Presentation on theme: "MODULE 4: HACKSAWS MECHANICAL WORKSHOP. MODULE OBJECTIVES After the completion of this module, student should be able to: Describe the basic hack sawing."— Presentation transcript:
MODULE 4: HACKSAWS MECHANICAL WORKSHOP
MODULE OBJECTIVES After the completion of this module, student should be able to: Describe the basic hack sawing process. Identify the parts of a hacksaw. Name the parts of a saw blade. Identify the correct blades that should be fitted for different materials. Demonstrate how to fit and remove a hacksaw blade correctly. Demonstrate the procedure used when cutting materials. Identify some defects of saw blades and their causes. Cut a metal work piece by using a hack saw to a given dimensions.
4.1. INTRODUCTION TO HACK SAWING Hack sawing is a process of cutting metal to size using a cutting tool called hacksaw.
The typical hacksaw consists of a saw blade supported by a frame fitted with a handle to give a firm grip 4.2 MAIN PARTS OF A HACKSAW
4.3 TYPES OF HACKSAW FRAMES There are two types of hacksaw frames: Type 1: Solid hacksaw frame In this type, only one particular standard length of blade can be used with this frame.
Type 2: Adjustable hacksaw frame In this type different standard lengths of blades can be fitted to this frame.
4.4 HACKSAW BLADES The hacksaw blade consists of different parts: -2 pin holes -Center line -Side -Back edge
CHARACTERISTICS OF A HACKSAW BLADE The hacksaw blade has 2 main characteristics 1- Teeth pitch which is the number of teeth per 25 mm. 2- Blade length which is the length between the centers of its pin holes. (See previous Slide)
4.4.2 HACKSAW BLADE PITCH The pitch of the hacksaw blades are divided into 3 classes: 1- Coarse pitch teeth 2- Medium pitch teeth 3- Fine pitch teeth The classification depends on the number of teeth per 25 mm also know as pitch
COARSE PITCH TEETH The coarse pitch blade has teeth/25 mm. It is used to cut thick and soft work pieces.
MEDIUM PITCH TEETH The medium pitch blade has teeth/25 mm. It is used to cut medium hard steel and copper alloys.
FINE PITCH TEETH The medium pitch blade has teeth/25 mm. It is used to cut thin and hard work pieces. Note: A fine pitch blade has more teeth per 25 mm than a coarse pitch blade.
Number Of teeth per 25 mm (Pitch) Name of Pitch Class Thickness Class used for Material Class used for 14 to 18Coarse Pitch TeethThickSoft 18 to 24Medium Pitch Teeth MediumHard Steel and Copper Alloys 24 to 32Fine Pitch TeethThinHard
TOOTH SELECTION Selecting a blade with the correct number of teeth depends on the thickness and type of the material to be cut. During the cutting process there should be at least 3 teeth in contact. For thin sections the highest number of teeth should be selected.
Fine Pitch Teeth Coarse Pitch Teeth
4.4.3 BLADE SETTING The teeth are set so that the blade makes a cut wider than itself. This helps to prevent the blade from jamming (becoming blocked) and provides for good chip clearance when cutting the metal
THE MOST COMMON TYPES OF SETS USED Alternate set: The teeth are arranged alternately
Wave set: the teeth are arranged like a wave form
4.4.4 INSTALLING THE BLADE IN THE HACKSAW FRAME. 1- Install the teeth point away from the handle of the hacksaw. 2- Tighten the wing nut until the blade is definitely under tension. This helps make straight cuts.
4.4.5 SAW BLADE DEFECTS AND THEIR CAUSES: 1.Fast Blunting If wrong teeth number is chosen. If saw blade is not tightened properly. 2.Teeth breaking Tooth pitch is too small while cutting thin elements If material is not tightened well. The hacksaw blade consists of different parts: -2 pin holes -Center line -Side -Back edge
SAW BLADE DEFECTS AND THEIR CAUSES: 3. Breaking of saw blade This occurred when the cutting material is not tightened properly 4. Curved cutting Wrong fixing of blade in the frame. Blade is insufficiently tightened.
DefectsCausesFigures Fast blunting1.Wrong teeth number 2.Blade is not tightened Teeth breaking1.Pitch too small 2.Material not tightened Breaking of saw blade 1. Cutting material is not tightened Curved cutting1.Wrong fixing of blade 2.Blade not tightened
4.4.6 HACKSAW BLADE CHECKLIST The following points should be taken in consideration before using the hacksaw 1.Select the correct pitch for the material you want to cut. 2.Ensure that the blade has the correct tension. 3.Ensure that the blade is not twisted or discolored. 4.Ensure that the teeth are pointed away from the handle. 5.Ensure that there are no broken or blunt teeth.
4.5 HACKSAW SAFETY TIPS 1.Always wear safety goggles while using a hacksaw. 2.Be sure that the hacksaw blade is properly tensioned. 3.Do not brush away chips with your hand; use a brush. 4.Never test the sharpness of a blade by running your fingers across its teeth. 5.Keep the saw blades clean, and use light machine oil on the blade to keep it from overheating and breaking.
4.6 CUTTING WITH THE HACKSAW 1.Hold the hacksaw properly at an angle of 30° 2.When cutting, move your body rather than just your arms. 3.Apply pressure only during the forward stroke (cutting stroke). 4.Use the entire length of the blade in each cutting stroke. 5.The usual cutting speed is from 40 to 50 strokes per minute