Annual rings:

Most species grown in temperate climates produce visible annual growth rings.  These rings show differences in density and color between wood formed early (springwood) and wood formed later (summerwood) in the growing season.  Springwood is generally the darker more compact portion of the wood while the summerwood  is the thicker more dense and lighter colored section.  When sawn conventionally the growth rings provide the grain or characteristic patterns of the wood.

 

Characteristics:

The pattern produced in a wood surface by annual growth rings is referred to as figure.  These patterns include rays, knots, and deviations from regular grain.

Rays extend radially from the core of the tree toward the bark. 

Flat grain can be recognized by its arched effect.  Lumber is considered flat grained when the annual growth rings are less 45 degrees. 

Radial grain referred to as vertical or edge grain is generally more dimensionally stable than flat grain.  Vertical grained boards are less likely to expand or contract with changes in moisture.  Lumber is considered vertical grained when the annual growth rings are more than 45 degrees.

In hardwoods, plain sawn lumber is mostly flat grained wood.  Quarter sawn lumber is nearly all vertical grained wood.  In softwood lumber the terms flat grained and vertical grained are used rather than plain sawn and quarter sawn to describe the type of saw cut.

 

Hardness and Durability:

Probably the most important strength property for wood flooring is its side hardness.  Side hardness represents the resistance of wood to wear, and to denting, and marring.  The hardness test measures the force required to embed a .444 inch steel ball to half its diameter in wood.  This test is known as the Janka hardness rating and is also a good indicator of how hard or easy a species will be to saw or nail.  See chart below.

 

Types of sawing cuts:

Plain Sawn is the most common and least expensive method of sawing.

Plain sawn lumber is obtained by making parallel cuts to the original cut made to the circumference of the log.  This provides the widest boards and the least waste.  Most wood flooring is cut this way.

 

Quarter Sawn lumber is generally more expensive and produces more waste than plain sawn lumber.

Quarter sawn lumber is produced by quartering the log then sawing perpendicular to the growth rings.  Quarter sawing produces relatively narrow boards, mostly all vertical grained and less likely to expand or contract than plain sawn lumber.

 

Rift Sawn is similar to quarter sawing with many of the same advantages and disadvantages.

While it enhances the vertical grain and minimizes the flake effect which is common in quarter sawn lumber.  The angle of the cut is changed so that fewer cuts are parallel to the rays.  Rift sawing creates more waste than quarter sawing or plain sawn lumber making it generally more expensive.

Relative hardness of selected wood flooring species:
(Ranked by Janka hardness rating)

Douglas Fir	660		Ash	1320
Southern Yellow Pine	870		White Oak	1360
Black Cherry	950		Hard Maple	1450
Black Walnut	1010		Hickory / Pecan	1820
Heart Pine	1225		Purpleheart	1860
Yellow Birch	1260		Merabau	1925
Red Oak	1290		Santos Mahogany	2200
American Beech	1300		Brazilian Cherry	2350

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