Engineering Graphics Questions and Answers

Answer: A

Correct answer: larger than the sheet it must be drawn on

A reducing scale is used when the object will not fit at full size - a building, a machine, a survey. An object too small to draw conveniently at full size calls for an enlarging scale instead, and the two are distinguished by whether the representative fraction is less than or greater than unity.

Answer: B

Correct answer: greater than unity

The representative fraction is the drawing length divided by the actual length, so a drawing larger than the object gives a fraction above one. A watch escapement drawn at 10:1 has a representative fraction of 10. Full size is exactly unity and any reduction gives a fraction between zero and one.

Answer: C

Correct answer: drawing length to the corresponding actual length

The representative fraction is defined as drawing length over actual length, both in the same units, so it is dimensionless and independent of the units used. Inverting it is the commonest error and produces a number that looks plausible but multiplies where it should divide.

Answer: D

Correct answer: maximum length to be measured

The scale must be long enough to read the greatest distance required, so its constructed length is that maximum multiplied by the representative fraction. A scale of 1/500 reading up to 60 m is therefore 12 cm long. The sheet size limits what is practicable but does not enter the calculation.

Answer: A

Correct answer: the drawing may later be reproduced at a different size

A drawing is photocopied, scanned, printed at another sheet size and stored on paper that moves with humidity, and each of these alters every length on it. Stating the scale records what the drawing was made at, so that a reproduction can be recognised as not being at that scale - and it is why written dimensions govern over scaled ones.

Answer: B

Metres and decimetres, or miles and furlongs, are the usual pairing, the main divisions carrying the larger unit and the subdivisions the smaller one. Reading a third unit from the same scale requires the diagonal construction instead.

Answer: C

Correct answer: at the end of the first main division from the left

The first main division is subdivided to give the smaller unit, and the zero is placed at its right-hand end so that the subdivisions read leftward from zero while the whole units read rightward. A distance is then set off by taking whole units to the right of zero and the fraction to the left, in one span of the dividers.

Answer: D

Metres, decimetres and centimetres can all be read from a single scale, the third unit coming from the diagonal divisions. It is the standard construction where a distance must be read to two places beyond the principal unit.

Answer: A

Correct answer: similar triangles divide a length proportionally

A diagonal drawn across a set of equally spaced parallels is cut by them into equal parts, because each pair of parallels forms similar triangles with the diagonal. The horizontal intercept at the nth parallel is therefore n tenths of the full division, which is how the third unit of measurement is obtained without subdividing the base line any further.

Answer: B

Correct answer: eleven parallel lines cut by a diagonal

Eleven equally spaced parallels give ten intervals, so the diagonal is divided into ten equal parts and each parallel yields a successive tenth of the smallest base division. That is what gives the diagonal scale its third significant figure, and the same construction extended gives finer divisions still.