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A Brief Introduction to Engineering Graphics

A Brief Introduction to Engineering Graphics 28
A Brief Introduction to Engineering Graphics Will Durfee Tim Kowalewski Department of Mechanical Engineering University of MinnesotaOpening comments • Engineering graphics is the method for documenting a design • Mechanical engineering students must be familiar with standards of engineering graphics as it is expected in industry • This set of slides introduces some of the basics, but is not comprehensive • For more, see • Engineering Graphics section on the Resources page of the course ME2011 website • Any engineering graphics textbookDocumenting a part requires... 1. SHAPE 2. SIZE 3. MATERIAL 4. TOLERANCE 5. FINISHEngineering drawings • Universal language • Conventions (drawing grammar) simplify communication; your drawing is at risk if you defy • CAD packages make formal drawing easy…if you follow the conventions • The machinist will laugh at you behind your back if you show up with a nonstandard drawingMultiview drawings TOP RIGHT FRONT SIDE rd “3 angle projection”Multiview drawings TOP Views MUST align RIGHT FRONT SIDE rd “3 angle projection”Multiview drawings TOP Views MUST align RIGHT FRONT SIDE rd “3 angle projection” You walk around Rotate the part part to the right (US) to the right (Europe)The Glass Box: Bertoline, Engineering GraphicsAlignment Orientation are preserved… Bertoline, Engineering GraphicsSix Principle views: obey layout Basic lines (the “alphabet of lines”) Object line Hidden line Center line Dimension lineHIDDEN LINESCENTER LINESInterpreting Center Lines Enough Info Enough InfoCOULD BE THIS...OR THIS Centerlines imply symmetry, NOT revolution per seHERE, ONLY 2 VIEWS NEEDED (Correct drawing)Find The MistakesFind The MistakesFRONTFRONT FIND THE MISTAKESCORRECT DRAWINGSECTIONS A A YES NOWorking with person sitting next to you copy this and draw the TOP VIEWPossible Geometries Working with person sitting next to you copy this and draw the TOP VIEWWorking with person sitting next to you, sketch the Section ViewOK OK Correct Section ViewsWrong Wrong Working with person sitting next to you, Find the MISTAKESWorking with person sitting next to you, sketch the Section ViewREVOLVED SECTION Preferred “True” sectionDIMENSIONING 1. SHAPE 2. SIZE 3. MATERIAL 4. TOLERANCE AND FINISH• Conventions exist for choice and placement Dimensioning • Not too many and not too few • Never should measure off drawing with a ruler 5 3 3 5Under/Over Dimensioning 5 5 3 3 3 2 5 5Dimensioning rules: …find the mistakes. 5 5 3 3 2 3 5 5Dimensioning guidelines 1. Don’t overdefine or underdefine the object. MOST IMPORTANT 5 2. Dimension to the visible contour or shape of the feature / Don’t dimension to hidden lines. 3 4. Don’t dimension to object lines (model edges), use extension lines. 5. Don’t overlap a dimension and the model. 5 Place dimensions away from the model’s surface. 6. Don’t cross extension lines if possible. 7. Group dimensions when possible unless it 5 become difficult to read. 3 8. Place dimensions on the side of the view 2 were adjacent views exist (for easy referencing). 3 5Design Detail ½” thick aluminum block Which is more expensive: A or B and why A B 6.0 6.0 4.0 4.1www.mcmaster.comDimensioning Choices Design Intent If change width of block to 8, what happens to the hole location A B 6 6 2 4 2 2 6 6Placement conventions extension line dimension small gap about 3/8" from part 2.00 about 1/4" between dimensions a little extended 3.00 letters about 1/8" tall 6.2 dimension line arrow touches 1.00 Lettering: 1 or 2 directions only .50 .50 .50 .50 OK OK NO .50 .50Extension Lines 1.000 no break in line 2.000 1.000 .375 .500 2.007 no gaps All on one side 2.739 .913 .907 .913 .907 2.739 YES NODimensioning Rounds 0.25 0.75 R 0.125 Place dimension on view that shows the circle Show diameter rather than radiusTOLERANCES www.efunda.com/processes/machining/drill.cfm www.efunda.com/processes/machining/drillpress.cfmTolerances • Matter because parts cannot be made to an exact dimension • Must specify dimension tolerance so that every part A fits every part B • Higher tolerance = higher cost • A ½ inch hole made on an ordinary drill press gives you a hole in the range 0.496 to 0.504 (+/ 0.004). For higher precision, drill undersize and use a reamer…but it will cost you more and take longer to fabricate. ½ inch drill bit: +/ .0040 ½ inch reamer: +.0003, .0000LEGOS • You can combine six 8stud bricks of the same color 102,981,500 different ways • 91 of all households with children in Denmark own LEGO products • During the period 19491990, 110,000,000,000 (110 billion) LEGO elements were molded • Bayer Corporation's Polymers Division is the official supplier of ABS plastic to the LEGO group. • Exact specifications of the Bayer resin supplied to the LEGO Group are a closely held secret. • Dimension tolerance of mold is 0.005 mm (0.0002 inch) D 5 8 1.7 9.6Representing tolerances 1.005 .995 1.000 3.005 2.995 3.000 +.005 1.000 ±.005 1.000 .005 +.005 3.000 ±.005 3.000 .005Tolerance stackup What is min and max height of stack 14.75 15.25 3.0  .05 5 high stackTolerance Stacking What’s the tolerance (+/) on dimension x Ans: +/ 0.3Chain or Baseline Dimensioning … You decide 1.0 ±.1 2.0 ±.1 1.0 ±.1 1.0 ±.1 3.0 ±.1 4.0 ±.1Chain or Baseline Dimensioning 1.0 ±.1 1.0 ±.1 2.0 ±.1 1.0 ±.1 3.0 ±.1 4.0 ±.11. Will all shafts fit into all holes Holes and shafts 2. What is maximum clearance hole shaft .626 .623 .625 .622 .623 .626 .622 .625.626 .623 .625 .622 ANSI standards for shaft holes Clearance Shaft smaller than hole for all shafts and holes Interference Shaft larger than hole for all shafts and holes Transition Smallest shaft fits in largest hole Running/Sliding RC1 (fit together, no play) to RC9 (fit loosely) Force/shrink FN1 (light drive and pressure) to FN5 (high stresses and pressures) …and others Like Locational, etc. Basic hole Use nominal size of hole as starting point Basic shaft Use nominal size of shaft as starting pointPreferred Fit Example…“Basic Hole” Tolerancing Example .0008 + .0012 1.0000 1.0000 .0000 .0016 Drawing shows 1 in. nominal, ANSI RC4 clearance fit “Basic Hole” means smallest possible hole = nominal, then size shaft for clearance RC4 clearance = 0.0008, 0.0028 = smallest holelargest shaft, largest hole smallest shaftTitle block information for tolerance ALL DIMENSIONS IN INCHES HOLD ALL DIMENSIONS TO ± 0.010 UNLESS SPECIFIED Dimension Tolerance X.X ± 0.1 X.XX ± 0.05 X.XXX ± 0.001Design Detail Bent aluminum sheet, 1/16” thick A or B: Which is more expensive and why A 0.030 + 4.0 B 0.003Tolerance vs. Cost 1.00 ±.075 1.00 ±.05 1.000 ±.005 1.0000 ±.00005 Manufacturing TolerancesGeometric Dimensioning and Tolerancing (GDT)Traditional tolerancing is ambiguous 1.000 ±.005 3.000 ±.005 Ambiguity… .25 ± .01 .25 ± .01 + + Square deviation Circular deviation Geometric Dimensioning and Tolerancing .125 +/ .002 .01 .25 • Ideal position of hole. .25, is marked with box and no +/ notation. • Feature control box shows how close hole is to exact; within circular tolerance zone with diameter .01Geometric Dimensioning and Tolerancing .25GDT Resources ME2011 website: https://sites.google.com/a/u mn.edu/me2011/resources • Efunda tutorial: http://www.efunda.com/de signstandards/gdtThreaded Fasteners What they are and how to indicate on a drawingThreaded Fasteners • Holes • Threads • Threaded fastenersHoles 19 DRILL – 0.75 DEEP or O .166 . 75 DEPTH 0.75 REF Pix from www.mcmaster.com unless notedThru holes 19 DRILL – THRU or O .166 Threads http://www.machinist.org/harvardcotreau/mshop6.html http://www.americanfastener.com/technical/threadterminology.aspThreaded Fasteners (screws, bolts) • Specify diameter, thread, length, head 1/420 x 1, RHMS ROUND HEAD MACHINE SCREW 1/4" DIA 1" LONG 20 THREADS PER INCHCommon screw thread sizes Unified Thread Standard • 256 • 1/420 • 440 • 3/816 • 632 • 1/213 • 832 • 5/811 • 1024 • 3/410 DIA. = (N.013) + .060 (inches)Alternate Thread CalloutHead shapes Cap screw Pan Socket head Flat cap screw (SHCS) Round Set screwDriving a fastener Slotted Hex cap Phillips Hex head Torx (Allen head)McMasterCarr www.mcmaster.comName the Fastener: Name the Fastener: Socket Head Cap Screw Socket Head Cap Screw with counterboreSocket Head Cap Screw with counterbore Phillips Flat Head Screw with countersinkSet Screw Countersunk, Phillips Flat headConvention for screws “SCHEMATIC” “SIMPLIFIED”Convention for threaded holes 632 THRU TOP FRONT FRONT SECTIONBlind threaded holes 1/2 – 13 x 1.325 DEEP .4219 1.50 1/2 – 13 1.325 THREAD DEPTH DRILL DEPTHCountersunk holes O .562 – 82 CSK, 1.125 .562 O 1.125 x 82Counterbored holes 19 DRILL – 29 CBORE, 14 DEEP 19 29 14 CBORE DEPTHOther Items for DrawingsLeaders notes FINISH TOP SURFACE SMOOTH NOTE BTITLE BLOCKS • Basic • Title • Name • Date • Units • Optional • Company name, sheet number, scale, tolerances, material, finish.... • Follow your company standardsMY PART W. DURFEE 10/2/2014 ALL DIMENSIONS IN INCHESA title block using a company template www.classiccomponents.co.ukProduction Drawings Many types of drawings can be produced from the CAD database ASSEMBLY SKETCHES MODEL SKETCHES DETAIL SKETCHES DETAIL DETAIL DETAIL DETAIL MFG BOM MANUALS PROCESS