Describe a Mini drafter.

Definition and function: A mini drafter is an engineering drawing instrument that combines the functions of a T-square, set-squares, scale and protractor. It is clamped to the drawing board and is used to draw horizontal, vertical and inclined parallel lines at any angle quickly and accurately.

Labelled diagram:

  [Drawing board edge]
   ||==(1) Clamp
   ||
    \  (2) Arm-1
     \
      O  (3) Joint / elbow
     /
    /   (4) Arm-2 (parallel links)
   /
  (5) Protractor head  [0-360 deg scale + (6) locking knob]
   |
   |==================== (7) Horizontal scale (blade)
   |
   |  (8) Vertical scale (blade)
   |

Description of parts:

1. Clamp: screws on to the top left edge of the drawing board and holds the whole drafter firmly.
2. Arms / links: two pairs of parallel steel links joined at an elbow; they form a parallelogram mechanism that keeps the scales parallel to their original orientation wherever the head is moved on the board.
3. Protractor head: a circular head graduated from 0° to 360°, usually with 15° click stops, used to set the scales at any required angle.
4. Locking / adjusting knob: fixes the protractor at the chosen angle; a fine-adjustment screw allows exact setting.
5. Scales (blades): two plastic/celluloid scales graduated in mm, fixed at exactly 90° to each other on the head; used for measuring and drawing lines.
6. Handle/grip: used to move the head across the board.

Working: The clamp is fixed to the board, the scales are aligned with the board edges and the head is locked at 0°. Moving the head anywhere on the sheet keeps the scales parallel, so horizontal and vertical lines can be drawn directly; inclined lines are drawn by unlocking the head, rotating it to the required angle and locking it again.

Advantages: saves time, gives accurate parallel and angular lines, replaces several instruments, and is easy to use.