BS EN 14081-2-2018 pdf free download.Timber structures – Strength graded structural timber with rectangular cross section Part 2: Machine grading; additional requirements for type testing
Operational accuracy of transducers shall ensure that production machines meet the requirements of this European Standard, and are compatible with grade settings derived for the machine type. The grading machine shall not damage the timber during the grading operation to an extent that it affects the intended use of the timber.
For example, in bending type machines, damage should not be caused by large compression perpendicular to grain stresses and/or large bending stresses.
NOTE When approving a new machine, consideration of already approved machines having the same technology can contribute to the approval procedure, including settings derivation. Grading machines whose indicating property does not take account of the material properties along the whole length of each piece of timber, but whose indicating property measurements are influenced by strength reducing characteristics away from the measuring position (as in bending type machines), shall measure the indicating property to within 800 mm of each end of the piece of timber. Where the indicating property is influenced only by strength reducing characteristics at the measuring position (as in radiation type machines), the measurements shall be made to within 150 mm of each end.
When a new species is required to be graded by a machine that has already been shown to meet the requirements of this European Standard, those requirements given in this clause that are not likely to be affected by species differences may be disregarded for the new species. Machine settings that were derived in accordance with previous versions of this standard remain valid unless there is evidence that the required grade determining properties are not met. In that case, new settings shall be derived according to this version of the standard.
6 Derivation of settings for machine control systems
6.1 Requirements on sampling
Sampling shall be representative of the timber to be graded. The timber shall represent the timber source, species, range of sizes and quality to be graded in production with the most demanding surface finish for the performance of the grading machine.
NOTE 1 Annex A gives guidance on sampling. For each species or species combination, the minimum number of specimens required for deriving or expanding settings shall be taken from Table 1:
The minimum size of a setting area defined in this standard is normally a country or standardized area. Parts of countries or standardized areas may also be considered if they are clearly geographically defined. Sampling for a setting area that includes more than one country shall contain at least one sample from each country, unless information exists which verifies that timber from one country can be safely graded using settings from another country without being included in the sampling.
The range of permitted thickness and width for which settings shall be used in production shall not be extrapolated more than 10 % from the maximum and minimum thickness and widths tested. This requirement should be considered when carrying out the sampling. The minimum cross section area for which settings shall be used in production shall not be extrapolated more than 10 % from the minimum cross section area tested.
This requirement should be considered when carrying out the sampling. A minimum of 40 pieces shall be included in the sampling on all ends of the cross section thickness and width.
This means that at least 40 pieces shall be in the range of 10 % of the upper tested timber thickness and width and at least 40 pieces shall be in the range of 10 % of the lower tested timber thickness and width. A minimum of 40 pieces shall be included in the sampling for the smallest cross section area.
6.2 Requirements for grading process, destructive testing and calculation of grade determining properties
6.2.1 Grading process Each piece shall be graded by the machine at the critical feed speed while documenting the moisture content, all variables necessary for calculating the IP, and any other variables that may affect the IP.
6.2.2 Destructive testing Each piece shall be tested to determine the grade determining properties in accordance with EN 384 and EN 408. The characteristic values shall be calculated based on EN 384 and rounded to three significant digits. In the case of a portable machine, the kv factor (given in EN 384) shall be taken as 1.
6.2.3 Calculations of grade determining properties One or more models (e.g. mathematical, statistical) relating the machine’s measured parameters to one or more indicating properties to the grade determining properties shall be developed. Models may include variables such as size and moisture content, or may be determined from the data after adjusting the properties for such variables. Where the machine measures the moisture content of each piece, moisture content may be used to adjust the settings model.BS EN 14081-2 pdf download