Orthographic Projection Questions and Answers

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.

Answer: C

Correct answer: two

The front view and the plan are two of the six principal views, so if between them they leave nothing undefined, two is the number required. Drawing a third would add nothing and would only create an opportunity for inconsistency, which is why the rule is the minimum that describes the object completely.

Answer: D

Correct answer: plus or minus 0.8 mm

In a chain each dimension is measured from the previous feature, so the position of the last is the sum of four independent dimensions and the worst-case tolerances add arithmetically: \[ 4 \times 0.2 = 0.8\ \text{mm}. \] This accumulation is the central drawback of chain dimensioning, and it grows with every link added.

Answer: A

Correct answer: plus or minus 0.2 mm

Measuring from a datum makes each feature’s position depend on one dimension only, so the last hole is held to the tolerance of its own dimension - plus or minus 0.2 mm - regardless of how many features lie between it and the datum. Compare the chain arrangement, where the same tolerances accumulate to plus or minus 0.8 mm.

Answer: B

Correct answer: 80 mm by 50 mm

The plan is the view from above, so it shows the two horizontal dimensions: the length of 80 mm and the width of 50 mm. Height does not appear in it at all. At a scale of 1:1 the dimensions on the sheet equal those on the object, so the plan occupies 80 mm by 50 mm.

Answer: C

Correct answer: 50 mm by 30 mm

The side elevation is the view along the length, so it shows the width and the height: 50 mm by 30 mm. Between them the three principal views show each dimension twice - length in the front view and plan, width in the plan and side elevation, height in the front and side elevations - which is what makes the views project on to one another.

Answer: D

Correct answer: transposed left for right

The two systems place the side views on opposite sides of the front view. Read a first angle drawing as third angle and the view drawn on the right, which was taken from the left, will be taken as the view from the right - so the part is made as a mirror image. The dimensions are all correct, which is what makes the error so easy to miss.