Woods suited to self bows have a high ratio of bending strength to stiffness

The summary today

A single analysis, carried out on data rather than on bows, points this way. Across 431 samples of 326 wood species, taken from public databases of wood dried to 12 per cent, density, bending strength and stiffness are correlated with one another, while the ratio of bending strength to stiffness varies on its own, on a principal component orthogonal to the others; the first two components explain over 90 per cent of the variance. The three woods considered the best in the world for self bows, Osage orange and the two yews, cluster where that ratio is highest, next to secondary woods such as maple, hickory, ash, oak and elm, while poplar and lime end up in the low-density, low-strength zone where the analysis expects them. Two samples of the same species fall in the same zone, with correlations between 0.85 and 0.90, even though within a species the properties vary by up to 30 per cent. The limit lies upstream: which woods are suitable is decided by the bowyers' literature, not by a test, and in the same study the Australian species that the builders on a forum rate as good fall almost entirely outside the zone of suitable woods. No bow has been built and tested.

Also phrased as: "best wood for a self bow"; "which wood for a bow"; "yew and osage for bows"; "ratio of MOR to MOE"

Evidence

• 2024
  For Equipment tests Published later

  A principal component analysis of 431 samples of 326 species, using public data for wood dried to 12 per cent: bending strength 106 MPa on average (22 to 213), elastic modulus 13,300 MPa (3,400 to 28,000), density 0.7 g/cm³ (0.24 to 1.4), ratio of strength to stiffness times 100 equal to 0.8 (0.53 to 1.36). The absolute properties are correlated with one another, the ratio is not, and it loads on an orthogonal component; the first two components explain over 90 per cent of the variance. Among repeated samples of the same species, about 105 pairs, the correlation is between 0.85 and 0.89 for the individual properties and 0.90 for the first component, but within a species the properties vary by up to 30 per cent and the component scores by up to 15: the species tells you where a wood falls, not how good the individual piece is.

  Is Australian Flora Unsuitable for the Bow-and-Arrow? · Nicholas George

• 2024
  For Equipment tests Published later

  The three woods considered the best in the world for self bows (Maclura pomifera, Taxus baccata and Taxus brevifolia, 9 samples) cluster with the highest ratio of strength to stiffness, next to 44 samples of secondary woods such as maple, hickory, ash, oak, elm, mulberry and black locust; poplar and lime fall in the zone of low density, low tensile strength or low stiffness.

  Is Australian Flora Unsuitable for the Bow-and-Arrow? · Nicholas George

• 2024
  Context Equipment tests Published later

  Of the native species reported as suitable on an Australian bowyers' forum (about 7,000 posts between 2005 and 2023, 24 species, 7 without mechanical data) almost none cluster with the suitable woods: the exception the author names is Eucalyptus macrorhyncha, which falls with the secondary ones, and of the Australian species the analysis picks out only Eucalyptus camaldulensis is mentioned on the forum as good. The author leaves several explanations open, from an analysis that fails to capture a wood's suitability to local builders' limited experience of woods from other continents.

  Is Australian Flora Unsuitable for the Bow-and-Arrow? · Nicholas George

Status history

1. 2024 Reported The first and only analysis, across 431 samples of 326 species, finds that the ratio of bending strength to stiffness varies independently of density and absolute strength, and that the species bowyers consider the best in the world cluster where that ratio is highest, while poplar and lime fall where the analysis expects them. Two pieces of the same species end up in the same zone, with correlations between 0.85 and 0.90, even though the variation within a species reaches 30 per cent. In the same study, though, the Australian species that builders rate as good do not square with the analysis, and no bow has been built and tested: reported.

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