Teknologi Dan Rekayasa HAND TOOLS

COLD CHISELS Objectives : After studying this unit, the student should be able to : Identify and describe the types of cold chisels. Select the proper cold chisel for the job Use and sharpen a cold chisel properly Teknologi dan Rekayasa

COLD CHISELS The cold chisel is a wedge shaped tool used to cut metal softer than itself. Chiseling is the process of removing or cutting metal by means of a cold chisel and a hammer or pneumatic gun. The pneumatic gun is used when a good deal of metal is to be removed. Cold chisels are usually forged from octagonal tool steel containing approximately 80 percent carbon. This steel is tough enough to withstand the blow of the hammer, and yet the cutting end can be hardened and tempered to prevent the tool from becoming dull rapidly. Teknologi dan Rekayasa 3

TYPES OF CHISELS A variety of chisel is available for different kinds of work. The common types are flat, cape, diamond point, and round nose. Chisels are ordered by the width of the cut and the overall length. A flat chisel is used for cutting sheet metal, band iron, and wire, and for removing stock from flat surfaces, a process known as chipping. It is also used to cut off the heads of rivets and bolts. The other chisels are used mainly for cutting narrow grooves of different shapes and for cutting corners. Teknologi dan Rekayasa 4

TYPES OF CHISELS FLAT COLD CHISEL CAPPE CHISEL DIAMOND POINT CHISEL ROUND NOSE CHISEL Teknologi dan Rekayasa 5

CUTTING ANGLES AND EDGES A sharp, correctly ground chisel should be used at all times. The cutting angle of the chisels is determined by the strength of the material being cut. Chisels used on hard metal require a strong cutting edge with an included angle of 70 degrees. This angle can be decreased to 60 degrees for softer metals because less pressure is needed in the cutting process. Teknologi dan Rekayasa 6

CUTTING ANGLES AND EDGES 70 degree included angle 70° Mushroomed head The head of a chisel should be dressed by grinding to its original shape (beveled slightly) if it becomes mushroomed while in use. It is dangerous to use a chisel with a mushroomed head because the burrs may fly off and cause injury. Always return a chisel to the tool crib in good condition. Teknologi dan Rekayasa 7

CUTTING ANGLES AND EDGES When the chisel does not maintain a sharp cutting edge, it should be rehardened and ground to the proper cutting angle. Cracks and breaks in chisels are caused by improper forging or heat treating. Cracks indicate that the tool was either forged at too cold a temperature or heated too much when hardening. Breaks are usually caused by poor tempering. Teknologi dan Rekayasa 8

CUTTING ANGLES AND EDGES The flat chisel gives better results if ground with a slightly convex cutting edge. With a convex cutting edge, there is less tendency for the corners to dig into the surfaces being chiseled. This method of grinding also centralizes the pressure exerted on the tool. When the head of the chisel is struck, the impact is taken up by the center of the tool where it has more material to withstand the strain. Convex cutting edge Teknologi dan Rekayasa 9

HOW TO DRESS A GRINDING WHEEL Support the dresser on the tool rest so that the point of contact between the wheel and the dresser is slightly above the center of the wheel. Pass the dresser back and forth across the face of the wheel while it is in motion. Form the face of the wheel to an even surface which is approximately square with the sides of the wheel. Teknologi dan Rekayasa 10

HOW TO DRESS A GRINDING WHEEL 4. Stop the grinder and inspect the face of the wheel to see that all shiny spots are removed and that the pores of the wheel are clean. Dressing a grinding wheel Teknologi dan Rekayasa 11

HOW TO GRIND A FLAT CHISEL Adjust the tool rest so that an included angle of 70 degrees is formed. Hold the flat part of the of the chisel on the rest and lightly press the beveled surface against the grinding wheel face. Grinding a flat chisel Teknologi dan Rekayasa 12

HOW TO GRIND A FLAT CHISEL 3. Rotate the chisel slightly while grinding to form a convex cutting edge on the tool CAUTION : Too much pressure should not be applied while grinding a chisel because the heat generated may draw the temper. The chisel should during grinding by immersing it in cold water. 4. Turn the chisel over to the other side and repeat steps1 through 3. Teknologi dan Rekayasa 13

HOW TO CUT LIGHT SHEET METAL Select the proper chisel and a riveting or ball peen hammer. For ordinary work, a ¾ inch flat chisel and a 1 pound hammer are used. Prepare the chisel as necessary. Obtain vise jaws or angle iron and protective goggles CAUTION : Make sure that the head of the chisel is not mushroomed because particles may break off and cause injury. Teknologi dan Rekayasa 14

HOW TO CUT LIGHT SHEET METAL Place the cutting line on the stock flush with the edges of the angle irons and secure the work and angle irons firmly in the bench vise. Proper placement of chisel cutting edge Teknologi dan Rekayasa 15

HOW TO CUT LIGHT SHEET METAL 2. Hold the stock of the chisel firmly enough to guide it. 3. Starting at the center of the cut line, place the cutting edge of the chisel CAUTION : Hold the chisel at an angle to the job Chisel held at angle to work Teknologi dan Rekayasa 16

HOW TO CUT LIGHT SHEET METAL Grasp the hammer near the end of the handle so that it can be swung with an easy forearm movement. Strike the head of the chisel with a sharp blow CAUTION : Watch the cutting edge of the chisel and not the head in order to direct the cut better. With practice, one can learn to strike the head of the chisel without looking at it. Teknologi dan Rekayasa 17

HOW TO CUT LIGHT SHEET METAL 6. Reset the cutting edge of the chisel on the cut line and repeat steps 4 and 5 until the cut is completed CAUTION : Begin chiseling at the center of the line to be cut and follow the line each way to prevent tearing the metal at the corners Teknologi dan Rekayasa 18

HOW TO MAKE A STARTING SLIT Place the job across an opening or at the end of the bench Cut a cross with the flat chisel and a hammer Starting Slit Teknologi dan Rekayasa 19

HOW TO REMOVE A RIVET Place the riveted job so that one end is held firmly against a solid object Hold the flat cold chisel at the rivet head with the cutting edge parallel to the stock surface Strike the chisel with a hammer until the rivet head is removed Removing rivet with a cold chisel Teknologi dan Rekayasa 20

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