Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Cutting Tools
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Cutting Tools
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Subject: Welding & Fabrication
Class: Senior Secondary 2
Term: 1st Term
Week: 1
Theme: Tools / Equipment And Maintenance
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This topic introduces students to the essential cutting tools used in welding and fabrication workshops. Understanding and correctly using these tools is fundamental to preparing materials for welding, shaping components, and carrying out repair work in various industries across Nigeria, from small-scale workshops fabricating gates and windows to larger construction and manufacturing sectors. Mastery of these tools enhances precision, efficiency, and safety in vocational practice, contributing to the development of skilled labour crucial for Nigeria's economic growth.
Tools / Equipment And Maintenance Cooling/Lubrication (Optional but Recommended): For extended cuts or harder material, apply cutting fluid or a few drops of oil to reduce friction and heat.
9. Finish the Cut: As the cut nears completion, reduce pressure and support the free end of the rod to prevent it from snapping off unevenly or falling.
1
0. Clean Up: Carefully remove the cut rod. Deburr sharp edges if necessary.
Commentary: This solution directly addresses the selection of the correct tool and details the sequential, safe, and effective steps for its use, aligning with the performance objective.
Question 2: A welder needs to quickly remove excess weld spatter and a small protruding metal burr from a fabricated steel frame. Describe how a cold chisel would be used for this task, including relevant safety measures.
Solution 2: A cold chisel would be used in conjunction with a hammer to chip off the weld spatter and remove the metal burr.
Steps for Using a Cold Chisel:
1. Wear PPE: Don safety goggles or a face shield and heavy-duty gloves to protect against flying metal fragments.
2. Inspect Chisel: Check the chisel head for mushrooming; if present, grind it down before use to prevent pieces from breaking off. Ensure the cutting edge is reasonably sharp.
3. Secure Workpiece: If possible, clamp the steel frame securely. If not, ensure it's stable and won't shift.
4. Position Chisel: Hold the chisel firmly with one hand, positioning its cutting edge against the weld spatter or burr. For spatter, aim to get the chisel slightly under the spatter. For a burr, position it to shear the burr off.
5. Chisel Angle: Hold the chisel at an appropriate angle (e.g., 35-45 degrees) to the surface to allow for effective chipping/shearing.
6. Strike with Hammer: With the other hand, strike the head of the chisel squarely and firmly with a club hammer or ball-peen hammer. The force should be sufficient to chip or shear the metal.
7. Control and Repeat: Adjust the chisel's position and angle as needed, making controlled, repetitive strikes until the spatter or burr is removed.
8. Clean Up: Collect removed metal fragments.
Commentary: This solution explains the practical application of a cold chisel for common fabrication cleanup tasks, emphasizing both technique and the critical safety measure of wearing PPE and checking the chisel's condition.
Question 3: An apprentice needs to cut a large curve in a thin sheet of galvanized iron for a ducting project. Which type of tin snips should be selected, and what is a crucial safety consideration when handling the cut sheet metal?
Solution 3: For cutting a large curve in a thin sheet of galvanized iron, Left-cut snips (red handles) or Right-cut snips (green handles) would be selected, depending on the direction of the curve relative to the operator's dominant hand. For a large curve, aviation snips are suitable due to their leverage. Crucial Safety Consideration When Handling Cut Sheet Metal: The most crucial safety consideration is wearing heavy-duty gloves. Cut sheet metal edges are extremely sharp and can cause severe lacerations. Students must always handle cut sheets with gloves and be aware of burrs and sharp corners.
Commentary: This question tests knowledge of specific tool types for particular tasks and highlights a paramount safety aspect often overlooked when working with sheet metal.
5. Independent Practice (Questions Only)
1. List three common types of cutting tools used in a typical Nigerian welding workshop, distinguishing between manual and power tools.
2. Describe the steps for securely clamping a workpiece before using any cutting tool, and explain why this step is critical.
3. A student is using an angle grinder with a cutting disc to cut a steel plate. List four mandatory Personal Protective Equipment (PPE) items that must be worn and briefly explain why each is necessary.
4. Explain the importance of selecting the correct TPI (teeth per inch) for a hacksaw blade when cutting different thicknesses of metal. Provide an example.
5. What is "mushrooming" on a cold chisel head, and why is it dangerous? How should it be rectified?
6. Outline the proper technique for making a continuous, straight cut through a sheet metal using tin snips.
Cutting Tools Term: 1st Term Week: 11 ---
1. Overview and Learning Objectives This topic introduces students to the essential cutting tools used in welding and fabrication workshops. Understanding and correctly using these tools is fundamental to preparing materials for welding, shaping components, and carrying out repair work in various industries across Nigeria, from small-scale workshops fabricating gates and windows to larger construction and manufacturing sectors. Mastery of these tools enhances precision, efficiency, and safety in vocational practice, contributing to the development of skilled labour crucial for Nigeria's economic growth.
Specific Performance Objectives: Students will be able to identify and describe various cutting tools used in welding and fabrication. Students will be able to demonstrate the correct and safe method for using common cutting tools such as hacksaws, cold chisels, tin snips, and angle grinders with cutting discs. Students will be able to select the appropriate cutting tool for specific fabrication tasks and materials. Students will be able to outline essential safety precautions when operating cutting tools. Connection to Real-World Applications in Nigeria: These skills are directly applicable in a wide range of Nigerian contexts, including: Roadside Fabrication Workshops: Cutting steel bars for gates, window frames, and security doors.
Automobile Repair: Cutting damaged body panels, exhaust pipes, or chassis components.
Construction Sites: Cutting rebar, metal sheets, and structural profiles.
Artisan Craftsmanship: Shaping metal for sculptures, decorative items, and furniture.
Agricultural Equipment Repair: Cutting and shaping parts for farm implements.
Pipeline Fabrication: Cutting pipes to specific lengths for water supply or oil and gas infrastructure.
2. Key Concepts and Explanations Definition of Cutting Tools: Cutting tools in welding and fabrication are hand tools or power tools designed to remove material from a workpiece by shearing, sawing, chipping, or grinding action, resulting in separation or shaping of the material. Their primary purpose is to prepare materials to size, create specific profiles, or facilitate dismantling. General Safety Precautions for Cutting Tools: Safety is paramount when using cutting tools. Negligence can lead to severe injuries.
1. Personal Protective Equipment (PPE): Always wear appropriate PPE, including safety goggles or face shield, heavy-duty gloves, safety boots, and hearing protection (especially for power tools like angle grinders). Overalls or work clothes should be non-flammable and fit properly to avoid snagging.
2. Workpiece Securing: Ensure the workpiece is firmly clamped or secured in a vice. Loose material can shift during cutting, causing injury or an inaccurate cut.
3. Work Area: Maintain a clean, clear, and well-lit work area. Remove obstructions, oil spills, and combustible materials, especially when using tools that generate sparks (e.g., angle grinders, oxy-fuel torches).
4. Tool Inspection: Before use, inspect tools for damage (e.g., dull blades, cracked handles, frayed power cords, damaged guards). Never use damaged tools.
5. Correct Tool for the Job: Use the appropriate tool for the specific material and task. Forcing the wrong tool can damage the tool or workpiece and cause injury.
6. Concentration: Maintain full concentration while cutting. Avoid distractions.
7. Power Tool Specifics: Ensure power tools are properly earthed or double-insulated. Disconnect power before changing accessories or performing maintenance. Keep hands and body clear of moving parts. Always use guards provided by the manufacturer.
Types of Cutting Tools and Their Usage:
A. Hacksaw Description: A hand tool used for cutting metal. It consists of a frame, a handle, and a replaceable blade.
Parts: Frame: Holds the blade under tension. Can be adjustable for different blade lengths.
Blade: A thin strip of high-carbon steel with teeth on one edge. Teeth usually point away from the handle.
Handle: Provides grip for the user.
Wing Nut/Tensioning Device: Used to adjust blade tension.
Blade Selection: Hacksaw blades are specified by their length and the number of teeth per inch (TPI).
Coarse Blades (14-18 TPI): For softer metals (aluminium, brass) and thicker sections.
Medium Blades (20-24 TPI): General purpose, for medium sections and steel.
Fine Blades (28-32 TPI): For thin-walled tubing, sheet metal, and hard materials where a finer finish is required.
Rule of Thumb:* At least 3 teeth should be away from the handle.
Handle: Provides grip for the user.
Wing Nut/Tensioning Device: Used to adjust blade tension.
Blade Selection: Hacksaw blades are specified by their length and the number of teeth per inch (TPI).
Coarse Blades (14-18 TPI): For softer metals (aluminium, brass) and thicker sections.
Medium Blades (20-24 TPI): General purpose, for medium sections and steel.
Fine Blades (28-32 TPI): For thin-walled tubing, sheet metal, and hard materials where a finer finish is required.
Rule of Thumb: At least 3 teeth should be in contact with the workpiece at all times.
How to Use a Hacksaw:
1. Secure Workpiece: Firmly clamp the material in a vice, ensuring the cutting line is clear and close to the vice jaws to minimize vibration.
2. Select Blade: Choose the appropriate blade based on the material thickness and type.
3. Install Blade: Position the blade with the teeth pointing forward (away from the handle). Tension the blade firmly using the wing nut, ensuring it produces a clear "ping" sound when plucked, but not over-tightened to prevent snapping.
4. Starting the Cut: Place the blade on the cutting line. Use a thumb as a guide (with a glove) to start the cut with a series of short, light forward strokes. Alternatively, use a file to create a small notch to guide the blade.
5. Cutting Technique: Hold the hacksaw firmly with both hands (one on the handle, the other on the frame). Apply steady downward pressure only on the forward stroke. Release pressure on the return stroke. Use the full length of the blade (about two-thirds to three-quarters) to distribute wear evenly. Maintain a cutting rate of approximately 40-50 strokes per minute. Periodically apply cutting fluid (e.g., soluble oil or even engine oil) for hard materials to reduce friction and extend blade life.
6. Finishing the Cut: As the cut nears completion, reduce pressure and support the part being cut off to prevent it from breaking unevenly or falling, which could cause injury.
Maintenance: Keep blades clean. Loosen blade tension slightly after use for long-term storage to prevent frame distortion. Replace dull or broken blades.
B. Cold Chisel Description: A hand tool made of hardened steel, used for cutting, chipping, or shearing cold metal (i.e., metal not heated to a malleable state). It is used in conjunction with a hammer.
Types (common in fabrication): Flat Chisel: Most common, used for general chipping, cutting, and shearing.
Cape Chisel: Narrower than a flat chisel, used for cutting grooves or keyways.
Cross-Cut Chisel: Similar to cape, but often with a wider cutting edge.
Round-Nose Chisel: Used for cutting semi-circular grooves or for chipping concave surfaces.
Diamond-Point Chisel: Used for cleaning out corners.
How to Use a Cold Chisel:
1. Secure Workpiece: Firmly clamp the material to be cut or chipped.
2. Wear PPE: Always wear safety goggles or a face shield.
3. Hold Chisel: Grip the chisel firmly with one hand, keeping the fingers away from the top (head) of the chisel. Position the cutting edge on the marked line or area to be removed.
4. Hold Hammer: Use a hammer (e.g., ball-peen or club hammer) in the other hand. The hammer weight should be appropriate for the chisel size and task.
5. Striking Technique: Strike the head of the chisel squarely and firmly with the hammer. Vary the force of the blows depending on the material and desired depth of cut.
6. Chisel Angle: The angle at which the chisel is held relative to the workpiece is crucial. For general cutting or chipping, an angle of 35-45 degrees to the surface is often effective. A steeper angle will tend to dig in, while a shallower angle will skim the surface.
7. Direction of Cut: When shearing or cutting through material, direct the chisel along the desired line.
Safety: Ensure the chisel head is free of "mushrooming" (burrs formed from repeated hammer blows), which can cause metal fragments to fly off. Grind mushroomed heads regularly. Avoid glancing blows with the hammer. Always