Materials, Power Tools and Shop Safety

Wood Classifications, Dimensions, and Grain Behavior

In workshop woodworking, lumber is classified into two primary botanical groups: hardwoods and softwoods. Hardwoods originate from deciduous or broadleaf trees, which include species such as oak, maple, walnut, and cherry. Softwoods come from conifers, such as pine, fir, spruce, and cedar, which typically feature needles or scale-like leaves. A fundamental principle to remember is that this botanical classification does not strictly dictate the physical hardness or density of the wood. Woodworkers also categorize cuts by their direction relative to the wood grain. A crosscut is a cut made perpendicular across the direction of the wood grain, whereas a rip cut is a cut made parallel along the direction of the wood grain. Furthermore, solid wood is dimensionally dynamic; it expands across its grain during periods of high humidity and contracts across its grain during periods of low humidity.

Lumber grades are assigned to reflect appearance, defects, or strength, and structural lumber can be graded visually or by machine. When purchasing lumber, boards are identified by nominal dimensions, which are standard trade names such as 2 × 4. However, the processes of drying and surfacing usually leave the actual dimensions smaller than the nominal trade name. For example, a standard two-by-four board has actual surfaced dimensions of 1-1/2 inches by 3-1/2 inches. Volume in lumber is measured in board feet. A board foot is a unit of lumber volume equal to 144 cubic inches, which corresponds to one square foot of wood that is one inch thick.

Engineered wood panels provide alternatives to solid lumber by altering how wood fibers and adhesives are assembled. Plywood is an engineered wood panel manufactured from thin veneer sheets glued together with alternating grain directions, a structural layout that provides dimensional stability. Medium-density fiberboard (MDF) is manufactured by breaking wood residuals down into individual fibers and bonding them together with resin under heat and pressure. Particle board is an inexpensive engineered wood panel made by compressing sawdust and wood shavings together with synthetic adhesives.