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Module 4: Hacksaws

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.

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Module 4: Hacksaws

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  1. Module 4: Hacksaws Mechanical Workshop

  2. 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.

  3. 4.1. Introduction to hack sawing • Hack sawing is a process of cutting metal to size using a cutting tool called hacksaw.

  4. 4.2 Main parts of a hacksaw • The typical hacksaw consists of a saw blade supported by a frame fitted with a handle to give a firm grip

  5. 4.3 Types of hacksaw frames • There are two types of hacksaw frames: • Type 1: Solid hacksaw frame • In this type, only oneparticular standard length of blade can be used with this frame.

  6. Type 2: Adjustable hacksaw frame • In this type different standard lengths of blades can be fitted to this frame.

  7. 4.4 Hacksaw blades • The hacksaw blade consists of different parts: • 2 pin holes • Center line • Side • Back edge

  8. 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)

  9. 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

  10. Coarse pitch teeth The coarse pitch blade has 14-18 teeth/25 mm. It is used to cut thick and soft work pieces.

  11. Medium pitch teeth • The medium pitch blade has 18-24 teeth/25 mm. It is used to cut medium hard steel and copper alloys.

  12. Fine pitch teeth • The medium pitch blade has 24-32 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.

  13. Tooth selection • Selecting a blade with the correct number of teeth dependson 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.

  14. Coarse Pitch Teeth Fine Pitch Teeth

  15. 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

  16. The most common types of sets used • Alternate set: The teeth are arranged alternately

  17. Wave set: the teeth are arranged like a wave form

  18. 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.

  19. 4.4.5 Saw blade defects and their causes: • Fast Blunting • If wrong teeth number is chosen. • If saw blade is not tightened properly. • 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

  20. 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.

  21. 4.4.6 Hacksaw blade checklist • The following points should be taken in consideration before using the hacksaw • Select the correct pitch for the material you want to cut. • Ensure that the blade has the correct tension. • Ensure that the blade is not twisted or discolored. • Ensure that the teeth are pointed away from the handle. • Ensure that there are no broken or blunt teeth.

  22. 4.5 Hacksaw safety tips • Always wear safety goggles while using a hacksaw. • Be sure that the hacksaw blade is properly tensioned. • Do not brush away chips with your hand; use a brush. • Never test the sharpness of a blade by running your fingers across its teeth. • Keep the saw blades clean, and use light machine oil on the blade to keep it from overheating and breaking.

  23. 4.6 Cutting with the hacksaw • Hold the hacksaw properly at an angle of 30° • When cutting, move your body rather than just your arms. • Apply pressure only during the forward stroke (cutting stroke). • Use the entire length of the blade in each cutting stroke. • The usual cutting speed is from 40 to 50 strokes per minute

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