- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2400) Unit Title: WOODWORKING ____________________________________________________________________________ (CLF2401) Topic: SELECTING WOOD & LUMBER Time Year(s) 2 hours 1 / 2 / 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (I-1) - Select kinds, grades, and quantity of lumber for a given task. Special Material and Equipment: Samples of different kinds of wood and grades of lumber and plywood. References: Phipps, Lloyd J., & Reynolds, Carl L. (1990). MECHANICS IN AGRICULTURE (4th ed.). Danville, IL: Interstate Publishers. Wagner, W. H. (1987). MODERN CARPENTRY. South Holland, IL: Goodheart Willcox. Evaluation: Quiz by instructor. TOPIC PRESENTATION: Selecting Wood & Lumber A. Kinds of Wood 1. Softwood comes from needleleaf, evergreen trees called conifers. a. White pine--which is easy to work with and straight--is used for shelving, interior finish, exterior trim, and door frames. b. Yellow pine--which is wear resistant and tough--is used for benches, stairs, and other places where a semi-hard surface is desired. c. Fir--which is light, straight, and strong--is used for framing members (dimension lumber), siding, sheathing, and gates. d. Redwood--which has excellent decay resistance--is used for posts, fences, patios, and siding. e. Cedar--which is light and easy to split--is used for fence posts, sills, and shingles. f. Spruce--which is light, straight, strong, and resonant--is used for aviation and musical instruments. 2. Hardwood comes form broadleaf trees that lose their leaves each fall season, called deciduous trees. a. Oak--which is tough, strong and open-grained--is used for floors, interior finish, barrels, and furniture. b. Walnut--which has a beautiful, brown, open grain--is used for fine furniture. c. Maple--which is a very durable and light-grained--is used for floors, interior finish, furniture, and guitar necks. d. Mahogany--which is reddish in color--is used for fine furniture. e. Birch is used for surface veneer on cabinets and doors. B. Log Cutting Methods and Lumber Finishes 1. Cutting Methods a. Slash sawing cuts a log so that the annular rings form an angle of less than 45 degrees with the surface of the lumber. 1) Softwood lumber cut in this fashion is referred to as flat- grained. 2) Hardwood lumber cut in this fashion is referred to as plain-sawed. b. Quarter sawing cuts a log so that the annular rings form an angle of more than 45 degrees with the surface of the lumber. 1) Softwood lumber cut in this fashion is referred to as edge-grained. 2) Hardwood lumber cut in this fashion is referred to as quarter-sawed. 2. Finishes a. Rough lumber comes directly from the sawmill unplaned and varying in dimensions from piece to piece. b. S2S is lumber surfaced on two sides allowing all pieces to have the same thickness, but varying widths. c. S4S is lumber surfaced on four sides allowing exact dimension from piece to piece. The actual sizes are 1/2 inch less than the nominal sizes; for example, the actual size of a 2 x 4 is only 1 1/2" x 3 1/2." C. Kinds of Lumber and Wood Panels 1. Wood cut into uniform thickness, width, and length is called lumber. a. Boards are lumber used for flooring, sheathing, paneling, and trim. b. Dimension lumber is used for sills, plates, studs, rafters, and other framing members. c. Timbers are lumber used for posts, beams, and heavy stringers. 2. Wood panels (usually 4' x 8') are made through various methods. a. Plywood consists of thin layers of wood glued together with the wood grain turned at right angles in each successive layer. b. Composite board consists of a core of wood fibers bonded on either side with veneer. c. Hardboard consists of refined wood fibers pressed together to form a hard, dense material (55 - 75 lb. per cu. ft.). d. Particle board consists of wood flakes, chips, and shavings bonded together with resins or adhesives to form a less dense material (42,45, or 47 per cu. ft.). e. Waferboard consists of high quality flakes of wood (about 1 1/2 inch square) bonded together under heat and pressure with the waterproof adhesive, phenolic resin. f. Oriented strand board is similar to wafferboard in appearance, but consists of wood fibers bonded together in successive layers arranged at right angles to one another. D. Grades 1. The Basis of Lumber Grades a. Lumber grades are based on the appearance and soundness of the wood. b. The fewer and less obvious the defects, the more the lumber costs. 1) A lumber defect is an irregularity in or on the wood that reduces its strength, durability, or usefulness. 2) A lumber blemish is a defect that impairs only the wood's appearance. c. The common lumber defects include the following: 1) Knots are embedded branches or limbs in the lumber. 2) Holes can be caused by mishandling or insects and worms. 3) Splits and checks are separations of the wood fibers along the grain and across annular growth rings. 4) Shakes are separations of wood fibers along the grain and between annular growth rings. 5) Pitch pockets are cavities that contain or have contained liquid or solid pitch. 6) Honeycombing is the separation of wood fibers inside the lumber, which may not be visible on the surface. 7) Wane is the presence of bark or the absence of wood along a board's edge. 8) Decay is the disintegration of wood fibers caused by fungi. 9) Blue stain is the discoloration caused by any of various fungi (as of the genera Ceratostomella, Penicillium, or Fusarium) 10) Warp is any variation from a plane surface, including cups, bows, crooks, and twists. 2. Basic Lumber Grades a. Select refers to lumber of good appearance and finishing qualities. 1) Grades A and B are suitable for natural finishes. 2) Grades C and D are suitable for paint finishes. b. Common refers to lumber containing defects and blemishes. 1) Common no. 1, 2, and 3 are suitable for use without waste. 2) Common no. 4 and 5 are suitable for use permitting waste. 4. Plywood Grades a. A grade lettering system is used to indicate the quality of the veneer used on the face and back of the panel. 1) N is a veneer with a smooth surface suitable for natural finishes. 2) A is a veneer with a smooth surface suitable for painting. 3) B is a veneer with a solid surface. 4) C Plugged is an improved C veneer with splits limited to 1/8 inch width, and knotholes and bore holes limited to 1/4 x 1/2 inch. 5) C is a veneer with tight knots to 1 1/2 inch. 6) D is a veneer with knots and knotholes to 2 1/2 inch width across the grain which is limited to interior, Exposure 1 and 2 panels. 7) G2S means the veneer is good on two sides. 8) G1S means the veneer is good on only one side. c. Mills which are members of the American Plywood Association (APA) indicate the panel's intended use or performance rating with an APA trademark stamp, which includes the following information: 1) Panel grade indicates its use, such as sheathing. 2) Span rating is indicated by a pair of numbers separated by a slash, such as 32/16. a) The 32 indicates the maximum recommended span in inches when used as roof sheathing. b) The 16 indicates the maximum recommended span in inches when used as subflooring. 3) Thickness in inches (common sizes being 1/4, 3/8, 1/2, 5/8, and 3/4). 4) Exposure durability classification is indicated by three names: a) Exterior is bonded with a 100% waterproof glue allowing it to be used outdoors and continually exposed to moisture. b) Exposure 1 is interior plywood that can be exposed to moisture for extended periods. c) Exposure 2 is interior plywood that can withstand some leakage or high humidity for short periods. E. Factors to Consider When Selecting Lumber 1. Quality construction does not require that all the lumber be of the best grade. 2. Several grades of lumber may be appropriate in a single structure. 3. Good economical construction requires the proper use of the lowest grade lumber suitable for the purpose. _________________________________________________________ ACTIVITY: 1. Practice identifying different kinds of wood. 2. Practice identifying different kinds of lumber and wood panels. 3. Practice identifying wood defects. 4. Practice identifying lumber and plywood grades. 5. Select lumber and wood panels for an ongoing project, such as a toolbox or sawhorse. _________________________________________________________ 6/19/91 OLR/tf #%&C