**ENGINEERING GRAPHICSCourse No. 1

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** The engineering thinking and creation combines spatial imagination, spatial situations analysis and synthesis, with the engineering art and with an own language of communication.

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The representation of a real or an imaginary object, of an idea that exist in the mind of the engineer or designer before becoming reality, executed either on a classical support (paper), or on a modern one (computers screen), is realized in a graphic way.

** Although different languages are spoken throughout the World, a universal language existed from ancient times, the graphic language. This natural, elementary mean of idea communication is limitless both in space and time.

**The engineering graphics is more than a language, it is a whole conception of space and of the spatial object representation; it is the solutions source of the spatial problems and situations. Thats why the engineering graphics is a science.

**The components of this science are: Descriptive geometryTechnical drawingComputer graphics (computer aided drawing).

**1.2.1 SHEETS (FORMATS) SR ISO 5457-94 (STAS 1-84). The support of the drawings is rectangular The sheet can be set vertically (Fig. 1.1-a), or horizontally, meaning on the long side (Fig. 1.1-b), their indexing being done as in the presented examples:

A(ab) A(ba) a). b).Fig. 1.1abab

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Preferred sheets Exceptional sheets A0 841 1189 A02 1189 1682A1 594 841 A13 841 1793A2 420 594 A23 594 1261A3 297 420 A24 594 1682A4 210 297 A25 594 2102Special sheets A35 420 1482 A36 420 1783A33420 891 A37 420 2080A34420 1189 A46 297 1261A43297 630 A47 297 1471A44297 841 A48 297 1682A45297 1051 A49 297 1892

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Fig. 1.2297

**1.2.2 LINES STAS 103-84. Taking into account the destination, there are two thicknesses of lines that can be used: Thick or heavy (thickness=b); thin or fine (b/3 or b/2).

The line thickness depends on the dimensions and complexity of the parts to be drawn, as well on the purpose and size of the drawing. For b there are given the values: 0,18; 0,25; 0,35; 0,5; 0,7; 1; 1,4; 2; 2,5; 3,5; 5.

**The following types of lines are used as they are needed: continuous line wavy line zigzag line dashed line dash dot line heavy open dash dot line two dots dash line

**1.2.3 LETTERING SR ISO 3098/1-93 (STAS 186-86). The character of lines and the lettering gives the drawing what is known as technique, a phase of drafting which is too often neglected. The height of the capitals or of the figures (numbers), defines the size of the lettering by h: 2,5; 3,5; 5; 7; 10; 14; 20. It is permitted the use like slant the vertical writing or the inclined writing at 75 degrees, and like shape, a normal one (10/10xh the height of capitals, and the thickness of the writing line h/10), or a longed one (14/14xh, the thickness of the writing line h/14).

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1.2.4 TITLE BLOCK (INDICATOR) SR ISO 7200-94 (STAS 282-87). the identification zone : - the registration number or identification of the drawing; - the name of the drawing; - the name of the legal owner of the drawing.the zone of supplementary information: - indicative; - technical; - administrative.

**TITLE BLOCK1702025152515201055A(b x a)Fig. 1.3

NameSign.(Material) (Drawing No.)(Student No.)StudentProfessor(Mass)(Fac. Year Group)121 E(Scale)1:1 (Drawing Name)(Date) 06.10.11

**1.3 GENERAL NOTIONS ABOUT GRAPHIC REPRESENTATIONSIn the technical field the drawing is used as means of communication. The shape is best described through projection, a procedure of getting an image by rays of observation or of sight. The direction of the rays can be parallel (when the observer is located at an infinite distance from the object), or conic (if the distance is a finite one), leading to get parallel projections, or central (perspective) projections (Fig. 1.4 - a and b).

**parallel projection central (perspective) projection

** SYSTEMS OF PROJECTIONSA system of projection is compound by four elements:the observers eye; the rays formed by lines of sight;the object to be projected; the plane of projection.According to the space order of these four elements there are two principal systems of projections: European system (fig. 1.5) American system (fig. 1.6).

**The graphic representations used in technique, impose a very good knowledge of elementary geometry (plane and spatial), of the descriptive geometry, and of the technical drawing.Descriptive Geometry establishes laws which are to enable the representation of spatial objects and of spatial situations. These laws (rules) are coming directly from the elementary geometry.Technical drawing relies on orthogonal (orthographic) projection, which supplies the best conditions for describing shape of an object, and it is best fitted to make dimensioning, which is the second function of a technical drawing.

**1.3.2 COMPUTER GRAPHICS. Charles Babbage, an English mathematician, developed the idea of a mechanical digital computer in the 1830s, and many of the principles used in Babbages design are the basis of todays computers. The computer appears to be a mysterious machine, but it is nothing more than a tool that just happens to be a highly sophisticated electronic device. It is capable of data storage, basic logical functions, and mathematical calculations. Computer applications have expanded human capabilities to such an extent that virtually every type of business and industry utilizes a computer, directly or indirectly. The first demonstration with a computer, as a tool of drawing and design, was made at the Institute of Technology of Massachusetts, in 1963, by Dr. Eng. Ivan Sutherland, with his system called Sketchpad.

**The CAD (Computer Aided Design or Drawing) techniques, using specialized programs led to the increase of the quality of realism contained in the drawing realized by means of computer.The computer is able to do many things, very quickly, but it is still an electronic equipment, without brains, at least for the moment. It cannot think and cannot do anything more or anything less than what it was told to do. A CAD system is not creative, but it can help a lot the user to become more productive, earn time. The creator is the man with his so-called limit of his incompetence.

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Fig. 2.1THE SYSTEM OF PROJECTIONDIHEDRALS

**TRIHEDRALS

[H] [V] = - abscises axis[H] [L] = - depth axis[V] [L] = - quotas axis;Fig. 2.2

**a horizontal projection a - verticalprojection a- lateral projection

T1T2T3T4T5T6T7T8x++++----y+--++--+z++--++--

** a is defined by the coordinates pear (x,y); a - is defined by the coordinates pear (x,z); a - is defined by the coordinates pear (y1,z);

Fig. 2.5EPURA

**a. - A1(20, 40, 30)

b. - A2(20, -40, 30)

**c. A3(20, - 40, -30)d. A4(20, 40, -30)

**e. A5(-20, 40, 30)f. A6(-20, - 40, 30)

**g. A7(-20, - 40, -30)

h. A8(-20, 40, -30)

Fig. 2.6

**PARTICULAR POSITION OF A POINTH(x, y, 0)V(x, 0, z)L(0, y, z)K(x, 0, 0)M(0, y, 0)N(0, 0, z)H [H]V [V]L [L]K [H] [V]M [H] [L]N [V] [L]

**Given the point A1(20; -40; 30), represent epura of A1 and A2, its symmetrical to the origin. To what trihedral these points belong? Solution: the coordinates of the point A2are obtained by changing the sign of the point A1 all coordinates A2(-20; 40; -30). A1T2, and A2T8 (Fig. 2.8)

*3 STRAIGHT LINE IN DESCRIPTIVE GEOMETRY Fig. 3.1

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*3.1 LINE TRACES. POINT LOCATED ON A STRAIGHT LINE. Fig. 3.2*

** 1. Given the point A(40; 30; 50), change the abscissa, depth and quota of A, to make it belong to every eight trihedrals. Represent these B, C, D, E, F, G, and I points in epura.

2. Given the point A(50; 20; -30) represent it in epura together with the points B symmetrical of A to [H]; C - symmetrical of A to [V]; D - symmetrical of A to [L]; E - symmetrical of A to 0x; F - symmetrical of A to 0y; G - symmetrical of A to 0z. HOME WORK HW- 01: POINTS PROJECTIONS

**LAB L- 01: POINTS AND STRAIGHT LINES Represent in epura the points: H(40; 30; 0), V(20; 0; 40), L(0; 40; 25), K(30; 0; 0), M(0; 40; 0), N(0; 0; 30), T(0; 0; 0). Where belongs every point ? They are given the points: A(70; 50; 35) and B(45; 15; 25). Obtain the traces H and V of the line define by the points A and B. They are given the points: A(10; 25; 40), B(35; 5; 10) and M(70; 50; 40). Construct the rhombus [ABCD], if one of its diagonals is located on the line defined by the points A and M.

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