- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2400) Unit Title: WOODWORKING ____________________________________________________________________________ (CLF2405) Topic: FASTENING WOOD JOINTS Time Year(s) 3 hours 1 / 2 / 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (I-4) - Cut and assemble wood parts. (I-5) - Know the basic joints used in woodworking and demonstrate the application of two. Special Material and Equipment: 13 oz. curved claw hammer, 16- and 20-oz. ripping claw hammers, various nails, screws, bolts, white polyvinyl glue, clamps, clean rags, standard & Phillips screwdrivers, wrenches, scrap wood References: Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Jones, M. M. (1955). SHOPWORK ON THE FARM (2nd ed.). New York: McGraw-Hill 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: Fastening Wood Joints A. Basic Wood Joints 1. Butt Joints a. Butt joints are formed by joining two boards end to end, or edge to edge (in line or at a right angle). b. Butt joints can be reinforced by fastening thin wood or metal gussets to the corners or across the flat surfaces where the boards join. 2. Lap Joints a. Lap joints, which are stronger than butt joints, are formed by joining two boards face to face. b. Lap joints can be strengthened by offsetting the boards so they fit into each other. 3. Dado Joints a. A dado is a rectangular groove cut into a board. b. Dado joints are formed by inserting the end or edge of another board into this groove. 4. Rabbet Joints a. A rabbet is a rectangular groove cut in the end or edge of a board. b. Rabbet joints are formed by inserting the end or edge of another board into this groove. 5. Miter Joints a. Miter joints formed by cutting the ends of two boards at a 45 degree angle and joining them together to form a 90 degree angle. b. Miter joints are usually (depending on the grain direction at the joint) stronger than butt joints because they provide more surface contact at the joint. B. Fastening Wood Joints with Nails 1. Hammers a. Two types of hammers are commonly used. 1) The curved claw hammer is the most common; it is designed for pulling nails. 2) The ripping claw hammer has a straight claw which can be driven like a chisel between two fastened boards to pry them apart. b. In order the claw hammer's size is indicated by the weight of its head, which ranges from 7 oz. to 20 oz. 1) A general purpose claw hammer usually comes in the 13 oz. size. 2) Framing hammers used by carpenters usually come in either the 16 oz. or 20 oz. size. 2. Driving Nails a. In order to drive a nail, the following steps should be performed: 1) To start the nail, hold it between the thumb and index finger and place its point on the desired spot. 2) To avoid smashing the fingers if the hammer accidentally hits them, place them high on the nail to allow them to be knocked free rather than against the wood. 3) To prevent splitting a dry or thin board when driving the nail, use a smaller nail, or blunt the tip of a chisel-shaped nail; if using small nails, cut them off square. 4) Grasp the hammer near the end of the handle with the free hand, and keeping your eyes focused on the nail head, tap the nail one or two times with the hammer until it stands on its own. 5) Use the weight of the hammer to drive the nail, using mostly wrist action for light driving; combine wrist action that with elbow action for heavier driving; combine both wrist and elbow action with shoulder action for very heavy driving. 6) Continue to drive the nail until its head is flush with the surface and the two pieces of wood are tightly fastened; careful not to leave a hammer mark with the final blow. b. The type of nailing is determined by the kind of joint and by the wood thickness. 1) In flat nailing, nails are driven at a right angle through two flat boards and bent over (clinched) flush with the wood. 2) In end nailing, nails are driven through the thickness of one board and into the end with the grain of another. 3) In toe nailing, nails are driven at an angle near the end of one board into the face of the other when two large pieces of lumber must be fastened at right angles. c. A nailed joint's strength depends on the location and spacing of the nails. 1) Stagger the nails if possible. 2) Allow adequate separation between nails. 3) Do not drive nails in line with the grain. 3. Pulling Nails a. If the nail head extends above the surface of the wood, slip the hammer's claws under it. b. If the nail head is flush with the surface of the wood, use a pair of pincers or cloven nail pulling tool to extend the head far enough for the hammer claws to slip under it. c. Pull the handle of the hammer until it is perpendicular to the surface, then stop. d. Place a block of wood under the head of the hammer, and then continue to pull on the handle until the nail is removed. C. Fastening Wood Joints with Screws 1. Measure the thickness of the boards to be joined. 2. Select a screw length that is three times as long as the thickness of the board being joined unless the screw extends through the second board; in that case, use a shorter screw. 3. Properly space and mark the screw locations. 4. Select a screw diameter that looks in balance with the spacing, closer screws being smaller in diameter. 5. Using a chart, determine the drill size for the shank and pilot holes. 6. Install the pilot hole bit into a hand drill or power drill and adjust the length of the exposed bit to equal the length of the screw. 7. Hold or clamp the two boards together and drill the pilot hole through both boards. 8. Install the shank hole bit into a hand drill or power drill, and use it to enlarge the hole in the first board so that the screw can move freely through it. 9. If a flathead screw is being used, use a countershink tool to make a countersink in the enlarged hole that fits the screw head. 10. Using a screwdriver or screw bit that fits the slot, turn the screw until the two boards are fastened together snugly, but do not overtighten the screw. D. Fastening Wood Joints with Bolts 1. Select the type of bolt required, usually a carriage bolt since it is designed especially for wood. 2. Select the diameter and length of bolt required. 3. Hold the two boards together and drill a hole through them the same diameter as the bolt. 4. If a machine bolt is being used instead of a carriage bolt, place a flat washer on it, and then insert the bolt in the hole. 5. Place a flat washer on the threaded end of the bolt; a lock washer is often not necessary since the wood provides back pressure on the nut. 6. Place a nut on the bolt and turn it until the boards are joined tightly, but not so tight as to crush the wood fibers or draw the bolt below the surface. E. Fastening Wood Joints with Glue (White Polyvinyl or Yellow Aliphatic) 1. Make sure the mating surfaces of the two boards to be glued have a good fit and are free of dirt, paint, grease, or wax. 2. Drill the screw or bolt holes if required, and adjust the clamps to fit the boards. 3. Apply small beads of glue on both boards' mating surfaces. 4. Spread the beads of glue out evenly over the mating surfaces. 5. Join the two boards together, and secure them by nails, screws, bolts, or clamps. 6. Check to make sure the joint is properly aligned, and retighten the clamps if used. 7. Using a putty knife or wood chisel, remove the glue runs after they have partially dried. 8. Wipe the glue marks with a clean wet rag, and then wipe them again with a clean dry rag. 9. The clamps can be taken off after 30 minutes, but a stronger bond can be obtained by leaving the clamps on at least 12 hours. _________________________________________________________ ACTIVITY: 1. Cut and assemble two of the basic wood joints. 2. Practice driving and pulling nails. 3. Fasten wood joints with nails, screws, bolts and glue. 4. Assemble and fasten the pieces of an ongoing woodworking project such as a toolbox or sawhorse. _________________________________________________________ 6/17/91 OLR/tf #%&C