DFTG-1305 Technical Drafting Prof. Francis Ha

Transcription

1 DFTG-1305 Technical Drafting Prof. Francis Ha Session 5 Dimensioning Geisecke s textbook: 14 th Ed. Chapter 10 p th Ed. Chapter 11 p. 502 Update:

2 Dimensioning Part 1 of 2

3 Dimensioning Summary What will we learn in this Chapter? How to dimension a multiview projection using proper dimensioning techniques. Key points Dimensions affect how a part is manufactured.

4 Mechanical Drawing Multiview Projection: A shape description of an object (front, top, right side, etc views). Detailed Drawing: A multiview projection, complete with all the dimensions and specifications needed to manufacture the object.

5 A typical Drawing Detailed Drawing Example The increasing need for precision manufacturing and interchangeability has shifted responsibility for size control to the design engineer or detail drafter. Practices for dimensioning architectural and structural drawings are similar in many ways to those for dimensioning manufactured parts, but some practices differ. Refer to the following standards: ANSI/ASME Y Dimensioning and Tolerancing ASME Y Digital Product definition Data Practices ASME B (R1999) Preferred Metric Limits and Fits

6 Dimensioning 2-2) Learning to Dimension

7 Learning to Dimension What is our goal when dimensioning a part? A clear and concise manner. Includes everything needed to produce and inspect the part exactly as intended by the designer.

8 Learning to Dimension Dimensioning techniques require the knowledge of the following: Dimension Appearance/Techniques Dimensioning and Locating Features Dimension Choice

9 Learning to Dimension 1. Dimension Appearance/Techniques: Dimensions use lines, arrows, symbols and texts: a) Types of lines used in dimensioning b) Method of dimension c) Dimension symbols d) Dimension spacing and readability e) Dimension placement

10 Dimensioning 2-3) Dimension Appearance and Techniques

11 Lines used in Dimensioning Three lines: Dimension line Extension lines Leader line All three lines are drawn thin so that they will not be confused with visible lines.

12 Dimension Line Dimension line: A line terminated by arrowheads, which indicates the direction and extent of a dimension.

13 Extension Line Extension line: An extension line is a thin solid line that extends from a point on the drawing to which the dimension refers.

14 Leader Line Leader Line: - A straight inclined, thin, and solid line that is usually terminated by an arrowhead. A note to tell what kind of the materials, etc

15 Avoid: Crossing leader lines. Long leaders. Leader Line Leaders that are parallel to adjacent dimension, extension or section lines. Small angles between the leader and the terminating surface.

16 Arrowheads Arrowheads are drawn between the extension lines if possible. If space is limited, they may be drawn on the outside.

17 Types of Dimensions Dimensions are given in the form of linear distances, angles, and notes. Linear distances - They are usually arranged horizontally or vertically, but may also be aligned with a particular feature of the part.

18 Types of Dimensions Dimensions are given in the form of linear distances, angles, and notes. Angles - Used to give the angle between two surfaces or features of a part.

19 Types of Dimensions Dimensions are given in the form of linear distances, angles, and notes. Notes - Used to dimension diameters, radii, chamfers, threads, and other features that can not be dimensioned by the other two methods.

20 Exercise 2-1 Dimension types

21 Exercise 2-1 Count the different types of dimensions. How many linear horizontal dimensions are there? 5

22 Exercise 2-1 Count the different types of dimensions. How many linear vertical dimensions are there? 3 3

23 Exercise 2-1 Count the different types of dimensions. How many angular dimensions are there? 1

24 Lettering Lettering should be legible, easy to read, and uniform throughout the drawing. Upper case letters should be used for all lettering unless a lower case is required. The minimum lettering height is (3 mm) for printed-out size A paper.

25 Dimensioning Symbols Dimensioning symbols replace text. The goal of using dimensioning symbols is to eliminate the need for language translation.

26 Term Dimensioning Symbols Diameter Spherical diameter Radius Spherical radius Symbol n Sn R SR Reference dimension (8) Counterbore / Spotface v n1,x1 X n2,x2 Countersink w n1,x1 X n2,x2 Number of times or places v w 4X

27 Spacing and Readability Dimensions should be easy to read, minimize the possibility for conflicting interpretations.

28 Spacing and Readability a) The spacing between dimension lines should be uniform throughout the drawing. b) Do not dimension inside an object or have the dimensioning line touch the object unless clearness is gained.

29 Spacing and Readability c) Dimension text should be horizontal which means that it is read from the bottom of the drawing. d) Dimension text should not cross dimension, extension or visible lines.

30 Exercise List the dimensioning mistakes and then dimension the object correctly. How many mistake? 6

31 1) Spacing 2) Don t dim. inside the object. 3 & 4) Text 5) No Gap 6) Missing dim. (DIA of hole)

32 Correctly Dimensioned

33 Spacing and Readability e) Dimension lines should not cross extension lines or other dimension lines. Extension lines can cross other extension lines or visible lines. f) Extension lines and centerlines should not connect between views.

34 Spacing and Readability g) Leader lines should be straight, not curved, and point to the center of the arc or circle at an angle between 30 o 60 o.

35 Exercise List the dimensioning mistakes and then dimension the object correctly. How many mistake? 4

36 1) Leader line 3) Text 2) Center line 4) Crossing of dim. and ext. line

37 Correctly Dimensioned

38 Spacing and Readability h) Dimensions should not be duplicated or the same information given in two different ways. If a reference dimension is used, the size value is placed within parentheses (e.g. (10) ).

39 Exercise Find the duplicate dimension s and cross out the ones that you feel should be omitted.

40 Are there any duplicates in this group? Which one should be omitted?

41 Which ones should be omitted? Are there any duplicates in this group?

42 Which one should be omitted? Are there any duplicates in this group?

43 Dimension Placement Dimensions should be placed in such a way as to enhance the communication of your design.

44 Dimension Placement a) Dimensions should be grouped whenever possible.

45 Dimension Placement b) Dimensions should be placed between views, unless clearness is promoted by placing some outside. 2) Between views

46 Dimension Placement c) Dimensions should be attached to the view where the shape is shown best.

47 Dimension Placement d) Do not dimension hidden lines.

48 Exercise List the dimensioning mistakes and then dimension the object correctly. How many mistakes? 5

49 t dim. hidden lines 2) Between views 3) Grouping 4) Dim where feature shown best 5) Long ext. line

50 Correctly Dimensioned

51 Dimensioning 2-4) Dimensioning and Locating Simple Features

52 Dimensioning Features a) A circle is dimensioned by its diameter and an arc by its radius using a leader line and a note.

53 Exercise Circular and rectangular views Answer questions about the cylindrical and hole features of the part shown.

54 Find the hole and cylinder. Circular view Which view is considered the circular view and which is considered the rectangular view? Rectangular view

55 Looking at just the top view, can you tell the difference between the hole and the cylinder? No

56 Why is the diameter of the hole given in the circular view and diameter of the cylinder given in the rectangular view? So that the cylinder is not confused with a hole.

57 b) Holes are dimensioned by giving their diameter and location in the circular view. Dimensioning Features

58 c) A cylinder is dimensioned by giving its diameter and length in the rectangular view, and is located in the circular view. Dimensioning Features

59 DFTG-1305 Technical Drafting Dimensioning End of Part 1 of 2

60 Dimensioning Part 2 of 2

61 Dimensioning Features d) Repetitive features or dimensions may be specified by using the symbol X along with the number of times the feature is repeated. There is no space between the number of times the feature is repeated and the X symbol, however, there is a space between the symbol X and the dimension.

62 Dimension the object shown. Exercise

63 How do we dimension the hole diameters?

64 How do we locate the holes?

65 How do we dimension the cylinder diameters?

66 How do we dimension the cylinder heights?

67 Completely dimensioned.

68 Skip advanced topic Dimensioning 2-5) Dimensioning and Locating Advanced Features

69 Dimensioning Features a) If a dimension is given to the center of a radius, a small cross (center mark) is drawn at the center.

70 Dimensioning Features a) Where the center location of the radius is unimportant, the drawing must clearly show that the arc location is controlled by other dimensioned features such as tangent surfaces.

71 Dimensioning Features b) A complete sphere is dimensioned by its diameter and an incomplete sphere by its radius.

72 Dimensioning Features d) If a hole goes completely through the feature and it is not clearly shown on the drawing, the abbreviation THRU follows the dimension.

73 Dimensioning Features e) If a part is symmetric, it is only necessary to dimension to one side of the center line of symmetry. Symmetry symbol

74 Dimensioning Features f) Counterbored holes

75 Dimensioning Features f) Counterbored holes Drill DIA C Bore DIA C Bore depth

76 Dimensioning Features f) If the thickness of the material below the counterbore is significant, this thickness rather than the counterbore depth is given.

77 Application Question 2-1 What do you think a counterbored hole is used for?

78 h) Countersink Holes Dimensioning Features Drill Depth Drill DIA Space C Sink DIA C Sink angle

79 Application Question 2-2 What do you think a countersunk hole is used for?

80 Dimensioning Features g) Spotfaced Holes: The difference between a C BORE and a Spotface is that the machining operation occurs on a curved surface. Notice that the depth can not be specified in the note.

81 Dimensioning Features i) Chamfers: Dimensioned by a linear dimension and an angle, or by two linear dimensions.

82 LOCATION DIMENSIONS

83 Application Question 2-3 What do you think a chamfer is used for?

84 Application Question 2-3 What do you think a chamfer is used for? Answer: - Safety. - Improve engagement of mating parts.

85 Drawing Notes Drawing notes give additional information that is used to complement conventional dimension. manufacturing requirements treatments and finishes blanket dimensions (e.g. size of all rounds and fillets on a casting or a blanket tolerance). The note area is identified with the heading NOTE:...

86 Dimensioning 2-6) Dimension Choice

87 Dimension Choice Dimension placement and dimension text influences the manufacturing process used to make the part. Manufacturing process should not be specifically stated on the drawing. Choose dimensions based on function first then manufacturing.

88 Units and Decimal Places a) Decimal dimensions should be used for all machining dimensions. You may encounter a drawing that specifies standard drills, broaches, and the like by size. For drill sizes that are given by number or letter, a decimal size should also be given.

89 Units and Decimal Places b) Metric dimensions are given in mm and to 0 or 1 decimal place (e.g. 10mm, 10.2mm). When the dimension is less than a millimeter, a zero should proceed the decimal point (e.g. 0.5). Foot note may be added: Unless otherwise specified, all dimensions are in millimeters.

90 Units and Decimal Places c) English dimensions are given in inches and to be at least 3 decimal places (e.g ). d) For some complicated drawing (i.e. PC Board), there are 7 places or more. e) zero should not be shown before the decimal point for values less than one inch (e.g..75 ).

91 Dimensioning Methods of Dimensioning: - Traditional - Datum - Advanced datum

92 Locating Features Using Datums How do we choose which surface will be a datum feature? Good datum features are: functionally important surfaces mating surfaces big enough to permit its use in manufacturing the part

93 Locating Features Using Datums a) Datum dimensioning is preferred over continuous dimensioning. Two types of dimensioning method: Continuous Dimensioning: Traditional Datum Dimensioning:

94 Cumulative Tolerance Continuous dimensioning has the disadvantage of accumulating error. It is preferable to use datum dimensioning to reduce error buildup.

95 Cumulative Tolerances What is error build up? e = individual dimension error x.e x.e + x.e + x.e = 3x.3e 3x.e

96 Locating Features Using Datums b) Dimensions should be given between points or surfaces that have a functional relation to each other Slots, mating hole patterns, etc...

97 Datum dimensioning for precise part (explained by instructor in class)

98 Exercise Dimension Accuracy

99 Exercise 2-9 Which dimensions have implied tolerances and which have stated tolerances?

100 Exercise 2-9 Which dimensions have implied tolerances and which have stated tolerances? Implied Implied Stated

101 Exercise 2-9 Write down the range in which the dimension values are allowed to vary. > 0.5 < 1.5

102 Exercise 2-9 Write down the range in which the dimension values are allowed to vary. > 0.5 < 1.5 > 0.95 < 1.05

103 Exercise 2-9 Write down the range in which the dimension values are allowed to vary. > 0.5 < 1.5 > 0.95 <

104 Rounding Off The more accurate the dimension the more expensive it is to manufacture. To cut costs it is necessary to round off fractional dimensions.

105 Rounding Off How do we round off? Let s round off to the second decimal place nd decimal place 3 rd decimal place

106 Rounding Off If the third decimal place number is: greater than 5, we round up and increase the second decimal place number by

107 Rounding Off If the third decimal place number is: less than 5, we truncate after the second decimal place

108 Rounding Off If the third decimal place number is: exactly 5, whether or not we round up depends on if the second decimal place number is odd or even: - If it is odd, we round up - If it is even, it is kept the same Odd Even

109 Exercise Round off Round off the following fractions to two decimal places according to the rules stated above. (5/16).3152? (5/32).1562? (1/8).375? (3/8).125?

110 Exercise Round off Round off the following fractions to two decimal places according to the rules stated above. (5/16) (5/32).1562? (1/8).375? (3/8).125?

111 Exercise Round off Round off the following fractions to two decimal places according to the rules stated above. (5/16) (5/32) (1/8).375? (3/8).125?

112 Exercise Round off Round off the following fractions to two decimal places according to the rules stated above. (5/16).3125 (5/32).1562 (1/8).375 (3/8) ?

113 Exercise Round off Round off the following fractions to two decimal places according to the rules stated above. (5/16).3125 (5/32).1562 (1/8).375 (3/8)

114 Dimensioning End of Part 2 of 2 (End of official lecture)

115 Dimensioning Student s Home Exercises

116 Exercise 4-1 List the dimensioning mistakes and then dimension the object correctly (inches)

117 What are the 5 dimensioning mistakes? Student s home practice 1

118 1 & 2) 2 decimal places / No leading zero 3) Use datum dimensioning 4) Symbol / Decimal 5) Don t dim. hidden features

119 Correctly Dimensioned

120 Exercise 4-2 Dimension the following object using proper dimensioning techniques.

121 Notice the datum features that were used. Did we need the right side view?

122 Exercise 4-3 Dimension the following object using proper dimensioning techniques.

123

124 Exercise 4-4 Dimension the following object using proper dimensioning techniques.

125

126 Exercise 4-5 Dimension the following object using proper dimensioning techniques.

127

128 Dimensioning The End