DRAWING INSTRUMENTS
The drawing instruments which are used to perform drawing work. The different types of drawing instruments mention below.
DRAWING BOARD
Along the left edge of the board, a groove is cut and a perfectly straight ebony edge called working edge, is inserted into the groove. The drawing board should be placed on the table, always with the working edge at the left side.
| DESIGNATION | LENGTH IN TO WIDTH IN mm | RECOMMENDED FOR USE WITH USE WITH SHEET SIZE |
| B0 | 1500×1000 | A0 |
| B1 | 1000×700 | A1 |
| B2 | 700×500 | A2 |
| B3 | 500×350 | A3 |
T-SQUARE
This is made of well seasoned hard wood and consists of two parts, namely blade and stock . The blade which moves on the surface of the board, has a working edge. The working edge is bevelled and in some types of T-Square, it is made of transparent plastic edge so that the immediate lines hidden by it will be visible. Its main use is to draw horizontal lines and it also used as a support to place the set-square over it
SET-SQUARES
These are two in number. One is 60° -30° set-square and another is 45° set-square These are made of celluloid. These are used to draw vertical, inclined and parallel line and for the combination of the angles
PROTRACTOR
This is made of celluloid. Protractor will be either semicircular or circular. It is used to set up and measure any given angle
CLINOGRAPH
This is used to draw a series of parallel and perpendicular lines.
TEMPLATES
To avoid the use of instrument box, scale, and set squares which are time consuming, some equipment specially designed in different shapes to draw circles polygons, alphabets, numbers etc. are used. These special tools which are readily available are known as “Templates” The letters in the form of “Stencils” are also available in all sizes for saving of time in lettering.
FRENCH CURVES
Circles and arcs can be drawn by compass and templates of different sizes. But for drawing irregular curves, french curves made of transparent celluloid are used
DRAFTING MACHINE AND MINIDRAFTER
Drafting machines are used by professional draughtsmen to produce the drawings with ease and rapidity. The drafting machine combines all the function of the “T” square, Square, set-squares, protractor and clinosgraph.
Functions of Mini-Drafter:
1. Clamp: Clamp is used to hold the drafter to the board properly, to minimise the errors caused by relative motion.
2. Link Mechanism: The link mechanism is provided in the drafter to move the set of scales in a fixed way that the position of the scales is always in the same direction at any position on the drawing sheet.
3. Pivot Plate: The pivot plate is instrumented to couple the upper areas and lower areas.
4. Protractor: The protractor is provided to rotate the scales in any required angles including vertical and horizontal.
5. Scale: It used to draw the lines.
6. Knob: The knob is provided above the protractor to fix the position of it in any required angle.
Procedure of using mini drafter:
1. Fix the clamp of the mini drafter at the top left hand corner of the drawing board.
2. Set the protractor head with the reference mark indexing zero degree.
3. Align the edge of the scale with either of the boarder lines or edges of the drawing sheet.
4. The protractor may be used by adjusting the knob and fixing new positions. It facilitates in drawing inclined lines and parallel lines.
5. Use one hand (generally left) for positioning the head and draw the lines with other hand. The same may reversed for left handers.
PENCILS
Drawing pencils are graded and designated by the letters as 6B, 4B, 3B, 2B, В. HB, in the decreasing order of softness., and blackness and F, H. 2H, 3H, 4H, 5H, 6H. 7H, SH, 9H in the increasing order of hardness. For students use, H, 2H and HB pencils are necessary. Drawings are done by using 2H pencils and finished with H or HB pencils.
There are two methods to prepare the pencil to work.
1. Conical Point: Is used for dimensioning, drawing and printing.
2. Chisel Point: Is used for drawing, boarder lines.
Mechanical Clutch Pencil: Now-a-days mechanical clutch pencils are preferred than wooden pencils. Pencil leads of 0.5 mm thick leads. 2H, HB and H grades leads are used in mechanical pencils.
SCALES
Scales are measuring devices usually made either of cardboard or of plastic. They are available in one set consisting of eight scales, designated from M1 to M8. The standard recommended scales to be used in an engineering drawing are given in table.
COMPASS
The compass is an instrument used for drawing circles and arcs of circles in any instrument box, there will be two compasses one big and the other small.
1. Long Compass: It consist of two legs, hinged at one end. One leg contains a needle at its end. The other leg is so arranged that it can receive either a lead or a pen. It is used to draw circles upto 150 mm dia or arcs with pencil or ink. A pencil lead is to insert a distance of 1 mm between pencil lead and steel needle. The compass can be adjusted for drawing bigger diameter circles.
DIVIDERS
