Critique of a Design Presentation Sheet
A student submits an A2 design presentation sheet for a plywood desk tidy. It carries a freehand isometric sketch on a 5 mm grid, a marker rendering, three orthographic views laid out at 1:5 in first-angle positions, and a title block. On review: the outlines of the views are drawn with the same 0.5 mm pen as the hatching and the centre lines; dimensions are written inside the views and dimension lines cross the object; arrowheads are used on some dimensions and oblique strokes on others; no units are stated anywhere; the projection symbol in the title block is the third-angle symbol; the scale box names 1:5 only, and the isometric carries no note. The client will read the sheet for approval and a technician will use it to set out the job.
1. Sort the faults into those that could cause a wrong part and those that are presentational, and justify the ranking.
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Wrong-part risks, in order:
- The projection symbol. The views are laid out in first angle but the symbol says third angle. The two systems place the side view on opposite sides and mirror the part, so a technician who trusts the symbol will make a handed, non-fitting component. This is the single critical fault.
- Missing units. Drawing practice assumes millimetres, but the sheet also states a scale, so a reader could reasonably take the figures as centimetres or as scaled values. Units must appear in the title block or against the dimensions.
- Dimensions written inside views and crossing the object, with mixed arrowheads and strokes. These break the standard convention (dimensions outside the outline, one arrow style throughout, no dimension line crossing another or the object) and create genuine misreading risk, but a careful technician can still decode them.
Presentational only: 4. Faulty line hierarchy (outline, hidden, centre, hatching all at 0.5 mm) - affects legibility and professional credibility, not correctness. 5. No note on the isometric. Pictorials are conventionally not to scale, so the fix is a 'pictorial - not to scale' note rather than a scale.
2. Rewrite the dimensioning of the two Ø10 mm fixing holes to standard practice.
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Current fault: the holes are dimensioned from inside the view, with lines running across the outline and inconsistent terminators, so the reader has to disentangle the numbers from the geometry.
Correct approach:
- Call the holes once: '2 × Ø10' with a leader pointing to one hole, or Ø10 on each with a leader, never a duplicated overall dimension.
- Locate each centre by two coordinates from datum edges - for example 20 mm from the left face and 25 mm from the bottom face - using extension lines taken from the holes' centre lines, not from their outlines.
- Take all dimensions to a single datum pair (left face, bottom face) so the tolerance stack is defined; do not chain from hole to hole.
- Keep dimension lines outside the outline, the first about 10 mm clear of the object and successive lines 6–8 mm apart; extension lines start about 1 mm off the outline and overrun the dimension line by about 2 mm.
- Use one terminator style throughout: arrowheads roughly 3 mm long, 1 mm wide, or oblique strokes, but not both.
- Never dimension to a hidden line; put diameters on the view where the circle is true.
3. Specify the corrected line hierarchy for the sheet and outline the freehand sequence for the isometric.
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Line hierarchy (pen weights on the finished sheet):
- Visible outlines: 0.7 mm, firm and continuous.
- Hidden detail: 0.35 mm, dashes about 3 mm with 1 mm gaps.
- Centre lines: 0.25 mm chain line, long dash–short dash, extended 3–5 mm beyond the feature.
- Hatching: 0.25 mm continuous at 45°, spacing 3 mm, stopping at outlines and never over dimensions or text.
- Dimension, extension and leader lines: 0.25 mm, lighter than the outlines.
- Grid and construction lines: not inked at all on the final sheet. Everything must read at arm's length: the outline should dominate the hatched area, not match it.
Freehand isometric sequence:
- Light construction box at the overall 70 × 40 × 25 envelope, using the 30° axes on the grid.
- Lightly block in the three main masses and the centre lines of every hole before any curve.
- Work from the whole to the detail: chamfer intercepts set out along the axes, then the ellipses for holes on receding faces.
- Firm up outlines only after the proportions are agreed; do not erase construction work, let it be over-drawn.
- Add shading and the marker rendering last, keeping the outline weight intact.