- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2100) Unit Title: TOOL USE AND MAINTENANCE AND SHOP SAFETY ______________________________________________________________________________ (CLF2107) Topic: TOOL SHARPENING Time Year(s) PROCEDURES 6 Hours 1 / 2 / 3 / 4 ______________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (E-2) - Sharpen selected cutting tools correctly, including chisels, screwdrivers, twist drills, blades, hoes, axes, knives, scissors, and shears. Special Materials and Equipment: Demonstration examples of chisels, screwdrivers, twist drills, blades, hoes, axes, knives, scissors, and shears. Files, rasps, whetstones, and various grinders should be available in the lab or at work stations. If possible, have the students bring tools from home that need to be sharpened. 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 on the proper methods of sharpening tools. Satisfactory completion of tool sharpening exercises. Appendix II contains a tool sharpening list. Appendix III contains a scoresheet to evaluate sharpening exercises. TOPIC PRESENTATION: Tool Sharpening Procedures A. Tool fitting is defined as the sharpening, cleaning, redressing, and adjustment of tools so they can better do the work they were designed to do. B. There are several important reasons to fit tools: 1. Workers are able to produce more work safely and with less effort when tools of the trade are well-fitted. A dull axe will not cut into wood as well as a sharp axe, so extra labor is required to do the same amount of work. Since a dull axe does not catch the wood as well, it is more likely to bounce off the wood and injure the worker than a sharp axe. Even a dull axe will break the skin. 2. It is more economical to sharpen a dull tool than to buy a new one. C. Tool Sharpening Procedures 1. A cold chisel is a hand tool used to cut metal. a. There are several different tip shapes for cold chisels which require a variety of different sharpening techniques. Tip shapes include flat, diamond point, round nose, and cape. b. To sharpen a flat chisel, use a template to correctly grind the beveled side of the chisel. The correct angle ranges from 60 to 75 degrees. _____________________________________________________________________________ *** NOTE TO INSTRUCTOR *** A tool sharpening template is useful in determining the correct angle to use when sharpening different tools. The Burke & Wakeman reference has a good illustration of a tool sharpening template on page 35. Page 241 in the Cooper text gives an illustrated example of a tool sharpening gauge. A T-level, a combination level, or a protractor can also be used to measure the angles. ______________________________________________________________________________ c. The cutting edge of the chisel is ground first to remove all chips and gaps. Use the thumb and forefinger to guide the chisel towards the grinder while using the tool rest for support. d. After the cutting edge has been cleared of rough edges, turn the chisel over and grind the edge to the appropriate angle. Stop and check the angle of the bevel often to prevent overgrinding. Overgrinding will decrease the strength of the chisel cutting edge. e. Cool the chisel with water often while grinding to prevent overheating and a loss of temper. f. Check the manufacturer's recommendations for the correct angle to use on a diamond point chisel. Round nose and cape pointed chisels require equal grinding on all sides. 2. Wood chisels are hollow ground to obtain a razor sharp tip. a. Wood chisels are sharpened on one side only to an angle of 29 degrees. The angle can be determined with the use of a template. b. The first step is to grind the cutting edge to make it square and to remove all nicks. c. Adjust the tool rest so that the angle to the wheel matches the 29 degree angle of the tool. d. Grind the edge of the tool, while checking frequently for the correct angle. e. Put a fine edge on the chisel with the use of a whetstone. 3. Screwdriver tips often get worn or bent out of shape and must be fitted. a. Select a flat-head screw with a slot the same width as the screwdriver blade tip. b. Grind the tip square and remove all gaps and twists in the screwdriver blade. Apply light pressure to the blade while moving it back and forth across the grinding wheel. c. Turn the screwdriver frequently to keep both sides parallel. d. If ground correctly, the tip should fit completely into the screw slot with no gaps. 4. A twist drill is used to drill holes in metal or wood. a. It is important to know the parts of the cutting tip of the twist drill before sharpening. 1) The two cutting lips of the drill perform the actual cutting. 2) The heel is the outer, rounded edge of the drill bit. 3) The dead center is the edge that separates the two cutting lips. The dead center must be exactly centered on the drill bit after it is sharpened. b. The two cutting lips are ground at an angle of 59 degrees to the center line of the drill shank. The two cutting lips together form a 118 degree angle. A 118 or 120 degree gauge is useful in determining the angle. c. The clearance of the twist drill is the difference between the heel and the edge of the cutting lip. The clearance should be 12 degrees. Too large a clearance will cause the cutting lips to break off. Too small a clearance will cause the drill to ride on the heel and the drill will not cut. d. The procedure for sharpening a twist drill is as follows: 1) Set the tool rest horizontal to the face of the grinding wheel. 2) Hold the drill shank between the thumb and index finger. Rest the back of the index finger on the tool rest. 3) Be sure that the cutting lip is straight across the face of the wheel at the beginning of each stroke. When the drill comes in contact with the wheel, push the drill shank downward and to the left at a slight angle. At the same time, rotate the drill a half turn so that the other lip is just visible. 4) Repeat this process on the other lip to sharpen the entire twist drill. 5) Check the cutting angle and clearance by using a template. e. A hand jig can be used to sharpen drills when a grinder is not available. It is recommended that beginners practice with a hand jig. 4. Rotary mower blades can be sharpened to increase the effectiveness of a lawn mower or a field mower. Sharp blades do a faster, better looking mowing job and reduce the amount of damage to the plants. a. Only one side of the rotary blade is sharpened. Try to maintain the original angle of the cutting edge. If this cannot be determined, sharpen the blade to a 45 degree angle. b. To maintain balance in the mower, the blade must be sharpened equally along its edge. A blade that is not sharpened evenly will rotate out of balance and cause the mower to vibrate. This creates wear on the engine, shaft, and body of the mower. c. It is more desirable to use files rather than power grinders to sharpen blades. It is more difficult to properly position a blade edge on a grinder. Uneven grinding may occur which will cause the blade to rotate out of balance. d. The first step in sharpening blades is to remove all nicks and chips from the cutting edge. e. Clamp the blade into a machinist's vise and restore the edge using a large, flat file. f. Check the angle of the cutting edge frequently, using a sharpening template. 5. Shovels, hoes, and spades can be easily sharpened with grinders or files. a. Shovels are always sharpened on the inside edge. Check other digging tools for the side on which they were previously sharpened. b. Remove all excess metal, nicks, and chips from the cutting edge. c. File or grind a new cutting edge into the tool. Spades and hoes should be sharpened to their original angle. If this is unknown, sharpen to a 20 to 30 degree angle. 6. Axes have a rounded metal side behind the cutting edge. This convex shape requires a special sharpening technique called convex grinding. a. The blade of the axe should face up on the edge of the grinder. Use an up and down motion as the axe blade is drawn across the face of the grinding wheel. Stop the downward motion when sparks first appear to prevent the dubbing off of the axe blade. b. The up and down motion should cover a distance of only 3/4" to 5/8" with each stroke. c. A whetstone can be used to remove the wire edge created by the grinder and to put a fine cutting edge on the axe. Draw the blade across the stone at a 30 degree angle. Repeat this process on both sides of the blade. 7. Knives can be sharpened with either a whetstone or an electric grinder. Since there are often rules regarding the use of knives by students at school, the students should receive permission from the instructor before bringing their own knives to school for this exercise. a. Only smooth-edged knives can be sharpened using this procedure. Serrated knives should be sent back to the manufacturer for sharpening. b. Select a fine grit wheel since the knife blade is thin and often fragile. c. Hold the knife with the cutting edge up and slowly move it back and forth across the grinding wheel. Do not apply much pressure to the knife as the blade may be damaged. Cool the blade in water often to prevent the blade from heating up. d. Use an oilstone or a whetstone to put a fine cutting edge on the knife. 1) Hold the knife flat to the stone with the back slightly raised. 2) Draw the knife, edge first, across the stone; then flip the knife over and push it in the opposite direction. 3) Sharpening oil should be applied to the stone before sharpening to prevent damage to the stone and blade. 4) Properly clean the stone after using by wiping the excess oil from the face. 8. Scissors and shears each have two blades that must be sharpened. a. Only one side of the blade is sharpened. The shape of the edge is concave and the edge should have an angle of 80 degrees. b. Never sharpen the flat side of the blades. The strength of the metal is on this side. c. Grind all nicks and chips from the cutting edge. d. Grind to an 80 degree angle. e. Put a fine edge on the blade using a whetstone. __________________________________________________________ ACTIVITY: 1. Construct a tool sharpening template. Page 246 of the Cooper reference contains a pattern and directions for this exercise. 2. Bring from home various tools that need to be sharpened. Permission should be obtained for some tools, such as knives. 3. Identify correctly and incorrectly sharpened tools. 4. Practice sharpening each of the tools listed in this lesson. __________________________________________________________ AGRICULTURAL MECHANICS Tool Sharpening List The following lists of tools are those which are to be sharpened by the student in order to complete the exercise for this lesson. Each student MUST sharpen one tool in sections A, B, and C. Tools in section D are exactly what they are, extra credit. Extra credit tools may not be substituted for required tools. Required tools must be completed before extra credit assignments are accepted. A. DRILL BIT B. CONVEX GRIND COLD CHISEL CENTER PUNCH AXE HATCHET C. HOLLOW GRIND WOOD CHISEL PLANE IRON BLADE D. EXTRA CREDIT PIN PUNCH DRIFT PUNCH FIT A HANDLE ON A TOOL POCKET KNIFE (optional) Name: ____________________________ Date: ____________________________ Period:____________________________ Agricultural Mechanics Tool Sharpening Score Sheet (75 Points) A. TWIST DRILL correct lip angles __________ correct clearance angles __________ cutting lips the same length __________ workmanship __________ TOTAL __________ B. CONVEX GRINDING EXERCISE square on the tip __________ symmetrical on both sides __________ correct angle __________ correctly convex ground __________ workmanship __________ TOTAL __________ C. HOLLOW GRINDING EXERCISE square on the tip __________ correct angle __________ correctly hollow ground __________ whetstone finish __________ workmanship __________ TOTAL __________ ANY EXTRA CREDIT __________ GRAND TOTAL................ __________ HANDS-ON EXERCISE INSTRUCTIONS: Correctly sharpen the twist drill. Be sure to write your name on a masking tape flag and attach this to your drill so it can be graded. DRILL BIT SCORE SHEET CORRECT LIP ANGLE 15 _________ LIPS THE SAME LENGTH 15 _________ CORRECT CLEARANCE ANGLE 10 _________ NOT OVERHEATED 10 _________ TOTAL 50 _________ ----------------------------------------------------------------------------- 7/11/91 DLF/RRE/tf #%&C