Understanding of Engineering drawing basics
- 2. 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. Effectiveness of Graphics Language The word languages are inadequate for describing the size size, shape shape and features features completely as well as concisely. You can easily understand that … 2
- 3. Graphic language in “engineering application” use l lines ines to represent the surfaces surfaces, edges edges and contours contours of objects. A drawing can be done using freehand freehand, instruments instruments or computer computer methods. Composition of Graphic Language The language is known as “drawing drawing” or “drafting drafting” . 3
- 4. Introduction An engineering drawing is a type of technical drawing, used to fully and clearly define requirements for engineered items, and is usually created in accordance with standardized conventions for layout, nomenclature, interpretation, appearance size, etc. Its purpose is to accurately and unambiguously capture all the geometric features of a product or a component. The end goal of an engineering drawing is to convey all the required information that will allow a manufacturer to produce that component. 4
- 5. Purpose of an Engineering Drawing 1. An engineering drawing is not an illustration. 2. It is a specification of the size and shape of a part or assembly. 3. The important information on a drawing is the dimension and tolerance of all of its features. 5
- 6. Importance of technical graphics Technical drawings: A language used in the design process for communicating, solving problems, quickly and accurately visualizing objects, and conducting analysis A graphical representation of objects and structures and is done using freehand, mechanical, or computer methods Users of engineering and technical graphics in industry
- 7. From traditional “linear” design process to new“concurrent” design process Traditional: A linear, segmented activity involving problem identification, preliminary ideas, design refinements, analysis, optimization, and documentation Concurrent: A team activity involving coordination of the technical and non-technical functions of design and manufacturing within a business The CAD database becomes a communication medium.
- 8. Samples of drawing conventions and standards
- 9. Elements of Engineering Drawing Engineering drawing are made up of graphics language graphics language and word language word language. Graphics language Describe a shape (mainly). Word language Describe size, location and specification of the object. 9
- 10. Basic Knowledge for Drafting Graphics language Word language Line types Geometric construction Lettering Projection method 10
- 12. PROJECTION METHOD Perspective Oblique Orthographic Axonometric Multiview Parallel 12
- 13. Parallel to projection plane Normal to projection plane Orthogonal Inclined to projection plane Normal to projection plane Axonometric Parallel to projection plane Inclined to projection plane Oblique Orthographic projection ( Parallel projectors) Categories of orthographic projection Principal plane of object Projectors
- 14. Projection Methods Projection Methods The four principal types of projections: a Multiview b Axonometric c Oblique d Perspective
- 15. Axonometric projection Axonometric projection • axon = axis; metric = measure, in Greek • Axonometric projection is a parallel projection technique to create a pictorial drawing of an object by rotating the object on an axis relative to a projection or picture plane
- 16. Axonometric projection Axonometric projection • Axonometric projection – Trimetric – Dimetric – Isometric
- 18. Isometric projection Isometric projection • Isometric projection is a true representation of the isometric view of an object • Isometric view is created by rotating the object 45 degree about vertical axis, and tilting it forward 35 deg 16’
- 19. Isometric projection: axes Isometric projection: axes • The 3 axis meet at A,B form equal angles of 120 deg and they are called Isometric Axes • OA is vertical, OB is inclined at 30deg to the right, OC is inclined at 30deg to the left • Any lines parallel to these – Isometric Line • Any planes parallel – Isometric Planes
- 20. Selection of Isometric Axes Selection of Isometric Axes • Main purpose of isometric view is to provide a pictorial view which reveals as much detail as possible • Selection of principal edges is important • Figure shows different isometric views of the same block
- 21. PROJECTION THEORY The projection theory is based on two variables: 1) Line of sight 2) Plane of projection (image plane or picture plane) The projection theory is used to graphically represent 3-D objects on 2-D media (paper, computer screen). 21
- 22. Line of sight Line of sight is an imaginary ray of light between an observer’s eye and an object. Line of sight Parallel projection Parallel projection Line of sight Perspective projection Perspective projection There are 2 types of LOS : parallel converge and 22
- 23. Plane of projection Plane of projection is an imaginary flat plane which the image is created. The image is produced by connecting the points where the LOS pierce the projection plane. Parallel projection Parallel projection Perspective projection Perspective projection Plane of projection Plane of projection 23
- 24. Disadvantage of Perspective Projection Perspective projection is not not used by engineer for manu- facturing of parts, because 1) It is difficult to create. 2) It does not reveal exact shape and size. Width is distorted 24
- 26. Orthographic projection • Orthographic" comes from the Greek word for "straight writing (or drawing)." This projection shows the object as it looks from the front, right, left, top, bottom, or back, and are typically positioned relative to each other according to the rules of either “First Angle” or “Third Angle” projection. 26
- 27. Pictorial 3-dimensional representations One-point one vanishing point lines that are not vertical or horizontal converge to single point in distance Two-point or Three-point two or three vanishing points With two points, vertical or horizontal lines parallel, but not both With three-point, no lines are parallel Isometric Drawing shows corner of object, but parallel lines on object are parallel in drawing Shows three dimensions, but no vanishing point(s) 27
- 29. Symbols for Third Angle (right)or First Angle (left). First angle projection is the ISO standard and is primarily used in Europe. The 3D object is projected into 2D "paper" space as if you were looking at an X-ray of the object: the top view is under the front view, the right view is at the left of the front view. Third angle projection is primarily used in the United States and Canada, where it is the default projection system according to BS 8888:2006, the left view is placed on the left the top view on the top. 29
- 30. 5 Orthographic projection Orthographic projection is a parallel projection technique in which the parallel lines of sight are perpendicular to the projection plane MEANING Object views from top Projection plane 1 2 3 4 5 1 2 3 4 30
- 31. Image of a part represented in First Angle Projection 31
- 32. Orthographic / Multiview • Draw object from two / three perpendicular views / Orthographic What it looks like pictorially 32
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- 35. ORTHOGRAPHIC VIEW Orthographic view Orthographic view depends on relative position of the object to the line of sight. Two dimensions of an object is shown. Three dimensions of an object is shown. Rotate Tilt More than one view is needed to represent the object. Multiview drawing Multiview drawing Axonometric drawing Axonometric drawing 35
- 36. Multiview Drawing It represents accurate shape and size. Advantage Advantage Disadvantage Disadvantage Require practice in writing and reading. Multiviews drawing (2-view drawing) Example 36
- 37. Axonometric (Isometric) Drawing Easy to understand Right angle becomes obtuse angle. Circular hole becomes ellipse. Distortions of shape and size in isometric drawing Advantage Advantage Disadvantage Disadvantage Shape and angle distortion Example 37
- 39. Auxiliary Views • Used to show true dimensions of an inclined plane. 39
- 42. Drawing Standard
- 43. Introduction Standards Standards are set of rules that govern how technical drawings are represented. Drawing standards are used so that drawings convey the same meaning to everyone who reads them. 43
- 44. ISO International Standards Organization Standard Code ANSI American National Standard Institute USA JIS Japanese Industrial Standard Japan BS British Standard UK AS Australian Standard Australia Deutsches Institut für Normung DIN Germany Country Code Full name 44
- 45. Partial List of Drawing Standards JIS Z 8311 Sizes and Format of Drawings Sizes and Format of Drawings JIS Z 8312 Line Conventions Line Conventions JIS Z 8313 Lettering Lettering JIS Z 8314 Scales Scales JIS Z 8315 Projection methods JIS Z 8316 Presentation of Views and Sections JIS Z 8317 Dimensioning Code number Contents 45
- 46. Standards Organizations involved in developing the standards for technical drawings: ANSI (American National Standards Institute) ASEE (American Society for Engineering Education) SAE (Society of Automotive Engineers) ASME (American Society of Mechanical Engineers) ISO (International Standards Organization) American National Standard Drafting Manual
- 47. Some Important ANSI standards • ANSI Y14.1 (1980) Drawing Sheet Size and Format. • ANSI Y14.2M (1979) Line Conventions and Lettering. • ANSI Y14.3 (1975) Multiview and Sectional View Drawings • ANSI Y14.5M (1982-1994) Dimensioning and Tolerancing. • ANSI Y14.6 (1978) Screw Thread Representation • ANSI Y14.6aM (1981) Screw Thread Representation (Metric Supplement) • ANSI Y14.7.1 & Y14.7.2 (1978) Gear Drawing Standards Internet Explorer.lnk
- 48. ANSI Standard Sheet Sizes & typical title block layouts
- 49. Drawing Sheet Trimmed paper of a size A0 ~ A4. Standard sheet size (JIS) A4 210 x 297 A3 297 x 420 A2 420 x 594 A1 594 x 841 A0 841 x 1189 A4 A3 A2 A1 A0 (Dimensions in millimeters) 49
- 50. Drawing space Drawing space Title block d d c c c Border lines 1. Type X (A0~A4) 2. Type Y (A4 only) Orientation of drawing sheet Title block Sheet size c (min) d (min) A4 10 25 A3 10 25 A2 10 25 A1 20 25 A0 20 25 50
- 51. Drawing Scales Scale Scale is the ratio of the linear dimension of an element of an object shown in the drawing to the real linear dimension of the same element of the object. Size in drawing Actual size Length, size : 51
- 52. Drawing Scales Designation of a scale consists of the word “SCALE” followed by the indication of its ratio, as follow SCALE 1:1 for full size SCALE X:1 for enlargement enlargement scales (X > 1) SCALE 1:X for reduction reduction scales (X > 1) Dimension numbers shown in the drawing are correspond to “true size” of the object and they are independent of the scale used in creating that drawing. 52
- 53. Basic Line Types Types of Lines Appearance Name according to application Continuous thick line Visible line Continuous thin line Dimension line Extension line Leader line Dash thick line Hidden line Chain thin line Center line NOTE : We will learn other types of line in later chapters. 53
- 54. Visible lines Visible lines represent features that can be seen in the current view Meaning of Lines Hidden lines Hidden lines represent features that can not be seen in the current view Center line Center line represents symmetry, path of motion, centers of circles, axis of axisymmetrical parts Dimension and Extension lines Dimension and Extension lines indicate the sizes and location of features on a drawing 54
- 55. Types of Line 55
- 56. 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 56
- 57. 1 2 3 4 5 6 7 8 9 10 14 13 12 11 Viewing-plane line Extension line Dimension Line Center Line Hidden Line Break Line Cutting-plane Line Visible Line Center Line (of motion) Leader VIEW B-B SECTION A-A Section Line Phantom Line 57
- 59. Text on Drawings Text on engineering drawing is used : To communicate nongraphic information. As a substitute for graphic information, in those instance where text can communicate the needed information more clearly and quickly. Uniformity Uniformity - size - line thickness Legibility Legibility - shape - space between letters and words Thus, it must be written with 59
- 60. Example Placement of the text on drawing Dimension & Notes Notes Title Block 60
- 61. Lettering Standard ANSI Standard This course Use a Gothic text style, either inclined or vertical. Use all capital letters. Use 3 mm for most text height. Space between lines of text is at least 1/3 of text height. Use only a vertical Gothic text style. Use both capital and lower-case letters. Same. For letters in title block it is recommend to use 5~8 mm text height N/A. Follows ANSI rule. 61
- 62. Dimensioning
- 63. Dimensioning Guidelines The term “feature” refers to surfaces, faces, holes, slots, corners, bends, arcs and fillets that add up to form an engineering part. Dimensions define the size of a feature or its location relative to other features or a frame of reference, called a datum. The basic rules of dimensioning are: 1. Dimension where the feature contour is shown; 2. Place dimensions between the views; 3. Dimension off the views; 4. Dimension mating features for assembly; 5. Do not dimension to hidden lines; 6. Stagger dimensioning values; 7. Create a logical arrangement of dimensions; 8. Consider fabrication processes and capabilities; 9. Consider inspection processes and capabilities. 63
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- 65. Important elements of dimensioning Two types of dimensioning: (1) Size and location dimensions and (2) Detail dimensioning 65
- 66. Geometrics • The science of specifying and tolerancing shapes and locations of features of on objects 66
- 67. Geometrics • It is important that all persons reading a drawing interpret it exactly the same way. • Parts are dimensioned based on two criteria: – Basic size and locations of the features – Details of construction for manufacturing • Standards from ANSI (American National Standards Institute) 67
- 68. Scaling vs. Dimensioning • Drawings can be a different scales, but dimensions are ALWAYS at full scale. 68
- 69. Units of Measure • Length – English - Inches, unless otherwise stated • Up to 72 inches – feet and inches over – SI – millimeter, mm • Angle – degrees, minutes, seconds Angle Dimensions 69
- 70. Elements of a dimensioned drawing (Be familiar with these terms 70
- 71. Arrangement of Dimensions • Keep dimension off of the part where possible. • Arrange extension lines so the larger dimensions are outside of the smaller dimensions. • Stagger the dimension value labels to ensure they are clearly defined. 71
- 72. Dimensioning Holes • Dimension the diameter of a hole. • Locate the center-line. • Use a notes and designators for repeated hole sizes 72
- 73. Dimensioning the Radius of an Arc Dimension an arcs by its radius. Locate the center of the radius or two tangents to the arc. 73
- 74. Drilled Holes, Counter bores and Countersinks • Use the depth symbol to define the depth of a drilled hole. • Use the depth symbol or a section view to dimension a counter bore. • Countersinks do not need a section view. 74
- 75. Angles, Chamfers and Tapers • Dimension the one vertex for an angled face, the other vertex is determined by an intersection. • Chamfers are generally 45 with the width of the face specified. 75
- 76. Rounded Bars and Slots • The rounded end of a bar or slot has a radius that is 1/2 its width. • Use R to denote this radius, do not dimension it twice. • Locate the center of the arc, or the center of the slot. 76
- 77. Limits of Size • All dimensions have minimum and maximum values specified by the tolerance block. • Tolerances accumulate in a chain of dimensions. • Accumulation can be avoided by using a single baseline. 77
- 78. Fit Between Parts Clearance Fit Interference Fit Transition Fit 1. Clearance fit: The shaft maximum diameter is smaller than the hole minimum diameter. 2. Interference fit: The shaft minimum diameter is larger than the hole maximum diameter. 3. Transition fit: The shaft maximum diameter and hole minimum have an interference fit, while the shaft minimum diameter and hole maximum diameter have a clearance fit 78
- 80. Dimension text placement P. 80
- 81. Unidirectional or aligned dimensioning? 81
- 83. Dimensioning Basic Shapes -Assumptions • Perpendicularity – Assume lines that appear perpendicular to be 90° unless otherwise noted • Symmetry – If a part appears symmetrical – it is (unless it is dimensioned otherwise) – Holes in the center of a cylindrical object are automatically located 83
- 84. Dimensioning Basic Shapes • Rectangular Prism 84
- 85. Dimensioning Basic Shapes • Cylinders – Positive – Negative 85
- 86. Dimensioning Basic Shapes • Cone Frustum 86
- 87. Dimensioning Basic Shapes • Circle Pattern Center Lines 87
- 88. Grouping Dimensions • Dimensions should always be placed outside the part Yes No 88
- 89. Dimension guidelines Dimensions should be placed in the view that most clearly describes the feature being dimensioned (contour (shape) dimensioning) 89
- 90. Dimension guidelines Maintain a minimum spacing between the object and the dimension between multiple dimensions. A visible gap shall be placed between the ends of extension lines and the feature to which they refer. 90
- 91. Dimension guidelines Avoid dimensioning hidden lines. Leader lines for diameters and radii should be radial lines. 91
- 92. Where and how should we place dimensions when we have many dimensions? 92
- 93. Where and how should we place dimensions when we have many dimensions? (cont.) 93
- 94. Staggering Dimensions • Put the lesser dimensions closer to the part. • Try to reference dimensions from one surface – This will depend on the part and how the tolerances are based. 94
- 96. Repetitive Features Use the Symbol ‘x’ to Dimension Repetitive Features 96
- 97. Symbols for Drilling Operations 97
Editor's Notes
- #6: -The drafting and design phases comprise more than 52 percent of the engineering process.
- #46: ANSI is the governing body that sets the standards used for engineering and technical drawings ANSI standards are periodically revised to reflect the changing needs of the industry and technology The Y series of ANSI standards are the ones most important for technical drawing. ISO is made up of a group of standards institutes from 145 different countries
- #67: Instructor: It is not only critical that everybody using a drawing interpret it the same way, it is important to do the dimensioning in the simplest way. There are lots of ways to dimension an object following the standards and yet have a drawing that is difficult to read. In Engineering, the ANSI standards are available for lots of different areas and they are not just about engineering graphics.
- #68: Instructor: Here is an important concept. Scale deals with how you draw something – the dimensioning is always done at full scale. Remind your students that while the computer is comfortable with any scale, you want the final drawing printed at some recognizable scale. These recognizable scales would be the ones that were discussed earlier in the term. For example, if you are printing a set of house plans you probably want them in ¼” = 1 foot or 1/8” = 1 foot.
- #69: Instructor: While most construction of buildings and roads is done in feet and tenths of a foot, architects are working in feet and inches. A mechanical or industrial engineer may be building products that have both inches and mm.
- #83: Instructor: There are some features of dimensioning that are assumed. Right angle that appear as right angles are 90 degrees apart. The same thing is true for symmetry in an object.
- #84: Instructor: In this figure the dimensions for height, width and depth are shown. When possible all dimensions should be placed between views as long as they are not crowded. All three dimensions are needed for complete description of a 3D object.
- #85: Instructor: Cylinders are dimensioned where they are viewed as rectangles. Holes are dimensioned where you see the circle representing the hole. Note that the symbol, phi, is used for diameters and precedes the number. Note also that the phi is used whether you are looking at the circle representing the hole or whether you are dimensioning the rectangular view of the cylinder.
- #86: Instructor: Cones can be dimensioned in a variety of ways. Any of these are OK. Note that the diameter of the
- #87: Instructor: When you have a series of holes on a circular centerline, the centerline is referred to as the bolt circle. You may want to ask the class what other dimensions are needed to completely dimension this object. Answer: the diameter and number of holes and the overall diameter of the object.
- #88: Instructor: The figure on the left is dimensioned correctly but the horizontal dimensions on the steps could have been done with any two of the three steps. Here the left and center steps were dimensioned. Another important point to make here is the spacing between sets of dimensions. You do not want the dimensions to be crowded.
- #94: Instructor: Note that the diameter dimensions on the left side of the figure have the numbers staggered so that it takes up less room on the page.
- #95: Instructor: There are situations where features are so close together that arrowheads cannot be shown without have the arrow on the extension line. In cases like these it makes sense to leave a gap in the extension line.
- #96: Instructor: We looked at the location of holes on a circle in a prior slide. Here we use the number of holes X size of the hole to complete the dimensioning.
- #97: Instructor: In the past, the symbols shown here were labeled by the operation that produced the feature. For example, the counterbore and countersink were operations. Now the ANSI standard say to show the shape by a graphic symbol and then it is up to the manufacturing staff to determine how that shape will be made. Make sure that the students memorize the symbols and how they are used correctly. This will be on the quiz and on the mid-term. These symbols are also part of the library of symbols in CAD packages.