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MIET2012 1 Lecture 8: Dimensioning and tolerencing MIET2093 Computer Aided Design by: Dr. Toh Yen Pang tohyen.pang@rmit.edu.au 9925 6128 B251.3.22 School of Aerospace, Mechanical & Manufacturing Engineering 2 RMIT University©2015 Teaching Week Lecture Topics Tutorial Topics Assessments/ Tasks Week 7 Section View 3D modelling (emphasise on Section views) Week 8 Dimension & Tolerance Generative Drafting Fundamentals Week 9 Assembly & Drafting Assembly Design workbench Week 10 Reverse Engineering 3D scanning (AMP building 55, level 4) Quiz 4 Week 11 Rapid Prototyping 3D printing (AMP building 55, level 4) Teaching Schedule School of Aerospace, Mechanical & Manufacturing Engineering 3 RMIT University©2015 AMP (Week 10 – Week 11) School of Aerospace, Mechanical & Manufacturing Engineering 4 RMIT University©2015 School of Aerospace, Mechanical & Manufacturing Engineering 5 RMIT University©2015 Group Project Report due in Week 12 (Template given)−leader to submit e-report. pdf and CATIA file online Problem identification Analysis Documentation Refinement Ideation Decision process/ Design selection Implementation Generate design idea/ possible solution Evaluate the ideas against the criteria School of Aerospace, Mechanical & Manufacturing Engineering 6 RMIT University©2015 Group Project (2/2) Identify the Design problem Generate design idea/ possible solution Evaluate the ideas against the criteria Document (Written Report) School of Aerospace, Mechanical & Manufacturing Engineering 7 RMIT University©2015 Overview • Dimensioning and Tolerancing • Dimensioning • Symbols, Abbreviations and General notes • Manufacturing features • Placement of dimension • Tolerancing • Apply tolerances to dimensions School of Aerospace, Mechanical & Manufacturing Engineering 8 RMIT University©2015 Dimensioning School of Aerospace, Mechanical & Manufacturing Engineering 9 RMIT University©2015 Dimensioning • Before an object can be built, complete information about both the size and shape of the object must be available. • The exact shape of an object is communicated through orthographic drawings, which are developed following standard drawing practices. • The process of adding size information to a drawing is known as dimensioning the drawing. • A dimension is a numerical value used to define the size, location, geometric characteristics of a part or feature. School of Aerospace, Mechanical & Manufacturing Engineering 10 RMIT University©2015 RMIT Drawing Template School of Aerospace, Mechanical & Manufacturing Engineering 11 RMIT University©2015 3-minute discussion Sketch the assigned problems. Each grid square equal to 2mm. Completely dimension the drawings. School of Aerospace, Mechanical & Manufacturing Engineering 12 RMIT University©2015 8 12 4 8 4 12 8 φ4 School of Aerospace, Mechanical & Manufacturing Engineering 13 RMIT University©2015 Definition Dimensioning is the process of specifying part’ s information by using of lines, number, symbols and notes. Notes 1. Lines to be used are always thin continuous line. 2. Symbol or abbreviation commonly found in a drawing are - “diameter” is represented by a symbol “φ ”. - “radius” is represented by a letter “R ”. School of Aerospace, Mechanical & Manufacturing Engineering 14 RMIT University©2015 Unit of measure • Length – Drawings are typically dimensioned using either millimeters or decimal inches – A general note similar to ‘Unless otherwise stated, all dimensions are in millimeters (or inches)’ appears. • Angle – Degrees, minutes, seconds School of Aerospace, Mechanical & Manufacturing Engineering 15 RMIT University©2015 Applying the dimensioning components Extension line, dimension line and dimension number Mostly done by using Leader line and note The appropriate method depends on the object’s features. 27 φ10 Notes Detail of a local note depends on the object’s features. Example Example School of Aerospace, Mechanical & Manufacturing Engineering 16 RMIT University©2015 Arrangement of Dimensions • Keep dimension off of the part where possible • Arrange extension lines so that the large dimension are outside of the smaller dimensions. • Stagger the dimension value labels to ensure they are clearly defined. 60 45 30 20 30 40 School of Aerospace, Mechanical & Manufacturing Engineering 17 RMIT University©2015 Basic concepts of dimensioning School of Aerospace, Mechanical & Manufacturing Engineering 18 RMIT University©2015 Dimensioning components Extension lines Dimension lines (with arrowheads) Leader lines Dimension numbers (or dimension figures) Notes 20 13 φ10 - indicate the location on the object’s features that are dimensioned. - indicate the direction and extent of a dimension, and inscribe dimension numbers. - indicate details of the feature with a local note. - local or general note R16 Example School of Aerospace, Mechanical & Manufacturing Engineering 19 RMIT University©2015 Extension line Always leave a visible gap (≈ 1 mm) from a view or center lines before start drawing a line. Extend the lines beyond the (last) dimension line 2-3 mm. Good practice Poor practice 1 2 3 2 4 School of Aerospace, Mechanical & Manufacturing Engineering 20 RMIT University©2015 Good practice Poor practice Dimension lines should be appropriately spaced apart from each other and the view. 25 34 At least 2 times of a font size 30 At least 1 time of a font size 25 34 30 25 34 30 Too close Too far Dimension line School of Aerospace, Mechanical & Manufacturing Engineering 21 RMIT University©2015 Dimension number School of Aerospace, Mechanical & Manufacturing Engineering 22 RMIT University©2015 The height of numbers is suggested to be 2.5~3 mm. Place the numbers at about 1 mm above and at a middle of a dimension line. General Good practice Poor practice 25 34 25 34 30 30 School of Aerospace, Mechanical & Manufacturing Engineering 23 RMIT University©2015 Angular dimension is expressed in degree with a symbol “o” places behind the number (and if necessary minutes and seconds may be used together). Length dimension is expressed in millimeters without a necessity to specify a unit symbol “mm”. 25 Good practice Poor practice 25 m m Unit School of Aerospace, Mechanical & Manufacturing Engineering 24 RMIT University©2015 16.25 or If there is not enough space for number or arrows, put it outside either of the extension lines. 1 Not enough space for number Not enough space for arrows 1 1 16.25 16.25 Good practice Poor practice Narrow Space Situation School of Aerospace, Mechanical & Manufacturing Engineering 25 RMIT University©2015 1. Aligned method 2. Unidirectional method The dimension figures are placed so that they are readable from the bottom or right side of the drawing. The dimension figures are placed so that they can be read from the bottom of the drawing. Do not apply both systems on the same drawing or on the same series of drawing (JIS Z8317). 1st choice 2nd choice Orientation School of Aerospace, Mechanical & Manufacturing Engineering 26 RMIT University©2015 30 3030 30 EXAMPLE : Orientation of a length dimension 30 30 30 30 30 30 30 30 1. Aligned method 2. Unidirectional method School of Aerospace, Mechanical & Manufacturing Engineering 27 RMIT University©2015 45o 45 o 45o 45 o 45o 45o 45o 45o 45o 45o 45o 45o EXAMPLE : Orientation of an angular dimension 1. Aligned method 2. Unidirectional method School of Aerospace, Mechanical & Manufacturing Engineering 28 RMIT University©2015 Poor practice Place near to the feature which they apply but should be placed outside the view. Always be lettered horizontally. 12 Drill 12 Drill ≈ 10mm Too far Must be used in a combination with a leader line. Good practice 12 D ril l Placed above the bent portion of a leader line. 12 Drill Local notes School of Aerospace, Mechanical & Manufacturing Engineering 29 RMIT University©2015 3-minute discussion Sketch the assigned problems. Each grid square equal to 2mm. Completely dimension the drawings. School of Aerospace, Mechanical & Manufacturing Engineering 30 RMIT University©2015 8 6 6 4 4 4 8 4 4 16 8 2 5 10 2 x φ2 4 12 2 x R2 4 2 x R1 School of Aerospace, Mechanical & Manufacturing Engineering 31 RMIT University©2015 Dimensioning the object’s features School of Aerospace, Mechanical & Manufacturing Engineering 32 RMIT University©2015 Basic Concepts • The term ‘feature’ refers to surfaces, faces, slots, corners, bends, arcs and fillets that add up to form an engineering part • Dimensions defined the size of a feature or its location relative to other features or a frames of reference, called a datum Rxx School of Aerospace, Mechanical & Manufacturing Engineering 33 RMIT University©2015 Dimensioning holes φ 50 Use extension and dimension lines Use diametral dimension line Use leader line and note φ 50 Rxx School of Aerospace, Mechanical & Manufacturing Engineering 34 RMIT University©2015 Dimensioning components Information to be dimensioned Angle - Angle between edges. A circular dimension line must have its center at the vertex of the angle. Poor practice Example Extension and circular dimension lines, and dimension number School of Aerospace, Mechanical & Manufacturing Engineering 35 RMIT University©2015 The note and the arrowhead should be placed in a concave side of an arc, whenever there is a sufficient space. R6.5 Place a note and an arrow outside Insufficient space for both Radius of an Arc R62.5 Place a note outside Sufficient space for arrowhead only R62.5 Sufficient space for both. Example : Radius of an arc School of Aerospace, Mechanical & Manufacturing Engineering 36 RMIT University©2015 R62.5 R62.5 Arc : Common mistakes R62.5 R62.5 R62.5 62 .5 School of Aerospace, Mechanical & Manufacturing Engineering 37 RMIT University©2015 If the arc has its center lies outside the sheet or interfere with other views, use the foreshortened radial dimension line. Arc A drawing sheet Method 1 Example Method 2 School of Aerospace, Mechanical & Manufacturing Engineering 38 RMIT University©2015 Curve (A combination of arcs) Leader line and local note - Radius - Location of its center Dimensioning components Information to be dimensioned Extension and dimension lines, and dimension number Poor practice Example : Radius of the arcs R20 R40 School of Aerospace, Mechanical & Manufacturing Engineering 39 RMIT University©2015 Fillets and Rounds Dimensioning components Information to be dimensioned - Radius 1. Leader line and local note 2. General note 3. Combination of both NOTE: All fillets and round are R6.5 1. All fillets and rounds have an equal radius NOTE: All fillets and round are R6.5 unless otherwise specified. R12 2. Most of fillets and rounds have an equal radius except for some places Example School of Aerospace, Mechanical & Manufacturing Engineering 40 RMIT University©2015 Cylinder Dimensioning components Information to be dimensioned - Diameter - Length Extension and dimension lines, and dimension number Diameter should be given in a longitudinal view with the symbol “φ ” (read phi) placed in front of a number. φ 70 150 Example Measurement of object’s diameter School of Aerospace, Mechanical & Manufacturing Engineering 41 RMIT University©2015 External chamfer Dimensioning components Information to be dimensioned - Linear distance 1. Leader line and local note or - Angle S θ S S S S Case of 45 degrees Case of 45 degrees S S 2. Extension and dimension lines, and dimension number School of Aerospace, Mechanical & Manufacturing Engineering 42 RMIT University©2015 Rounded Bars and Slots pad pad Locate the center of the arc, or the center of the slot. Use R to denote the radius, do not dimension it twice. School of Aerospace, Mechanical & Manufacturing Engineering 43 RMIT University©2015 Placement of dimensions or Dimension guidelines School of Aerospace, Mechanical & Manufacturing Engineering 44 RMIT University©2015 Extension lines, leader lines should not cross dimension lines. Poor practice Extension Line Practices 1 Example Place longer dimensions outside shorter ones. School of Aerospace, Mechanical & Manufacturing Engineering 45 RMIT University©2015 Extension lines should be drawn from the nearest points to be dimensioned. Poor practice Example Extension Line Practices 2 School of Aerospace, Mechanical & Manufacturing Engineering 46 RMIT University©2015 Extension lines of an internal feature can cross a visible line without leaving a gap at the intersection point. Example Wrong Extension Line Practices 3 School of Aerospace, Mechanical & Manufacturing Engineering 47 RMIT University©2015 Do not use visible, center, and dimension lines as an extension lines. Dimension guidelines (1/5) Example Poor practice School of Aerospace, Mechanical & Manufacturing Engineering 48 RMIT University©2015 Avoid dimensioning hidden lines. Poor practice Example Dimension guidelines (2/5) School of Aerospace, Mechanical & Manufacturing Engineering 49 RMIT University©2015 Place dimensions outside the view, unless placing them inside improve the clarity. Example 1 2 Dimension guidelines (3/5) School of Aerospace, Mechanical & Manufacturing Engineering 50 RMIT University©2015 Apply the dimension to the view that clearly represents the contour or shape of a feature being dimensioned Example Poor practice Dimension guidelines (4/5) School of Aerospace, Mechanical & Manufacturing Engineering 51 RMIT University©2015 Avoid repeat a dimension (superfluous dimensions). Example Poor practice Dimension guidelines (5/5) School of Aerospace, Mechanical & Manufacturing Engineering 52 RMIT University©2015 Dimension lines should be lined up and grouped together as much as possible. Grouping Dimensions Example Poor practice School of Aerospace, Mechanical & Manufacturing Engineering 53 RMIT University©2015 Good Good Poor Poor Poor Poor Good Good Practice yourself Determine an appropriateness of the given dimensions. Click on the button below to see the answer. (Also, try to think about the reason and how to give a better dimension.) 1 2 34 5 6 7 8 1 2 3 4 5 6 7 8 School of Aerospace, Mechanical & Manufacturing Engineering 54 RMIT University©2015 Put the lesser dimensions closer to the part. Staggering Dimensions Example School of Aerospace, Mechanical & Manufacturing Engineering 55 RMIT University©2015 Dimensions from common line School of Aerospace, Mechanical & Manufacturing Engineering 56 RMIT University©2015 Use the symbol ‘x’ to dimension repetitive features. Example Repetitive Features School of Aerospace, Mechanical & Manufacturing Engineering 57 RMIT University©2015 Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor Poor Good Good Good Good 1 2 3 4 5 6 7 8 Practice yourself Determine an appropriateness of the given dimensions. 1 12 3 4 5 6 7 9 10 11 13 14 15 2 8 9 10 11 12 13 14 15 MIET2012 Tolerance School of Aerospace, Mechanical & Manufacturing Engineering 59 RMIT University©2015 Tolerance is the total amount dimension may vary. It is defined as the difference between the upper and lower limits. TOLERANCE School of Aerospace, Mechanical & Manufacturing Engineering 60 RMIT University©2015 TOLERANCE: Purpose 1. To control an interchangeability of parts. 2. To ensures the mating part will have a desired fit. School of Aerospace, Mechanical & Manufacturing Engineering 61 RMIT University©2015 TOLERANCE Representation Tolerance can be expressed in several ways: Direct limit or as tolerance values applied directly to a dimension Geometric tolerances School of Aerospace, Mechanical & Manufacturing Engineering 62 RMIT University©2015 Direct Tolerance ALL METRIC DIMENSIONS TO BE HELD TO ± 0.05 School of Aerospace, Mechanical & Manufacturing Engineering 63 RMIT University©2015 Geometric Tolerance Geometric characteristic symbol Diameter symbol Stated tolerance Datum feature School of Aerospace, Mechanical & Manufacturing Engineering 64 RMIT University©2015 Symbols School of Aerospace, Mechanical & Manufacturing Engineering 65 RMIT University©2015 Plus & Minus Tolerance School of Aerospace, Mechanical & Manufacturing Engineering 66 RMIT University©2015 Fit The degree of tightness between mating parts is called the fit. School of Aerospace, Mechanical & Manufacturing Engineering 67 RMIT University©2015 Clearance & Interference Fit School of Aerospace, Mechanical & Manufacturing Engineering 68 RMIT University©2015 Fit Type Determination School of Aerospace, Mechanical & Manufacturing Engineering 69 RMIT University©2015 Summary • Dimensioning is a method of accurately communicating size information for objects and structures so that they can be produced. • There are standards to guide the proper use and placement of dimensional information on engineering drawings. • Tolerances allow a dimension to vary within limits. • Toleranced dimensions are useful in the accurate manufacture of assembled parts.
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