How to quote a drawing

Before starting to dimension a drawing, it is important to know the reference standards that regulate this practice.

In particular, there are two main organizations that establish technical standards for dimensioning:

• ISO (International Organization for Standardization): an international organization that defines technical standards globally.
• UNI (Ente Nazionale Italiano di Unificazione): an Italian organization that defines national technical standards.

As far as dimensioning is concerned, ISO and UNI standards establish the symbols to be used, the conventions to be followed, and the criteria for choosing the dimensions to be reported on technical drawings.

The symbols of dimensioning

The symbols of dimensioning are represented by lines, arrows, and letters. Their meaning varies depending on the type of dimension to be reported on the drawing. For example:

• The continuous line represents a main dimension;
• The dashed line represents a secondary dimension;
• The arrow indicates the extension of the dimension (i.e., the length between two points);
• The letters indicate the type of dimension (for example, "D" for diameter or "H" for height).

The conventions of dimensioning

To ensure clarity and legibility of the drawing, there are some conventions to follow in dimensioning. For example:

• The dimensions must be reported outside of the drawing, preferably corresponding to the bottom sides;
• The dimensions must not overlap with the lines of the drawing;
• The dimensions must be written clearly and legibly.

The criteria for choosing dimensions

The choice of dimensions to be reported on the drawing depends on the type of object represented and the purpose of the drawing itself. In general, the dimensions must be precise enough to ensure the correct realization of the object, but also clear and legible enough to allow easy interpretation of the drawing.

In addition, it is important to avoid reporting too many dimensions on the drawing, otherwise it may become heavy and unclear.

How to choose the most suitable dimensioning system

The choice of dimensioning system depends on the type of drawing being created and specific project requirements. The following are the main dimensioning systems used:

Linear dimensioning

Linear dimensioning is a simple and effective system for indicating the dimensions of an object. It consists of a continuous line with arrows at each end that indicates the dimension of the object. This system is commonly used for technical drawings, such as those in mechanical or civil engineering.

Radial dimensioning

Radial dimensioning is used to indicate circular dimensions of objects, such as holes or shafts. It consists of a series of radial segments that extend from the center of the object and terminate with an arrow.

Angular dimensioning

Angular dimensioning is used to indicate the angles between two lines or surfaces. It consists of a continuous line with an arrow at one end and a central arc indicating the measured angle.

Functional dimensioning

Functional dimensioning is used to indicate the functional specifications of components, such as material strength. This system can be very complex and requires a deep knowledge of engineering principles.

• To choose the most suitable dimensioning system, it is important to consider the specific needs of the project.
• Linear dimensioning is the most common system and is used to indicate object size.
• Radial dimensioning is used to indicate circular dimensions of objects.
• Angular dimensioning is used to indicate the angles between two lines or surfaces.
• Functional dimensioning is used to indicate the functional specifications of components.

In general, it is important to select the dimensioning system that best fits the project's needs and allows for clear and precise communication of necessary information. A well-dimensioned drawing can facilitate the production of a high-quality product and reduce production times.

The basic rules of dimensioning: dimensions, position, and tolerances

Dimensioning is fundamental for producing a precise and accurate technical drawing. To be effective, dimensioning must follow some basic rules concerning dimensions, position, and tolerances.

Dimensions

Dimensions are the first element to consider in dimensioning. All necessary measurements to accurately produce the drawn object must be indicated. Dimensions must be expressed in clear and understandable units of measurement, such as millimeters or inches.

In addition, repeating the same measurements multiple times in the drawing should be avoided, otherwise confusion and uncertainty about the actual dimensions of the object may arise.

Position

The position of elements in the drawing is equally important as dimensions. The precise location of objects within the drawing must be indicated, for example using Cartesian coordinates or specific reference points.

In addition, overlapping between dimension lines and elements in the drawing should be avoided, otherwise confusion about the actual position of objects may arise.

Tolerances

Tolerances are acceptable variations in object dimensions. Tolerances for each measurement in the drawing must be indicated, so that an object that meets the required specifications can be produced.

In addition, attention should be paid to tolerances of parts of the object that interact with each other, such as the diameter of a hole and that of the screw passing through it.

Practical examples of how to dimension a drawing

To better understand how to dimension a drawing, let's look at some practical examples:

Example 1: Dimensioning a horizontal line

Let's imagine we have a drawing that represents a table with a horizontal line. To dimension this line, we need to indicate its length. We can do this in different ways:

• Indicating the length in millimeters or centimeters;
• Using the symbol "L" followed by the length in millimeters or centimeters;
• Indicating the length in inches.

For example, if the horizontal line has a length of 10 cm, we can dimension it in this way: "L=10cm" or "10cm".

Example 2: Dimensioning an angle

Now let's suppose we have a drawing that represents a right triangle. To dimension the right angle, we need to indicate its value. We can do this by using the degree symbol (°) and writing the angle value next to it. For example, if the right angle has a value of 90 degrees, we can dimension it in this way: "90°".

Example 3: Dimensioning a circumference

Let's imagine we have a drawing that represents a wheel. To dimension the circumference of the wheel, we need to indicate its diameter or radius. We can do this in the following ways:

• Indicating the diameter preceded by the letter "D" followed by the value in millimeters or centimeters;
• Indicating the radius preceded by the letter "R" followed by the value in millimeters or centimeters.

For example, if the circumference of the wheel has a diameter of 50 cm, we can dimension it in this way: "D=50cm" or "50cm". If instead we know the radius of the wheel and want to dimension it, we can write for example: "R=25cm" or "25cm".

In general, to correctly dimension a drawing, it is important to be precise and use standardized symbols and conventions. In this way, anyone who reads the drawing will be able to understand the indicated measurements without ambiguity.

Conclusion

Dimensioning a drawing is a fundamental operation for anyone working in the field of design or engineering. Thanks to the use of standardized symbols and conventions, it is possible to accurately indicate the measurements of different parts of the drawing, avoiding ambiguity and possible errors.

We hope that these practical examples have been useful for you to better understand how to dimension a drawing. Always remember to be precise and use correct symbols, in order to make your drawing clear and understandable for everyone.