T- square

 A T-square is made up of hard quality wood such as teak or mahogany, etc. It consists of two parts - the stock and the blade - joined together at right angles to each other by means of screws and pins. T- square is used with its head against the ebony edge of the drawing board to draw horizontal lines, parallel lines and to guide/hold the setsquares, stencils etc. The stock is placed adjoining the working edge of the board and is made to slide on it as and when required. The blade is fitted with an ebony or plastic piece to form working edge of T-square. The blade lies on the surface of the board. Its distant edge which is generally beveled, is used as the working edge and hence, it should be perfectly straight. The nearer edge of the blade is never used. The length of the blade is selected so as to suit the size of the drawing board. Now-a-days T- square is also available of celluloid or plastic with engraved scale.

Fig. 1 T- square

Uses

1) The T-square is used for drawing horizontal lines. The stock of the T-square is held firmly with the left hand against the working edge of the board and the line is drawn from left to right as shown in Fig. 2. The pencil should be held slightly inclined in the direction of the line (i.e. to the right) while the pencil point should be as close as possible to the working edge of the blade. Horizontal parallel fines are drawn by sliding the stock to the desired positions. 

Fig. 2 Drawing using T-square

2) The working edge of the T-square is also used as a base for set-squares to draw vertical, inclined or mutually parallel lines. A pencil must be rotated while drawing lines for uniform wear of lead. The T-square should never be used on edge other than the working edge of the board. It should always be kept on the board even when not in use.

Testing the straightness of the working edge of the T-square

Mark any two points A and B (Fig. 3) spaced wide apart and through them, carefully draw a line with the working edge. Turn the T-square upside down as shown by dashed lines and with the same edge, draw another line passing through the same two points. If the edge is defective the lines will not coincide. The error should be rectified by planning or sand papering the defective edge. 

Fig. 3 Testing the straightness of the working edge of the T-square

T-square should never be used as a hammer or as guide for trimming papers. T-Square is used as a base for drawing various angles with the help of set squares. The standard ‘T’ square are designated as follows with dimensions shown in mm as per IS:1360-1989.

Table 1 Designation of T-square

Sl. No.	Designation of T-square	Blade length (mm)	To be used with Drawing Board
1	T0	1500 ± 10 mm	D0
2	T1	1000 ± 10 mm	D1
3	T2	700 ± 5 mm	D2
4	T3	500 ± 5 mm	D3