DIN Standards Committee Timber and Furniture
DIN 68100
Tolerance system for wood working and wood processing - Concepts, series of tolerances, shrinkage and swelling
Toleranzsystem für Holzbe- und -verarbeitung - Begriffe, Toleranzreihen, Schwind- und Quellmaße
Overview
The system of tolerance ranges for wood and wooden products specified in this standard allows for the choice of suitable tolerances for parts which shall be joined together without rework. The tolerance system applies to length dimensions, for instance lengths, widths, thicknesses, heights, external dimensions, internal dimensions, centre holes, diameters, fillet radii as well as angle dimensions, inclinations, parallelism and straightness with an agreed moisture content of the parts. If two or more components are combined or one component is introduced into a surrounding installation situation, a dimensional conformity must exist between the components. Otherwise the functions or perceived performances are not assured. Generally an adequate conformity of the components with the required measurements is sufficient; complete conformity would be uneconomical. For example, in order to ensure function of fit the actual size must lie between two specification limits or limit dimensions. In contrast to many other materials where the dimensional fluctuations of manufacturing must lie within the functionally-required tolerance range, wood and wooden materials add further fluctuations in shape and dimension due to swelling and shrinkage. This standard provides corresponding classes for the dimensional accuracy required for the different functions. At the same time, the swelling and shrinkage values assure that the tolerance-dependant function or perceived performance may also be present for wood moisture produced during later use. The standard has been revised with the aim that the tolerance concept shall be used as a general specification for complete components in the sense of general tolerances for shape and orientation (similar to DIN 7168, but including swelling and shrinkage). The tolerance specifications can thus be used for internal quality assurance, the securing of supply, as well as for process and machine capabilities analyses. The specifications of this standard aim first and foremost for statistical toleration. They can, however, also be a necessary part of a concept for the statistical toleration which does not aim at full interchangeability. Here, the distribution fluctuations through the manufacture and the swelling and shrinking, or the corresponding measurement uncertainties can be observed. This could lead to an extended range of tolerance specifications and thus to an increased efficiency. Conversely, for instance specifications for fluctuation margins of moisture can be calculated when using statistical toleration. This possibility exists with the set of rules provided by this standard. While revising the standard, an additional, finer series of tolerances HT 1 to HT 4 have been added, which take into account increased accuracy requirements, for example, for floor elements made of wood and wooden materials. Furthermore, information regarding shrinkage and swelling values for wooden materials has been updated with regard to the current European standards. Regarding the shrinkage and swelling values for solid wood, on the one hand, types of wood that are no longer relevant on the market have been deleted and, on the other hand, new types of wood have been added. The Committee responsible for this standard is NA 042-04-03 AA "Toleranzen und Zeichnungen" ("Tolerances and drawings") at DIN.
