Introduction to Engineering Drawing

1. ENGG1100 Introduction to Engineering Design Introduction to Engineering Drawing Professor Yunhui Liu Dept. of Mechanical and Automation Engineering Spring, 2014 MAE Dept., The Chinese University of Hong Kong 1

2. What is Engineering Drawing? • An engineering drawing is a type of technical drawing used to fully and clearly define requirements for engineered items (from en.wikipedia.org) • a formal and precise way (graphic language) for communicating information about the shape and size of physical objects. • a mean for specifying the precision of physical objects. Important as it is a legal document, i.e., if the drawings are wrong, it is the fault of the engineers! MAE Dept., The Chinese University of Hong Kong 2

4. Why ? Effectiveness of Engineering Drawing 1. Try to write a description of this object. 2. Test your written description by having someone attempt to make a sketch from your description. You can easily understand that … The word languages are inadequate for describing the size, shape and featurescompletely as well as concisely. MAE, CUHK From Lec. Bhuiyan Shameem Mahmood

5. The language is known as “drawing” or “drafting” . A drawing can be done using freehand, instrumentsor computermethods. Graphic Language Graphic languagein“engineering applications”uses linesto represent the surfaces, edges and contoursof objects. From Lec. Bhuiyan Shameem Mahmood

6. Example Freehand drawing The lines are sketched without using instruments other than pencils and erasers. From Lec. Bhuiyan Shameem Mahmood

7. Example Instrument drawing Instruments are used to draw straight lines, circles, and curves concisely and accurately. Thus, the drawings are usually made to scale. From Lec. Bhuiyan Shameem Mahmood

8. Example Computer drawing The drawings are usually made by commercial software such as AutoCAD, SolidWorks etc. From Lec. Bhuiyan Shameem Mahmood

9. Graphics language Describe a shape(mainly by projected views). Word language Describe size, location andspecification of the object. Elements of Engineering Drawing Engineering drawing is made up of graphics language and word language. Projections of the object From Lec. Bhuiyan Shameem Mahmood

10. Perspective Parallel Oblique Orthographic Axonometric Multiview PROJECTION METHOD From Lec. Bhuiyan Shameem Mahmood

11. The projection theory is used to graphically represent 3-D objects on 2-D media (paper, computer screen). The projection theory is based on two variables: 1) Line of sight 2) Plane of projection (image plane or picture plane) PROJECTION THEORY From Lec. Bhuiyan Shameem Mahmood

12. There are 2 types of LOS : Line of sight Line of sight Line of sightis an imaginary ray of light between an observer’s eye and an object. parallel converge and Parallel projection Perspective projection From Lec. Bhuiyan Shameem Mahmood

13. The image is produced by connecting the points where the LOS pierce the projection plane. Plane of projection Plane of projection Plane of projectionis an imaginary flat plane which the image is created. Parallel projection Perspective projection From Lec. Bhuiyan Shameem Mahmood

14. Object views from top 1 2 3 4 1 2 3 4 5 5 Projection plane Orthographic Projection Orthographic projectionis a parallel projection technique in which the parallel lines of sight are perpendicular to the projection plane From Lec. Bhuiyan Shameem Mahmood

15. ORTHOGRAPHIC VIEW Orthographic view depends on relative position of the object to the line of sight. Rotate Two dimensions of an object is shown. Tilt More than one view is needed to represent the object. Multiview drawing Three dimensions of an object is shown. Axonometric drawing From Lec. Bhuiyan Shameem Mahmood

16. Multiview Projections • Project an object from six principal directions (front, back, top, bottom, right, left) (From lecture notes of course MAEG2010) MAE Dept., The Chinese University of Hong Kong 16

17. Auxiliary Views • Used to show true dimensions of an inclined plane. From Lec. Bhuiyan Shameem Mahmood

18. Isometric Drawing • Represent 3-D objects by a 2D view in the projection in which the coordinate axes appear equally foreshortened. • It is easy to understand the 3-D shape • However, the projection causes shape and angle distortions Circular hole becomes ellipse. Right angle becomes obtuse angle. MAE Dept., The Chinese University of Hong Kong 18

19. Drawing standards are used so that drawings convey the same meaning to everyone who reads them. Drawing Standards Standards are set of rules that govern how technicaldrawings are represented. From Lec. Bhuiyan Shameem Mahmood

20. Drawing Standards • Standards on • Sizes and Format of Drawings • Lines • Scales • Projection methods • Presentation of view and sections • Lettering • Dimensioning • … MAE Dept., The Chinese University of Hong Kong 20

21. Standard on Placement of Projected Views: First Angle Projection ISO standard Used in Europe, etc. From mytvmoments.com Directly project images along the line of sight • Front view is put at the middle • Top view is put at the bottom • Right view is put on the left Bottom view Left view Right view (En.wikipedia.com) Back view Front view Top view

22. Standard on Placement of Views: Third Angle Projection • The positions of the viewpoint and location of the projection view are the same • Right side view is located at right • Left side view is located at left • … • Mainly used in US MAE Dept., The Chinese University of Hong Kong 22

23. Drawing Sheet A4 Trimmed paper of a size A0 ~ A4. A3 Standard sheet size A4 210 x 297 A3 297 x 420 A2 420 x 594 A1 594 x 841 A0 841 x 1189 A2 A1 A0 (Dimensions in millimeters) From Lec. Bhuiyan Shameem Mahmood

24. Continuous thick line Visible line Dimension line Extension line Leader line Continuous thin line Dash thick line Hidden line Chain thin line Center line Basic Line Types Name according to application Types of Lines Appearance From Lec. Bhuiyan Shameem Mahmood

25. Types of Line From Lec. Bhuiyan Shameem Mahmood

26. Alphabet of Lines Visible lines Hidden lines Center line Break line Dimension & extension lines Section lines Cutting plane lines Phantom lines From MAE 2010

27. Line Conventions • Visible Lines – solid thick lines that represent visible edges or contours • Hidden Lines – short evenly spaced dashes that depict hidden features • Section Lines – solid thin lines that indicate cut surfaces • Center Lines – alternating long and short dashes • Dimensioning • Dimension Lines - solid thin lines showing dimension extent/direction • Extension Lines - solid thin lines showing point or line to which dimension applies • Leaders – direct notes, dimensions, symbols, part numbers, etc. to features on drawing • Cutting-Plane and Viewing-Plane Lines – indicate location of cutting planes for sectional views and the viewing position for removed partial views • Break Lines – indicate only portion of object is drawn. May be random “squiggled” line or thin dashes joined by zigzags. • Phantom Lines – long thin dashes separated by pairs of short dashes indicate alternate positions of moving parts, adjacent position of related parts and repeated detail • Chain Line – Lines or surfaces with special requirements From Lec. Bhuiyan Shameem Mahmood

28. Dimensioning Two types of dimensioning: (1) Size and location dimensions and (2) Detail dimensioning From Lec. Bhuiyan Shameem Mahmood

29. Units of Dimensions • Length • English - Inches, unless otherwise stated • SI – millimeter, mm • Angle • degrees, minutes, seconds Angle Dimensions From Bhuiyan Shameem Mahmood