Technical Drawing practice questions.

An orthographic drawing of a machined block is set out in third-angle projection. Where is the view looking at the right-hand end of the block placed?

• To the right of the front view
• To the left of the front view
• Directly above the front view
• Directly below the front view

Answer: To the right of the front view

In third-angle projection every view is drawn on the same side as the direction from which the object is seen, so the right-hand end view sits to the right and the plan sits above the front view. First-angle projection reverses both placements, which is why the projection symbol has to be read before any view is interpreted.

A pressed steel bracket has one sloping face that appears as an edge in the front view and foreshortened in the plan and end views. Which additional view is added so that the fitter can read the true shape of that face?

• A sectional view taken through the inclined face
• An auxiliary view projected from the inclined face
• An exploded view of the bracket and its fixings
• An isometric view of the whole bracket

Answer: An auxiliary view projected from the inclined face

An auxiliary view is projected at right angles to the sloping face, so that face alone is drawn to true size and true shape; the principal views show it only as an edge or foreshortened. A sectional view exposes internal detail and a pictorial view distorts at least two faces, so neither gives a dimensionable outline.

Six mounting holes in a long rail are dimensioned one from the next, each measurement starting at the previous hole, and every dimension carries a tolerance of plus or minus 0.2 mm. What follows for the position of the sixth hole relative to the first?

• Its tolerance stays at plus or minus 0.2 mm
• Its position error can build up to plus or minus 1.0 mm
• Its position is fixed by the overall length of the rail
• Its tolerance is halved because the errors cancel out

Answer: Its position error can build up to plus or minus 1.0 mm

Chain dimensioning adds the tolerance of every step, so five steps of plus or minus 0.2 mm allow the sixth hole to sit up to 1.0 mm from its nominal position relative to the first; dimensioning every hole from one datum edge keeps each error independent of the others. Tolerances state a worst case, so they accumulate rather than cancel.

On the view from which a section is taken, which line shows where the cutting plane passes through the component?

• A thin dashed line running across the whole view
• A thin continuous line broken by a narrow zig-zag
• A chain line thickened at its ends and at each turn
• A thick continuous line drawn around the cut area

Answer: A chain line thickened at its ends and at each turn

The cutting plane is drawn as a chain line that is thickened where the plane begins, ends and changes direction, and it carries arrows giving the direction of viewing. A chain line of uniform thin thickness is a centre line marking an axis, not a cut, and a zig-zag break line shows that part of the object has been left out.

A detail drawing carries the third-angle projection symbol. The view looking down on the part is placed directly below the front view, and the view looking at the left-hand end of the part is placed directly to the left of it. One of those two views is in the wrong position. Which is it, and where does it belong?

• The end view; it belongs to the right of the front view.
• The end view; it belongs directly above the front view.
• The plan; it belongs directly above the front view.
• The plan; it belongs to the right of the front view.

Answer: The plan; it belongs directly above the front view.

In third-angle projection every view is placed on the side from which it is seen, so the plan sits above the front view and the left-hand end view to its left. Putting the plan below the front view is the first-angle arrangement, and mixing the two is the classic reading error.

In a pictorial drawing of a rectangular storage box the two receding top edges are measured on the print and found to be the same distance apart at the front of the box as at the back. Which conclusion follows from that single observation?

• The drawing is a parallel projection, so it is not a perspective view.
• The drawing is a two-point perspective with distant vanishing points.
• The drawing is an oblique projection, as only oblique keeps edges parallel.
• The drawing is a one-point perspective, in which verticals alone converge.

Answer: The drawing is a parallel projection, so it is not a perspective view.

Isometric, oblique and planometric are all parallel projections: receding edges stay parallel and lengths can be taken off with a rule. Any perspective drawing converges on vanishing points, so a constant spacing rules perspective out, though it does not say which parallel system was used.