It makes no sense to make the same calculations several times if the original data does not change. A round log with a diameter of 20 cm and a length of 6 meters will always have the same volume, regardless of who and in what city is counting. Only the formula V=πr²l gives the correct answer. Therefore, the volume of one OCB will always be V=3.14×(0.1)²×6=0.1884 m³. In practice, in order to exclude the moment of carrying out standard calculations, cubes are used. Such useful and informative tables are created for various types of lumber. They help to save time and find out the cubic capacity of round timber, boards, CBM, and timber.
The name of this building guide is due to the fact that the volume as a physical quantity is measured in cubic meters (or cubic meters). For a simpler explanation, they say "cubature", respectively, the table was called "cubature". This is an ordered matrix, which contains data on the volume of one product for various initial parameters. The base column contains sections, and the row contains the length (molding) of the material. The user only needs to find the number located in the cell at their intersection.
Let's consider a specific example - a cubic yard of roundwood. It was approved in 1975, is called GOST 2708-75, the main parameters are diameter (in cm) and length (in meters). Using the table is very simple: for example, you need to determine the V of one log having Ø20 cm with a length of 5 m. At the intersection of the corresponding row and column, we find the number 0.19 m³. A similar cube for round timber exists according to another standard - ISO 4480-83. Reference books are very detailed in increments of 0.1 m, as well as more general, where the length is taken in 0.5 m.
little secrets
The very use of the cube is not difficult, but the main nuance is the correct data. Round wood is not a cylinder, but a truncated cone, in which the lower and upper cuts are different. One of them can be 26 cm, and the other - 18. The table assumes an unambiguous answer for a particular section.
Various sources suggest doing it in two ways: calculate the average value and take the volume from the reference book for it, or take the size of the upper cut as the main section. But if the tables were compiled according to certain standards, then they must be used in accordance with the accompanying instructions. For a cubature GOST 2708-75, the diameter of the upper saw cut of the log is taken. Why is the raw data moment so important? Because with a length of 5 meters for Ø18 cm we get 0.156 m³, and for Ø26 cm - 0.32 m³, which is actually 2 times more.
Another nuance is the correct cubes. If complex formulas for truncated cones were used in the GOST 2708-75 table, calculations were carried out, and the results were rounded to thousandths, then modern companies that make up their own cubes allow themselves “liberties”. For example, instead of 0.156 m³, there is already the number 0.16 m³. Often, frankly erroneous cubes are posted on Internet sites, in which the volume of a log 5 meters long with Ø18 cm is indicated not 0.156 m³, but 0.165 m³. If an enterprise uses such directories, selling roundwood to consumers, then it makes a profit, in fact deceiving customers. After all, the difference in 1 product is significant: 0.165-0.156=0.009 or almost 0.01 m³.
The main problem of round timber is a different section. Sellers offer to resolve issues with calculations in the following ways:
- calculation of the volume of each unit and summation of the obtained values;
- storage method;
- finding the average diameter;
- method based on the density of the wood.
1. It must be said right away that the first of the indicated options gives the correct results. Only the calculation of the volume of each log and the subsequent addition of the numbers guarantees that the buyer will pay for the timber that he will receive from the company. If the length is the same, then it is enough to find the cross-sectional areas of all the trunks, add them up, and then multiply by the length (in meters).
2. Warehousing method.
It is assumed that the stored round timber occupies a part of the space that has the shape of a rectangular parallelepiped. In this case, the total volume is found by multiplying the length, width and height of the figure. Given that there are voids between the stacked trunks, 20% is subtracted from the resulting cubic capacity.
Minus - the acceptance as an indisputable fact that the tree occupies 80% of the total space. After all, it may well happen that the bars are folded inaccurately, thereby the percentage of voids is much greater.
3. Density based method.
In this case, you need to know the mass of the forest and the density of the wood. The cubature is easily found by dividing the first number by the second. But the result will be very inaccurate, since a tree of the same species has a different density. The indicator depends on the degree of maturity and humidity.
4. Average method.
If the trunks of harvested trees are almost the same in appearance, then any 3 of them are chosen. Measure the diameters, and then find the average value. Further, according to the cubature, the parameter for 1 product is determined and multiplied by the required amount. Let the results show: 25, 27, 26 cm, then the average is Ø26 cm, since (25 + 26 + 27) / 3 = 26 cm.
Given the disadvantages of the considered methods, the only correct way to calculate the cubature can be considered to be the volume of each log using the cubature GOST 2708-75 or ISO 4480-83 and summing up the data obtained.
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