a long, inclined, oblique or correction cut. According to the author, it is more professional to guide the hacksaw with the thumb of the non-working hand. With the correct and controlled position of the hand, this is also safe, but allows constant visual control of the position of the hacksaw and control of the sawing process. The left hand is placed on the workpiece, pressing it, at a distance of 2.5-3 cm from the cut. Thumb bent upwards to the right and touches the hacksaw 3-5 cm above the teeth. It is practically excluded from the dangerous zone of influence of the hacksaw teeth. The most injured is the index finger. It, like the other fingers, is bent, placed on the workpiece with nails, and thus the workpiece is pressed. Or they grasp the workpiece together with the stop, controlling the position index finger. Constantly being in a state of control over your actions completely eliminates the possibility of injury. The rule must apply: not a single thoughtless movement or action, i.e. not a single automatic action. This is the beginning of the development of self-control, which should always be turned on.

An inclined cut is carried out as follows: we make a cut on the far edge, move the hacksaw to a horizontal position and cut to a depth of 1-1.5 mm. Then we tilt the hacksaw to the required angle, orienting it along the marking line, and cut along it. Several trial bevel cuts allow you to fully master this process. Oblique cuts are carried out in the same way as straight ones. A special feature is that it is somewhat difficult to cut - when cutting on an edge, the hacksaw moves at an angle to the fibers and tends to slip off them. In this case, we proceed as with inclined sawing: we make a notch on the edge perpendicular to the fibers (in no case cutting the marking line) and then, turning the hacksaw to the marking line, calmly saw with a horizontal hacksaw, controlling the cut along the vertical (or other necessary) marking lines.

Using a hacksaw to shape a groove wider than its thickness, for example for a thin key, is done as follows: mark the groove, make a vertical (or other necessary) cut to the full required depth along the right marking line. Then, as when correcting a cut, we lay the hacksaw almost flat on the workpiece (angle 5-10°) with its teeth towards the second marking line and with horizontal movements of the hacksaw we bring its teeth to the left marking line. We turn the hacksaw to a vertical position (or another necessary one) and, pressing the hacksaw tightly to the left side of the cut, we cut the resulting ledge, forming left side groove. In this way, grooves up to 4...5 mm wide can be easily made. Children learn this exercise easily and do it well.

It is useful to note the use of a hacksaw to adjust the thickness of the tenon. The workpiece is installed horizontally with the tenon plane facing up. A hacksaw is applied to the plane of the tenon perpendicular to it with its teeth. The thumb of the left hand fixes it as if making a gash. Now we make sawing movements with a hacksaw, at the same time moving it with the thumb of our left hand along the plane of the tenon. We carry out movements both perpendicular to the axis of the workpiece and slightly at an angle to the right and left. In several passes along the plane, a layer of up to 2 mm can be easily removed. This method is easier, more accurate and better than processing the tenon with a rasp or file. In addition, we perfectly roughen the surface for subsequent gluing.

As a result, we know that sawing produces precise dimensional processing, prepares the surface for gluing, and corrects errors. It is the accuracy of sawing that ensures the quality of fit of the joint surfaces. Sawing is a responsible and at the same time fascinating wood processing operation.

Tools related to sawing wood.

Saw for self made consists of two main parts: the machine or handle by which the saw is held during operation, and the toothed saw blade.

Each saw tooth represents a cutter. The saw teeth, bent alternately to the sides, form a so-called set, which facilitates the movement of the saw blade, since the cut is wider than the thickness of the blade.

Depending on the shape of the tooth and its sharpening, transverse, longitudinal and universal saws are distinguished. Saws can be manual or mechanized.

Based on the size of the teeth, saws are divided into fine-toothed (tooth height up to 3 mm), normal (tooth height 4-5 mm) and coarse-toothed (tooth height 6-8 mm).

Fine-tooth saws are used for precise work, and coarse-tooth saws are used for rough sawing on soft or raw wood.

Hand saws

A crosscut saw is designed to cut wood across the grain; its teeth are shaped.

A rip saw is used to cut wood along the grain. Its main difference from a cross-cut saw is the absence of side edges on the teeth.

A saw for universal sawing, used for sawing in both longitudinal and transverse directions, differs in the shape of the tooth.

According to their design, saws are divided into saws with a tensioned blade and saws with a free blade.

The bow saw is a type of saw with a tensioned blade. It can be used for a wide variety of jobs, depending on the width of the supplied blade and the shape of its teeth.

Hacksaws (ship saws, ax saws) have a free wide blade with teeth of various shapes and sizes. Thanks to their ability to maintain the direction of the cut, hacksaws are very convenient for modeling.

Sharpening hand saws

Working with a dull or faulty saw is difficult and unproductive, so before you start working, you need to put the saw in order and make sure it is sharpened correctly. To do this, remove tar and rust from the surface of the saw with a rag soaked in kerosene, then, if the saw was bent, straighten it. The saw should be straightened with a mallet on a flat metal surface.

The straightened saw is clamped in a bench or special vice with the teeth up and the teeth are aligned in height and shape with a triangular personal file, and then they begin to set them. When setting the saw, the teeth along the entire length of the saw are bent alternately in opposite directions.

As a result of setting the teeth, the cut is wider than the blade, and the saw moves easily in the cut.

A poorly set saw produces an uneven cut and leads to the sides.

The saws are set with a special tool - a spreader. The saw teeth are bent one after another in one direction, and the missing teeth are bent in the opposite direction. If there is no wiring, this work can be done with a screwdriver.

After setting, the saw is sharpened with a personal triangular or diamond-shaped file.

Jigsaws are a type of small manual or mechanical machine with tensioned thin saw blades, so-called jigsaw blades.

Jigsaws are used for the most delicate and delicate work, mainly for cutting shaped holes and curved cuts.

The design of the jigsaw depends on the size of the parts being cut and what material needs to be cut. To work on hard wood, plastics and metal, metal jigsaws with a slight offset are used. To work on plywood, use a wooden or metal jigsaw with a large offset.

Jigsaw blades are known to be sold under common name"metal files" and "wood files." Working with a jigsaw requires great care, since even with a slight misalignment of the jigsaw, the file easily breaks.

As a rule, a jigsaw is used on a stand that is screwed to a board or table. Especially small work on plastic and metal is done by clamping the part in a table vise.

When working in a vice, the file is clamped in the direction “tooth away from the handle”, when working on a stand - “tooth towards the handle”.

Good jigsaw files should be elastic and have clear sharp teeth. The file should not have one-sided burrs resulting from the manufacture of the file, as they cause inevitable deviation of the cut to the side. To avoid jamming, leading to breakage, files wider than 1 mm must have a routing.

Along with flat files, round files are sometimes used, which allow you to make cuts in any direction without turning the jigsaw, simply by pressing its handle in the desired direction.

To cut grooves in plates, for example, ribs, several files are successfully used, which are clamped simultaneously. The cutting width is adjusted by the number of files.

If you don’t have files, you can make them yourself from flattened wire or a clock spring 1-2 mm wide.

To do this, you need to straighten the workpiece and clamp it in a vice, cut through the teeth through one with a small needle file, then turn the workpiece and saw through the missing teeth on the other side in the opposite direction. By using this method, the formation of one-sided burrs on both sides is avoided, and the canvas receives a unique layout.

You can make a file in another way. To do this, a straightened clock spring or a strip of spring steel of the required thickness is clamped between two plates in a vice and the teeth are cut with a sharp chisel.

Mechanical jigsaws

The performance of internal sawing work is greatly facilitated and improved with the help of mechanical jigsaws.

For mechanical jigsaws, files up to 200 mm long with a tooth height of 0.8 to 2 mm are used, depending on the thickness of the material being cut. Thanks to the correct movement of the saw and the large number of strokes per minute on mechanical jigsaws, you can saw several parts of the same type at once in a package up to 30-40 mm thick.

By design, there are spring and frame mechanical jigsaws.

A spring jigsaw consists of a frame and a crank mechanism with a return spring. The simple design of such a machine allows you to make it yourself in a locksmith workshop.

A frame jigsaw consists of a movable frame on which a file is stretched, a table frame and a crank mechanism that drives the frame. A frame jigsaw provides slightly more favorable conditions for saw operation than a spring jigsaw.

Working methods and accessories for sawing

Devices make work easier and also increase accuracy. These include stop bars on the table, a vice on the workbench, and a wedge for clamping the part on the workbench.

For precise cutting at a given angle, a device called a miter box is used. This is a wooden box made of well-fitted blocks with precise slots located at angles of 90°, 45° and 30° to longitudinal axis box. When working in a miter box, the part is clamped with a clamp or wedge inside it so that the cut passes in the right place. The saw blade, inserted into the slot, does not have the opportunity to move to the sides when moving, which ensures an accurate and even cut.

First of all, you should pay attention to sawing, that is, the beginning of the cut. It is important to prevent the saw from jumping and start cutting exactly according to the markings. To do this, as shown in the figure, use the thumb of your left hand to support the saw blade above the level of the teeth.

Mechanical saws

A circular or circular saw consists of a frame with an electric motor and a spindle on which saw blades of various diameters, thicknesses and various shapes teeth depending on the nature of the sawing.

A necessary device is also a movable ruler, which is installed at the required distance from the plane of the saw blade and ensures straightness of cutting.

Cuts in the transverse direction or at an angle are made using a pusher that moves along the groove of the table. It has a rotating ruler with a clamping bolt.

To prevent the sawn strip from moving to the side, you need to press it against the ruler with your left hand, and push the entire pusher forward with your right hand. To cut at an angle, the ruler is set at the desired angle and secured with a clamping bolt.

Sharpening the teeth of saw blades is carried out according to the same principle as for hand saws.

In the absence of special discs, you can also use disc cutters for metal 1-2 mm thick, having previously sharpened them.

Resharpening can be done on a sharpening machine with a thin slotted wheel or, after releasing the saw first, with a round or triangular file.

The saw blade of a planing saw in its peripheral part has a constant thickness, and starting from 2/3 of the radius towards the center, its thickness decreases.

The disadvantage of these saws is that they do not maintain the direction of the cut well, leading it along an oblique layer or towards the dull surface of the saw. This drawback can be eliminated by carefully grinding the side surfaces of the disc.

When working on a circular saw, keep in mind that the rotating a large number rpm saw blade is great danger for the hands of the worker. Therefore, you should use devices, and when finishing the cut, push the material to be cut with a rack or pusher.

To avoid splinters and sawdust getting into your eyes while working, it is recommended to use safety glasses.

Working with a circular saw with unset or poorly sharpened teeth is ineffective and does not provide high-quality cutting. In addition, it is dangerous, since the disk can jam, and there are cases of the sawn part being thrown towards the worker. If the fuel is not properly charged, the saw will overheat and may become deformed and burst.

When installing the disk on the shaft, you need to check the sharpness and integrity of the disk - there are no cracks or broken teeth. Then you need to put the washers, tighten the nut by hand, locking the saw blade with a block, and finally tighten it with a wrench. After this, having turned the saw, you need to make sure that the disk does not hit, lower the guard, connect the current and test turn on the machine and cut.

It is necessary to set up, correct and remove the machine only after it has stopped completely,

Band saw is a high-performance machine for cutting shaped contours.

This machine consists of a frame on which the driving and supporting wheels of the saw blade and an electric motor are fixed, driving the driving wheel through the drive.

The tension of the saw band is adjustable, and its location is fixed with a stop and two rollers near the table.

The saw blade is made from a band saw blade, the width and size of the teeth of which are determined depending on the size of the machine and the type of work in the same way as for hand-held bow saws. Sharpening and setting are carried out according to the type of universal tooth profile.

To form a closed strip, the ends of the saw blade are connected by soldering with copper solder, brass or copper. The same applies to repairing torn fabric.

Soldering of band saws in the factory is carried out using a special electric welding machine.

In small workshops, you can successfully solder saws using the torch described in Chapter II, or using special pliers.

Can be recommended next process soldering: the place of soldering (the joint of the saw) is ground “on a mustache”, then, cutting out a strip of brass 0.3-0.4 mm thick along the width of the saw, moistened with water, sprinkled with borax powder (borax serves as a flux that protects the soldering place from oxidation when heated ) and placed between the surfaces to be soldered. Meanwhile, the massive jaws of the mites are heated in a forge or gas burner until light red color(800-1000 °C). The pliers are applied to the soldering area and squeezed.

The red-hot massive jaws of the pliers transfer heat to the saw, and it quickly heats up to the temperature of the jaws themselves. Brass and borax melt and, spreading over the joint, form a reliable connection.

After allowing the tape to cool in a clamped state until the solder becomes hard, the pliers are removed, and the soldering area is wiped with a wet rag so that it restores the hardness lost during heating (heated up). In this case, it is necessary to ensure that the rigidity of the soldering area is the same as the rigidity of the rest of the saw. If the joint turns out to be too hard after cooling, it must be heated again with tongs until a straw-colored tarnish appears and allowed to cool gradually. If it turns out to be too soft, then the pliers should be heated red-hot, warm the joint with them, and then cool the joint more sharply.

During cooling, it is important to ensure that the pliers do not become soldered to the saw blade. To do this, their sponges are lubricated with a solution of liquid glass and chalk before heating.

When installed on a band saw, the blade is placed on the upper and lower discs and tensioned with a special handle. Then, by rotating the upper disk, check that the web passes correctly over the disks and thrust rollers. If necessary, make adjustments using the device available on the machine. After this, the machine is turned on for a short time and additional adjustments are made.

It is necessary to ensure that the saw guard is installed and the blade guards are closed during operation.

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.

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.

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 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, 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.

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.

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, several unedged boards are cut from the middle zone of the log, 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.

At sector method Sawing operations first saw the log longitudinally along the axis of the log into pieces that have the form 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.

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.

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 P< 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 cross section 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

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.

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 and cross saws?

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

5. What cutting methods do you know?

Saws and sawing. Saws are made of high quality steel with cut teeth. For carpentry and joinery work, use a wide hacksaw, a hacksaw with a butt, or a narrow hacksaw; a saw with a cutting depth limiter (reward), a bow saw, and also a plywood file (knife) (Fig. 1).

A wide hacksaw is made from a steel strip 0.7 m long, 11 cm wide at the handle and 2...7 cm at the narrow end. The handle can be wooden, metal or plastic. A narrow hacksaw is used for cutting curved through holes in large-width parts. The jigsaw (Fig. 2) has a narrow and thin (0.3 mm thick, 1...2 mm wide) file with fine teeth. The file is fixed in an arched frame and can be easily removed. Thin parts (plywood) of a curved shape are cut out with a jigsaw. Before starting work, the end of the file is inserted into a pre-made hole, and the other end is secured in the frame. Sawing is carried out according to the markings. At the end of the work, release the end of the file and remove it from the hole in the part.

Hacksaws with a back are used for shallow sawing, for example, sawing grooves in wide workpieces to fit parts during their assembly. The top of the canvas is reinforced with a steel backing, which increases the rigidity of the canvas. The fine teeth have the shape of an isosceles triangle. Use a hacksaw to cut in both directions (Fig. 1, c).

Based on the shape of the teeth, saws for longitudinal, mixed and cross-cutting are distinguished (Fig. 3).

For sawing along the grain, saws with oblique teeth are used. They cut wood in one direction - away from themselves. The cavity between the teeth is called the sinus. The tooth pitch is the distance between the tips of adjacent teeth. The height of a tooth is equal to a perpendicular drawn from the top of the tooth to its base. There are three edges in the saw tooth (Fig. 3, a). In rip saws, the cutting is performed by a short cutting part - the front edge, and the side edge only separates the wood fibers.


Rice. 1. : a - wide hacksaw: b - the same, narrow; c - axing hacksaw; g - reward; d - plywood saw.

Rice. 2. Jigsaw.	Rice. 3. : a - saw elements; b - saw tooth angles; I - for longitudinal sawing; II - for mixed sawing; III - for cross cutting: 1 - side cutting edges; 2 - front edge; 3 - front cutting edge; 4 - step; 5 - top; 6 - sinus; 7 - height; 8 - line of the base of the teeth.

A bow saw is used for longitudinal and cross cutting. It consists of a beam frame with a tensioned saw blade. The latter is made of steel strip about 1 m long, 45...60 wide and 0.4...0.7 mm thick. The pitch of the teeth is 4...5 mm, the height of the teeth is 5...6 mm. The ends of the saw blade are fixed at the bottom of the beam frame posts. The canvas is stretched with a string of twine secured between the upper ends of the posts and twists. The saw blade is rotated using handles. This saw can be operated by one person. The cut is smooth and even. The teeth of crosscut saws cut the fibers, the side edges of the teeth, and the leading edge only separates them. In rip saws, the leading edge of the tooth cuts the wood. This is taken into account when determining the sharpening angles of saw teeth for transverse and longitudinal sawing.


Rice. 4. Sawing along the grain with a bow saw if the material is in horizontal position: to the right - the position of the worker’s feet while sawing.

Rice. 5. Stands: a - wooden with a movable support: b - metal with a roller; c - wooden with a roller.	Rice. 6. Sawing with a bow saw along the grain while securing the material vertically: a - the position of the worker’s hands during sawing; b - the same, feet.	Rice. 7. Cross cutting: a - sawing techniques; b - supporting the sawn part with your hand at the end of sawing.

In saws for longitudinal sawing of soft wood, the sharpening angle is 40...45°, in saws for hard wood - up to 70°, in cross-cut saws, the angle between the cutting edges of the teeth is 60...70°, and the sharpening angle is 45... 80°. Saws for mixed sawing have a sharpening angle of 50… 60°. The angles of the saw teeth are as follows: for longitudinal sawing - 60...80°, for transverse sawing - 90 -120°, for mixed - 90°. For sawing shallow grooves and sockets of tenon joints, the so-called reward is used. To regulate the cutting depth, it has a movable stop. Saw blade thickness 0.4…0.7 mm, length -100…120 mm.

Types and techniques of sawing. According to the type of fastening of the part in the workbench, they are distinguished: horizontal sawing along the grain, vertical sawing along the grain, horizontal sawing across the grain and sawing at an angle. When sawing horizontally along the grain, the workpiece is secured by pressing it against the table with clamps (Fig. 4) so that the sawn part protrudes beyond the edge of the workbench. In this case, the worker’s body should be slightly tilted forward, and the saw should be held vertically. First, they make a cut, moving the saw up several times, after the cut becomes deep, they begin sawing, moving the saw up and down. A wedge inserted into the cut prevents the saw blade from jamming.

When vertical sawing along the grain, the workpiece is secured in the workbench with a front or rear clamp (Fig. 6). The figure shows the position of the worker's legs during the sawing process. When sawing a thin board, it is clamped so that it does not bend, lifting it upward as it is sawed. Sawing begins with a cut, after which they work to the full swing of the saw blade, without pressing on it. Short workpieces are sawed starting from one end, and then, turning the workpiece over, from the other. Sawing long boards (along the grain) is carried out by resting their ends on stands (see Fig. 5).

Rice. 8. : a - correct; b - incorrect (cutting angle is too large); c - splintered cut, due to improper sawing, flakes and damage to the edges are possible; g - sawing along the fibers with a hacksaw; d - sawing with a bow saw using a template (miter box); e - sawing with a narrow hacksaw through drilled holes; g - template for trimming the ends of boards placed in bags; 1 and 2 - side posts - guides for the saw; 3 - board attached to the racks; 4 - fastening nail of the auxiliary device; detail A - the position of the hand on the frame of the bow saw during sawing.

When sawing the workpiece across the grain, the sawn end is pushed beyond the edge of the workbench (Fig. 7). Before starting sawing, make a gash; during the sawing process, monitor the position and inclination of the saw blade and ensure that the cut is straight and the sawn surface is flat.

To avoid flakes, the sawn part of the workpiece (Fig. 7, b) should be supported by hand at the end of sawing. For tenon joints or other parts that require mating at an angle of 45 or 90°, use a template (miter box) (Fig. 8, e). With repeated use, the cuts on the wall of the miter box may become excessively wide and it will not give the exact size of the angle. To extend the durability of the miter box, its side walls are made of hardwood boards. To trim boards (one width), use a special template (Fig. 8, jar). The side posts of the template serve as guides for the saw; they are made of hard wood. For boards of a certain width, a custom template is required. Sawing wood by hand is acceptable for small volumes of work.