Worked example · Design Technology · Year 10
DCF: Producing → Creating digital content
A completed design with a net that genuinely folds up, and every number worked out so you can check it on a calculator. Show it after Part B, once pupils have attempted their own closure check. If a pupil's four side faces do not add up to their perimeter, their box will not close — that is the one thing worth stopping the class for.
| Arrangement of the six cakes | Two stacks of three, lying flat, side by side along the length of the box. A single stack of six would be 6 × 15 = 90 mm tall and would topple; two stacks of three are only 45 mm tall and the lid holds them down. |
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| Space the cakes occupy | Two 60 mm circles side by side = 120 mm long, 60 mm wide, and 3 × 15 = 45 mm high. So 120 × 60 × 45 mm. |
| Internal box size, with clearance | L = 125 mm, W = 65 mm, H = 50 mm. That is 5 mm of clearance on the length and width and 5 mm on the height — enough to get the cakes in and out without crushing the edges, not enough to let them slide about. |
| Internal volume | 125 × 65 × 50 = 406,250 mm³ = 406.25 cm³. The cakes themselves are roughly 6 × π × 30² × 15 = about 254 cm³, so the pack is about 62% full — sensible for something fragile, and not the half-empty box people complain about. |
Evidences criterion 1: the internal sizes are derived from the real cake dimensions and the arrangement is justified, including why a stack of six was rejected.
| Perimeter of the box: 2 × (L + W) | 2 × (125 + 65) = 2 × 190 = 380 mm |
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| My four side faces added together | 125 + 65 + 125 + 65 = 380 mm — they match, so the strip wraps round exactly once and the glue tab has something to stick to. |
| Top panel against the opening | Lid is 125 × 65 mm; the opening is L × W = 125 × 65 mm. It covers it exactly, and the 25 mm tuck flap folds down inside the front face, which is 50 mm deep, so the flap has room and does not foul the base. |
| Overall flat size | Width: 380 + 15 (glue tab) = 395 mm. Height: 25 + 65 + 50 + 65 + 25 = 230 mm. An A3 sheet is 420 × 297 mm, so it fits with 25 mm and 67 mm to spare. |
Criteria 2 and 3: the strip equals the perimeter, the lid equals the opening, the tuck flap is shorter than the face it folds into, and the whole blank fits on one A3 sheet. Cut and fold lines are distinguished and every panel carries its real dimensions.
| Part | Material | Why | What I am giving up |
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| The box | A — recycled cartonboard, 350 gsm | Card is collected kerbside almost everywhere in Wales, it is the cheapest of the six at £0.42/m², and recycled fibre has the lowest embodied carbon here. | The grey-brown base makes the printed colours look dull, and because recycled fibre is shorter I need 350 gsm rather than B's 300 gsm for the same stiffness — so my box is heavier than it would be in virgin board. |
| Grease barrier | F — glassine paper liner, 40 gsm | Butter will mark bare card within a day. A paper liner fixes it for about 0.6 p, keeps the whole pack paper-based, and is home compostable as well as kerbside recyclable. | It is only good for about three days, it adds nothing structurally, and it is a second component somebody has to cut and fold in on the morning of the fair. |
| Window | None | D, the rPET film, would turn the pack into mixed material and sorting lines commonly reject the whole box for the sake of one window. E, the PLA film, is not collected in Wales at all. A printed photograph of the cakes on the lid does the selling job instead. | Customers cannot see the actual cakes, and that genuinely loses sales. I am covering it by keeping one open box on the stall as a display. |
| Print and finish | Water-based inks, no laminate, PVA-type glue | None of these affect recyclability. A gloss laminate would look smarter and cancel out every other decision on this sheet. | Colours are slightly less punchy, and the box marks if it gets rained on going home. |
Criterion 4: every row names a real drawback from the datasheet, including the awkward one — no window costs sales — and the pack is deliberately kept single-material so the recycling claim is honest.
| Board area in the net | Side strip 380 × 50 = 19,000 · lid 125 × 65 = 8,125 · base 8,125 · two tuck flaps 125 × 25 = 3,125 each = 6,250 · glue tab 15 × 50 = 750. Total = 42,250 mm² |
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| In square metres | 42,250 ÷ 1,000,000 = 0.04225 m² |
| Mass of one blank | 0.04225 × 350 = 14.8 g of card, plus the liner: 180 × 120 mm = 0.0216 m² × 40 gsm = 0.9 g. 15.7 g per pack. |
| Board cost for one box | 0.04225 × £0.42 = £0.0177, so 1.8 p, plus 0.0216 × £0.30 = 0.6 p for the liner. 2.4 p per pack. |
| For all 120 boxes | 120 × 2.4 p = £2.88 |
| Total card put into the world | 120 × 15.7 g = 1,884 g, about 1.9 kg — all of it kerbside recyclable, which is the whole point of choosing A and F. |
| The catch I nearly missed | Only one 395 × 230 mm net fits on a 420 × 297 mm sheet, so in practice I buy a whole sheet per box: 0.42 × 0.297 = 0.1247 m² × £0.42 = 5.2 p, not 1.8 p, and I throw away 27% of every sheet. £6.29 for 120. To fix that I would either rotate the net or buy board on a reel. |
Criterion 5: every figure comes from this design's own net area and board weight, and the last row spots the difference between the board the net uses and the board you actually have to buy.
Every line of that is true of the materials chosen. If I had taken the rPET window I would have had to print "check local recycling" instead, because a mixed-material box is likely to be rejected — and a customer reading that would be right to think the pack was not really recyclable at all.
Criterion 4 and 5 together: the claim on the pack matches the datasheet, and the pupil states what the label would have had to say under the rejected option.