For many centuries, humanity has been using wood as a building material and, despite the constant emergence of new ones, modern materials, the popularity of natural wood is not decreasing at all.
How to choose the right lumber from a huge assortment? What causes the differences in price and quality?
Quality finished materials made from wood depends on many parameters - the type of wood and the quality of the original timber, the professionalism of the machine operators, compliance with the technology of drying lumber and the production of finished products. Another factor that has a significant impact on the quality and appearance lumber, as well as their mechanical properties, is the method of cutting wood that determines the texture of the board.
There are several types of wood cutting - tangential, radial, rustic and transverse, of which the first two are most widespread. To understand the difference between types of cuts, you need to have a good knowledge of the structure of wood and understand the technology of sawing wood.
In cross-cutting, wood is cut across the grain. The method is used in production artistic parquet. A rustic cut is any cut made under acute angle to the direction of the fibers. The method is used in the production of lumber for rustic flooring - the most heterogeneous and original in pattern and shade.
With a tangential cut, the cut plane runs tangentially to the annual layers of the tree at some distance from the core. Since wood fibers, as a rule, do not have a single direction, they create natural patterns on the surface of the board in the form of fancy “arches”, “curls”, “rings”. The texture of the resulting board tangential cutting heterogeneous, possible presence of wood pores. Some of the dry boards may develop delaminations on the surface after finishing planing. After tangential cutting, boards are characterized by higher coefficients of shrinkage and swelling; moreover, such a scheme for sawing logs allows an increase in the useful yield, which in turn leads to a reduction in the cost of the board.
For radial cutting of wood, the cutting plane is located perpendicular to the annual rings. With this method, the texture of the board is quite uniform with minimum distance between annual layers. This not only creates beautiful drawing, but also helps to increase the strength of lumber.
Radial cut boards have good resistance to external influences, have greater resistance to deformation and wear resistance than tangential cut boards.
The shrinkage and swelling coefficients of radially cut lumber are 0.18% and 0.2%, respectively, which is almost two times better than that of tangentially cut lumber. The reason for this phenomenon is that for radial cut boards, shrinkage and swelling occur along the thickness of the material, in contrast to tangential cut boards, in which dimensional changes occur along the width of the board. This explains the fact that finished products (parquet boards, floor boards, block houses, imitation timber, lining) made from radially cut lumber have front surface almost no gaps are observed, which is not excluded in products made from tangentially cut lumber. To obtain laminated veneer lumber by splicing wood without knots, blanks and boards of radial and semi-radial cuts are used, since the mechanical and geometric characteristics of the timber depend on the resistance of the fibers, which increases when gluing layers with multidirectional annual rings with an inclination angle of up to 45°.
The average useful yield of radial cut boards is only 10-15%. This explains their high cost. Radial cutting includes lamellas in which the angle between the annual rings and the blade is 60-90°. If the specified angle is in the range of 45-60°, such boards are classified as semi-radial cut. The best performance properties are found in lumber in which the angle between the annual layers and the cutting plane is 80-90 degrees. Taking into account semi-radial cut boards, the useful yield coefficient can reach 30%.
Typically, when radial sawing, the log is initially sawn into quarters, and then from each quarter, boards are sawn off alternately from two layers. For sawing logs in a radial way, for example, UP-700 longitudinal sawing machines can be used. The microprocessor control and optimization system UP-700 is important, which is used by technologists to determine the percentage of yield of radial cut boards based on the criteria for optimizing the maximum yield finished products, as well as the conditions of radial and semi-radial cutting.
Comparing radial and tangential types of cuts, several conclusions can be drawn:
as well as three additional types:
Scheme of types of log cutting
Radial cut- this is a cut in which the axis of the cut passes through the core of the log and, as a result, the lines of annual rings in the section of the board form an angle of 76 - 90 degrees. with its faces (two main planes of the board). The wood of radial cut boards is quite uniform in color and texture. Such boards practically do not deform when dried and do not swell when moistened, because the change in wood dimensions occurs mainly along the line of the rings (across the grain), and for radial cut boards they are located along the thickness. Radial cut lumber has the highest performance indicators compared to lumber of other types of cut.
Tangential cut- This is a cut that is made along tangents to the lines of the annual rings of the trunk at some distance from its core. The surfaces of such boards have a pronounced texture and a bright wave-like pattern of annual rings. For tangentially cut boards, the coefficients of shrinkage and swelling from moisture are twice as high as for radially cut boards, which causes their significant deformation when the humidity state changes. For this reason, tangential cut boards are less preferable for use in wet conditions than radial cut boards.
Rustic (semi-radial) and mixed cuts- these are cuts with signs of two main types of cuts at the same time: radial and tangential and, as a result, have indicators averaged between them. In a rustic cut, the lines of annual rings have the form of straight lines located at angles of 46 - 75 degrees. to the layers, and in a mixed cut these lines change from straight at the edges (along the width) of the board to arched in the middle.
Central cut- This is a cut made directly in the center of the trunk and including its core. Considering that the core of the trunk consists of the least durable wood, center-cut lumber has the most heterogeneous structure in terms of strength of all the types considered.The main products of sawmill production are sawn materials. Minor – sawdust and wood chips, which are used for the manufacture of particle boards, fuel pallets, etc.
If you follow the “letter” of GOST 18288-77, the materials that are produced at the sawmill include:
Lumber– wood blanks with two plane-parallel layers and certain dimensions specified in the standards.
Blanks– edged lumber with wane and edges that are sawn perpendicular to the facets in whole or in part. These include plates (half sections of logs) and quarters;
Lagging– material with an internal sawn and an external unsawed (or only partially sawn) face. Plank obapol - with a convex part sawn half or more, used for the production of fence pickets and in the construction of formwork, scaffolding, strengthening mine workings;
Gorbyl– the outermost parts of the log that remain during sawing. The croaker differs from the obapole in that certain ratios of thickness, width and minimum length requirements are not established for it. Most often used as an environmentally friendly fuel or for the production of wood chips.
Plast– wide longitudinal surfaces of the sawn log and any side of the lumber square section. The inner surfaces are those closest to the core of the log, and the outer surfaces are the surfaces that are farthest from the core.
Edges– narrow surfaces, the processing method of which determines the division of lumber into edged, partially edged and unedged;
Edge– the intersection of adjacent two sides of lumber;
Ends– surfaces perpendicular to the edges.
Depending on the location of the layers to the annual layers, lumber is divided into:
A radial cut is a cut in which the cut passes through the core of the log, at right angles to the rings. In this case, the surface of the layers is uniform in texture and color, and the distances between the annual rings are minimal.
Boards made by radial sawing have excellent quality indicators (swelling coefficient 0.2%, shrinkage coefficient 0.19%). Therefore, radial lumber is in demand for the manufacture of parquet, timber, lining, block house - the finished products have practically no gaps, in comparison with similar tangentially cut products.
Lumber made by radial sawing is the most durable and expensive. They are used in construction, in the production of massive panels and window beams. The yield of a radial board is usually small (30% is already a good indicator), and depends on the method chosen for cutting the log. Optimal scheme cutting to obtain radial and semi-radial boards is considered as follows.
When cutting a log tangentially, the saw passes tangentially to the annual layers of the trunk without touching the core of the tree. Such lumber has a wavy pattern, which clearly shows the patterns of annual rings and beautiful wood structure.
For tangential boards, the coefficient of shrinkage and swelling is at least twice as high as that of radial material, so their cost is more affordable and the quality of the products is lower. Such boards are not used for the main building elements - the wood can be deformed and the product will “lead”. But, nevertheless, due to its high aesthetic qualities and low price, the demand for tangential wood is high - it is used for decorative finishing furniture, doors, building elements.
Since time immemorial, people have known about the high technological and decorative qualities that wood has. Indeed, nature has rewarded us with truly valuable material, available for processing by the most simple tools(for example, with a knife or saw).
Talking about positive properties of this material, primarily focus on its low thermal conductivity. In addition, wood is distinguished from many other materials by its fairly high strength and resistance to various substances, ease of processing.
Wood is a “breathing” material. If it is soaked in a protective solution, it can be protected from rotting. For finishing work wood material is also of interest because it has a unique texture pattern that decorates finished goods and giving them an attractive appearance. The characteristics and properties of wood of various species as a building material are simply invaluable. For example, it can be noted that timber lumber, as well as round wood withstand the loads that fall on the entire structure of the house. The only difficulty you may have to face is initial stage, is to decide the issue of choosing the right type of wood for making beams, rafters, various kinds of racks and joists, and trusses. In addition, select suitable material will be necessary before you begin making stairs, windows and doors. Should be prepared in advance wooden boards for covering the ceiling and floor, constructing partitions.
Read also: Kinds door hinges and their correct choice
The tree trunk provides a source of material for making basic building elements such as beams and boards. All other parts of the tree - branches and roots - can be used, but to a limited extent due to the complexity of their shape and the difficulties that arise during processing (for example, in the manufacture of fittings, small household items).
In order to obtain high-quality boards and beams, it is necessary to perform the sawing correctly. There are 3 types of cuts: radial, transverse and tangential. Types of wood cuts are shown in the figure.
On a cross cut you can see concentric circles, on a radial cut - longitudinal stripes, a tangential cut is presented in the form of cone-shaped winding lines. Identify the growth rings on different types cuts, as we see, do not seem difficult.
Lumber - wood materials (beams, boards and whetstones) obtained by sawmilling. There are lumber of radial, tangential and mixed sawing. Lumber with sawn edges is called edged, while lumber with unsawed edges is called unedged.
Large, high-quality logs (these are logs from the bottom, butt part of the tree) provide the most valuable lumber. When sawing such logs, you need to decide on the thickness of the resulting boards in order to maximize the volume and cost of the resulting material. Since prices for lumber depend on its thickness, and in addition, when sawing at thick timber less sawdust is produced, this decision seriously affects income. However, if the quality of the thick material is lower, even if the best edge is almost pure, then sell it for good price It won't be easy. The sawyer should try to reduce the size of the material being cut when he sees that the quality of the wood begins to decline.
If the log is good, producing large lumber and railroad ties from the central part of the log is, to say the least, unwise. Because the price of timber is always less than the price of boards.
For logs high grades Circular sawing is recommended. In fact, cutting to the taper of the log and angling the log so that the cut is parallel to the bark is recommended for all "good" edges. The result will be clean wood along the entire length, more valuable pieces of lumber, and this will avoid the need to saw the clean wood later into short pieces. When you reach the low-grade part of the log, move on to the shape of the beam and minimize the operation of cutting the beam on the sides.
Durable but low-quality logs should be cut as quickly as possible. These logs are of little use - the profit is very small, or none at all, which means that these logs need to be removed from the machine, the faster the better. Any sawing method is suitable here. Most often they are sawed onto timber, or simply sawed right through. Turning logs into in this case In general, it is better to reduce it to absolute zero.
Fragile logs provide such an insignificant profit and such a huge risk of breaking the product that it is better not to deal with them at all.
Logs of average quality can produce a significant amount of good lumber, and here a lot depends on the sawyer, on how he will turn the log. Here the decision to rotate the log is critical to profit.
First, you need to select the worst part of the log and cut it without taking into account the runoff. But you can't cut too much on this side. For small logs, you generally need to cut one layer, that is, cut once along the entire length of the log, or a layer and a short board, and then turn the log over to the opposite side.
Another way is to choose the best side of the log and start cutting taking into account the taper of the log. Then this particular part is sawed for a long time before the log is turned over.
Lumber is sawed from one side until the sawyer expects that the next board on that side of the log will be at least as good as the boards that can be obtained from the other side. There is an exception: if you start sawing from the worst edge of the log, you must saw until you get a completely smooth cut surface in order to turn the log over onto it. In other words, the good side of the log needs to be cut deeply, and the bad side is simply removed with a layer or layer and one board.
If we take a log with a diameter of 60 cm, although this is true for all logs of any size, when sawing with a 180° turn, we get 8 boards that need to be additionally trimmed on the sides, and using less effective method, always turning to the adjacent face, we get 13 such boards. This circumstance alone can already be a significant argument in favor of turning the log 180°, especially for small enterprises. In addition, this method of sawing produces more wide boards, which are usually more valuable. When flipped over to the adjacent edge, you get 8 tangentially cut boards, which are subject to severe warping when drying. Further, if it is walnut or red oak with a narrow sapwood part, then with a 180-degree turn of the log we will get 10 boards with sapwood, with another turning method - 13 boards. Sapwood causes problems during drying. And when the log is turned 180 degrees, the internal tension of the wood is relieved, which results in the avoidance of cracks and cracks.
Flipping to an adjacent face may be easier, but with economic point From the point of view and from the point of view of sawing safety, rotating the log by 180° is more advantageous.
After two opposite edges of the log have been sawn, you need to move on to the third and fourth. As usual, the worst of these edges is cut first, without taking into account the taper of the log. However, a good quality edge should always be sawn parallel to the bark to increase yield. good lumber from a log.
The width of the first layer when sawing from all four sides of the log is critical.
If the edge is of good quality, that is, the first sawn board can be classified as good grade, Then minimum width The sawn timber should be 15-1 cm. Of course, this depends on the size of the log itself. To take into account further processing of the board, planing or even cutting on the sides, 15-1 cm is recommended, and not 15 cm.
If the edge Bad quality, then it makes sense to cut boards with a width of at least 10-1 cm. The length of such boards should be at least 1.2 m. In general, you need to produce boards of no less length at your sawmill.
When it comes to logs of frankly poor quality, it makes sense to cut them from the “belly” or from the “ears”, rather than looking for a good edge. The "ears" are usually removed with 1 or 2 passes of the saw, revealing a smooth surface inside the log. Cutting from the “belly” requires more manipulation, and as a result you get several short but clean boards.
Timber has a number of advantages compared to thin boards. The timber often has a beautiful wood pattern that buyers love. When dried, it dries out half as much as boards (3% versus 6% for boards). Less cracking during drying. When humidity changes environment the beam is more stable. When the floor is covered with it, it hardly wears out.
Also, when sawing timber, the exit useful product from logs is 20% lower. Its production speed is much lower. It requires 15% more drying time. The timber dries out in thickness 2 times more than narrow boards. Sharp branches that remain in the timber, in contrast to round branches in the boards, greatly reduce the strength of the material.
Radial called a cut, in which the plane of the cut passes through the core of the trunk. The wood of such boards is quite uniform in color and texture, the inter-ring dimensions are minimal. Radial cut boards are resistant to external influences, are practically not subject to deformation and have high wear resistance. The radial cut board has a shrinkage coefficient = 0.19% and a swelling coefficient = 0.2%. These indicators for radially cut lumber are twice as good as for tangentially cut boards. For a radial cut board, the process of shrinkage and swelling occurs along the width of the fibers - the thickness of the board, and for a tangential cut along the width of the board because the fibers of the “tangent” are located along the width. Accordingly, at the floor board, parquet board, imitation timber, block house, lining of radial cut, there are practically no cracks compared to similar products of tangential cut. Since the yield of radial cut boards is 10 - 15% of the total volume, their cost is quite high.
Radial cutting of wood is a method of cutting a log in which all the fibers in the board run along the direction of the annual rings. When radially cut, lumber has the best physical and mechanical properties. The strength and hardness of wood with radial cutting is higher than with tangential cutting.
The yield of radial cut boards is usually small (does not exceed 30%). On the UP-700 longitudinal sawing machines, the yield of radial cut boards reaches 60%. This high rate is achieved thanks to the cutting optimization system. By choosing among the optimization criteria the maximum output of a radial cut board, the conditions of radial and semi-radial cutting, the technologist determines the percentage of output of the radial board.
Radial cutting can also be done using other equipment. But the percentage yield of a radial cutting board on other equipment depends on how the operator cut the log. Typically this figure is significantly less than 50%. Due to the microprocessor control system and optimization system on the UP-700, you can obtain the maximum possible number of radial cut boards.
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| Cut texture: 1 - tangential cut; 2 - radial cut; 3 - semi-radial cut. | ||
Tangential called a cut, in which the plane of the cut passes at a distance from the core, tangentially to the annual layer of the trunk. Such boards have a pronounced texture and a rich wave-like pattern of annual rings. Tangential cut boards have higher shrinkage and swelling rates, but are more affordable.
The sawing operation involves decisions about board thickness, turning the log, and compensating for the log's taper. This depends on many factors: the type of wood, the quality of the log, its size, the design of the machine and the grade of lumber that needs to be obtained. There are 3 standard schemes cut:
Simple sawing
The log is sawed until its core is exposed, and then turned 180° and sawed to the end. This is the fastest and easiest sawing method; however, with this method, each piece of lumber must be cut on the sides. Lumber sawn in this way is somewhat wider and heavier, of lower quality and has a lot of waste. It is extremely susceptible to warping during drying. Therefore, simple sawing or sawing through is justified only in the case of very low quality logs, when all of the above disadvantages are no longer particularly important.
Circular sawing
When sawing in a circle, a cut is first made, and the log is turned over to a new edge, sawed, and turned over again until at least 5 turns have occurred. From a financial point of view this is best way for logs of medium and high quality, although at the same time, at some sawmills it is difficult to carry out such a log turnover, and the daily productivity will be low. Of course, a machine with hydraulics solves this problem.
Sawing timber
Sawing timber maximizes the productivity of the sawing machine (number of boards per day) and, as a rule, is used in industry when working with medium and medium-sized logs. large sizes. In this case, the log is sawed first as when sawing in a circle, but the central part of the log, which can have dimensions of 18x23 or 25x25 and so on, is either transferred for processing to another machine according to technological line, or sold as a large and heavy timber. Basically, logs of medium and low quality are sawn in this way, when it is impossible to obtain valuable lumber from the central part of the log. This saves time and effort in producing a product that is not of very high quality and therefore not of very high price.
Deciding which side of the log to start cutting on, which cut surface to open first, is the most important part of sawing. We divide the log into 4 sides, each of which extends along the entire length of the log and occupies a certain part of its circumference. The choice of the first face is determined by the position of all the others.
When sawing in a circle and sawing timber, two basic rules apply:
The worst edge of the log is sawn first without any consideration for the taper of the log. Counting the slope of a log means raising or tilting the log so that the saw cuts parallel to the bark. Since this is the worst part of the log, this means that it will produce short boards and a lot of slabs. Since we do not take into account the taper of the log, this gives us the opportunity to do the opposite, the best side The logs should be sawed parallel to the bark, without lifting or tilting the log. This means that from this best part of the log more boards of high quality will come out, which also match the length of the log.
Cut the best edge of the wood first, taking into account the taper of the log. This means that the log needs to be raised or tilted so that the first cut is made parallel to the bark.
The end result of both methods will be approximately the same, but the second method has one advantage. In this case, it is easier for the sawyer to rotate the log, because the open edge is the cleanest and has no defects. In the case of the first rule, the best part of the tree is the part opposite the open edge. It is not visible, and it is impossible to accurately rotate the log. Usually, if the wood is of good quality, then both rules work almost the same. But if you encounter a worse log, it is better to use the second rule.
Many of the techniques used for sawing hardwood are also suitable for softwood. But there are also some differences. Of course, safety considerations must take precedence over the desire to produce as much product as possible.
Position the log so that when sawing, minor defects in the material appear inside the lumber, of course, if these defects are not so serious as to affect the strength of the final product. If possible, you should cut so that all knots and defects are located on one side of the lumber, while the other side remains 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.
Select the worst side of the log and start sawing from there, producing short lumber. The first lumber will be the worst and therefore must be short to be salable.
After the log has been sawn from the bad edge along the entire length of the log, you need to move to the opposite edge and cut 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 do not need to be transferred to large building structures.
You should always turn a log from one side to another if the lumber from the new side is best quality than from the one that was just sawed.
Logs from waste. It is necessary to cut the “ears” in one pass of the saw, then turn the log over onto its “belly”, perhaps at least a few short boards can be made from it.
