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# FoundationsofComputerAidedDesign MEM201

Drexel

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This 61 page Class Notes was uploaded by Jada Daniel on Wednesday September 23, 2015. The Class Notes belongs to MEM201 at Drexel University taught by Staff in Fall. Since its upload, it has received 68 views. For similar materials see /class/212416/mem201-drexel-university in Mechanical Engineering at Drexel University.

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Date Created: 09/23/15

MEM 201 Fundamentals of Computer Aided Design Dimensions in Engineering Drawings Dept of Mechanical Engineering and Mechanits Dreer University Today s Learning Objectives What are dimensions Fundamental Rules of Dimensioning Guidelines for good dimensioning in engineering drawings Dimensioning in AutoCAD uepl u Dimensions A dimension is for size and position of the designedmodeled shape A DIMENSION is a numerical value expressed in appropriate units of measurement and used to define the size location orientation form or other geometric characteristics of a part A method of communication to machinists in the Production facility Different kinds Linear Aligned Angular RadiusDiameter Reference uepl u Dimension Basic Terminology 1 Dimension Basic dimension value 175 2 Dimension line minimum 10 mm dislonce j I 50 Z 3 Termination symbol arrowhead 175 4 Extension line note visible gap i i r 5 Radius symbol R gt 20 gt K 6 Leader line radial 39 R135 mo L 7 Diameter symbol a rB Center line no gap 4 W 9 Not to scale 7 23900 r1O Reference dimension 1 J l f i 4 v Dept of Mechanical Engineering and Mechanics Drexel University Units of Measure decimal inches preferred fractional inches feet and fractional inches SI or metric millimeter mm leading zero metric yes inches no If units eg IN or mm are not included with each dimension specify the units used with a note on the drawing for example UNLESS OTHERWISE SPECIFIED ALL DIMENSIONS ARE IN INCHES uepl u Dimensioning in General Datum Plane Dimensioning Continuous uepl u Dimensioning Cylindrical Dimensioning Angles 400 850 100 P I Dimensioning Angles in Views using COORDINATE method uepl u Dimensioning Angles 403 250 j Dimensioning Angles in Views using ANGULAR method uepl u Dimensions Chamfers Or 45x 025 025 g pfufes SQ45X3 00 4 45 ChamFer 45 ChamFer uepl u 9399038 I gt8m Detail Dimensioning in Views I275 Note an 4 cl leader to identify Encircle the area of interest l250 Enlarge label and scale ALL FILLETS R125 TlP TOP TOOL CO 10L 101 BEARING RETAINER DETAILA 511 rscu N0 owo no an SCALE 31 Al 1 AX12 345 0 Hi 1 I Isarn 2 or 4 Dept of Mechanical Engineering and Mechanics Drexel University Fundamental Rules of Dimensioning l at l l LLA ws 3 s l S l 1 Size 8 dimensions are used to define length width height diameter of circles and radius of arcs 2 Position dimensions locate L the center of circles and other key features 4 Igt 3 The size and position of each feature is defined only once Dept of Mechanical Engineering and Mechanics Drexel University Fundamental Rules of Dimensioning 4 Dimension the feature in a view where its characteristic shape is shown 5 English parts are dimensioned in inches with decimals not fractions 6 Metric parts are dimensioned in mm w decimals 7 Units are omitted from the dimension numbers since they are normally understood to be in millimeters or inches 8 Always leave at least 38 in 10 mm between the object and the rst row of dimensions Successive rows of dimensions should be equal and at least 025 in 6 mm apart uepl u Fundamental Rules of Dimensioning 9 Place dimensions outside of the views except for large circles Keep dimensions at least 38 inches or 10 mm from the view 10 Place longer dimensions outside of shorter ones 11 Place the dimension text between the dimension lines 12 Use arrow heads at the end of the dimension lines 13 Inch drawings do not include a preceding zero for dimensions less than one For example use 50 to indicate 12 inch Metric dimensions require a preceding zero eg use 050 to indicate 12 millimeter Deptofquot 39 39 quot39 39 39 andquot 39 39 Drexel Guidelines for Dimensioning A Check List 1 All overall dimensions forthe object are shown 2 Dimensions are not duplicated in two views 3 No dimension is included that is not needed to produce the object 4 There is no need to calculate scale or assume any dimension to define or check features of the object 5 Dimensions are related to the view that best shows the features being dimensioned 6 Multiple rows of dimensions are spaced uniformly with at least 14quot between rows and 38quot from views uepl u Guidelines for Dimensioning 7 Longer dimensions are placed outside shorter ones so that witness lines do not cross dimension lines 8 All strings ofdimensions are lined up 9 Whenever possible dimensions are not given to hidden lines 10 Dimension lines do not cross other dimension lines or witness lines 12 The radius of all arcs and fillets and the diameters of all circles have been specified uepl u Examples of Wrong Dimensioning 75 250 00 lt 1 75 39 6 5 mVoo I se gd O1DO39 3 2 50 I 125 I f 1J5 I 115 50 I L r 3 I 92750 9285 i r7375 ELSO L 1 25 m 25 L l I225 I 3 75 0 GOOD GROUPING b POOR GROUPING Dept of ing and Drexel Do not use lines of the model as dimension extension lines Group Dimensions Examples of Wrong Dimensioning De pt of Incorrect and 39 39 Drexel Dimensioning in AutoCAD a r39 wmg 0w EH2 Edrt WW Insarl Fonrat Too D39aw Moufy Expvzss Mndow Hap IDwC Dw4mmlr lQmmwv WMhmadgwmm M JG 1mm 7 7 ByLsyev Mgn O39mnnte 39m NW Radu r1sz gg mg xmo 5411 Standard Uamete39 Angular Basehne Cormnue maogjob r To srzrnz Center Mark 00 03W Mgn Text A w 39 39 39 39 39 39 L QUESTIONS uuuu u MEM 201 Fundamentals of Computer Aided Design Geometrical Dimensioning amp Tolerancing GDampT A llll Aquot 39 andquot 39 39 Today s Objectives Tolerances and why do we need them Different types of tolerances To learn how to effectively tolerance parts in engineering drawings AllowanceClearance Expressing tolerances in AutoCAD Department of Mechanical Engineering and Mechanics Tolerancing Definition Allowance for a specific variation in the size and geometry of part Why is it needed No one orthing is perfect l Hence engineers have come up with a way to make things close to perfect by specifying Tolerances l Since variation from the drawing is inevitable the acceptable degree of variation must be specified Large variation may affect the functionality of the part Small variation will effect the cost of the part requires precise manufacturing requires inspection and the rejection of parts Department of Mechanical Engineering and Mechanics When does Tolerances become important Assemblies Parts will often not fit together if their dimensions do not fall with in a certain range of values Interchangeability If a replacement part is used it must be a duplicate of the original part within certain limits of deviation The relationship between functionality and size or shape of an ob39ect varies from part to part mum L Tolerances do not affect its function tofu dand Tolerances are important here Food for thought Tolerance levels in this mechanism Department of Mechanical Engineering and Mechanics Tolerance in relation to Cost generally increases with smaller tolerance Small tolerances cause an exponential increase in cost Therefore your duty as an engineer have to consider Do you need 1310001in or is 101in good enough Parts with small tolerances often require special methods of manufacturing Parts with small tolerances often require greater inspection and call for the rejection of parts 9 Greater Quality Inspection 9 Greater cost Do not specify a smaller tolerance than is necessary Department of Mechanical Engineering and Mechanics How are Tolerances Specified Size Limits specifying the allowed variation in each dimension length width height diameter etc are given on the drawing Geometry Geometric Tolerancing Allows for specification of tolerance for the geometry of a part separate from its size GDT Geometric Dimensioning and Tolerancing uses special symbols to control different geometric features of a part Department of Mechanical Engineering and Mechanics Value of Tolerance The tolerance for a single dimension may be specified l with the dimension and then the tolerance The tolerance is total variation between the upper and lower limits E HIUE UMIU mm Department of Mechanical Engineering and Mechanics General Tolerances These are specified when all dimension in the drawings have the same tolerance 0 These notes are used to reduce the number of dimensions required on a drawing and to promote drawing clarity 1 EXCEPT WHERE STATED OTHERWISE TOLERANCES ON DIMENSIONS IO1O 2 UNLESS OTHERWISE SPECIFIED IOO7 TOLERANCE ON MACHINED DIMENSIONS I1O TOLERANCE ON CAST DIMENSIONS ANGULAR TOLERANCE I139 Department of Mechanical Engineering and Mechanics Tolerances specified for size Limit Tolerances 12751225 PlusMinus Tolerances Unilateral Tolerances 1200 or xxx Bilateral Tolerances 1200 xxx xxx These tolerance values indicate the MMC Maximum Material Condition LMC Least Material Condition Department of Mechanical Engineering and Mechanics Limit Tolerances l quotI39 ME 125 1225 LMC l 7 1 M Fulfill Mumii Galatians mm lollika mum m m m Mum may may rm Mm II 5 155 LlU Fi g inn ali g uquot if f rquotff lquot5 J 7 1 ag um I 311 um 15 i z i j I mu a m uu gt nplIIll MMC Maximum Material Condition LMC Least Material Condition Department of Mechanical Engineering and Mechanics Limit Tolerances gig r 7 a 150 140 JL 150 1 75 28439 28039 Departm en t of PlusMinus Tolerances oo 250 05 b BILATERAL TOLERANCING 05 m4500 15 w16010 28239i239 Department of Mechanical Engineering and Mechanics Allowance and Clearance ALLOWANCE Allowance is defined as an intentional difference between the maximum material limits of mating parts Allowance is the minimum clearance positive allowance or maximum interference negative allowance between mating parts The calculation formula for allowance is ALLOWANCE MMC HOLE MMC SHAFT CLEARANCE Clearance is defined as the loosest fit or maximum intended difference between mating parts The calculation formula for clearance is CLEARANCE LMC HOLE LMC SHAFT Department of Mechanical Engineering and Mechanics Types of Fit Types of Fit Clearance fit The parts are toleranced such that the largest shaft is smaller than the smallest hole The allowance is positive and greater than zero Interference fit The max clearance is always negative The parts must always be forced together Transition fit The parts are toleranced such that the allowance is negative and the max clearance is positive The parts may be loose or forced together Department of Mechanical Engineering and Mechanics BASIC FITS OF MATING PARTS Standard ANSI Fits Running and Sliding fits RC are intended to provide a running performance with suitable lubrication allowance The range is from R01 to R09 Force fits FN or Shrink fits constitute a special type of interference fit characterized by maintenance of constant pressure The range is from FN1 to FN5 A force fit is referred to as interference fit or a shrink fit The smallest amount of interference is MIN INTERFERENCE LMC SHAFT LMC HOLE The greatest amount of interference is MAX INTERFERENCE MMC SHAFT MMC HOLE Locational fits are intended to determine only the location of the mating parts Department of Mechanical Engineering and Mechanics Sample Calculation Given Diameter of shaft 15mm Upper Limit Tolerance 003mm Lower Limit Tolerance 004mm Given Diameter of Hole 148mm quot Upper Limit Tolerance 003mm Lower Limit Tolerance 005mm Allowance MMCHole MMCShaft Answer 143 153 01mm Allowance O1mm Clearance LMCHole LMCShaft ClearanCe 005mm 151 146 005mm Type of Fit Transition Fit Department of Mechanical Engineering and Mechanics Geometric Dimensioning amp Tolerancing GDampT Position E atness Concentricity ElCircularityRolundness E Symmetry E Straightness paranelism Profile Df 21 Surface Perpendicularity Profile of a Line Anguiarity Circular Runout Cylindricity Total Runout Department of Mechanical Engineering and Mechanics Tolerance of Form i003 Straightness v nW f l l l g Straightness Tolerance Zone LSD iics Depamnen of Mechanical Engineering and Mechav Straightness Tolerance Tolerance of Form DRAWING FLATNESS MEANS TOLERANCE VALUE FLATNESS SYMBOL FLATNESS TOLERANCE ZONE 39 FLOATS BETWEEN LIMITS 16 04 quot quot39 quot V quot i 200 b Note 016 lt 05 size tolerance Department of Mechanical Engineering and Mechanics Tolerance of Form Circularity El circularity olerance Zone we Deparlrmnl nlMechzniml Engineuing A Circularin Tolerance m Meuhznics Tolerance of Form Cylindricity mmmmmmmmmmm a C A f Cylindricity Tolerance Department of Mechanical Engineering and Mechanics Tolerance of Orientation Perpendicularity Perpendicularity Tolerance Zone 1 WE UUU UVD 775 t Perpendicularity Tolerance Tolerance of Orientation Parallelism H001 Tolerance Inna weaxngz a xquot 001 G A ll T Tangent Plane 139 Parallelism Tolerance 5130 i GUS epa men 0 ec anlca nglneerlng an ec anlcs Tolerances in AutoCAD 3r ry He Eda ew Insert Format Tools Draw Maury apress Wndw Hetp a x qmck D mensvan I W 5 rs 725 LINE 7 Angned Ordwnati J 0 1 F 9 Q N 0 0 can 1 Q L1 7 13 we r Sty Overnde u date 7 Reassndate mmens39ans y Communicanun Center 5 I uchD Express Tools Copyrlght zanzizuua Autodesk Inc LThe easvwavmk vnuandvaursa wareup39mrdale 11 Ht 1 ed m uchD men 1 115 load Co Departme t or Iwecnanlcal39Engmeernng and Mechanics Tolerances in AutoCAD V Genmetric Tolerance ngyanca Z Damm II D D I I I I j I Pymemau Tu evancz Zune I Tulamnce Datum Damm 3 Sym I HEIQM Damm Hemmer 0K Mater al Condition Department of Mechanical Engineering and Mechanics T 1153i 325 SPEEE FIE D TDLEEHJHCE UHEFE39EIFIED TUILEHANEE T g HEE PLACE TDLE HCE WED 05 THE DIMEHSiUH IN H DWE JR TITLE EL D EK UNLESS DIHERMSE SFEEIFED re nances ma HES MW 1 1 Puma ms t 1 i 35 2 PLEIZE EMS i m t 125 2 PLACE DEcaHALE ARE 9225 quot5quot i 7quot i m Tammie m A gauzm Hui 1 L 32 rim5H 25 u in 32 u u i TDLERAHEEE quotH A TliiiLE BLOCK mark 1 SEEM 12h bniimnm an lib dimmiun In I menl mm m ln lb inning title in Department of Mechanical Engineering and Mechanics GEOMETRY DIMESIONING AND TOLERANCE FOR CADDCAM Some dimensioning and tolerance guidelines for use in conjunction with CADDCAM Geometry tolerancing is necessary to control speci c geometric form and location Major features ofthe part should be used to establish the basic coordinate system but are not necessary de ned as datum Subcoordinated systems that are related to the major coordinates are used to locate and orient features on a part De ne part features in relation to three mutually perpendicular reference plans and along features that are parallel to the motion of CAM equipment Establish datum related to the function of the part and relate datum features in order of precedence as a basis for CAM usage Completely and accurately dimension geometric shapes Regular geometric shapes may be de ned by mathematical formulas A pro le feature that is de ned with mathematical formulas should not have coordinate dimensions unless required for inspection or reference Coordinate or tabular dimensions should be used to identify approximate dimensions on an arbitrary profile Use the same type of coordinate dimensioning system on the entire drawing Continuity of pro le is necessary for CADD Clearly de ne contour changes at the change or point of tangency Define at least four points along an irregular pro le Circular hole patterns may be de ned with polar coordinate dimensioning When possible dimension angles in degrees and decimal parts of degrees Base dimensions at the mean of a tolerance because the computer numerical control CNC programmer normally splits a tolerance and works to the mean While this is theoretically desirable one can not predict where the part will be made Dimensions should always be based on design requirements If it is known that a part will be produced always by CNC methods then establish dimensions without limits that conform to CNC machine capabilities Bilateral pro le tolerances are also recommended for the same reason Department of Mechanical Engineering and Mechanics Further Reading Interpretation of Geometric Dimensioning amp Tolerancing by Daniel E Puncochar Geometric Dimensioning and Tolerancing by Alex Krulikowski GeoMetrics lll The Application of Geometric Dimensioning and Tolerancing Techniques Using the Customary Inch Systems by Lowell W Foster Tolerance design a handbook for developing optimal specifications by CM Creveling Dimensioning and Tolerancing Handbook by Paul J Drake Inspection and Gaging by Clifford W Kennedy Geometric Dimensioning and Tolerancing by Cecil H Jensen Tolerance StackUp Analysis by James D Meadows Department of Mechanical Engineering and Mechanics Home Work 2 i x Find TH TS Allowance C Find TH TS Allowance C Cmm and what kind of fit it is Hole F 66 upper deviation 0051 lower deviation 00 Shaft F 66 upper deviation 0024 lower deviation 0050 max ImaX and what kind of fit it is Hole F 32 upper deviation 002l lower deviation 00 Shaft F 32 upper deviation 0029 lower deviation 0016 IllaX9 If a shaft is 10i005 inch what is its maximum and least material conditions Please draw circularity and perpendicularity symbol blocks with geometric tolerance of 0005 for each and sketch their tolerance zones for a cylinder and a upside down T shape block respectively Department of Mechanical Engineering and Mechanics Home Work 2 contd Th tolerance of hole Ts Tolerance of shaft Cmax Maximum clearance 0min Minimum clearance lmax Maxiumum interference F66 and F32 indicates the nominal dimensions of the hole or shaft Refer Notes and AutoCAD text book for help in solving problems Home works should include your names and the section you belong to Will be due during the next Lecture Class Department of Mechanical Engineering and Mechanics MEM 201 Fundamentals of Computer Aided Design Sectional Orthographic Views Dept of Mechanical Engineering and Mechanits Dreer University Today s Learning Objectives Need for Sectional View Contents of Sectional view Identifying different kinds of sectional views Sectional View Guidelines and good practices Cross Hatching in AutoCAD Sectional Views These are views that show internal features such as cuts holes step cuts as orthographic views Sectional Views EDGE Vle O CUTTING PLANF N at FL LL SECTION VIEW Depictassembl Show internald Replace co Describe materl mple 41 m39x lt m g tail of parts assembly orthographic views MNJl quotIll lull WWWA Purpose of Sectional Drawings Contents of a Sectional View Sectional views have Cutting plane shown as edge view cutting plane line Cutting plane arrow representing the direction of line of sight Section lines hatch shows where areas of solid material are present Dept of Mechanical Engineering and Mechanics Drexel University Different Kinds of Sectional Views Full Section Half Section Offset Section Aligned Section Full Sectional View Cutting plane cuts fully through object No Hidden Lines are shown Visible Lines behind the cutting plane must be shown CUTTlNG mm PASSES FULV rmu PARY VCR snow FULL SECTlON uepl u

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