A2 Sheet Layout for a Cast-Iron Bracket
A candidate is laying out a drawing of a cast-iron bracket on an A2 sheet. The bracket’s overall size is 420 mm long, 260 mm high and 180 mm deep. Three views are required: front view (length × height), top view (length × depth), and right-hand side view (depth × height). The sheet is A2 (594 mm × 420 mm) with a 20 mm border on all sides, an extra 25 mm filing margin on the left, and a 180 mm × 60 mm title block in the lower right corner. The candidate allows 30 mm between views. They propose a scale of 1:1 and line widths of 0.35 mm for visible outlines, 0.5 mm for hidden edges, and 0.25 mm for centre lines; dimension numerals are to be 2.5 mm high. The drawing must also carry a general note and a surface-finish symbol. The workshop instructor rejects the layout before any construction is started.
1. Determine whether the 1:1 layout fits. Then select the largest standard scale from 1:1, 1:2, 1:5 and 1:10 that fits the stated sheet, border, filing margin, title block and 30 mm view spacing. Show the available area and the view envelope.
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Available drawing width = 594 − (20 + 20) − 25 = 529 mm. Available height = 420 − (20 + 20) = 380 mm. A conservative layout height after reserving the 60 mm title-block band is 380 − 60 = 320 mm.
At 1:1 the three-view envelope is width = 420 + 30 + 180 = 630 mm and height = 260 + 30 + 180 = 470 mm (front above top, side to the right). Both exceed 529 mm × 320 mm, so 1:1 fails.
At 1:2 the envelope is width = 210 + 30 + 90 = 330 mm and height = 130 + 30 + 90 = 250 mm. This fits 529 mm × 320 mm with clearance. 1:5 also fits but is smaller than necessary.
Largest standard scale = 1:2. Check: the side view height 130 mm plus title block 60 mm is only 190 mm, so the right-hand column does not overlap the title block.
2. Critique the proposed line widths and lettering height. State the corrected hierarchy and one layout check that prevents projection misalignment.
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The proposal reverses the line hierarchy: hidden edges at 0.5 mm are heavier than visible outlines at 0.35 mm. In a standard line group, visible outlines should be the heaviest of the object lines (e.g. 0.5 mm), while hidden, centre, dimension and extension lines should be thinner (e.g. 0.25 mm); the border and title block may be heavier still (e.g. 0.7 mm). Centre lines must be thin, with long-short-long dashes, and should extend 2–3 mm beyond the outline. Dimension numerals at 2.5 mm are the smallest common size and are legible, but 3.5 mm is preferable on an A2 sheet; the main error is the reversed weights.
Layout check: draw the main centre lines and axes first, then project the front view to the top view with vertical projectors and to the side view with horizontal projectors. Measure the overall envelope before darkening any line.
3. List the sequence you would use to lay out the sheet, and explain why the title block should not be drawn first in final line weight.
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Sequence: (1) trim and secure the sheet; (2) draw the border and filing margin lightly; (3) block in the title block lightly; (4) establish the view centres and principal axes; (5) block in the three views with light construction lines, maintaining projection alignment; (6) check overall dimensions and spacing; (7) darken visible outlines, then hidden, centre and dimension lines; (8) complete dimensions, notes and surface-finish symbols; (9) final check and clean.
The title block should be blocked in early for space allocation but darkened late. If it is finalised first, later erasing and construction lines can smudge it, and a late change in scale or view position may force it to be moved. Light construction keeps the layout adjustable until the envelope is confirmed.