- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2100) Unit Title: TOOL USE AND MAINTENANCE AND SHOP SAFETY ______________________________________________________________________________ (CLF2109) Topic: CUTTING TOOL CONSTRUCTION Time Year(s) AND REPAIR 2 Hours 1 / 2 / 3 / 4 ______________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (E-3) - Construct and repair a cutting tool such as a cold chisel and demonstrate proper hardening and tempering techniques. Special Materials and Equipment: Gas or electric forge, emery cloth, electric grinders, tool steel, tongs, machinist hammer, ball peen hammer, oxyacetylene torch. References: Burke, Stanley R., & Wakeman, T. J. (1990). MODERN AGRICULTURAL MECHANICS (2nd ed.). Danville, IL: Interstate Publishers. Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Evaluation: Quiz administered by the instructor and the completion of a cutting tool project to the satisfaction of the instructor. TOPIC PRESENTATION: Cutting Tool Construction and Repair A. Before a person can become proficient at properly sharpening and fitting cutting tools, he or she must have an understanding of the properties of the metal that make it desirable for tool manufacture. Constructing a cutting tool is a good way to learn the desired properties of the metal. The importance of achieving the correct hardness and toughness in the metal is learned when making tools. B. Cutting tools should be tempered to increase the hardness, yet reduce the brittleness of the metal. Tempering can be accomplished through the heating and cooling of the metal stock. C. Since the students will be required to heat metal for these exercises, the safety rules for hot metal work should be reviewed. 1. When using a gas furnace: a. Check for leaking gas. b. Light the furnace correctly, keeping the doors open and standing to one side. c. Use tongs to insert and remove the metal. d. Use a flint lighter to start the furnace. Never use matches. 2. When using an electric furnace: a. Check for frayed or damaged wiring to avoid electrical shock. b. Clear the furnace grating of all scale that can short or burn out the coils. c. Keep the doors of the furnace closed when not in use. d. Use tongs to insert or remove the metal stock. 3. When using an acetylene torch to heat the metal: a. Review the gas welding safety procedures. b. Never aim the torch at yourself or anyone else. c. Hold the metal stock securely with tongs or place it in a vise. d. Hold the stock well away from the body when heating. 4. After heating, the metal is shaped on an anvil. When using the anvil: a. Secure the anvil and never strike it directly with a hammer. b. Keep the anvil face clean and always hold the metal stock with tongs when striking. Never secure metal to be pounded with your hands. D. Making a Cutting Tool 1. A high quality tool steel must be used in making cutting tools. a. The steel must contain at least 0.2% carbon. 2. Cut the desired length of metal stock and clean it with an emery cloth or a grinder. 3. Heat the metal to a cherry red color and use tongs to remove it from the heat source. 4. Holding the metal securely with the tongs against the face of the anvil, pound it with a machinist's hammer or a ball peen hammer. Reheat the metal when the hammer strikes lose their effect on the metal shape. 5. Repeat this process until the desired shape of the tool has been achieved. E. Once the tool is made, the metal must be tempered to give it the correct hardness. Tempered metal will enable tools to last longer and maintain the cutting edge. NOTE: Only high quality tool steels can be tempered successfully. The quality is determined by the amount of carbon in the metal. 1. To temper, heat the metal tip to a cherry red color. The color will constantly change so the worker must constantly monitor the heating process. If the metal is not heated to a proper temperature, it will become coarse-grained and weak. 2. Quickly dip the end to be tempered in water and move it up and down slightly to speed the cooling process. Cool only the end to be tempered. The rest of the metal should still be hot. 3. Immediately brighten the cooled end with a file or emery cloth. This must be done before the heat of the remaining metal creeps into the cooled tip of the tool. 4. Colored rings will begin moving towards the cooled tip. Each ring represents a different amount of heat and thus a different amount of hardness. To make a cold chisel, the desired colored ring will be purple. When the purple ring has just reached the cooled end, immediately plunge the tip back into cold water and stir the tool in the water. 5. The tip of the chisel now has a different hardness than the rest of the tool. Once the tip has been properly cooled, the rest of the tool can be dipped in the water and cooled. E. All driven tools--such as punches, chisels and wedges--will flatten out at the top and cause the surface to mushroom. This mushroom shape can be very dangerous. If not properly ground, fragments of steel can chip off when struck and fly into the face or body. 1. Beveling the edges of the surface will help prevent mushrooming. 2. Specific terminology for the driven end of the tools must be learned in order to repair them. a. The crown is the flat top portion that is struck by the hammer. b. The bevel is the rounded edge between the crown and the tool body. c. The head consists of both the crown and the bevel. 3. Tool Head Reshaping Procedure: a. Using a new tool head as a guide, grind a taper from the tool body to the crown using a medium grinding wheel. b. Slowly twirl the tool so that all corners are slightly rounded. Round tools will have an even taper in a circular pattern around the crown. _______________________________________________________________ ACTIVITY: 1. Discuss the dangers involved with using tools with mushroomed heads. 2. Show examples of tools with mushroomed heads. 3. Use tools with different amounts of hardness to stress the importance of proper tempering procedures. 4. Practice making tools and tempering to the correct hardness and toughness. _______________________________________________________________ 7/11/91 DLF/RRE/tf #%&C