Orthographic Projection Questions and Answers

Answer: A

Correct answer: the interior and the exterior in one view

A half section cuts away one quarter of a symmetrical object, so one half of the view shows the interior in section and the other half the exterior as normal. It saves a view on a symmetrical part. By convention no hidden lines are drawn on the unsectioned half, since the sectioned half already shows what is inside.

Answer: B

Correct answer: is stepped to pass through several features

An offset section lets one view show features that do not lie on a single plane - holes at different radii, say - by stepping the cutting plane from one to the next at right angles. The steps are marked on the cutting plane line but no line is drawn where the plane changes direction in the section itself, since no such edge exists on the object.

Answer: C

Correct answer: superimposed on the view at the point of the cut

A revolved section shows the cross-sectional shape of a rib, arm or spoke by rotating the cut through ninety degrees and drawing it directly on the view at that station, outlined in a thin line. It is compact and unambiguous about where the section is taken. Drawing it elsewhere on the sheet makes it a removed section instead.

Answer: D

Correct answer: thin lines at 45 degrees, evenly spaced

Hatching is drawn thin so it does not compete with the outline, at 45 degrees to the principal outline, and evenly spaced with the spacing chosen to suit the size of the area. Where 45 degrees would run parallel to an outline, another angle is used. Adjacent parts in an assembly are hatched in opposite directions or at different spacings so the joint is visible.

Answer: A

Correct answer: shown unsectioned even when the plane passes through them

Sectioning a solid shaft, bolt, nut, key, rivet or web would show a solid area of hatching that conveys nothing, and in the case of a web would falsely suggest a solid flange. The convention is to draw such parts unsectioned even when the cutting plane passes along them, so the drawing shows the shape rather than the cut.

Answer: B

Correct answer: outside the outline of the view wherever possible

Dimensions placed outside the outline keep the view itself clear and avoid extension lines crossing the drawing. They are arranged so that the shorter dimensions lie nearest the view and the longer ones outside them, so that extension lines do not cross dimension lines. Dimensioning inside the outline is done only where clarity actually demands it.

Answer: C

Correct answer: one common reference face or line

Datum dimensioning measures every feature from a single face or line, so each dimension is independent of the others and no error accumulates. Chain dimensioning measures each feature from the one before, which is convenient for a sequence of equal steps but lets tolerances build up along the chain.

Answer: D

Correct answer: tolerances accumulate along the chain

Each dimension in a chain carries its own tolerance, and the position of the last feature is the sum of them all, so the uncertainty grows with the number of links. Four dimensions at plus or minus 0.2 mm give plus or minus 0.8 mm at the far end. Datum dimensioning avoids this by measuring every feature from the same reference.

Answer: A

Correct answer: once only, on the view that shows the feature best

Repeating a dimension invites the two copies to disagree after a revision, and there is then no way to tell which is correct. So each dimension appears once, on the view where the feature is seen most clearly, and any figure repeated for information is enclosed in parentheses to show it is not to be worked to.

Answer: B

Correct answer: placed in parentheses

A reference dimension is given for convenience - an overall length that is the sum of others, say - and is not itself to be worked to or inspected. Parentheses mark it as such, so the reader knows the figure is derived. It preserves the rule that each dimension is stated once while still letting a useful total be shown.