Computer Aided Engineering Drawing for beginners.pptx

Definition of Engineering Drawing, Projection and their types, Difference between first and third angle projections, Types of dimensioning

1. Engineering Graphics

2. What is Engineering Drawing? It is the graphic representation of physical objects and their relationships. It is prepared, based on certain basic principles, symbolic representations, standard conventions, notations, etc. It is the only universal means of communication used by engineers. It is the graphic language, from which a trained person can visualize the object. E ngineering drawing is called the universal language of engineers.

3. What information should be available on engineering drawing? A  perfect engineering drawing should have the following information: Shape of an object Exact Sizes and tolerances of various parts of the object The finish of the product The details of materials The company’s name Catalogue no of the product Date on which the drawing was made The person who made the drawing

4. What you will learn in this course? Visualization  – the ability to mentally understand visual information. Graphics theory – geometry and projection techniques used for the preparation of drawings. Use of standards – set of rules for the preparation of technical drawings. Use of conventions – commonly accepted practices in technical drawings. Tools – devices used to create technical drawings and models. Applications – the various uses for technical drawings.

5. Methods of developing an engineering drawing

6. Drawing Instruments/ Draughting Tools Drawing board Mini-draughter Instrument box, containing the following: Compass Bow-compass Spring bow-compass Divider 45°-45° and 30° -60° set-squares Protractor Set of scales French curves

7. Drawing Instruments/ Draughting Tools Drawing board Mini- Draughter Spring bow compass Set Squares Roll n draw French Curves

8. Drawing Board Sizes (BIS)

9. Drawing Sheet Sizes

10. Drawing Pencils

11. Layout of Engineering Drawing The drawing should contain a note: ALL DIMENSIONS ARE IN MM. (Bottom left corner outside the title box)

12. Title Block The drawing should contain a note: ALL DIMENSIONS ARE IN MM. (Bottom left corner outside the title box)

13. Types of Lines and their Applications

14. Lettering The verbal information, in writing, given in the drawing is known as lettering. Lettering forms an important part of the drawing and is used to write letters, dimensions, notes, and such other necessary information as may be required for the complete execution of the drawing of an object. Lettering is used to write titles, sub-titles, dimensions, scales, and other details on a drawing. Lettering types generally used for creating a drawing are Lettering A – Height of the capital letter is divided into 14 equal parts Lettering B – Height of the capital letter is divided into 10 equal parts The ratio of height to width varies but in case of most of the letters it is 6 : 5. Main titles are generally written in 6 mm to 8 mm size, sub-titles in 3 mm to 6 mm size, while notes, dimension figures etc. in 3 mm to 5 mm size.

15. Lettering

16. Specifications of Type-A Lettering

17. Specifications of Type-B Lettering

18. Single Stroke Lettering The Bureau of Indian Standards (IS: 9609-1990) recommends single stroke lettering for use in engineering drawing. These are the simplest forms of letters and are usually employed in most of the engineering drawings. The word single stroke should not be misconstrued to mean that the letter should be made in one stroke without lifting the pencil. It actually means that the thickness of the line of the letter should be such as is obtained in one stroke of the pencil. The horizontal lines of letters should be drawn from left to right and vertical or inclined lines from top to bottom

19. Single Stroke Vertical Capital Letters and Figures

20. Single Stroke Inclined Capital Letters and Figures

21. Single Stroke Vertical and Inclined Lower Case Letters

22. Gothic Letters Stems of single-stroke letters, if given more thickness, form what are known as gothic letters. The thickness of the stem may vary from 1/5 to 1/10 of the height of the letters.

23. Dimensioning The size and other details of the object essential for its construction and function, using lines, numerals, symbols, notes, etc. are required to be indicated in a drawing by proper dimensioning. The dimension unit is millimeter. The unit of the dimension is omitted while writing the dimension fig. and a footnote stating “ALL DIMENSIONS ARE IN MM” is written at the prominent place on the drawing sheet . Types of dimensioning system: ( i ) Aligned System: D imensions are placed perpendicular to the dimension line in such a way that it may be read from the bottom edge or right-hand edge of the drawing sheet.  (ii) Unidirectional System: Dimensions are so oriented such that they can be read from the bottom of the drawing.

24. Aligned and Unidirectional System

25. Continuous and Progressive Dimensioning Continuous Dimensioning Progressive Dimensioning

26. Rules to be followed for Dimensioning As far as possible, it should be placed outside the view. It should be taken from a visible line rather than hidden lines. Dimensioning of a centre line should be avoided except when the centre line passes through the centre of holes. The dimension should be placed on the view or section which is most clear to the corresponding features. Each dimension should be dimensioned once on a drawing. Each drawing should have the same dimensional unit. More than one dimension should not be used for features of the same parts.

27. Dimensioning Common Features

28. How to prepare for starting a drawing Clean the drawing board and all the drawing instruments using duster. Fix the drawing sheet on the drawing board. Fix the mini-drafter in a convenient position. Draw border lines using HB pencil. Complete the title box using HB pencil . Plan spacing of drawings b/n two problems/views beforehand. Print the problem number on the left top and then commence the drawing work.

29. How to keep your drawing clean Never sharpen pencils over drawing. Clean pencil point with a soft cloth after sharpening. Keep drawing instruments clean. Rest hands on drawing instruments as much as possible – to avoid smearing the graphite on the drawing. When darkening lines – try to work from the top of the drawing to the bottom, and from left to the right across the drawing. Use brush to remove eraser particles. Never use hands. Always use appropriate drawing pencils.

30. Symbols used in Electrical Engineering

31. What is a Projection? A three-dimensional object can be repre­sented in a single plane, such as on a sheet of paper, using projecting lines and planes. All projection theory is based on two variables:  line of sigh t (projecting lines) and  plane of projection . A  line of sight (LOS)  is an imaginary line between an observer’s eye and an object. A  plane of projection  (i.e., an image or picture plane) is an imaginary flat plane upon which the image is projected. If straight lines are drawn from various points on the contour of an object to meet a plane, the object is said to be projected on that plane. The figure formed by joining, in correct sequence, the points at which these lines meet the plane, is called the projection of the object. The lines from the object to the plane are called projectors

32. Types of Projections

33. Parallel and Perspective Projections Parallel Projections Perspective Projections

34. Orthographic Projections A projection is called an orthographic projection when the point of sight is imagined to be located at infinity so that the rays of sight are parallel to each other and intersect the plane of projection at right angle to it.

35. Planes of Projection and Four Quadrants The two planes employed for the purpose of orthographic projections are called reference planes or principal planes of projection. They intersect each other at right angles. The vertical plane of projection (in front of the observer) is usually denoted by the letters V.P . It is often called the frontal plane and denoted by the letters F.P . The other plane is the horizontal plane of projection known as the H.P. The line in which they intersect is termed the reference line and is denoted by the letters xy . The projection on the V.P. is called the front view or the elevation of the object. The projection on the H.P. is called the top view or the plan .

36. First-Angle Projections In this projection, the object is assumed to be situated in front of the V.P. and above the H.P. i.e. in the first quadrant, and then projected on these planes. This method of projection is known as the first-angle projection method. The object lies between the observer and the plane of projection. In this method, when the views are drawn in their relative positions, the top view comes below the front view.

37. Third-Angle Projections In this method of projection, the object is assumed to be situated in the third quadrant. The planes of projection are assumed to be transparent. They lie between the object and the observer. When the observer views the object from the front, the rays of sight intersect the V.P., The figure formed by joining the points of intersection in the correct sequence is the front view of the object. The top view is obtained in a similar manner by looking from above.

38. Reference Line Reference Line ( xy )

39. Symbols for First and Third Angle Projections

40. Six Views of an Object Front View Top View Left-hand side view Right-hand side view Bottom View Back View

41. Reference Planes

42. Auxiliary planes Two views of an object, viz. the front view and the top view (projected on the principal planes of projection), are sometimes not sufficient to convey all the information regarding the object. Additional views, called auxiliary views, are therefore, projected on other planes known as auxiliary planes.

43. Projection of Points A point represents a location in space or on a drawing, and has no width, height, and depth. A point is represented by the intersection of two lines.

44. Summary