Q. When looking at the strength of a leg, what factors are important?

A. A quick summary. Obviously, the size (especially the smallest diameter) and the species are important. In general, the denser species are stronger. But even within a single species, the density can vary substantially; you need to avoid pieces that are much lighter weight than normal. Another factor is the grain angle. If the grain (as determined by splitting a piece, as a split lengthwise follows the grain) is not parallel to the sides, the strength drops quickly.

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Grain slope   Degrees from parallel               Ultimate strength (MOR)

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                                                                        percent

Straight, parallel          0                                  100

1 in 25                         2                                  96

1 in 20                         3                                  93

1 in 15                         4                                  89

1 in 10                         6                                  81

1 in 5                                       11                                55

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Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.

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