Plain Scales Problem 1

Plain Scale Problem 1

The lesson demonstrates how to construct a plain scale with a representative fraction (RF) of 1:4, showing decimeters and centimeters, and capable of measuring up to 5 decimeters.

Calculation

An RF of 1:4 means the drawing length is one-fourth of the actual length.

Convert the maximum length to centimeters:

• 5 dm = 50 cm

Calculate the scale’s drawn length:

Scale length = RF × maximum actual length (1/4) × 50 cm = 12.5 cm

Therefore, draw a scale 12.5 cm long.

Construction Method

1. Draw a line 12.5 cm long to represent the full range of 5 dm.
2. Divide the line into five equal major divisions, each representing 1 dm.
   • For accurate divisions, draw an auxiliary line at an angle from one end.
   • Mark five equal intervals along the auxiliary line using equal-radius arcs.
   • Use a mini-drafter to draw parallel lines through those marks, transferring the divisions to the scale line.
3. Give the scale a suitable height, then draw its outline and division lines.
4. Place 0 at the first major division from the left.
   • Number the major divisions to the right of zero 1, 2, 3, and 4. These represent decimeters.
   • The major division to the left of zero represents 1 dm and is used for the smaller unit.
5. Divide the left-hand division into 10 equal parts. Each part represents 1 cm, since 1 dm = 10 cm.
   • Use the parallel-line technique to divide the interval evenly.
6. Label the scale with its units and RF:
   • Write dm to the right of zero for the main unit.
   • Write cm to the left of zero for the subdivided unit.
   • Add RF = 1:4.

The completed scale measures lengths in decimeters and centimeters, up to 5 dm.

Drawing Conventions

• Use a 4H pencil for thin, light construction lines.
• Use a harder, darker pencil for the heavier outline, numbers, and lettering.

Speaker

Manas Patnaik — instructor and narrator.