Sheet yield and costing for six bedside cabinets
A learner is costing a batch of six bedside cabinets from 18 mm plywood. Each cabinet needs seven parts: two sides 600 mm × 300 mm, top and bottom 600 mm × 300 mm, one shelf 560 mm × 280 mm, and two doors 590 mm × 300 mm. Grain must run vertically on the sides and doors. The plywood sheet is 1830 mm × 915 mm and costs 480 pula. The saw kerf is 3 mm; factory edges are square, so no extra trimming allowance is included. Hardware is 85 pula per cabinet, finish 40 pula, and labour is 6 hours at 25 pula per hour. Workshop overhead is charged at 15% of direct cost, and the school adds 20% profit on total cost. The learner plans to buy seven sheets to be safe and wants to know whether that is justified.
1. Calculate the minimum number of sheets needed and assess whether buying seven sheets is justified by the cutting list.
Read the worked answer
Each part fits a 600 mm × 300 mm cell: the 590 mm doors and 560 mm shelf are smaller. Along the 1830 mm sheet, three 600 mm lengths plus two 3 mm kerfs = 1806 mm, which fits. Across the 915 mm width, three 300 mm widths plus two kerfs = 906 mm, which fits. So one sheet yields nine cells. Six cabinets need 7 parts each = 42 parts. 42 ÷ 9 = 4.67, so five sheets are the minimum; five sheets give 45 cells, three spare. Buying seven sheets is not justified for yield alone: it adds two sheets at 480 pula each, 960 pula, and creates avoidable waste. Seven sheets might be justified only if the learner expects a high proportion of defective sheets or needs practice pieces, but that should be stated separately.
2. Calculate the direct cost, total cost and selling price per cabinet using five sheets. Show the effect of buying seven sheets.
Read the worked answer
Material: 5 sheets × 480 = 2400 pula for six cabinets, i.e. 400 per cabinet. Direct cost per cabinet: material 400 + hardware 85 + finish 40 + labour 6 × 25 = 150; total = 675. Overhead at 15% of direct cost = 101.25. Total cost = 776.25. Profit at 20% on total cost = 155.25. Selling price = 931.50 per cabinet. If seven sheets were bought, material would be 3360 ÷ 6 = 560, direct cost 835, overhead 125.25, total 960.25, price 1152.30. The extra sheet adds about 220.80 to the price of every cabinet, so it is a poor default.
3. Suggest one change that would reduce material cost and one quality risk that the change could introduce.
Read the worked answer
Reduce material cost by using the three spare cells in each sheet for the shelves and doors, and by nesting the 560 mm × 280 mm shelves into offcuts rather than treating every part as a full 600 mm × 300 mm cell. Also check whether the cabinet back and shelf can come from a cheaper 12 mm sheet or from offcuts. A quality risk is grain direction: if the doors and sides are rotated to improve yield, the vertical grain requirement may be lost and the cabinet will look wrong; another risk is cutting the doors from the same sheet as the sides without allowing for a 3 mm gap, so the doors bind after finishing. Mark grain direction on every part before cutting.