1. Computarized Engineering Graphics ENGR 2220
Department of Mechanical Engineering
Inter American University of Puerto Rico
Bayamon Campus
Dr. Omar E. Meza Castillo

2. Upon successful completion of the course, the student will be able to:
Course Objectives
Upon successful completion of the course, the student will be able to:
Identify types of software and hardware used for computer-aided design.
Clearly represent and control mental images.
Graphically represent technical designs, using accepted standard practices.
Use plane and solid geometric forms to create and communicate design solutions.
Describe the engineering design process.
Understand concepts and applications of 3-D modeling.
Understand the theory, techniques and standards of multiviews.
Apply the concept of cutting planes to create section views and sectioned 3-D .CAD models.
Apply the standard dimensioning practicing for mechanical drawings.
Apply tolerances to dimensions

3. Tentative Lecture Schedule
Topic
Lecture
Introduction: Graphics Communication /The Engineering Design Process and Design Visualization 1
Preliminary Learning: Standard/Instruments for Engineering Graphics 2
Sketching-2D: construction/Orthographic Projection/Dimensioning 3
Software -2D: Basic commands/Drawing of Basic Geometric/Drawing Multiviews and dimension placed 4
Sketching-3D: Projections Theory “Axonometric /Oblique Projections”, Section Views and Assembly Drawing 5
Software- 3D: Isometric drawing, Solid Modeling and Surfaces, Working Drawings and Assemblies 6

4. Reference
Bethune, James. Engineering Graphics with AutoCAD 2009, Prentice Hall, 2009.
Earle James. Engineering Design Graphics, 11th Ed., Pearson Prentice Hall

5. Graphics Communication Part 1
"Lo peor es educar por métodos basados en el temor, la fuerza, la autoridad, porque se destruye la sinceridad y la confianza, y sólo se consigue una falsa sumisión”
Einstein Albert
Chapter 3: Sketching, Text, and Visualization
Graphics Communication Part 1

6. Here’s what we talked about last time:
Lines may be defined as…….
A series of points in space organized in a rational order
The shortest distance between two points
The geometry created by the intersection of two planes or surfaces
4. A set of points organized that have length and direction, but no thickness

7. The “Alphabet of Lines”…
Lines have both style and precedence.
Object (visible) lines are the MOST important…then hidden lines… then center lines… etc.

8. Examples of line use and layout:
Note:
The center line has many variations.
It’s job is to show the theoretically perfect center of arcs, holes, circles, and cylinders.

9. Applications of lines

10. Sketching
Sketching is an important method of quickly communicating design ideas.
Sketching is a way of thinking as it is a method of recording ideas and communicating to others.
Most new designs are first recorded using design sketches.

11. Methods for creating drawings: Using T-squares, triangles, etc.
Sketches
Using T-squares, triangles, etc.
CAD produced drawings

12. Sketching the idea (ideation sketch)
Subsequent document sketch

13. Multi-view sketch:
Good for someone who understands technical drawings

14. Pictorial view:
Good for communicating the design. Suitable for nontechnical people.
NOTE: There are also “technical sketches” used in industry which may include notes, and several versions that show motion.

15. Sketching Grids:
Orthographic grid
Isometric grid
C. Perspective grid

16. Sketching lines

17. Sketching lines
The line is built up from a sequence of 2, 3 or more passes with a pencil.

18. Sketching Hold your pencil correctly, and have a relaxed grip.
Use a strip of paper to draw lines parallel to the edges of the paper.

19. Sketching How to draw a circle:
Each side of the square is equal to the diameter of the circle.
Draw the diagonals and mark the midpoints. On the diagonals mark 2/3 of the distance between the center and each corner.
An alternative method
Connect all the points.

20. Sketching How to draw a circle:
Examples of poorly drawn circles (with flat arcs and sharp corners)

21. Sketching techniques:
1- Proportion is important.
It is the ratio between any two dimensions of an object.

22. Sketches use “proportion”, not scale!
Proportion allows the designer to use approximate values to create a balanced looking object.
Sketches are accurate freehand drawings which use single lines to represent edges and features.
Multi-line sketching is NOT used in engineering design. (Scribbling!)

23. 4- Finish the sketch with darker lines.
1- Consider the correct proportion.
2- Draw the bounding box.
3- Draw the construction lines.
These are every light thin lines representing the details of the object.
4- Finish the sketch with darker lines.

24. You can use construction line to find the center of squares or rectangles

25. Sketching identically proportioned squares

26. Grid paper is used to scale an object.

27. Sketching at a distance:
Stand at a distance,
Hold a pencil at arm’s length in front of you,
Align the tip of the pencil with one edge of a feature,
Mark the length of the feature with your thumb,
Translate the same length to your sketch.
Repeat this for other lengths. Don’t change your position.

28. Classification of Sketches:
Each classification of sketch has a particular purpose from production use… to technical illustration.

29. QUESTION!
How do you know when a sketch or CAD drawing is complete?
ANSWER: When the production people can make the part without having to ask you any questions!
Most drawings not only have views of the object, but also it include written notes and dimensions to aid in its production.

30. Types of Lettering:
Simple Gothic is used for engineering design. Notice that it is “san serif” (no hats or shoes!)

31. Types of Lettering:
Inclined Gothic is often used for architectural drawings, and various types of technical illustrations.
(All the lettering used in these presentations is inclined gothic.)

32. Projection
Drawings use various types of projection (how we view the object), to enhance our ability to visualize what we are being asked to see or understand.
Let’s look at the various styles of projection used…

33. Most common types of projections:
Multiview (Showing 2 dimensions)
Pictorial (Showing 3 dimensions) OR
Most common types of projections:
Parallel
Perspective projections

34. Pictorial Projection:
Here’s how the same object may look using different projection styles.

35. Projection types:
Projection type is defined by the “line of sight” from the observer.
Let’s look at some of these….. 35

36. Perspective:
The line of sight is cone-shaped - which makes objects far away appear smaller to our view. Objects are not “true shape and size”. 36

37. Parallel:
The line of sight is always parallel regardless of how far away the object is from our view. This allows surfaces to be drawn “true shape and size. 37

38. Orthographic:
Ortho means “at 90 degrees”, and is a form of parallel projection.
Orthographic projections are used to show several views of the same object in one drawing set. 38

39. Orthographic:
The “principle views“ should be chosen to show the most detail of the object with the least number of hidden lines.
Here, the TOP, FRONT, and RIGHT SIDE were chosen. 39

40. Isometric:
A type of parallel projection that represents all 3 dimensions in one image. 40

41. Isometric sketch 41

42. Isometric representations of circles42

43. 43

44. 44

45. 45

46. Isometric sketches of common objects.46

47. Use a piece of scrap paper and mark one half of the major axis (AC) and one half of the minor axis (AB).
½ Major Axis
½ Minor Axis
Place A on the center and mark two points representing C and two points representing B (draw major and minor axes). Place C on the minor axis and hold B on the minor axis at any time, then place a mark at point A. Repeat this and connect all the points. 47

48. Understanding what Center Lines do…
Center lines show the theoretical perfect center of arcs, holes, and cylinders. They can be used to show symmetry, or used to aid in dimensioning an object.
Center lines NEVER start or stop on another line! 48

49. Steps in creating a 3-view sketch…
Layout the 3 principle views you have chosen with even margins between views and the outside border of your drawing area.
Step 2:
Rough out the general shape of each view. 49

50. Steps in creating a 3-view sketch…
Transfer any data from one view to its neighbor using “reverse construction”. This can be done by using a “miter line”.
Step 4:
Add hidden and center lines to the necessary views. 50

51. Steps in creating a 3-view sketch…
Erase all unnecessary lines and “snap” the lines on your views.
“Snapping” adds weight to the lines in each view and makes the drawing easier to read.
Step 6:
Add notes and/or dimensions to complete your drawing. 51

52. Here’s some tips on creating a multi-view drawing:
1. Lightly sketch all the information that you know first.
2. Use reverse construction to locate lines that may be
unknown such as compound angles.
3. Add all circles and other arcs to your drawing.
4. Snap all arcs and circles first, and then straight lines. 52

53. Week 3: Multiview Drawings 1
We have already seen how views are aligned with the surface of an object.
Using the “glass box” method of visualization helps us understand the relationship views have with one another, i. e. the front view is next to the top and right side views, etc. 53

54. Here we can see all the principle views of an object as the glass box is unfolded.
It is easy to see that some of the principle views have more detail through the use of object (visible) lines than others.
Always choose views that have the least amount of hidden lines in them and show the most detail. 54

55. Using miter and projection lines, we can easily transfer “space dimensions” between views.55

56. Projection methods: 3RD Angle (US Standard)
ISO (1ST Angle Metric Standard)
NOTE:
Reverse construction methods work just as well in 1ST Angle projection. 56

57. Here, we can see that surface C is shown as both as object and hidden lines depending on the view we are looking at.
Remember: One definition of a “line” is that it is the geometry on the edge of a surface. (Surface C appears in its edge view in the front and top views.) 57

58. When choosing which of the principle views to draw, remember these rules:
1. Choose as many views as it takes to show ALL the details of the object. The front view usually shows the most detail, or best view of the general shape of the object in its natural position.
2. Choose views that shows a majority of object (visible) lines, and a minimum of hidden lines.
3. Choose views that show features as surfaces first, and as lines second. 58

59. Always try to draw views in their most natural position.
This is obviously more difficult to visualize! 59

60. Why is the left side view not required?
ANSWER: It doesn’t add any new information! 60

61. ANSWER: It has too many hidden lines!
Why is the left side view not required?
ANSWER: It has too many hidden lines! 61

62. Surfaces will appear as edges at times
Surfaces will appear as edges at times. Edges may be foreshortened (shorter than normal), or “True Length” (TL). 62

63. Oblique edge lines are created by oblique surfaces.
These are surfaces that are neither true shape or true size in any principle view. 63

64. Even simple, primitive shapes often need several views to fully describe their topology.64

65. “Limiting Elements” are lines that show the outer boundaries of cylindrical or conical objects. How many views of such objects are usually needed to show its shape? 65

66. Remember: In multiview drawings, tangency is shown between to surfaces by the absence of any line.
Here, the arched and planar surfaces are tangent.
Arched and planar surfaces which are NOT tangent. 66

67. Holes and cylinders may appear “True Shape and Size” (TSS), or foreshortened depending on the view in which they appear. (Foreshortened circles will appear as ellipses.) 67

68. Draw the sketch of the following objects
Sketching Practice
Draw the sketch of the following objects

73. 73

74. 74

75. 75

76. Due, Wednesday, February 08, 2012
Homework2  WebPage
Due, Wednesday, February 08, 2012
Omar E. Meza Castillo Ph.D.