RULE T: CHARACTERISTICS, WHAT IS IT FOR, EXAMPLES - MATHS - 2025

The T-rule is a tool for drawing on paper technical, mechanical, architectural and electrical plans. It consists of a ruler at the end of which another shorter ruler is attached as a square, forming a right angle with the first.

The longest ruler is called the body and the shortest is called the head. The shape of the set resembles the capital letter t (T) and hence its name. The head protrudes from the ruler so that it can be supported and in contact with the edge of the drawing table.

Figure 1. The T ruler shown in the figure is an instrument used in technical drawing, in order to draw horizontal lines parallel to each other. Source: Wikimedia Commons.

Figure 1 shows a T-ruler placed on a drawing board. When the head of the T-rule is in contact with the edge or edge of the table, the main rule allows the drawing of lines perpendicular to the edge of the table.

By moving the head along the edge of the table, then another line can be drawn perpendicular to the edge and therefore parallel to those that were previously drawn.

Characteristics of a T rule

As indicated at the beginning, rule T is characterized by having two rules: a major and a minor.

The smaller rule is attached to the first one in such a way that their edges form a right angle (90º) between them. It has a straight edge and the other usually has a curved shape, as seen in the image.

This shorter ruler is called the head or head of the T ruler, while the main ruler longer than the head is called the body or simply the ruler. With it, the straight lines are made on the paper between the drawing table and the body of the ruler.

T-rule materials

The screed can be made of various materials and the choice of one of them depends on the end use that is given and the preferences of the user.

-The wooden T ruler has a completely flat body or main ruler and is ideal for making lines with graphite pencils, crayons and mechanical pencils. But they are not recommended for drawing with pencils or with rapidograf, since the ink can run under the rule.

- Combination of materials, for example wood and plastic. In these, the body or main rule is made of plastic, which is placed between another two wooden rules of less width, as a sandwich.

The plastic ruler is generally transparent and protrudes slightly from the main ruler. As there is a gap between the plastic edge of the main ruler and the paper on which it is drawn, there is no drawback that the ink from the pen or the rapidograph seeps under the edge of the ruler, due to surface tension.

- P lastic (generally transparent), are usually smaller than wood or wood-plastic, because the material is more brittle and tends to flex. The plastic T-rulers are those that are usually used for school work, on surfaces less extensive than a drawing board, such as the desk.

- At zero stainless, they are intended for industrial use, since they are used to make traces on metal sheets or on glass, generally using a tracer or cutter with a steel or diamond tip.

What is the T rule for?

With the T ruler you can draw straight lines parallel to each other. On the other hand, if it is used in combination with a set of squares, which rest and slide on the T rule, it is then possible to construct lines perpendicular to those drawn directly with the T rule.

Also, in combination with the square (another essential tool for the draftsman), oblique lines can be drawn with respect to the main rule of the T with angles of 45º, 60º and 30º.

Figure 2. Rule T, its parts and how to support it correctly to make horizontal lines. Source: SlideShare

How is the T rule used?

1.- To use the T rule, you need a drawing board or table where the sheet of paper on which the drawing will be made will be fixed with self-adhesive tape.

2.- Before starting to use the T rule, it is convenient to verify that the head of the same has no play (or movement) with respect to the body or main rule. If there is some movement between these two parts, the screws must be tightened, always making sure that the two parts form 90º. This check can be done with a square.

3.- If the draftsman is right, he must rest the head of the T-ruler against the left edge of the drawing board or table and slide the ruler up or down with the left hand, making sure that the head is always supported on the edge or edge of the board.

If the draftsman is left-handed, he must place the head towards the right side and make the lines with his left hand.

4.- Before definitively fixing the sheet of paper to the board, it must be verified that the horizontal of the paper (the lower edge of the same) follows the same direction of the rule. If there is any difference, the sheet of paper should be rotated until it is perfectly aligned. Then permanently fix the paper to the board with adhesive tape.

5.- With the ruler, horizontal lines can only be made, supporting the pencil on the edge of the ruler and tracing from left to right with the pencil tilted to the right, while the left hand keeps the ruler resting on the left edge of the board.

If you are left-handed, everything must be reversed, that is, trace with the left hand and fix with the right hand to the right edge of the board.

Examples

Plot of perpendiculars

In the previous section it was explained how to make horizontal strokes directly with the T ruler.

In case you want to make vertical lines, that is to say perpendicular to the ruler, you must use an auxiliary square that rests on the rule T. The vertical line is made by sliding the pencil along the perpendicular edge of the square.

Figure 3. Use of the T-rule to draw perpendiculars and obliques. Source: SlideShare

Oblique strokes

For oblique lines it is also necessary to use the squares in conjunction with the T rule.

There are two drawing squares: one is an iso-right triangle, that is, it has two 45º angles, and one is 90º. The other is a scalene right triangle whose angles are 30º, 60º and 90º, also known as a bevel.

The appropriate square should be selected depending on the angle of the oblique line to be drawn. By sliding the square on the T rule it is possible to draw a set of oblique lines parallel to each other.

References

1. Blogspot. Use of the T rule and squares. Recovered from: instruments martinez.blogspot.com
2. Geniusland. How to use a T rule. Recovered from: geniolandia.com
3. SlideShare. Technical drawing: Rule T. Recovered from: es.slideshare.net
4. Webscolar. Technical drawing instruments. Recovered from: webscolar.com
5. Wikipedia. Rule T. Recovered from: wikipedia.com