Canteen Servery Refit: Projection, Scale and Sheet Layout
Kaitoki College's canteen serves about 180 students in one 25-minute interval. The servery is a straight run 3.6 m long and 1.5 m deep, with an 810 mm doorway at the east end and a 900 mm-high counter along the front. The board has approved $4,000 for a refit that adds a second service point and a 600 mm-wide hand-wash sink. The builder works from drawings only and has never visited the site. A trainee teacher has issued a plan on A3 at 1:50, a front elevation at 1:20, and has labelled the plan 'first-angle projection'. The builder has emailed back: the elevation and plan do not align, and the sink position is ambiguous because it is dimensioned from the doorway at one end and from the counter return at the other. The property manager wants a corrected set by Friday.
1. Explain why the mixed scales and the projection label caused the builder's confusion, and state what the corrected set must specify.
Read the worked answer
Two separate faults are stacking up here.
Mixed scales. Orthographic views only work because features project straight across from one view to the next. At 1:50 the 3.6 m run draws at 72 mm; at 1:20 the same run would draw at 180 mm. Nothing lines up, so the builder cannot transfer the sink centreline from plan to elevation by projection and has to guess. Views on one sheet should share a scale unless a view is clearly labelled as a detail.
Projection label. The plan is labelled first-angle. New Zealand building and engineering practice works in third-angle (AS/NZS 1100.101), so a local builder reads the sheet expecting the plan to sit below the elevation and the left view to sit on the left. Labelling it first-angle while drawing it in third-angle is worse than saying nothing.
The corrected set must: draw both views in third-angle, place and label the third-angle symbol in the title block, state the scale in the title block for each view, add a 'do not scale from this drawing' note, and dimension the sink from one datum only.
2. The plan and elevation must share one A3 sheet (420 × 297 mm) with a 10 mm border all round and a 180 × 60 mm title block inside the border. Decide the scale using measurements, and justify your choice.
Read the worked answer
Usable drawing width = 420 − 20 = 400 mm. Usable height = 297 − 20 − 60 = 217 mm (title block occupying a full-width strip at the foot).
At 1:20: plan 3.6 m = 180 mm wide × 1.5 m = 75 mm deep; elevation 2.4 m high = 120 mm. Stacked with a 10 mm gap that is 75 + 10 + 120 = 205 mm, leaving 12 mm for dimension lines, notes and the gap to the border. Dimensions need at least 25–30 mm of clear space; this fails.
At 1:50: plan 72 × 30 mm; elevation 48 mm high. Stacked: 30 + 10 + 48 = 88 mm, leaving about 129 mm for dimensions, notes and a parts key. Width uses only 72 mm of 400 mm, so there is room for a second elevation or a small schedule.
Decision: both views at 1:50 on the one sheet, with the sink drawn as a separate 1:20 detail (600 mm = 30 mm at 1:20) in the free space. This keeps the projection consistent while still giving the builder enough size to read the sink and tap positions.
3. Describe the line weight and line type scheme you would apply to the corrected plan so the builder can read it quickly on site.
Read the worked answer
Use a small hierarchy, not many weights. A workable scheme for an A3 at 1:50:
- 0.7 mm – outlines of the walls, counter and sink that are cut in the plan; also the border.
- 0.35 mm – secondary visible edges: the counter return, door leaf swing, fixed equipment.
- 0.35 mm dashed – hidden edges such as the overhead extraction duct or the door frame in the wall.
- 0.25 mm – dimension lines, extension lines, leader lines and arrowheads; also centre lines as a long-dash-dot chain.
- Hatching at consistent spacing for the cut wall section, with a heavier boundary line than hatch lines.
Keep the heaviest weight at least twice the lightest so the drawing reads at arm's length on a wet site. Every line type must carry only one meaning across the whole set: if dashed means hidden in the plan, it cannot also mean 'future work'. Also dimension to visible edges wherever possible, since dimensioning to a hidden line forces the builder to interpret rather than read.