- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS (CLF2350) Unit Title: METALWORKING _____________________________________________________________________________ (CLF2356) Topic: COLD METALWORK Time Year(s) 5 Hours 1 / 2 / 3 / 4 _____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome # (H-2) - Identify 10 common metalworking tools by name and use. (H-4) - Make square and circular bends in metal, using an anvil or vise. (H-5) - Determine tap drill sizes for specific applications (H-6) - Use files and saw blades correctly. (H-8) - Cut threads with a tap and die. (H-9) - Layout and drill holes with a twist drill. (H-10) - Operate power tools such as drills and saws after completing appropriate safety tests. (See CLF2351) Special Materials and Equipment: Metalworking hand tools and power tools, a bench vise, various sizes of mild steel strap in different thicknesses from 1/4" to 1/2" References: Phipps, Lloyd J., & Reynolds, Carl L. (1990). MECHANICS IN AGRICULTURE (4th ed.). Danville, IL: Interstate Publishers. Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Evaluation: Quiz by instructor and evaluation of lab exercises and shop procedures. TOPIC PRESENTATION: Cold METALWORK A. Working metal cold is an easy and economical method of forming metal into various projects in a short time. Cold metalwork is the process of hand bending, drilling, taping, and cutting soft steels. It is one of the major types of manufacturing used to produce livestock and farm machinery (and equipment. B. Metalworking 1. Tools Used to Cut Cold Metal a. A hacksaw is a stiff-backed, bow-type saw with a replaceable metal cutting blade. There are from 16 to 32 teeth per inch. b. A cold chisel is used with a hammer to cut through bolts and round stock or to cut sheet metal. Cold chisels come in various sizes. c. A bolt cutter is a large-jawed cutting tool which can be used to cut round steel rods and soft bolts or small-square shaped steel bars. 2. Bending Metal Cold a. Vise - The standard shop vise with 3" to 5" size jaws works very well to secure and hold light steel to hand bend or form the metal to shape. Bending can also be done by allowing the jaws of the vise to remain open and use the pivots to bend gentle curves in strap steel and rod or pipe. b. Adjustable Open-end Wrench - A Crescent wrench is a suitable leverage device to cold bend the lighter steel shapes. A short length of pipe or a large hammer can also be used. c. To make a square bend: Clamp metal in the vise so the point of the bend is flush with the top of the vise jaw. Using a ball peen hammer or a rubber mallet, bend the metal by lightly striking just above the vise jaws (point of bend). Check for proper bend (90 degrees) using a square. d. Circular bends may be accomplished in one of several ways. 1) Fashion a jig out of 2 short pieces of pipe (size will be determined by desired degree of bend) and a flat piece of iron. Weld the pipe onto the iron at the desired distance. The jig can then be clamped into the vise. The metal can be placed between the jig pipes and manipulated for the desired bend. This procedure works best with strap steel and rod. 2) Bend shallow curves by manipulating the metal around the open jaw of the vise. 4. Filing Metal a. Files are used to remove small amounts of metal and to shape and smooth the surface. A file card should also be available to clean the file as needed. b. File Shapes - The shape of the file selected depends on the amount of contact surface to be filed or grooved. 1) Round - Round files come in different diameters and have a slight taper to the length of the file. It is not like a chainsaw sharpening file which is straight. 2) Flat - flat files come in many different cuts: a) rough cut d) second cut b) coarse e) smooth c) bastard f) dead smooth 3) A triangular file has three cutting sides and a narrow face. 4) A half round file has one flat face and one rounded face. 5) A knife file has two flat faces which come together as a sharp side or knife edge along one side. c. Safe Use of Files 1) Files should be cleaned with a file card whenever necessary. 2) All files should have a handle in order to prevent injuries to the hands. 3) Files should be held by both the front end and the handle. Hold the front end between the tips of the fingers and the thumb. Allow the file handle to rest in the palm of the hand. 4) Push the file forward with light yet steady pressure. Draw back with light yet steady pressure. Repeat steps as necessary. 5. Drilling Metal a. Punch mark a good center point before drilling. Go deep enough to allow the drill to center up on the mark. b. Twist drills come in three common sets or index groups and also a metric index. 1) Fractional Index - twist drill sizes from 1/16" diameter to 1/2" diameter by 64ths of an inch. 2) Lettered Index - twist drills from letter size 'A' to 'Z'; the letter 'A' is small and the letter 'Z' is big. 3) Numbered Index - twist drills from number 1 to number 60; number 1 is medium while number 60 is very small. 4) Metric Sizes - change by one millimeter per drill size. c. Drilling Procedure (drill press, portable electric hand drill) 1) Punch mark for a good center. 2) Select the correct size drill for the job. 3) Consult a drill speed chart to determine what RPM the drill should be operated (1/2" drill = 458 RPM). Change the drill press drive to the correct speed. 4) Chuck the drill securely into the drill press and check to see that the drill spins true. 5) Use a good quality cutting oil to lubricate and cool the drill while it is being used. 6) Use safety goggles when drilling with the drill press. 7) Drill with an even down pressure, but still allowing the drill to cut through the metal instead of being punched through. Relax the down pressure just before the drill breaks through the opposite side. 6. Taping Threads in Metal (threading the inside of a hole) Note: See Pipe Threading, CLF2550 a. Thread Sizes - All machine screw and bolt threads are straight cut threads which means that the first thread cut and the last thread cut are the same depth. The number of threads per inch varies depending upon the strength and torque required for the job and the size of the screw or bolt. b. Thread Pitch - This is the term given to the angle that the threads make to the head of the bolt. A coarse pitch will not hold as well as a fine pitch. These are usually referred to as national coarse and national fine thread bolts. 1) example: 1/4" diameter X 20 tpi National Coarse 2) example: 1/4" diameter X 28 tpi National Fine c. Selecting a Tap Drill - The tap drill is the correct size twist drill used to pilot just the right size hole through the metal to be followed by the selected tap. 1) A tap size chart with corresponding tap drill size is listed below: ____________________________________________________________ NATIONAL COARSE THREAD CHART Size Thread Threads/inch Tap Drill Size 1/4" 20 #7 (13/64" approx.) 5/16" 18 #F (1/4" approx.) 3/8" 16 5/16" 7/16" 14 #U (23/64" approx.) 1/2" 13 27/64" 9/16" 12 31/64" 5/8" 11 17/32" 3/4" 10 21/32" NATIONAL FINE THREAD CHART 1/4" 28 #3 (7/32" approx.) 5/16" 24 #I (17/64" approx.) 3/8" 24 #Q (21/64" approx.) 7/16" 20 25/64" 1/2" 20 29/64" 9/16" 18 33/64" 5/8" 18 37/64" 3/4" 16 1 1/16" ____________________________________________________________ 7. Using a Tap a. Taps vary by thread cut as well as the shape of the tap. There are three types of taps: 1) Taper Tap - This has a long, slender, easy starting entry into threading cutters, but must be allowed to tap entirely through the metal piece in order to cut all threads to the specified depth. 2) Plug Tap - This has a medium entry into the metal and can also be used to start the thread, but should continue the threading all the way through the metal. 3) Bottoming Tap - This tap does not start threads very well but will cut the thread all the way to the bottom of a blind hole which will then accept a bolt almost all the way to the bottom. b. Starting the tap in the metal straight and keeping it straight is the most difficult part of this job. Work slowly and align the vertical axis of the tap perpendicular to the surface of metal being tapped. Use a gentle but firm down pressure on the tap handle. c. Turn the tap several turns to get a good bite on the metal. Then as the tap is turned into the metal each half to full turn, back the tap up enough to break off the metal chip being cut (about one fourth turn). d. Be sure to clean all threading material out of the threads before they are used to twist in a bolt or screw. 8. Using a Die a. Putting threads on the outside of a rod to form a bolt is done using a die and die stock or handle. b. The dies also cut standard threads in National Coarse and National Fine sizes to match the taps discussed previously. c. Cutting threads involves most of the same procedures used in tapping threads with these additional hints: 1) Select the correct die thread size to go with the tap threads used or with a nut already selected. Set the alignment marks on the die cutters to be just across from one another. This will cut a standard clearance thread fit between the inside and outside threads. 2) Grind the tip of the rod to be threaded with a slightly chamfered end in order to allow the die to easily start straight. 3) Start the die with an even down pressure and hold the die stock level so the threads start an even cut. 4) Turn the die clockwise for one half to one full turn and then back off one fourth turn to clear the chips from the die. 5) When the threads have been cut as long as required, back the die off the threads and clean on a wire brush. 9. Using Power Tools for Cold Metalwork a. Power Hacksaw - This is a band-type saw designed to cut all metal angle, bar, strap, channel, pipe, and other shapes of construction steel. This saw is easy to operate. 1) Clamp the work firmly in the vise of the saw, at the desired cutting angle, in such a way that the most teeth of the blade will come in contact with the work when cutting begins. 2) Turn on the saw and lower the blade until it begins to cut and then set the balanced cutting weight of the saw to work. 3) The automatic shut-off of the saw should stop the saw when the piece has been cut through. b. Power Drill Press - A drill press can be either a floor model or a shorter bench model; both operate equally well. 1) When using a drill press always use a drill press vise to secure the work and assure a quality drilling job. 2) First select the correct drilling speed from the chart provided with the drill press. The speed (RPM) depends on the size of the drill; generally, the larger the drill size the slower the speed. 3) Place the drill bit in the chuck and tighten it using the chuck key. Then check to see that it spins true before turning on the drill press. 4) Check next to see if the drill is located and centered on the center punch mark already placed in the work. 5) Start drilling slowly to check the center alignment and then place a small amount of cutting oil in the hole and continue to drill with even pressure. Apply more cutting oil as the drilling progresses. 6) When close to finishing, relax the down pressure in order to go through the opposite side slowly. __________________________________________________________ ACTIVITY: 1. Select a tap drill for several different tap sizes. 2. Lay out several cuts and hole centers on a piece of steel and then cut, drill, and tap the material. __________________________________________________________ 7/17/91/ YNJ/tf #%&C