Essential Instruments for Technical Drawing
Instruments Used in Technical Drawing
The completion of a technical drawing requires calculation, measurement, well-planned lines, precision, and a number of conditions that necessitate the use of good tools, good materials, and theoretical knowledge put into practice by a skilled drafter.
Drawing Board
A drawing board is a tool used to hold the paper for drawing. Usually constructed of smooth, flat wood or plastic, it has straight edges which enable movement of the T-square.
The size depends on the format being used. For school use, a size of 40 inches tall and 60 centimeters wide is sufficient.
In technical drawing workshops, tables built specifically for this activity are used instead of boards, with adjustable size and inclination.
T-Square
The T-square gets its name from its resemblance to the letter T. It has two perpendicular arms, with the cross arm being shorter. They are made of wood or plastic.
It is used to draw horizontal parallel lines quickly and accurately. It also serves as a support for set squares and to align the format for fixing.
Ruler
A ruler is an instrument used to measure and draw straight lines. It is rectangular, flat, and has markings for decimeters, centimeters, and millimeters along its edges.
They are usually made of wood or plastic, although clear plastic is preferred to allow visibility of the lines being plotted.
Their lengths vary according to usage, ranging from 10 to 60 inches. The most common are 30 centimeters.
Set Squares
Set squares are used to measure and draw horizontal, vertical, and inclined lines. When combined with the T-square, they can draw parallel, perpendicular, and oblique lines. They may have markings in inches and millimeters.
The set squares commonly used in technical drawing are two:
- The 45-degree set square, which is shaped like an isosceles triangle with an angle of 90° and two angles of 45°.
- The 60-degree set square, also called a bevel, shaped like a scalene triangle, whose angles measure 90°, 30°, and 60°.
Protractor
A protractor is an instrument used for measuring or transferring angles. They are made of plastic and come in two types: a semicircle divided into 180 degrees and a full circle of 360°.
The numbers are arranged in two graduations so they can be read from right to left and from left to right, depending on the angle being measured.
Compass
A compass is a precision instrument used to draw arcs, circles, and transfer measurements.
It consists of two articulated arms at the top, which houses a cylindrical piece called the mango, used to drive the compass with the index finger and thumb.
One arm has an adjustable steel needle with a screw and a nut on a wheel. The other arm has a device that allows the placement of pencils or other accessories.
Compass Classes
- Part Compass: A standard compass that can hold accessories like a pencil or pen.
- Compass with Dry Ends: It has sharp steel points at both ends and serves to take or move measurements.
- Mustache Compass: Characterized by keeping the radius of opening fixed. The opening is adjusted with a screw or threaded shaft. It is used to draw small-sized circles and circles of equal radius.
- Pump Compass: Used to draw very small arcs or circles. The arm consists of a vertical shaft that turns the pencil around it.
Pencils
Pencils are essential for writing and drawing. They consist of a graphite core and a wooden sheath. They can have a round or hexagonal cross-section. Hexagonal pencils are preferred for drawing because they facilitate grip and prevent them from rolling off the drawing board.
Degrees of Hardness of the Core
Pencil cores have varying degrees of hardness, from the hardest to the softest. Harder cores produce fine gray lines, while softer cores produce bold black lines.
They are classified by letters and numbers. The letter H indicates hardness, F stands for firm, and B indicates blackness.
The hardest are: 4H, 3H, 2H, and H. Intermediate grades are: HB and F. The softer grades are: B, 2B, 3B, and 4B.