LESSON – WOOD BASICS

 

LUMBER

 

Lumber is a generic term that applies to various lengths of wood used as construction materials. Pieces of lumber are cut lengthwise from the trunks of trees and are characterized by having generally rectangular or square cross sections. (Source)

 

WOOD GRAIN

 

Grain is the term used to describe the alternating dark and light regions found in wood.  The grain patterns are a result of the growth of the wood.  Different types of wood result in different looking grains.

 

When we refer to the direction of the wood grain, we are in fact referring to the orientation of the wood’s fibers.

 

DIMENSIONS

 

A board of wood has three dimensions: length, width and thickness.  Each is shown in the image below.

 

SURFACES

 

There are three types of surfaces on a board: face, edge and end.  Of course, each board has two of each type of surface.

 

 

MEASUREMENT UNITS

 

In Canada, we are accustomed to working with the metric system.  In this system, the most common measurement units are:

 

 

 

Amount of mm

Millimeters

mm

1

Centimeters

cm

10

Meters

m

1 000

Kilometers

km

1 000 000

 

However, when working with wood and in construction, we are often forced to use the United States’ system – the imperial system.  The reason that we are forced to use the US’ system is that we import and export many construction materials from/to the US.

 

In the imperial system, the most common measurement units are:

 

 

 

Amount of inches

Inches

in  or  "

1

Feet

ft  or  '

12

Yards

Yd

36

Miles

Mi

63 360

 

As you can see, the metric system allows for easy conversions from one unit to another.  Conversions in the imperial system are a little more difficult.

 

BOARD FOOT

 

When purchasing a board of wood, one sometimes encounters the term board foot.  Some believe this is a unit of measure of distance.   However, it is in fact a unit of measure of volume.  It is equal to:

 

1 ft by 1 ft by 1 in

or

144 in3

 

NOMINAL VS ACTUAL DIMENSIONS

 

If you have ever purchased a 2 by 4 at the store and tried to measure its thickness and width, you surely discovered that they are not 2 inches by 4 inches.  The same is true for other sizes of construction lumber.  This is because the board is initially cut to 2 inches and 4 inches at the sawmill.  However, it is then dried and loses about 10% of its volume.  It is then planed to a set size.  A 2 x 4 is about 1.5 inches by 3.5 inches.

 

The nominal dimensions are 2 by 4.  The actual dimensions are 1.5 inches by 3.5 inches.

 

CLASSIFICATION

 

Lumber can be classified in three groups based on its nominal dimensions:

1.     Board – Less than 2 in thick and more than 1 in wide.  Some consider boards that are less than 6 in wide to be strips.

2.     Dimension – Between 2 and 5 in thick and 2 or more in wide.  Also classified as framing, joists, studs, small timber …

3.     Timber – Smallest dimension is 5 (or more) in.  Also classified as beams, stringers, posts…

 

WOOD DEFECTS/IMPERFECTIONS

 

When choosing a piece of wood to work with, you have to be aware of imperfections or defects.  When drying, wood sometimes curves or twists in one or more directions.  Each one has it’s specific term: cup, bow, crook and twist.

 

 

These curvatures have to be considered because they will cause greater waste when you are reducing your board to the desired dimensions.  In fact, you might not have enough wood left to create the desired piece.

 

Knots, splits and checking are imperfections that you want to avoid.  Some people (like Mr. Campeau) do enjoy the look of knots.  However, one has to be careful that the knot is not (no pun intended) loose or the piece could end up with a hole in it!  Cutting through a knot can also lead to poor cuts and breaking of edges.

 

TYPES OF WOOD

 

There are many types of wood that are used.  One can classify types of wood into two branches: softwood and hardwood.  As the names suggest, softwoods are usually softer than hardwoods.  However, this is not always the case.  For example, balsa wood is a hardwood and one of the softest woods.

 

Softwoods are generally evergreens while hardwoods are deciduous trees.  According to Wikipedia, about 80% of the entire world’s produced lumber is softwood. 

 

Softwood trees grow faster than hardwood trees and are therefore more renewable.  Softwood trees also tend to have long straight sections which are friendlier to lumber production.  These characteristics of softwoods lead to them being less expensive than hardwoods.

 

SPECIES

 

There are many species of woods.  In Canada, evergreen species include pine, cedar, larch, fir and spruce.  In fact, these are really families of species with several types in each.

 

Canadian deciduous trees include different types of ash, birch, oak, maple, poplar and elm.  

 

Click here to see a small list of species of wood and characteristics and uses for that species.  Note that this is not by any means a complete list.