Hardwoods & Softwoods > Mechanical Properties
The mechanical properties are those that affect the performance of the wood species and the ease with which you can work it. Is the wood sufficiently hard, strong, and stable for your project? Can you cut, assemble, and finish it easily? To answer these questions, refer to the appropriate categories in the chart of “Mechanical Properties of Wood” below. This chart includes the following categories.
Although specific gravity is technically a physical property, it’s usually included with mechanical properties. It’s a reasonably reliable indicator of the wood strength and ease with which it can be worked. Woods with high specific gravities are generally stronger and more difficult to work.
Because numbers so often make little sense when considered by themselves, I've given each species a simple comparative rating in these strength categories so you can instantly understand where it falls in the entire range. If you need the actual numbers, see the chart of "Relative Wood Strengths."
Wood changes dimension tangentially (across flat grain) and radially (across quarter grain). This movement is measured by determining the percentage that wood shrinks from when it’s green (freshly cut) to completely dry. The lower the percentage, the less the wood moves and the more stable it is. Additionally, a big difference between tangential and radial movement indicates that the wood is susceptible to warping, twisting, and bowing.
In yellow birch (top), there is a large discrepancy between the tangential movement (8.1%) and radial movement (3.6%). Consequently, the species is prone to warping, twisting, and bowing. In Honduran mahogany (bottom), on the other hand, the discrepancy is very small (4.1% versus 3.0%). This wood is much more likely to remain flat. (modulus of elasticity). This is a concern when the wood must withstand high amounts of stress.*
Before buying a wood species that you’ve never worked before, it helps to know how difficult it is to surface the wood with a hand plane or a thickness planer. Does it lend itself to strong glue joints? Is it incompatible with common finishes? These working characteristics depend on many factors. If the wood is extremely dense, it’s harder to cut. Irregular grain patterns make planning more difficult. The cell structure of some woods makes them prone to splitting and chipping. Waxy or resinous extractives interfere with cutting, gluing, and finishing. The chart of “Mechanical Properties of Wood” rates the following:
Finally, nothing helps so much in deciding whether or not to use a wood species for a project as knowing how other craftsmen use the same wood.
Biodiversity – Many useful wood species, especially those from fragile environments such as rainforests, are severely depleted from overuse and poor management. These are specified as “Endangered” in the Comments section of the chart of “Mechanical Properties of Wood.” This designation is determined by CITES (Council on International Trade in Endangered Species), the result of an international agreement an the conservation of species that began in 1973. You can search this list at:
You can find additional information on endangered wood species in the "Red List" from the International Union for the Conservation of Nature (IUCN).
Sometimes you get lucky. Although there are 28,000 species of fauna on the CITES endangered list and as many as 970 species of trees thought to be headed for extinction, occasionally we get some good news. This is a Judean Date, Phoenix dactylifera, a long-extinct palm tree important in Biblical times as a source of food and medicine (see Psalms 92:12). The species was revived, at least for a short time, from a 2000-year-old seed found at the archaeological dig in Masada, Israel.
The chart of “Mechanical Properties of Wood” is divided into three parts -- North American Hardwoods, North American Softwoods, and World Woods, or woods from other places than North America. To access any part, click on the title below. To see the properties for any wood species, click on its name.
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