Technical drawings are important in many areas of industry, but especially in mechanical design. The technical drawing represents the conclusion of the work of a designer or a technical draftsman on a component. With the technical drawing all qualitative and quantitative characteristics of a component, an assembly or
machine and plant are to be made understandable to other persons and a reproducible manufacturing of the components is to be made possible. In general, all product details are clearly recorded in the technical drawing.
What is a technical drawing? A technical drawing is a detailed image of already existing or planned components, which are required for the production of complex machines, for example.
To be able to read and understand the drawing, special knowledge is required. The symbols used and the required standards play an overriding role, as does the software with which the technical drawings are created in this day and age.
The technical drawing is a written document and means of communication between engineers and the manufacturing department in a company. It contains true-to-scale illustrations with dimensions and explanations. It is intended, for example, to show the functional or construction methods of individual parts and assemblies.
The goal of the technical drawing is a standard-compliant representation of an object. The drawing must be unambiguous. Only in this way can it be used to manufacture a depicted component. The creation of technical drawings is typical for engineers, designers, architects, draftsmen, etc..
The most famous representative of technical drawings in the 15th century AD was Leonardo da Vinci. He recorded his numerous inventions, such as his war machine, a flying machine or a link chain in countless technical drawings. Today's basic knowledge of geometry and its research goes back far before the birth of Christ. Pythagoras of Samos and Euclid of Alexandria led the way.
More recent evidence of technical drawing can be found around 1700 in the work of the French aviation pioneer Jacques de Vaucanson and in patent specifications from the 19th century.
The knowledge of technical drawing has developed further and further over the last centuries. Numerous tools were established that made it easier and easier to create drawings. Whereas drawing boards, ink pens, stencils, curve rulers and tracing paper or transparent drawing foils were mainly used for this purpose in the past, the age of computers has seen the establishment of more and more computer-aided drawing programs (CAD).
Today, it is not uncommon for the reverse route to be taken: from the finished product back to the precise technical drawing. Reverse engineering is used to examine and measure the outer and inner contours of finished components and industrially produced products. From the data obtained, corresponding specialist companies, such as Q-Tech in particular, generate precise 3D CAD models, which in turn form the basis for the technical drawing. Especially in the case of missing CAD data or spare parts, this is a great facilitation of work.
To ensure that technical drawings are clear and comprehensible everywhere, certain basic principles, representation rules and dimension entries must be observed. These are summarized in various standards, which regulate the exact structure of a technical drawing. One of these guidelines is, for example, the DIN standard of the Deutsches Institut für Normung e. V. (German Institute for Standardization), which is to be used as a binding aid when creating shapes and dimensions.
Although today many goods, commodities or devices are produced with the help of other manufacturing machines, technical drawings are still indispensable. Because these fulfill important, central tasks:
Therefore, the drawings are needed especially in areas where high accuracy and minimization of risks due to a faulty design are important. This is especially the case in mechanical engineering and also in technical documentation.
In mechanical engineering, technical drawings are required for the following purposes:
Technical drawings are required for the documentation of machines, systems and other products, especially if a CE declaration of conformity is required for placing the product on the market within the European Economic Area. The drawings are used to illustrate in detail all the functions, operation and possible sources of danger of a product.
Depending on the purpose, different types of representation are preferred for technical drawings. These can be:
Technical drawings contain the following elements: coordinates, title block, orthogonal views of the part, sectional views, detailed views and other notes for manufacturing.
The title block is always located in the lower right corner of a technical drawing. It contains all the basic information, including the product name, the names of all parties involved (design, testing and approval) and the name of the relevant company. Also noted in the title block are technical details about the dimensional system used, the projection angle, surface finish requirements, scale and material.
Especially with large and complex technical drawings, coordinates are noted in the margin for better orientation, for example in meetings.
The orthogonal view, also called orthogonal projection, contains the most important information about the geometry of the part. Thus, the dimensions and tolerances can be found in it. The orthogonal view corresponds to a two-dimensional image of the three-dimensional object from different angles. Typical for this are:
In the orthogonal projection, hidden lines of important components can also be drawn. As a rule, two or three orthogonal views are sufficient for the correct reproduction of the geometry.
The isometric representation is a three-dimensional, graphical representation of the object. Even if the isometric representation is not mandatory, it should still be included in technical drawings in practice. This is because it provides the mechanics with additional information, such as the assembly direction.
Section views are two-dimensional images of selected areas, a part of which has been cut off so that the internal features of the component, which are not apparent from either the isometric or orthogonal view, can be made visible. As a rule, the sections are positioned in line with the orthogonal views.
The imaginary cutting edge and cutting direction are indicated in the orthogonal projection with a labeled line. The resulting cut surfaces are marked with hatching. For complex parts, it is not uncommon for several section views to be displayed.
If the orthogonal projection contains complex features and areas that are difficult to recognize, these areas can be displayed in more detail with additional detail views. Detail views may differ in size and orientation from the orthogonal views. For better assignment, detail views are marked with a single letter that identifies the respective area of the orthogonal view.
Notes for manufacturing are usually placed on the lower left side of the technical drawing above the title block. This contains all information that is not apparent from the drawing. This can be instructions to the machinist, such as deburring, chamfering, or surface finishing.
Technical drawings of workpieces often have a scale of 1:1, which means that the drawing is the same size as the workpiece. For larger workpieces, the drawing is reduced accordingly. Depending on the size of the workpieces, the following scales are selected according to DIN 823:
For very small workpieces, the technical drawing is enlarged accordingly:
Important symbols on technical drawings
Information in technical drawings is represented by numerous symbols. There are:
It is important that the labeling of a drawing is always readable in the same direction as the reading direction of the title block.
The symbols and their meaning are in turn regulated in numerous standards. The same applies to their representation. For example, the dimensions of symbols for welding drawings or surface treatment symbols must not be changed. On the other hand, there are other symbols whose dimensions must be adapted to the component.
By means of the symbols geometrical tolerances can be defined in the technical drawings. A distinction is made between:
In this context, the symbol describes the respective geometric properties. Thus, a straight surface (straightness) is represented by a straight line, a roundness by a circle. Planes, on the other hand, are clarified by means of a parallelogram.
In addition, parallelism, perpendicularity, angularity, symmetry, concentricity and numerous other properties can be visualized with corresponding symbols.
The technical drawing cannot be compared with a normal picture. Rather, the drawing is a transmitter of ideas and information. Due to the prescribed standards, a technical drawing is sometimes even more precise and unambiguous than many a spoken word. Especially for the production of machines, but also in electrical engineering or construction, these drawings are indispensable. Nowadays, CAD software is usually used to create them. This means that dimensions and tolerances can be entered directly on the virtual model. This not only speeds up work processes - in the meantime, the technical drawing has become an international means of communication in technology, since the respective DIN standards take into account the recommendations of the International Organization for Standardization (ISO).
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