Lesson plan on the topic "Sawing wood along the grain." Open lesson of industrial training "sawing wood along, across the fibers and mixed sawing"

It is difficult to cut lengthwise, because the tool in this type of sawing goes along the fiber without cutting it and, thus, bogging down in it. Naturally, sawing across or obliquely is much easier.

If you do not have a hand or table saw (circular) saw, you must use a rip saw. It differs from transverse in that: a) her canvas freely enters the wood to the full width, according to the principle of a jigsaw; b) each tooth of such a hacksaw is not equilateral or isosceles triangle, but rectangular.

Use different hacksaws, up to the beam. Avoid wide crosscut saws.

Before starting work, check the sufficiency and uniformity of the wiring. If the wiring is insufficient, the hacksaw will quickly get stuck, if it is uneven, it will immediately move away from the markup. Mark the cutting line.

When ripping, try not to speed up the process too much, position the hacksaw blade quite hollow to the top surface of the workpiece, not quite perpendicular. Do not apply significant pressure to the hacksaw. To adjust the course of the hacksaw, make superficial movements along the markup, making a "notch".

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 shavings.

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

2. Classification of types of sawing

Wood sawing is classified according to several criteria.

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

For longitudinal sawing the plane of the saw is parallel or approximately parallel to the grain of the wood. According to principle ripping sawmills, circular saws and band saws operate, on which logs and beams are sawn into boards, sawn timber is cut along the width or thickness in the longitudinal direction.

When cutting across the plane of the saw is perpendicular or approximately perpendicular to the grain of the wood. Sawing is performed manually with cross-cutting saws, hacksaws or cross-cutting machines used to cut the whips into round assortments, remove wood defects and wane areas from the ends of the lumber, and also give the lumber a given length and quality.

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

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

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

– cross-cutting with circular, chain and jigsaw saws;

– mixed sawing with circular saws, band saws and jigsaws.

Depending on the number of simultaneously operating saws in the machine, the method of cutting lumber is individual and group. Cutting logs and lumber with one saw is called an individual saw, and several saws are called a group saw.

For individual cutting logs are sawn into lumber by separate cuts on circular saws, band saws, vertical or horizontal machines. Cutting is carried out taking into account individual characteristics quality zones of each log. This method of cutting is effective when sawing valuable wood, cutting logs of large diameter 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 is distinguished by the peripheral zone of the saw, the middle zone and the central zone of the saw, as well as sawing by the upper and lower zones of the saw.

When working in the peripheral zone saw teeth protrude above the surface of the workpiece by an amount equal to approximately 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. Such sawing is used in milling and sawing machines.

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

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

- the collapse of the log;

- the collapse of the beam;

- sawing with a bar for one or two bars;

– sawing out of asymmetric timber (sleepers);

- break-up-segment and beam-segment;

- circular;

- sector.

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

When cutting with bar The log is sawn in two passes. On the first pass, one or two double-sided beams, unedged boards and two slabs are obtained from the log. On the second pass, the beam is disintegrated 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 sawn from the middle part of the timber are obtained as radial. Boards sawn from the peripheral zones of the timber are tangential. The rest of the boards occupy an intermediate position.

With the break-up-segment method of cutting on the first pass from middle zone logs are sawn out by several unedged boards, and two segments are obtained from the side zone.

With a circular method of sawing logs, each subsequent cut can be directed parallel, perpendicular or at any angle to the previous one. This allows you to get radial and tangential sawn timber. Sawing up a log can be carried out parallel to its longitudinal axis or parallel to the generatrix. The circular method is especially effective when cutting large-sized raw materials.

With the sector method of sawing, the log is first sawn along the axis of the log into parts that have the shape of sectors in cross section. Then, one bar is sawn 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 sawn timber is obtained, with an angle of more than 45˚, but less than 60˚, mixed sawn timber is obtained, and with an angle of more than 60˚ - radial sawing.

3. Widen the kerf

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

To prevent clipping of the saw, widen its serrated edge. The kerf width must 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 saws with lateral undercut are used, or saws are equipped with hard alloy plates, the teeth of which are sharpened with lateral undercut.

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

Round planing saws (Fig. 2, in), have lateral undercuts at 15¢ and 25¢.

Saw teeth with hard alloy plates (Fig. 2, G) have the shape of spatulas with a lateral undercut.

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

where b– cutting width, mm;

S– saw blade thickness, mm;

S’ is the widening of the teeth on each side, mm.

Values S' It is recommended to take according to 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 saw cut is a narrow gap formed by a saw. Cut chips width b falls into a cut wide b P.

Due to the elasticity of the wood, the walls of the cut are partially restored after the passage of the tooth. Cutting 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, overcoming the forces of friction 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 pass in the workpiece

where a is the tangential pressure on the tooth from the friction of the chips in the cut (the specific friction force of the chips against 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 aD are found from (Table 1).

Table 1

Tangential pressure a on the saw tooth from chip friction in the kerf

	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 by 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 in the interdental cavities and taken out of the cut.

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

when sawing with frame saws

; (3)

when sawing with band saws

when sawing with circular saws

where t max is the maximum cutting height.

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

On 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 cut with flattened teeth. The areas of the layers cut by the 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 accepted

, (6)

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

7. Saw tooth shape for ripping and cross cutting

The sawing rule can be formulated as follows: when a tooth is inserted into wood, it is first necessary to cut the fibers, and then, with the least resistance, separate them from the array 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 face tends to press the incised chips from the array. Since the strength of wood in the plane of the fibers is weak, the incised part of the chips is chipped and falls into the interdental cavity.

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

When cutting across (Fig. 5, b) the work of cutting wood fibers is performed by the side cutting edges. To do this, the teeth are made with lateral sharpening. When the teeth are inserted into the wood to a depth of 0.8 mm, the stresses at the bottom of the cut, created by the beveled front edges of the teeth (Fig. 5, in), reach the ultimate shear strength along the fibers, and the cut fibers are sheared either to the left or to the right along the fibers.

When sawing wood transversely, 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 teeth of the saw are sharpened as follows: the cutting angle at the main cutting edge d > 90 ° , and the side cutting edge is made with an oblique sharpening anglej = 40...45 ° .

Control questions and tasks

Specify the number of the correct answer

1. When sawing wood circular saw, in which the thickness of the disk is 2 mm and the broadening of the teeth per side is 0.6 mm, the width of the cut is, mm

2. Widening of saw teeth is achieved by

1) divorce,

2) flattening,

3) use of saws with lateral undercut,

4) soldering plates with their subsequent oblique sharpening,

5) increase the thickness of the saw.

3. What is the difference between rip saw and cross cut saw?

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

5. What sawing methods do you know?

K category: Joinery

Sawing wood along the grain

To obtain a workpiece of the desired width and thickness, the board is sawn along the fibers. But first, the workpiece must be marked and fixed in the back clamp of the workbench (Fig. 1).

The rules for sawing wood along the grain have much in common with the rules for sawing across the grain, but there are some differences: the working posture is somewhat different, the position of the body is straight, the rhythm and pace of sawing are faster.

Here is the sequence of work when sawing the workpiece along the fibers:
Fastening the workpiece and the working posture of the carpenter.
1. Mark the cut points.
2. Clamp the workpiece vertically into the back clamp of the workbench. The edge of the workpiece should not be higher than shoulder level.
3. Prepare the instrument and take the established pose.
4. Make a cut along the marking line. Do not forget that at the blade of a bow saw you need to hold not a hand, but a block.
5. Start sawing with rhythm and pace.

Rice. 1. Sawing wood along the grain

When working, it is necessary to constantly monitor the position of the saw blade relative to the workpiece along the marking line, workbench, ruler. Make sure that the bottom of the cut is approximately at chest level (after all, the workpiece can always be raised and lowered). Follow the rules safe work. Before the end of sawing, work more slowly, without pressure, so as not to split the workpiece and injure your hands.

The quality of work can be checked with a ruler, a square.

When sawing along the fibers, the following types of marriage may occur:
1. The cut is not straight.
Causes:
a) you did not follow the marking line;
b) strongly pressed the saw;
c) did not operate the saw during operation.
2. The cut is not at right angles to the wide side of the workpiece.
That's why:
a) you started work not exactly at a right angle to the edge of the workpiece;
b) they sawed incorrectly, not along the workbench, not according to the markings;
c) did not control the saw blade.

Remember!
To avoid marriage when sawing, you must work carefully and strictly follow the established rules.

Of course, it is better to work without marriage. But if there are still some errors, do not worry!

Deficiencies can be eliminated with a planer planing.

Tools for work.

For sawing wood along the fibers, hacksaws, bow saws, tenon saws are used (Fig. 2, a, 6, c). For such saws, the teeth are inclined, have the shape of a triangle with an acute angle (Fig. 2, d). Therefore, they saw with these tools only in one direction, where the teeth are inclined (usually away from themselves). When moving backwards (toward yourself), the saw does not cut wood, this is an “idle” move.

Rice. 2. Saws for sawing wood along the fibers: a- hacksaw; b - beam; in - spiked; g - the shape of the teeth

But very often when working there is no time (or difficult) to change the tool, although you have to cut wood along the fibers, and across them, and obliquely. For these purposes, saws with a mixed tooth are used. The shape of the tooth is a right-angled triangle with a right angle directed towards the sawing.

Sawing technique. When sawing wood along the grain, as well as when sawing across the grain, the width of the cut depends on the thickness of the blade, the height of the teeth and their separation. The already drunk, that is, the thinner the canvas, the smaller the teeth and the smaller the divorce, the easier and faster it is to work.

Rice. 3. Sawing wood along the grain

Fix the workpiece in the clamps of the workbench and saw along the marking lines as shown in Fig. 3. The teeth of the saw should be tilted in the direction opposite to the hand, that is, away from you.

- Sawing wood along the grain

Depending on how thick the solid wood is chosen, one or another saw is used. And the sawing technique used during work depends on the fixing of the workpiece on the workbench. If you fix the workpiece on the workbench horizontally, and at the same time position the saw perpendicular to the part itself, then this technique is called horizontal. At the same time, the cutting place should slightly extend beyond the surface of the workbench so that it is impossible to damage the working board during work, and it will be much more convenient to perform the procedure.

A feature of the cross cut is that it does not pass along the fibers, but across them. This increases the likelihood of spalling both from the left part and from the sawn off part. Well, if the split occurred on the piece being sawn off - then you can easily remove excess wood from the desired part.

But if the spall occurred exactly where it is necessary to have a flat, smooth surface, then you will either have to restore the wood or cut out a new part.

A thin hacksaw with a “mouse tooth” will help to avoid such troubles.

When cutting, several movements are made with a hacksaw blade along an already marked line, thereby strengthening the blade in solid wood. During further work, only the movements of the hacksaw are corrected if its blade tries to get around a knot or a difficult area. There should be no physical effort with proper sawing: only a slight uniform pressure on the hacksaw during smooth movements will ensure an even cut.

The workpiece is best positioned so that the cut piece is on the left side. At the end of the sawing, the free left hand will more easily hold the unnecessary piece and prevent it from falling to your feet. All movements during sawing out of the part are done in a swing, that is, completely guiding the hacksaw blade along the cut.

You can cut along the workpiece (Fig. 57, a) and across it (Fig. 57, b), along the fibers and across, at an angle.

Rice. 57. Sawing a workpiece with a bow saw: a - along the fibers; b - across the fibers.

You can use a sawing box - shtoslada (or miter box), in the walls of which cuts are made at an angle of 30, 45, 60 and 90 ° (Fig. 58).

Rice. 58. Sawing with a saw box.

The board is placed in the sawing box with its end to the cut line and pressed against one of the sides. The main thing is that you need to cut with a sharp, well-spread saw, evenly and freely, without making sudden movements, not too hard, but firmly pressing the saw blade to the bottom of the cut. At the very end of the cut, the sawn off piece should be held by hand so that it does not break off under its own weight.

A wide saw is needed for sawing boards and bars. The teeth of such a saw are obliquely sharpened and made in the shape of a triangle. The teeth of a narrow hacksaw should be set apart. This saw is used for sawing tess and shalevka.

From the book: Korshever N. G. Works on wood and glass

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Details Category: Woodworking

Sawing with a carpentry saw

Sawing is one of the most responsible operations in the process of wood processing. The quality of manufacturing parts and saving wood largely depend on the quality of its implementation. By doing the sawing correctly, you can reduce the allowances for subsequent planing and the time to manufacture the part.

Hand joiner's saws are divided into stretched with a thin saw blade and loose with a free, thicker blade. Tensioned saws include all bow saws, and to saws with a free blade - hacksaws.

You can watch an excerpt from the film below. hand saws and hacksaws. Full version movies can be downloaded.

According to the direction of cutting the fibers are distinguished transverse, longitudinal and mixed sawing.
At transverse sawing the direction of the cut (cut) is perpendicular to the fibers.
At longitudinal sawing parallel to the fibres. At mixed sawing - directed at an angle to them.

cutting element any saw is tape with cut teeth. Each tooth is cutter. Saw teeth are also characterized step and height: height- the shortest distance between the base and the top of the tooth; step- the distance between the tops of adjacent teeth.
For cross cutting blanks are used saws, in which the teeth have straight triangular profile, and for ripping - saws with inclined profile teeth.

Hand saws are produced with small and large teeth.

Have saws for transverse When sawing, the sharp cutting edges of the tops of the teeth alternately incise the wood fibers and carry out the chipped particles of wood in the form of sawdust.
Have saws for longitudinal sawing, the cutting edges of the inclined teeth protruding forward cut off the fibers of the wood and the cut particles are chipped along the fibers, forming sawdust. The figures below show the shapes of the teeth and the patterns of cutting the fibers with longitudinal and transverse saws.

Technical characteristics of saw teeth

Tool	(triangle)			Tapering angle
Bow saws
transverse	Isosceles
prom	oblique
	Rectangular
small-toothed	Rectangular
Vykruzhnaya	Rectangular			50-60 or 80-85	Straight or small bore
Hacksaws
	Isosceles or rectangular			Depends on the shape of the teeth
	Rectangular
Obushkovaya	Rectangular
Reward	Isosceles

Purpose of sawing tools

Types of hacksaws and special saws	Purpose	Appearance and device
Wide	Cross cutting rough
Narrow (kurkovy)	Through-cutting flat and curved sawing
Sheath (slotted)	Fine sawing of shallow cuts and fitting products during assembly
Award (canvas from scraps of old saws)	Shallow cutting grooves

When sawing, the saw blade rubs against the walls of the separated parts of the wood. And so that it is not clamped in the cut, the saw teeth must be divorced(tooth setting) i.e. alternately bent in different directions. This makes the kerf slightly wider and makes sawing easier. The following shows the views wiring for cutting teeth.
There are wiring different forms. In the figure below on the left ( a) shows the main types of wiring. On the image b and in- shows correctly set teeth for the transverse ( b) and longitudinal sawing ( in).

When sawing blanks, they retreat from the marking line by 2-3 mm.

The hacksaw blade should move at right angles to the workpiece.

Sawing control carried out along the marking line. It should remain to the left of the cut on the workpiece.

For more precise sawing of wood or plywood blanks, saws with fine teeth are used. The tilt of the saw is shown in the figure.

They work with a hacksaw. The marked workpiece is placed on a board (1) on a carpentry workbench with a stop (2). The workpiece is pressed against the stop with the left hand, and washed down with the right hand. At the same time, the hacksaw is pressed against the stop and make several short smooth movements towards you. After sawing, the hacksaw is moved along its entire length, combining with the marking line of the cut.

By moving the saw along the line, an incision is made, then the bar is removed and the part is sawn off. At the end of sawing, the pressure on the saw is loosened so as not to chip the wood fibers at the exit of the saw. The position of the hands when sawing is shown in the figure.

For precise sawing of bars and boards at angles of 90 °, 45 °, 60 ° and others, miter box . miter box has a grooved shape. It consists of a bottom 1, two sidewalls 2, between which the sawn workpiece 3 is clamped. On the sidewalls, cuts are made at the desired angle. Saw blade 4 is inserted into these cuts and sawing is carried out at the desired angle.

Application miter box eliminates part marking, improves sawing accuracy, reduces the time spent on part marking, thus increasing labor productivity. The use of a miter box is especially effective in mass production details. The miter box may look like the one shown in the photo.

For ease of sawing, they also use tsulagu. Tsulaga very quickly made from a sheet of plywood or board and two bars. Thanks to the lower bar, it is easy to press it against the tabletop, and the upper one serves to stop the workpiece. Tsulagu can be made with a movable stop for sawing a large number the same details.

Sawing techniques using tsulagu, miter box, stops are shown in the figures.

For sawing different workpieces and curly sawing, different saws and hacksaws are used. Examples are given in the figure.

Hold the workpiece securely while sawing.
Use stops, miter box and other devices.
Sawing only with a serviceable, sharply sharpened saw.
Do not skew the saw when sawing.
Do not make sudden movements with the saw.
Do not keep left hand close to the saw blade.
Place the saw on the workbench with the teeth facing away from you.
Do not blow off sawdust or sweep it away by hand. Use only a brush.