2.1 Scales

• The meaning and purpose of scales in technical drawing
• Representative fraction (RF)
• Types of scale: full size, reduction and enlargement
• The plain scale: construction and interpretation
• The diagonal scale: principle, construction and interpretation
• Application of scales in real life and in power mechanics

• describe the diagonal scale used in drawing
• construct the diagonal scale used in drawing
• interpret the diagonal scale used in drawing
• appreciate the application of the diagonal scale in real life

“Why are scales important in real life?”

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1. What a scale is, and why drawings need one
   40 min · 1 practice tasks · quiz
   Why a real object cannot be drawn full size, what a scale is, and why it must always be stated.
2. Representative fraction
   40 min · 1 practice tasks · quiz
   RF as a fraction, converting units before dividing, and the commonest mistake in the whole topic.
3. Full size, reduction and enlargement
   40 min · 1 practice tasks · quiz
   The three kinds of scale, when each is used, and how to choose a scale for a given object and sheet.
4. Calculating with a scale
   40 min · 1 practice tasks · quiz
   Converting in both directions between drawing and object, and the sense check that catches a reversed calculation.
5. The plain scale
   40 min · 1 practice tasks · quiz
   What a plain scale is, how it is read from either side of zero, and the limit that makes a diagonal scale necessary.
6. Constructing a plain scale
   40 min · 1 practice tasks · quiz
   Calculating the length of the scale, then the five construction steps, worked on a real example.
7. Why the diagonal scale exists
   40 min · 1 practice tasks · quiz
   The limit of a plain scale in numbers, and the idea of using height to divide what cannot be divided along a line.
8. The principle of diagonal division
   40 min · 1 practice tasks · quiz
   Why a diagonal divides proportionally, proved by similar triangles, and what that means for reading.
9. Constructing a diagonal scale
   40 min · 1 practice tasks · quiz
   The full seven-step construction of a diagonal scale, worked on a 1 to 50 example reading to six metres.
10. Reading a diagonal scale
    40 min · 1 practice tasks · quiz
    Taking a three-figure reading with dividers, in the order metres, decimetres, then centimetres.
11. Where scales are used
    40 min · 1 practice tasks · quiz
    Six settings where scales do real work, and the answer to the inquiry question.
12. Common errors, and how to check a scale
    40 min · 1 practice tasks · quiz
    Six errors that spoil a scale, the check that catches each, and one test that verifies the whole thing.