Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Cutting and Filling Operation
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Cutting and Filling Operation
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Subject: Metal Work
Class: Senior Secondary 1
Term: 3rd Term
Week: 5
Theme: Handtools, Equipment And Bench Work
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Identify and select appropriate to ols for cutting. Name, select and use different types of files for various operations
This section provides in-depth explanations of cutting and filing tools and their operations. A. Cutting Operations and Tools Cutting in metalwork involves severing or removing material from a workpiece. The choice of cutting tool depends on the type of material, its thickness, the desired cut accuracy, and the available resources.
1. Chisels: Chisels are hand-operated cutting tools used for cutting, chipping, and shearing metal. They are typically made from high carbon steel, heat-treated to make the cutting edge harder than the body.
Parts of a Chisel: Head: The striking end, designed to be hit with a hammer. It should be free from mushrooming.
Body/Shank: The main part of the chisel, usually hexagonal or octagonal for a good grip.
Cutting Edge: The sharpened end that performs the cutting action. The angle varies with the hardness of the metal being cut (sharper for softer metals).
Types of Chisels (and their uses): Flat Chisel (Cold Chisel): The most common type. Its cutting edge is wider than the body.
Uses: General cutting of sheet metal, chipping excess metal, removing burrs, cutting rivets, and splitting nuts.
Cross-cut Chisel (Cape Chisel): Similar to a flat chisel but with a narrower cutting edge than its body, widening just behind the edge to provide clearance.
Uses: Cutting keyways, grooves, and slots in flat surfaces where a flat chisel would be too wide.
Round-nose Chisel: Features a rounded cutting edge.
Uses: Cutting semi-circular grooves, oil grooves in bearings, and concave surfaces. It can also be used to clean out corners or remove metal from curved sections.
Diamond-point Chisel: Has a square cross-section ground to a diamond-shaped point.
Uses: Cutting V-grooves, sharp corners, squaring up the bottom of drilled holes, and tidying up internal corners.
Half-round Chisel: Has a curved cutting edge, shaped like a half-moon.
Uses: Cutting concave grooves and channels, especially for clearing out half-round keyways.
2. Hacksaws: Hacksaws are manual cutting tools primarily used for cutting metals like bars, rods, pipes, and structural sections.
Parts of a Hacksaw: Frame: Holds the blade and handle. Can be fixed (for a specific blade length) or adjustable (for various blade lengths).
Blade: A thin strip of high-speed steel with teeth on one edge.
Handle: Provides grip and control, usually pistol-grip style.
Wing Nut/Tensioning Device: Used to adjust the tension of the blade.
Hacksaw Blades: Material: Usually high-speed steel (HSS) or bi-metal (HSS teeth welded to a flexible carbon steel body).
Pitch: The number of teeth per inch (TPI).
Coarse Pitch (14-18 TPI): For cutting soft metals, large sections, and faster material removal.
Medium Pitch (20-24 TPI): General purpose, for cutting medium sections of steel, brass, and copper.
Fine Pitch (28-32 TPI): For thin materials, tubing, and hardened metals, providing a smoother cut.
Setting: The teeth are offset (wavy or alternate set) to create a kerf (cut width) wider than the blade thickness, preventing binding.
Proper Use of Hacksaw:
1. Select the correct blade pitch for the material. At least two teeth should be in contact with the workpiece at all times.
2. Ensure the blade is correctly tensioned (tight, but not over-tight to avoid breakage). Teeth should point away from the handle.
3. Secure the workpiece firmly in a vice.
4. Maintain a stable stance, holding the saw with both hands.
5. Apply pressure on the forward stroke only; relieve pressure on the return stroke.
6. Use long, steady strokes (approximately 40-50 strokes per minute) across the entire blade length.
7. Lubricate the blade occasionally with cutting oil for hard metals to reduce friction and heat.
Safety Precautions: Ensure workpiece is clamped; avoid forcing the cut; use eye protection; do not use a dull or damaged blade.
3. Shears/Snips: These are hand tools used for cutting thin sheet metal.
Types: Straight Snips: For cutting straight lines.
Curved Snips (Right or Left Cut): For cutting curves.
Bench Shears: Larger, bench-mounted shears for cutting heavier gauge sheet metal.
Uses: Cutting patterns from sheet metal for roofing, ductwork, and small fabrication roughing down.
Second-cut: Finer than bastard, for reducing stock and producing a good finish.
Smooth: For producing a smooth finish and accurate dimensions.
Dead-smooth: Very fine, for achieving a highly refined finish and extreme accuracy.
2. Filing Techniques: Straight Filing: Pushing the file straight across the workpiece, perpendicular to the long axis. Used for general surface reduction.
Draw Filing: Holding the file with both hands, one at the tip and one at the handle, and pulling it sideways across the workpiece. Produces a very fine, smooth finish and a straight edge.
Cross Filing: Pushing the file across the workpiece at an angle (usually 45 degrees) to the long axis, changing the angle with each stroke. Helps prevent grooving and ensures a flat surface.
Care of Files: Use a file card (wire brush) to remove "pins" (metal particles lodged between teeth) regularly to maintain cutting efficiency and prevent scratching. Do not use files without a handle. Do not use files as hammers or pry bars. Store files separately or in racks to prevent teeth from dulling or breaking against each other. C. Scrapers (as mentioned in Evaluation Guide) Scrapers are precision hand tools used for removing very fine amounts of material from metal surfaces to achieve precise fitting or smooth finishes, especially in bearing surfaces or for decorative effects.
Types: Flat Scrapers: For flat surfaces.
Half-round Scrapers: For concave surfaces.
Three-corner (Triangular)
Scrapers: For deburring edges and corners.
Uses: Removing burrs and sharp edges after machining or cutting. Precision fitting of mating parts, like bearings (e.g., in engine rebuilding). Creating decorative patterns on metal surfaces. Spotting and levelling machine beds.
Safety Precautions for all Tools: Always wear appropriate Personal Protective Equipment (PPE), including safety glasses or goggles, and hand gloves where necessary. Ensure the workpiece is securely clamped in a vice. Use tools for their intended purpose only. Maintain tools in good condition (sharp, clean, with handles). * Keep the workbench tidy and free of clutter. the blade occasionally with cutting oil for hard metals to reduce friction and heat.
Safety Precautions: Ensure workpiece is clamped; avoid forcing the cut; use eye protection; do not use a dull or damaged blade.
3. Shears/Snips: These are hand tools used for cutting thin sheet metal.
Types: Straight Snips: For cutting straight lines.
Curved Snips (Right or Left Cut): For cutting curves.
Bench Shears: Larger, bench-mounted shears for cutting heavier gauge sheet metal.
Uses: Cutting patterns from sheet metal for roofing, ductwork, and small fabrication projects (e.g., in a local vulcanizing shop or sheet metal workshop). B. Filing Operations and Tools Filing is a process of removing small amounts of material from a workpiece using a file. It is used for shaping, smoothing, deburring, and finishing metal surfaces.
1. Files: Files are hand tools made of hardened high carbon steel, having parallel rows of sharp cutting teeth.
Parts of a File: Handle: Wood or plastic, for gripping. Essential for safety.
Ferrule: Metal ring on the handle to prevent splitting.
Tang: The pointed, unhardened part of the file that fits into the handle.
Heel: The part of the file nearest the tang, without teeth.
Face/Side: The broad cutting surface of the file.
Edge: The narrow cutting surface, usually with a single cut.
Point/Tip: The end of the file opposite the tang.
Classification of Files: By Cut (Arrangement of Teeth): Single-cut File: Has one set of parallel teeth cut diagonally across the face at an angle of 60-80 degrees.
Uses: Produces a smooth finish, used for sharpening tools, finishing operations, and on softer materials like brass, copper, and aluminum.
Double-cut File: Has two sets of teeth crossing each other (one set at 45 degrees, the other at 70-80 degrees).
Uses: Provides faster material removal and a coarser finish, used on harder metals like steel and cast iron for roughing operations.
Rasp-cut File: Has individual, sharp, pointed teeth spaced irregularly.
Uses: Used for very rough work on soft materials like wood, leather, lead, and aluminum, or for removing large amounts of material quickly.
Curved-cut File: Has teeth arranged in curved rows.
Uses: Primarily used on soft materials and body fillers in automotive repair for rapid removal without clogging.
By Shape: Flat File: Rectangular in cross-section, tapering slightly in width and thickness.
Uses: General purpose, for filing flat surfaces and outside convex curves.
Hand File: Similar to a flat file but parallel in width and tapered in thickness. One edge is "safe" (no teeth) to prevent damage to adjacent surfaces.
Uses: Precision filing on flat surfaces, especially when working close to a finished edge.
Half-round File: Has one flat face and one convex (curved) face.
Uses: Filing flat surfaces (flat side) and concave curves (curved side).
Round File (Rat-tail File): Circular in cross-section, tapering to a point.
Uses: Enlarging round holes, filing concave curves, and shaping circular openings.
Square File: Square in cross-section, tapering to a point.
Uses: Filing square or rectangular holes, slots, and keyways.
Triangular File (Three-square File): Triangular in cross-section, with 60-degree angles.
Uses: Filing internal corners, sharpening saw teeth, and filing V-grooves.
Knife-edge File: Has a very thin edge, like a knife blade.
Uses: Filing very narrow slots and acute angles.
By Grade (Coarseness of Teeth): Rough: Very coarse, for rapid material removal.
Coarse: General purpose for faster removal.
Bastard: A common grade for general purpose roughing down.
Second-cut: Finer than bastard, for reducing stock and producing a good finish.
Smooth: For producing a smooth finish and accurate dimensions.
Dead-smooth: Very fine, for achieving a highly refined finish and extreme accuracy.
2. Filing Techniques: Straight Filing: Pushing the file straight across the workpiece, perpendicular to the long axis. Used for general surface reduction.
Draw Filing: Holding the file with both hands, one at the tip and one at the handle, and pulling it sideways across the workpiece. Produces a very fine, smooth finish Teacher Activities: Introduction & Engagement (10 mins): Begin by asking students about their experiences with cutting or shaping metal, perhaps from observing local welders, mechanics, or artisans in their communities (e.g., "What tools do the local welder use to cut angle iron for a gate? How do they smooth the edges?"). Introduce the topic of cutting and filing, explaining their importance in metalwork and everyday life in Nigeria. Tool Identification & Demonstration (25 mins): Display actual cutting tools (various chisels, hacksaw with different blades, snips) and filing tools (various shapes and grades of files, file card, scraper). Point out each tool, name it, describe its parts, material, and primary function. Demonstrate correct grip and posture for holding chisels, hammers (for chiseling), hacksaws, and files. Emphasize safety precautions associated with each tool.
Operation Demonstration (30 mins): Cutting Demonstration: Demonstrate how to secure a mild steel bar in a vice and cut it using a hacksaw, explaining proper blade tension, stroke, and pressure application. Demonstrate chiseling a piece of sheet metal or removing a rivet, showing the correct angle and striking technique. Briefly show how to use snips for straight and curved cuts on thin gauge sheet metal.
Filing Demonstration: Demonstrate securing a metal piece in a vice. Illustrate straight filing, draw filing, and cross filing techniques on different surfaces. Show how to use different file shapes (e.g., flat, half-round, round) for appropriate tasks. Demonstrate cleaning a file with a file card.
Scraper Demonstration: Briefly demonstrate how to remove burrs from a cut edge using a scraper.
Practical Work Supervision (45 mins): Divide students into small groups. Provide each group with a workbench, vice, PPE, mild steel samples (e.g., 10mm x 10mm flat bar, thin sheet metal), hacksaws with blades, various files, chisels, and hammers.
Instruct students to practice: Cutting a specified length of mild steel bar using a hacksaw. Chiseling a straight line on a thin metal sheet or removing a small burr. Filing a flat edge of a metal piece to smooth it and achieve a square corner. Filing a curved edge using a half-round or round file. Circulate, observe, correct techniques, provide individual feedback, and ensure strict adherence to safety rules.
Recap and Q&A (10 mins): Review the tools and techniques covered. Answer any student questions. Reiterate key safety points.
Student Activities: Actively listen and observe teacher demonstrations. Ask clarifying questions during explanations and demonstrations. Identify various cutting and filing tools presented by the teacher. Practice safe handling of cutting and filing tools. Engage in practical exercises under supervision, including: Measuring and marking a metal bar for cutting. Safely securing workpieces in a vice. Cutting metal bar using a hacksaw, maintaining correct posture and technique. Using a chisel to chip metal or remove a burr. Performing straight filing, draw filing, and cross filing to smooth and shape metal edges. Selecting and using appropriate files for flat and curved surfaces. Clean tools and work area after practical sessions. Participate in group discussions about tool selection for specific tasks.
Local Metal Fabrication and Welding Workshops: In every Nigerian community, local welders (e.g., "Baba Welder") use hacksaws to cut angle iron, square pipes, and flat bars to construct gates, window grilles, security doors, and furniture. They also extensively use files to deburr sharp edges, smooth welds, and finish surfaces. Chisels are used for opening up joints, cutting off excess material, or modifying existing structures during repairs.
Automotive Repair and Panel Beating: Vehicle mechanics and panel beaters in Nigeria regularly use cutting and filing tools. Hacksaws are essential for cutting exhaust pipes or chassis components. Chisels are used for removing rusted bolts, breaking spot welds, or shaping body panels. Files are indispensable for smoothing out repaired bodywork, deburring cut edges, and preparing surfaces for painting or welding. Specialized files (like curved-cut files) are particularly useful for shaping body fillers. Artisan Craftsmanship and Entrepreneurship: Nigerian artisans involved in metal art, sculpture, jewellery making (e.g., making traditional brass ornaments), or even blacksmithing, rely heavily on precise cutting and filing. These skills enable them to shape intricate designs, create smooth finishes, and remove imperfections, turning raw metal into valuable commercial products or traditional crafts sold in local markets like Onitsha Main Market or Balogun Market. This directly connects the lesson to potential income-generating skills.