Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Wood machining
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Wood machining
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Machine Woodworking
Class: Senior Secondary 3
Term: 2nd Term
Week: 9
Theme: Wood Machine And Machining
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Wood machining involves the use of power-driven tools and equipment to shape, cut, and finish timber components with precision and speed. It is distinct from hand tool woodworking primarily due to the automation of cutting forces and control mechanisms, allowing for repetitive tasks and intricate designs.
The wood lathe is a machine used to rotate a piece of wood (the workpiece) while a cutting tool is applied to shape it. Turning produces cylindrical, conical, spherical, or irregular forms.
Key Components of a Wood Lathe: Headstock: Contains the motor and spindle, which rotates the workpiece.
Tailstock: Supports the free end of the workpiece and can hold drilling chucks.
Bed: The main frame that supports the headstock, tailstock, and tool rest.
Tool Rest: Adjustable support for the turning tools, providing leverage and control.
Spindle: The rotating shaft in the headstock, to which drive centres or faceplates are attached.
Live Centre (Tailstock): Rotates with the workpiece, reducing friction.
Drive Centre (Headstock): Drives the workpiece.
Faceplate: A circular disk attached to the headstock spindle, used for turning bowls, platters, and other items that are too wide to be supported between centres. Safety Precautions for Wood Lathe Operations: Always wear eye protection (safety glasses or face shield). Ensure the workpiece is securely mounted and balanced before starting. Rotate the workpiece manually to check for clearance before switching on. Use sharp turning tools; dull tools can cause kickbacks. Position the tool rest as close as possible to the workpiece (within 3-6mm) and slightly below the centreline. Never wear loose clothing, jewellery, or have long hair untied. Start the lathe at the lowest speed and gradually increase as needed. Remove the tool rest before sanding or polishing. Maintain a safe distance from the rotating workpiece. Operations for Producing Turned Legs (Spindle Turning): Material Preparation: Select straight-grained timber free of knots and defects. Cut stock to slightly oversized dimensions, square the ends.
Mounting: Mark the centres of both ends of the workpiece. Mount the workpiece between the drive centre (headstock) and the live centre (tailstock), ensuring it is secure and runs true.
Roughing: Set the tool rest. Start the lathe at a low speed. Using a roughing gouge, gradually turn the square stock into a cylinder.
Shaping: Increase speed as appropriate. Using various turning tools (e.g., spindle gouge, skew chisel, parting tool), progressively shape the leg according to the design. Use calipers to check dimensions.
Detailing: Refine details using smaller gouges and chisels.
Sanding and Finishing: Remove the tool rest. Sand the turning while it is still on the lathe, progressing through grits from coarse to fine. Apply finish if desired.
Removal: Stop the lathe. Remove the workpiece. Operations for Producing a Flower Vase (Faceplate Turning / Hollow Turning): Material Preparation: Select suitable timber. Cut a blank to the desired diameter and thickness.
Mounting: Securely mount the wooden blank onto a faceplate using screws or a chuck. Ensure the faceplate is firmly attached to the headstock spindle.
External Shaping: Set the tool rest. Start the lathe at a low speed. Shape the exterior of the vase using appropriate turning tools (e.g., bowl gouge, round nose scraper). Create the desired profile, including the base.
Hollowing (Interior Shaping): Once the exterior is largely complete, readjust the tool rest to facilitate hollowing. Using hollowing tools (e.g., specialized hollowing tools, long-reach gouges), carefully remove material from the inside of the vase. Work from the rim towards the centre, periodically checking wall thickness with calipers or dividers.
Refinement and Sanding: Refine internal and external curves. Remove the tool rest. Sand both inside and outside surfaces, progressing through grits.
Finishing: Apply desired finish.
Removal: Stop the lathe. Carefully remove the vase from the faceplate. The base may require further finishing if it was attached directly with screws. The spindle moulder (also known as a shaper) or a router table with a router, is used to cut decorative edges, mouldings, rebates, and grooves into timber. The spindle moulder is a heavier-duty machine typically found in professional workshops, while a router table combines a portable router with a fixed table, offering similar capabilities for lighter work. Key Components (Spindle Moulder / Router Table): Table: A flat surface on which the workpiece slides.
Spindle/Router Bit: The rotating shaft/cutter that removes wood.
Fence: Guides the workpiece straight past the cutter.
Pressure Guides/Hold-downs: Keep the workpiece firmly against the table and fence.
Guards: Protect the operator from the rotating cutter.
Dust Collection Port: For chip extraction.
Safety Precautions: Always wear eye and hearing protection. Ensure cutters are sharp, clean, and securely tightened. Use push sticks or push blocks, especially on narrow or short workpieces. Set the fence and cutter depth accurately before starting. Ensure proper feed direction (against the rotation of the cutter). Never remove more than a few millimetres of material in a single pass. Keep hands clear of the cutter. Ensure the machine is properly guarded. Always use anti-kickback fingers or hold-downs where appropriate. Operations for Producing Moulding (Ovolo Profile): Material Preparation: Select timber of appropriate dimensions, ensuring edges are straight and square.
Cutter Selection: Choose an ovolo profile cutter or router bit. Install it securely in the spindle moulder or router collet.
Machine Setup: Adjust the cutter height to achieve the desired profile depth on the workpiece edge. Set the fence to determine how much of the cutter engages the workpiece. For full edge moulding, the fence might be aligned with the furthest cutting edge. Perform a test cut on a scrap piece of the same material to check settings. Adjust as necessary.
Operation: Hold the workpiece firmly against the fence and table. Using push sticks or push blocks, feed the workpiece smoothly and consistently past the rotating cutter. Always feed against the direction of cutter rotation to prevent kickback. For deeper profiles, multiple light passes may be required, incrementally adjusting the fence or cutter height.
Inspection: Check the finished profile for consistency and smoothness. The bandsaw is a versatile machine used for cutting curved shapes, resawing thick timber, and cutting joinery. It uses a continuous loop (band) of toothed metal stretched over two or more wheels.
Key Components: Table: Workpiece support.
Blade: The continuous toothed steel band.
Blade Guides: Support the blade and prevent twisting.
Upper and Lower Wheels: Drive the blade.
Blade Tensioner: Adjusts tension for proper cutting.
Blade Guard: Covers the blade, adjustable for workpiece thickness.
Safety Precautions: Always wear eye protection. Ensure the blade is sharp, properly tensioned, and tracked correctly. Adjust the upper blade guide to be approximately 6mm above the workpiece. Never force the workpiece; allow the blade to cut at its own rate. Keep hands away from the blade. Use relief cuts when cutting tight curves to prevent blade twisting and binding. Never try to remove off-cuts while the blade is moving. Ensure the machine is stable and the floor is clear.
Operations for Cutting Circular Shapes: Material Preparation: Mark the desired circular shape onto the timber blank using a compass or template.
Machine Setup: Select an appropriate blade width (narrower blades for tighter curves). Adjust blade tension and guide height.
Cutting: Place the marked workpiece on the table. Carefully feed the workpiece into the blade, following the marked line. For tight curves, make relief cuts from the waste side up to the marked line to prevent blade binding. Guide the workpiece smoothly, allowing the blade to do the work. Avoid twisting the blade.
Finishing: The bandsaw cut will be rough. The circular shape can then be refined on a disc sander, spindle sander, or further shaped on a wood lathe (faceplate turning). The mortice and tenon joint is one of the strongest and most durable joints in woodworking, widely used in frame and panel construction, doors, and furniture. A hollow chisel mortiser is specifically designed to cut square or rectangular holes (mortices) rapidly and accurately. Key Components of a Hollow Chisel Mortiser: Chisel and Bit Assembly: A square hollow chisel encloses a rotating drill bit. The drill bit clears out waste, and the chisel pares the square corners.
Hold-down Clamp: Secures the workpiece.
Table: Supports the workpiece.
Depth Stop: Controls the depth of the mortice.
Lever: Operator uses to push the chisel and bit into the wood.
Fence: Guides the workpiece for accurate positioning.
Safety Precautions: Always wear eye and hearing protection. Ensure the workpiece is securely clamped before operation.
Set the chisel and bit correctly: the drill bit should protrude slightly (approx. 1.5mm) beyond the chisel cutting edges. Ensure the chisel is sharp and free of burrs. Never force the machine; let it cut at its own pace. Clear chips regularly from the mortice. Operations for Cutting Mortices (using Hollow Chisel Mortiser): Material Preparation: Mark the location and dimensions of the mortice on the workpiece. Ensure the timber is dimensionally stable and square.
Chisel and Bit Selection: Choose a chisel and bit size appropriate for the mortice width.
Machine Setup: Install the chisel and bit correctly. Adjust the depth stop to the desired mortice depth. Set the fence to position the mortice accurately on the workpiece. Ensure the hold-down clamp is functional.
Cutting: Place the workpiece against the fence and clamp it securely. Align the chisel with the marked mortice location. Engage the motor and apply steady, downward pressure with the lever to cut the mortice. For a longer mortice, make a series of overlapping cuts, moving the workpiece along the fence. Start by cutting the two ends, then clear the material in between. Clear chips after each plunge or series of plunges.
Inspection: Check the mortice for accuracy, squareness, and depth. Operations for Cutting Tenons (briefly mentioning Table Saw as common method): While the morticer is specific, tenons are typically cut on a table saw or bandsaw, often refined with a chisel.
Material Preparation: Mark the shoulders and cheeks of the tenon on the end of the timber.
Machine Setup (Table Saw): Install a clean, sharp blade. Adjust the blade height and fence setting precisely for the tenon shoulders and cheeks. A dado blade set can speed this up. Use a tenoning jig or crosscut sled for safety and accuracy.
Cutting: Cut the tenon shoulders first, ensuring consistency on all four sides. Then, cut the tenon cheeks by making multiple passes or using a dado blade. Perform test cuts on scrap material to ensure the tenon fits snugly into the mortice.
Refinement: Pare to final fit with hand chisels if necessary. ---
This topic is highly practical and directly applicable to numerous real-life scenarios in Nigeria, fostering entrepreneurial skills and contributing to various sectors. Furniture Manufacturing and Interior Design: Application: The skills in turning (for legs, balustrades, finials) and moulding (for decorative trim on doors, windows, cabinets, cornices) are fundamental to the Nigerian furniture industry. Manufacturers in hubs like Aba, Nnewi, and Lagos constantly produce furniture (chairs, tables, beds, wardrobes) that incorporate these machined components.
Integration: Students can explore local furniture showrooms or workshops to identify examples of turned legs, ovolo mouldings, and mortice and tenon joints in locally manufactured furniture. This helps them connect classroom learning to marketable products. This skill is vital for creating high-quality, durable joints for long-lasting furniture often found in Nigerian homes and offices. Crafts, Souvenirs, and Artisanal Products: Application: The ability to create circular shapes and turned forms (like flower vases) is essential for artisans producing craft items for local markets and the tourism industry. Examples include decorative plates, bowls, ceremonial objects, and unique gift items made from local Nigerian hardwoods.
Integration: Students can be encouraged to design and create small, saleable craft items or souvenirs using the learned techniques, potentially for a school craft fair or local market simulation. This directly promotes entrepreneurship and an understanding of product design and market needs within a Nigerian context.
Building and Construction (Carpentry): Application: Accurate mortice and tenon joints are critical in timber framing for houses, constructing strong doors and windows, and building durable roof trusses – all common in Nigerian construction practices. Mouldings are used for aesthetic finishing around openings and along ceilings.
Integration: A field trip (virtual or actual) to a local building site or a carpentry workshop can demonstrate how these joints and mouldings are integral to the structural integrity and aesthetic appeal of Nigerian buildings. Discussing local timber species used in construction (e.g., Iroko, Mahogany, Obeche) and their suitability for specific machining operations adds local relevance. ---