Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Estimation and Costing
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Estimation and Costing
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Subject: Carpentary And Joinery
Class: Senior Secondary 2
Term: 3rd Term
Week: 3
Theme: Construction Principles And Techniques
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In terpret drawing and sketches. Calculate and estimate cost of materials for constructing a simple project.
6 / 12 = 0.5 board feet Total for 4 legs = 4 × 0.5 = 2.0 board feet Rails (4 pieces): Each 2" x 1" x 0.66 ft Board feet per rail = (2 × 1 × 0.66) / 12 = 1.32 / 12 = 0.11 board feet (approx.) Total for 4 rails = 4 × 0.11 = 0.44 board feet Total Raw Timber: 2.0 + 0.44 = 2.44 board feet Add 15% Waste Factor for Rough Timber: 2.44 × 1.15 = 2.806 board feet (Round up to 3 board feet for purchase). b)
Plywood for Seat: Seat dimensions: 300mm x 300mm (approx. 1ft x 1ft)
Area required: 1 sq ft. One standard 8ft x 4ft plywood sheet has an area of 32 sq ft. Many 1ft x 1ft pieces can be cut from one sheet. For this single stool, it's a very small fraction of a sheet. A single stool would likely use a "quarter sheet" or a piece from scrap. For purchasing, a workshop might buy a full sheet, or if only making one, purchase a small offcut. For estimation, we calculate actual usage then consider purchase unit. If we must purchase in smallest common units: typically a quarter sheet (2ft x 4ft) might be bought, or a full sheet if many stools are to be made. Area of 1/4 sheet (2ft x 4ft) = 8 sq ft. This is much larger than needed. Let's assume the teacher intends for students to calculate exact use and then note that the smallest purchase unit is a full sheet or a cut piece if available.
Quantity needed: 1 piece (300mm x 300mm). c)
Other Materials: Wood Glue: 1 bottle Screws: 1 packet (assuming enough for 4 rails into 4 legs + seat attachment)
Varnish: The stool's surface area (top + 4 sides of seat + 4 legs + 4 rails) is approximately (0.30.3) + 4(0.050.45) + 4(0.050.2) + 4(0.0250.2) = 0.09 + 0.09 + 0.04 + 0.02 = 0.24 sq m. A 1-litre can covers typically 10-12 sq m. So, a small fraction of a litre. We'll round up to purchasing 1 litre as it's the smallest unit.
Step 3: Calculate Total Material Cost Timber: 3 board feet × NGN 3,000/board foot = NGN 9,000 Plywood (Seat): As a small offcut can be used, we might estimate 1/8 of a sheet (if a full sheet is cut) or consider the cost of purchasing a small cut piece. If we assume a full sheet purchase and then use a small part, the cost per stool gets diluted. For a single stool, if a workshop has to buy a whole sheet, the full sheet cost would apply if it's not reused. For this exercise, let's assume purchasing an offcut or attributing a portion of a sheet. Let's estimate it as 1/8th of a sheet for calculation purposes, acknowledging that a full sheet might be purchased. 1/8 sheet × NGN 18,000/sheet = NGN 2,250 Wood Glue: 1 bottle × NGN 1,500/bottle = NGN 1,500 Screws: 1 packet × NGN 1,000/packet = NGN 1,000 Varnish: 1 litre × NGN 3,000/litre = NGN 3,000 Sub-total Material Cost: NGN 9,000 + NGN 2,250 + NGN 1,500 + NGN 1,000 + NGN 3,000 = NGN 16,750 Add 10% Contingency/Buffer: NGN 16,750 × 0.10 = NGN 1,675 Total Estimated Material Cost: NGN 16,750 + NGN 1,675 = NGN 18,425 --- shelves, drawer bottoms, tabletops (if specified as sheet material).
2. Determine dimensions: Note the length and width of each piece.
3. Optimise cutting layout: Mentally or physically sketch out how these pieces can be cut efficiently from standard 8ft x 4ft sheets to minimise waste. This is a critical step for cost-saving.
4. Calculate the number of sheets: Divide the total area required by the area of one standard sheet (32 sq ft or approx. 2.97 sq m), or by visually fitting.
5. Add a waste factor: A smaller waste factor (e.g., 5-10%) may be added for sheet materials due to more efficient cutting. 2.4.
3. Other Materials (Hardware, Adhesives, Finishes)
Nails/Screws: Estimated by quantity (e.g., 1kg of nails, 1 packet of screws) or per joint/piece.
Wood Glue: Estimated per project, usually a small can or bottle.
Sandpaper: Estimated by sheets, considering different grits.
Varnish/Paint/Wood Finish: Estimated by surface area to be covered. Manufacturers' specifications on coverage rate (e.g., litres per square metre) are helpful. Hinges, Handles, Locks: Counted individually per item needed. 2.
5. Cost Calculation
1. Obtain Unit Prices: Research current market prices from local suppliers (e.g., sawmills, hardware stores in Bodija market Ibadan, Alaba International market Lagos, or building material markets in Abuja). Prices fluctuate, so current data is vital.
Example: Iroko timber NGN 4,500 per board foot; 18mm Plywood NGN 20,000 per sheet; 4-inch nails NGN 800 per kg; Varnish NGN 3,500 per litre.
2. Calculate Cost Per Material: Multiply the calculated quantity of each material by its unit price. Cost of Timber = Total Board Feet × Price per Board Foot Cost of Plywood = Number of Sheets × Price per Sheet Cost of Nails = Quantity of Nails (kg) × Price per kg
3. Sum Total Material Cost: Add up the costs of all individual materials to get the total estimated material cost for the project.
4. Add Contingency/Buffer: Always include a contingency fund (e.g., 5-10% of total material cost) for unforeseen price increases, minor material shortages, or errors in estimation. --- Worked
Example: Estimating and Costing for a Simple Wooden Stool Project: A simple wooden stool Dimensions: Height: 450 mm Seat: 300 mm x 300 mm Legs: 4 pieces, 50 mm x 50 mm x 450 mm Rails (aprons): 4 pieces, 50 mm x 25 mm x 200 mm (to connect legs under the seat)
Seat material: 18mm plywood Assumed Current Market Prices (Nigerian Context): Rough Timber (e.g., Obeche or a similar softwood): NGN 3,000 per board foot (for finished size 2x2 or 2x1) 18mm Plywood (8ft x 4ft sheet): NGN 18,000 per sheet Wood Glue: NGN 1,500 per medium bottle 3-inch Screws: NGN 1,000 per packet (approx. 50 pieces)
Varnish (clear): NGN 3,000 per litre Step 1: Interpret Drawing/Sketch and Prepare Cutting List Legs: 4 pieces.
Dimensions: 50mm x 50mm x 450mm Convert to inches and feet: 50mm ≈ 2 inches, 450mm ≈ 1.5 feet Dimension: 2" x 2" x 1.5 ft Rails: 4 pieces.
Dimensions: 50mm x 25mm x 200mm Convert to inches and feet: 50mm ≈ 2 inches, 25mm ≈ 1 inch, 200mm ≈ 0.66 feet (or 8 inches)
Dimension: 2" x 1" x 0.66 ft (or 8 inches length)
Seat: 1 piece.
Dimensions: 300mm x 300mm.
Material: 18mm plywood.
Step 2: Calculate Material Quantities a)
Timber for Legs and Rails: Legs (4 pieces): Each 2" x 2" x 1.5 ft Board feet per leg = (2 × 2 × 1.5) / 12 = 6 / 12 = 0.5 board feet Total for 4 legs = 4 × 0.5 = 2.0 board feet Rails (4 pieces): Each 2" x 1" x 0.66 ft Board feet per rail = (2 × 1 × 0.66) / 12 = 1.32 / 12 = 0.11 board feet (approx.) Total for 4 rails = 4 × 0.11 = 0.44 board feet Total Raw Timber: 2.0 + 0.44 = 2.44 board feet Add 15% Waste Factor for Rough Timber: 2.44 × 1.15 = 2.806 board feet This section provides a detailed breakdown of the core concepts for interpreting drawings, estimating material quantities, and calculating costs. 2.
1. Estimation Estimation in carpentry is the process of predicting the quantities of materials, labour, and other expenses required to complete a project before actual work begins.
Accurate estimation helps in: Budgeting: Setting a realistic financial plan for the project.
Pricing: Determining a fair and profitable price for clients.
Resource Management: Ensuring timely availability of materials and personnel.
Waste Reduction: Minimising excess material purchases, which is vital in a resource-conscious economy like Nigeria's. 2.
2. Costing Costing is the process of calculating the total monetary value of all resources consumed in producing a carpentry item or completing a project. For this lesson, the focus is primarily on material costing. Key components of material costing include: Material Identification: Knowing exactly what materials (e.g., wood type, plywood, nails, glue, varnish, hinges) are needed.
Quantity Determination: Accurately calculating how much of each material is required.
Unit Pricing: Obtaining current market prices for each unit of material (e.g., price per board foot of timber, price per sheet of plywood, price per kilogram of nails).
Total Material Cost: Summing up the costs of all individual materials. 2.
3. Interpreting Drawings and Sketches A drawing or sketch serves as the blueprint for a carpentry project.
Effective interpretation involves: Understanding Orthographic Projections: Recognising front, plan (top), and end (side) views.
Reading Dimensions: Identifying length, width, and thickness of all components. Dimensions are usually given in millimetres (mm) or metres (m), but sometimes feet and inches for timber.
Identifying Components: Clearly distinguishing between different parts of the furniture (e.g., legs, rails, stiles, panels, shelves, drawer fronts).
Material Specification: Noting the type of wood (e.g., Iroko, Mahogany, Obeche), thickness of plywood/MDF, and other hardware.
Assembly Details: Understanding how parts fit together (joints, fasteners). 2.
4. Material Calculation Techniques 2.4.
1. Timber (Lumber) Calculation (Board Feet) In Nigeria, rough timber is often sold by the 'foot' or 'board foot'. A board foot is a unit of volume equal to a piece of wood 1 inch thick, 12 inches wide, and 1 foot long (or its equivalent).
The formula for calculating board feet is: Board Feet = (Thickness in inches × Width in inches × Length in feet) / 12
Example: A plank measuring 2 inches thick, 6 inches wide, and 10 feet long. Board Feet = (2 × 6 × 10) / 12 = 120 / 12 = 10 board feet.
Converting from mm to inches: 1 inch ≈ 25.4 mm.
Converting from m to feet: 1 foot ≈ 0.3048 m.
Steps for Timber Calculation:
1. List all timber components: Identify every piece of wood required from the drawing (e.g., 4 legs, 2 long rails, 2 short rails, 1 top frame).
2. Determine dimensions of each component: Extract length, width, and thickness for each piece from the drawing.
3. Calculate board feet for each component: Use the formula above. Ensure all dimensions are in the correct units (inches for thickness/width, feet for length).
4. Sum up total board feet: Add the board feet for all individual pieces to get the total raw timber needed.
5. Add a waste factor: Always add an allowance for waste due to cutting, planing, defects, and errors. A common allowance is 10-15% for rough timber. 2.4.
2. Sheet Material Calculation (Plywood, MDF, HDF) These materials are sold in standard sheet sizes, commonly 8 feet x 4 feet (2440 mm x 1220 mm) or smaller cuts. * Steps:
1. Identify all sheet material components: Back panels, shelves, drawer bottoms, tabletops (if specified as sheet material).
2. Determine dimensions: Note the length and width of each piece.
3. Optimise cutting layout: Mentally or physically sketch out how these pieces can be cut efficiently from standard 8ft x 4ft sheets to minimise waste. This is a critical step for cost-saving.
4. Calculate the number of sheets: Divide the total area required by the area of one standard sheet (32 sq ft or approx. 2.97 sq m), or by visually fitting.
5. Add a waste factor: A smaller waste factor (e.g., 3.
1. Teacher Activities Introduction (10 minutes): Initiate a brief discussion on the importance of knowing material costs before starting any carpentry project. Ask students for examples where knowing costs would be beneficial (e.g., building a kitchen cabinet for a client, making school desks). Recap previous knowledge on measurement and types of wood.
Introduce the topic: "Estimation and Costing in Carpentry," and state the learning objectives clearly.
Presentation of Concepts (25 minutes): Explain what estimation and costing entail, differentiating between them. Demonstrate how to interpret technical drawings and sketches using a simple, clear diagram (e.g., a basic table or chair) on the whiteboard or projected. Point out views, dimensions, and component identification. Elaborate on different material types (timber, sheet materials, hardware) and their standard units of sale in Nigeria (board feet, sheets, kgs, litres, pieces). Clearly explain the Board Foot formula and its application, including unit conversions (mm to inches, m to feet). Provide simple examples. Discuss efficient cutting layouts for sheet materials to minimise waste. Explain how to estimate quantities for hardware, adhesives, and finishes. Discuss the importance of current market prices and how to obtain them. Present the step-by-step process of calculating total material cost, including the application of waste factors and contingency.
Guided Practice (20 minutes): Distribute a simple drawing (e.g., a small wooden box or a simple shelf) with dimensions.
Guide students through the process of: Identifying components and their dimensions. Calculating material quantities (timber in board feet, plywood in area/sheets, other items by count/volume). Assigning assumed market prices to each material (provide a list of prices). Calculating the total material cost. Encourage student questions and facilitate peer learning during this process.
Feedback and Clarification (5 minutes): Address any misconceptions or difficulties students encountered during the guided practice. Summarise key takeaways from the lesson. 3.
2. Student Activities Active Listening and Note-taking: Students will listen attentively to explanations and take comprehensive notes on definitions, formulas, and procedures.
Discussion and Q&A: Students will participate in class discussions, ask clarifying questions, and share their prior knowledge.
Drawing Interpretation Practice: Students will individually or in small groups practice interpreting sample technical drawings, identifying components and extracting dimensions.
Material Quantity Calculation: Using provided sketches and dimensions, students will calculate the required quantities of timber, sheet materials, and other items.
Cost Estimation Practice: Students will apply given unit prices to their calculated quantities to estimate the total material cost for a project.
Group Work: Students will collaborate in small groups to complete guided practice exercises, fostering teamwork and peer learning. ---
Entrepreneurship and Small Business Development: This topic is foundational for students aspiring to become self-employed carpenters or furniture makers in Nigeria. Accurate estimation and costing allow them to: Prepare competitive bids for jobs (e.g., making school desks for local government, building kitchen cabinets for new homes in Abuja or Lagos, crafting custom furniture for clients). Manage their finances effectively, ensuring profitability and avoiding losses on projects. Purchase materials judiciously from markets like those in Mile 12, Lagos, or timber markets across the country, preventing overstocking or shortages. Provide transparent and justifiable quotes to clients, building trust and reputation in the local community.
Home Improvement and Personal Projects: Students can apply these skills directly to their personal lives and homes. Estimating the cost of materials for building a simple shelf, repairing a broken table, or constructing a chicken coop for backyard farming. Making informed decisions about purchasing furniture, understanding the value of materials and craftsmanship. Advising family members or neighbours on renovation projects, ensuring cost-effectiveness and material efficiency. Construction Industry and Quantity Surveying: While carpentry focuses on wood, the principles of estimation and costing are transferable to the broader construction industry. Students gain an understanding of how quantity surveyors estimate materials for large-scale building projects (residential estates, commercial buildings, schools) in Nigeria. They learn the importance of meticulous planning to minimise waste, a critical factor in managing project budgets and promoting sustainable construction practices in a developing nation. This knowledge can open career pathways beyond direct carpentry, into roles such as site supervisors, procurement officers, or assistant quantity surveyors. ---