The Unreadable Drawing
A student has produced a third-angle orthographic drawing of a small bracket for a metalwork project. The drawing shows a front view, a plan, and a side view, all at 1:1 scale on A3 paper. A technician picks it up to make the bracket and finds: the side view is placed to the left of the front view; there are no hidden detail lines; three dimensions are given, but one is measured from a centre line to an edge without a leader; and the title block is blank. The technician cannot tell whether a hole is 8 mm or 10 mm because the dimension line crosses the hole. The student insists the drawing is correct because the views line up.
1. Identify the errors in the drawing and explain how each one would affect the technician making the bracket.
Read the worked answer
1. View placement. In third-angle projection the side view goes to the right of the front view. Placing it on the left is first-angle convention. A technician reading it as third-angle will machine the bracket mirrored - holes on the wrong side.
2. Missing hidden detail. Without hidden lines the technician cannot see the through-hole or the internal step. They may drill from the wrong face or miss the feature entirely.
3. Poor dimensioning. A dimension from a centre line to an edge should have a leader or be tied to the centre line clearly. A dimension line crossing a hole is ambiguous: the technician cannot tell whether 8 mm or 10 mm is the hole diameter or the distance to its edge. This is a direct scrap risk.
4. Blank title block. Without scale, material, title, date and name, the technician has no way to confirm the drawing is the current version or what it is made from. If two drawings exist, the wrong one may be used.
The student's claim that the views line up is true but irrelevant: alignment is necessary but not sufficient for a usable drawing.
2. Describe the corrections the student should make and explain the principle behind each.
Read the worked answer
Correct the projection. Move the side view to the right of the front view and add the standard third-angle projection symbol to the title block. Principle: the drawing must declare its convention so the reader interprets it the same way the drafter did.
Add hidden detail. Use dashed lines for the through-hole and internal step in every view where they are hidden. Principle: the drawing must convey all features needed to make the part, not just the visible ones.
Fix the dimensions. Give the hole diameter with a leader line and the symbol Ø (e.g. Ø8), and dimension the hole position from a clear datum edge or centre line. Do not let dimension lines cross features. Principle: each dimension should be unambiguous and given once, from a defined datum.
Complete the title block. Add title, scale (1:1), material, units, date, name and projection symbol. Principle: the drawing is a communication document; without its metadata it cannot be controlled or trusted.