Technical design - SpeedyLook encyclopedia

The drawing, a simple representation?

The technical design meets two essential needs of the process of technical design: to formalize the ideas to validate concepts, and to communicate. The representation by the drawing should not thus be limited to a simple description of forms.

Even if the perspective constitutes a sufficient general model to give an order of idea, it is a not very effective vector of geometrical data. Moreover, it can contribute to bad interpretations (see work of Maurits Cornelis Escher who knew to play of this insufficiency). Indeed projection on a sheet in two dimensions of an object with three dimensions is not a bijective transformation. It is not possible, on a prospect systematically to record the value of an angle: no angle is right on a cube represented in prospect, and sometimes two right angles appear with different values.

The strong idea of the technical design is the arbitrary suppression of a dimension, which makes it possible to reveal full-scale the two others. Blow, at least two different sights will be necessary to claim to hold the whole of the geometrical characteristics of the object represented.

The riding Perspective is registered to some extent halfway between the natural prospect (conical) and plane projection (like the isometric Perspective).

The electric diagrams, or of hydraulic systems belong to the technical designs. In this case the concern is to represent the organization of the technical components. In the same way the Organigramme S can be related with the technical design.

Rules of the technical design

the technical design must be included/understood by all. For that there must it be some rules of presentation.

Correspondence of the sights

The object is often represented according to several sights of which the relative tendency respects certain conventions. Any technical object presents obvious principal directions. In six particular directions of sight rise: of face, back, top, of in bottom, left, right-hand side. This principle of projection is based on the techniques of the descriptive Géométrie.

One can use two conventions to place the sights in correspondence, both having the front view like reference:

European convention or European projection: the sight of top is placed under the front view, the sight of right-hand side, on the left of the front view… What returns, between two sights, to make “roll” the part above the plan on which it is supposed being posed.
convention states-unienne or American projection: one places the sight of top at the top of the front view, the sight of left on his left… What amounts making roll the part in lower part of the plan.

Convention used is represented by a truncated cone placed in the cartouche.

The two representations are justified as follows:

European convention corresponds to the logic of projections: what is seen “of right-hand side” (since the line) is thus projected on the left, and takes shape on the left, etc
convention states-unienne privileges the practical aspect: the details on the left in the front view are neighborly with their representations in the sight of left (that allows the proximity of quotations).

Each sight can represent the object only according to two dimensions. Two adjacent sights in correspondence thus have a principal direction jointly. In this direction the same detail is represented in opposite: for example the bottom of the part must be with the same height on the front views and of right-hand side. The height of the part can indifferently be raised in the two sights.

In a concern will associate some additional sights to him (often one or two) to erase any ambiguity. For example:

a part of revolution can be entirely defined in an axial sight. Indeed its symmetry of revolution confers an identical plane geometry to him.
a parallelepipedic part without too many holes will be completely defined under two sights.
for a car, the front view is… the side view, which defines best the line.

According to European convention, one will thus have, in general, on a A4 sheet placed vertically, the front view in the left upper part of the sheet, the sight of top under the front view, and the sight of left in the right upper part of the sheet, leaving the right lower part for the cartouche and the texts. The sights of left and top are aligned on the front view, but one does not let remain the lines of recall.

Finally the cross-sections should be privileged for the definition of the hidden forms, the features strong being easier to interpret, and the hatchings locating the full of ones matter best.

Features

The use of the various features follows standard NF E 04-520 ISO 128. One uses two line weights overall: extremely (or thick , or fatty ) and fine . The feature can be full (or continuous ), stopped (or discontinuous : small of the same features mixed length) or (in alternation, long feature, milks short).

See detailed article: Milked (technical design)

Organization of the sheet

The sheet has a margin of 1 cm for the smallest formats A4, A3 and A2, and a margin of 2 cm, for the formats A1 and A0. The sheet in general includes/understands several sights distributed in a balanced way.

Cartridge

A cartouche is a datum field comprising inter alia the name of the part, the mechanism from which it is resulting, the scale applied and a whole of data intended for filing of the document.

Traditionally this cartridge is a rectangle placed in bottom and on the right of the sheet, this one being placed vertically for the “even” formats (A4, A2, A0) and horizontally for the others (in other words the multiple dimension of 210 is placed horizontally). The origin of this tradition is related to the arrangement of the “plans”, folded with a4 format and piled up in shelves of cupboard. After folding, whatever the format used, the cartouche appeared placed in bottom, and gave access information directly by simply raising that which recovered it (placed in top, to be read, it would oblige to draw all the document out of the pile).

This type of arrangement is hardly any more practiced (foldings are frightening!), the large drawers extra-dishes, the suspended files with side or higher opening, saw the cartridges moving according to their accessibility, and their place became a “standard house”, according to the type of arrangement used in the company.

The appearance of the computer and the CAD, it quasi disappearance of file-paper returns the problem of the very secondary access to information: the computer will seek at the same speed the cartouche, file among the files, where that it is, possibly out of the drawing itself.

The text

The text follows standard NF E 04-505 ISO3098.

So that a drawing paper is readable rather easily, the heights of characters were defined as follows:

Title H = 7 mm
Subtitle H = 5 mm
Text large H = 3,5 mm
normal Text H = 2,5 mm

H is the nominal height , which corresponds to the height of the capital (inter alia). This name is not used in typography and corresponds to the eye more the jamb or more the pole - in technical design, pole and jamb have the same size. The thickness of the feature is of one 10th the height.

See article: Writing (technical design)

Codified representations.

Cross-sections

When a part is represented by a cross-section, i.e. skinned so that certain details, hidden for an external observer, become apparent. The reading of the full features in is definitely easier. One practices a hatching of the zones then where the matter was truncated, thus marking a contrast between the full ones and hollows. By convention, the central part (which does not have anything to hide) is not cut.

For a design drawing, independently of material, the regular hatchings, parallels and, are in continuous feature forming an angle of 45° or 30° compared to the edges of the sheet.

For an overall drawing, the hatchings are characterized by a reason associated with a type of materials and more generally with a physical property or technical. On each sight, the same part must have the same reason (orientation and frequency). It is necessary to alternate if possible the orientation of the hatchings between two joint parts. One will distinguish:

ferrous metal (Iron, Steel, cast iron); these materials are employed for the majority of the parts.
Alloys of Aluminum, known as light, for the parts which one wishes to minimize the mass.
Alloys of Copper, used for the parts of friction
Plastics Polymeric (for example joint): two cross networks of hatchings with continuous fine feature making 45° one compared to the other
wood
the parts of small size will be sometimes grayed, even blackened when they are really too small (almost jointed contours).

Technological functions

threading: to see the article Threaded rod > Representation in draftsmanship
tapping: to see the article Tapped hole > Representation in draftsmanship

Gears S and Groove S.

Techniques of drawing

The technical design is practiced on tables provided with a pantograph: this device maintains two rules (laid out with right angle) in a constant direction, which helps with the construction of the parallels (correspondence of the sights). On certain tables, one can modify the orientation of this square, for the execution of the hatchings for example.

There exist many software of Dessin computer-assisted (CAD) directed Mechanical engineering, metal or structure, such as for example Autocad, Cadkey etc And Catia developed by Dassault Aviation, to build planes of soldier. In addition to the assistance with data-processing management (filing), they propose a whole of graphic tools and libraries of standardized components (screw, bearings…) or specific manufacturers (jacks, bodies of construction…) allowing a real time-saver. The use of this software however requires the knowledge of the rules of the technical design since here the mouse replaces simply the pencil, a feature remaining a feature.

The software of Conception computer-assisted (CAD) opened a door towards the integrated design: Catia, SolidWorks, Autodesk Inventor, Solidedge, Pro-Engineer etc Also directed “trade”, they allow the creation of objects by virtual assembly of elementary voluminal “functions” (cylinder, parallelepiped…) or technological (drillings, veins, folds of sheet…). They are often associated with additional software allowing the Simulation operation, calculations by finite elements (which make it possible to determine the places of “tiredness” of the various parts), calculations of checking of behavior or the edition of a synthesized image in made realistic. The edition of the plan is then automatic, and the last versions allow already, for sometimes complex parts, a plan not requiring any final improvement.

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