Selecting and Identifying Materials

Materials and Processes

Unit Objectives

• Define the terms hardwood and softwood

• Select the best kind of wood for a particular job

• Explain the various lumber grading systems

• Define the types of lumber defects• Calculate board footage

Hardwoods and Softwoods

Softwood comes from the evergreen or needle bearing trees. These are sometimes called conifers because they bear cones.

Hardwoods on the other hand come from broadleaved trees that shed their leaves. But where it gets confusing is some hardwood trees produce wood that is softer than softwood trees.

Hardwoods and Softwoods

Examples of hardwood:

White Oak, Red Oak, Cherry

Examples of Medium Hardwood:

Douglas Fir, Red Cedar, Mahogany

Examples of Softwoods:

Balsa, Pine, Spruce, Basswood

Wood Selection

It takes time and patience to find the right kind of wood for your project. There are many things to consider so don’t just use the piece of wood on the top. Sort through the lumber or bring in some from home that you feel will represent your project best. Plywood along with other woods can also help save money and time and won’t warp easily like some woods might.

Grades of Lumber

Softwood Grades are based on the American Softwood Lumber Standard. They are broken into three classifications: Boards, Dimension Lumber, and Timbers.

Boards are mostly for appearance such as cabinets or paneling

Dimension Lumber represents 2 x 4’s and other light framing needs

Grades of Lumber

Timbers are for beams and stringers (stairs).

Hardwood Grades are established by the National Hardwood Association. The best grade is the FAS (First and Seconds). This piece of wood cannot be less than 6 in. wide by 8ft. Long and yield at least 83 1/3 percent clear

Grades of Lumber

The next lower grade is Selects. This grade of wood permits boards to be 4in. wide by 6ft. long. with more defects on the back side.

Grades of Lumber

The next lower grade is the No. 1 Common. It permits smaller pieces and 66 2/3 percent clear cuttings. No. 2 Common requires 50 percent and No. 3 Common requires 33 1/3 percent but retailers usually cut out the defects and sell them as smaller pieces

Lumber Defects

A defect is a irregularity occurring in or on wood that reduces its strength, durability, or usefulness. Some common defects are:

Knots- embedded limb or branch of the tree. It reduces the strength but might improve the appearance.

Splits/Checks- a separation of the wood along the grain and across the grain

Shakes- a separation of wood along the grain and between the growth rings

Wane- the presence of bark or absence of wood along the edge of the board

Lumber Defects

Warp- any variation from a true or plain surface and may include any one or combination of the following: cup, bow, crook, and twist.

Quality of Lumber

The quality of lumber is indicated by the method of drying.

Green lumber from a freshly cut log will have excessive moisture (sap). The moisture must be removed before it can be used.

Air Dried lumber is simply exposed to the air over a period of time until the moisture content is reduced to 12 to 18%

Quality of Lumber

Kiln Dried lumber is the kind used in making furniture. Basically wood is placed in huge temperature controlled ovens until the moisture is at a 7 to 10 percent level. This reduces the stresses more common in air dried lumber and reduces the amount of lumber defects.

Figuring Board Footage

Lumber is always measured in board feet. A board foot is a piece 1” thick x 12” wide x 12” long. A piece 1 x 12 x 10 feet long is 10 bd. Ft. If it were 6” wide it would be 5 bd. Ft. The formula you need to use is:

Bd. Ft = (no. pcs. X T x W x L)/(1 x 12 x 12)

Figuring Board Footage

Stock that is less than 1” thick is considered 1”. Stock that is more than 1” uses the closest quarter inch. If the thickness is 1 ½ we would write it as 3/2 and in the formula put the 3 on the top in place of the T and the 2 would take the place of the 1 on the bottom.

Plywoods are measured in square feet!!