Teknologi Dan Rekayasa HAND TOOLS

HAND HACKSAW Objective : After studying this unit, the student should be able to : 1. Identify and describe the types of hacksaw blades and frames commonly used. 2. Select the proper blade of the job. 3. Use the hacksaw for cutting various metals properly

HAND HACKSAW The hand hacksaw is used for cutting materials by hand if power hacksaws and other cutting methods are not available or not convenient. The hand hacksaw is one of the most abused tools in the shop as shown by excessive breakage of the saw blades. To prevent breakage and to make satisfactory cuts, it is necessary that the correct blade be selected for the job and that the hacksaw be used skillfully.

HACKSAW FRAMES The two types of hacksaw frames are the straight handle and the pistol grip. The pistol grip is more practical, while the straight handle is used infrequently. Either type may be purchased with an adjustable frame to accommodate 8, 10 and 12 inch blades, or with a solid steel frame to hold a blade of a definite length. Sliding adjustable studs provide a means of setting the blade to cut parallel to or at right angles to the frame for long or deep cuts.

Straight handle hacksaw HACKSAW FRAMES Tension is applied to the blade by turning the threaded handle in the straight handle frame, and in the pistol grip, by turning a wingnut. Straight handle hacksaw Pistol grip hacksaw

HACKSAW BLADES Hacksaw blades are made of 90 percent to 1.10 percent carbon tool steel, tungsten alloy steels, and high speed steel. Steels containing 90 percent carbon harden to give maximum cutting speed without being too brittle. Adding 1.25 percent tungsten overcomes some of the brittleness. Blades are hardness and classified as all hard and flexible. Only the teeth of flexible blades are hardness. This renders them less likely to break during cutting than the all-hard blades. Flexible blades are used to cut thin metal.

HACKSAW BLADES The length of saw blades varies from 8 to 12 inches. This length is determined by the distance between the centers of the holes in the blade. The thickness of hand hacksaw blades is approximately 025 inch. The width of the blade ranges from 7/16 to 9/16 inch.

HACKSAW BLADES The number of teeth per inch is the most important factor to be considered when selecting a blade for the work. Blade are made with 14 to 32 teeth per inch. A special type of blade is available in which each tooth varies in size; the finer teeth are located at the front end of the blade. The graduation in teeth, often called points, facilitates making the starting cut.

HACKSAW BLADES LENGTH SINGLE CUT DOUBLE CUT 1 ʺ TEETH PER INCH

HACKSAW BLADES To provide clearance for the saw blade and to prevent it from binding, the teeth are set to cut wider than the blade. The teeth can be arranged in an alternate set, a raker set, or a wave set. On the alternate set blade, one tooth is bent slightly to the right and the next to the left. On the raker set blade, every third tooth is straight to clear the chips from the cut. On the wave set blade, short section of teeth are bent in opposite directions. Wave sets are used on fine tooth blade.

HACKSAW BLADES Alternate set Raker set Wave set Straight set SET OF BLADE Alternate set Raker set Wave set Straight set

CUTTING SPEEDS AND PRESSURE The ease with which a piece of metal may be cut depends on the speed and the pressure applied to the saw. Manufacturers recommend a cutting speed of 40 to 50 strokes a minute. This permits the worker to saw without tiring and also gives him a chance to relieve the pressure on the return stroke.

CUTTING SPEEDS AND PRESSURE If the work is sawed too rapidly, the heat generated draws the temper of the blade, making it soft and useless. Enough pressure should be applied when cutting to prevent the blade from slipping. Slipping causes the cutting teeth to become glazed, thereby ruining the saw.

SELECTION OF HACKSAW BLADES Table below shows the proper number of teeth per inch to use for the different materials and shapes of work. The result of using the wrong number of teeth is also shown. As a general rule, when selecting a blade for tubing or thin material, choose one which will have two or more teeth in contact with the surface being sawed.

SELECTION OF HACKSAW BLADES TEETH PER INCH USE 14 per inch For large sections and mild materials 18 per inch For tool steel, stainless steel, high carbon, and high speed steel 24 per inch For angle iron, brass, copper, iron pipe, BX, and electrical conduit 32 per inch For thin tubing and sheet metal

HOW TO USE THE HAND HACKSAW 1. Select a saw blade for the job. 2. Place the blade in the frame so that the teeth point away from the handle and the saw cuts only on the forward stroke. 3. Tighten the blade in the frame to prevent the saw from buckling and cutting off the mark.

HOW TO USE THE HAND HACKSAW CAUTION : Use judgment when tightening the frame to prevent breaking the blade, shearing thr pins, of bending the frame. If too tight, the blade will cant (bend upward). If too loose, the blade will bend while being used and may break.

HOW TO USE THE HAND HACKSAW 4. Clamp the work in the vise so that as many teeth of the saw blade as possible come in contact with the surface of the material to be cut, and in such a way that the saw cut line can be seen, if the work has finished surfaces, use soft jaws in the vise to prevent marring. Place the work so that the cut line is approximately ¼ inch from the vise jaws. This prevent the work from vibrating. In addition, the saw cut line should be at right angels to the face of the vise jaws.

HOW TO USE THE HAND HACKSAW CAUTION : when band iron or sheet metal is to be cut, be sure that at least two teeth are in contact with the surface being cut. For instance, if a 32 teeth per inch blade is being used, metal 1/16 inch thick (2 x 1/32) is the thinnest metal that can be across the thin edge.

HOW TO USE THE HAND HACKSAW

HOW TO USE THE HAND HACKSAW 5. Indicate the starting point by nicking the surface with a file to break any sharp corner which might tend to strip the teeth. This mark also helps the beginner star the saw at the proper place. 6. Grasp the handle of the frame firmly with the right hand, the front end of the frame is held by the left hand to help guide the saw when cutting.

HOW TO USE THE HAND HACKSAW 7. To start the cut, place the front end of the blade on the mark in the position. Apply a little pressure and make the stroke by pushing the saw straight across the surface of the work. Release the pressure and return the saw to the starting position.

HOW TO USE THE HAND HACKSAW STARTING THE CUT RIGHT WRONG BAND IRON RIGHT WRONG ANGLE IRON

HOW TO USE THE HAND HACKSAW 8. Repeat the process by adding a little pressure on the succeeding strokes. Continue the process at the rate of 40 to 50 strokes a minute for average work. No lubricant is necessary when cutting by hand. However, a little oil applied to the sides of the blade helps in making a deep cut.

HOW TO USE THE HAND HACKSAW CAUTION : The following points should be carefully noted while cutting to prolong the life of the saw blade. a. Too much pressure should not be applied on the cutting stroke. b. Make full length strokes to prolong the life of the blade and make the cutting easier. c. Cutting too rapidly ruins the blade

HOW TO USE THE HAND HACKSAW d. Make an even stroke so that the blade will not be twisted while sawing e. If the saw cuts off the mark, it should not be straightened by twisting. Start a new cut f. When a saw is broken in an unfinished cut, the cut should be resumed in another place on the work because the set of a new saw is thicker than that of a used saw. A new blade will break if forced into the old cut.

HOW TO USE THE HAND HACKSAW 9. When the work is nearly cut through, use less pressure to prevent the saw teeth from catching. 10. Remove any burrs left by the saw with a smooth cut file. 11. Return the hacksaw to the place provided for it.

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