Janka hardness rating scale
The hardness of a wood is rated on an industry wide standard known as the Janka hardness test. This test is used to measure a type of wood’s ability to resist dents and scratches.
The Janka hardness rating scale was named after Gabriel Janka (1864–1932), an Austrian wood researcher. His work was based on similar studies conducted by August Brinell (1849 –1925), a Swedish metallurgical engineer.
Janka and Brinell were interested in the surface hardness of materials. In both instances, the men conducted tests based on the amount of pressure or effort required to press a steel ball into a certain substance to a specific depth.
The Janka hardness test measures the force required to embed an 11.28 millimetres (0.444 in) diameter steel ball halfway into a sample of wood. This measurement is recorded and repeated several times until an average can be calculated. The end result is the Janka hardness rating.
At the hard end of the scale is Australian Buloke (5060) and in the softest range is balsa (70). The median rating is approximately 1290, which is the hardness of red oak.
The Janka scale has become an industry standard for comparing wood flooring. The scale is also useful in the construction industry for giving builders a sense of how difficult it will be to work with different types of wood.
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