1 Mechanical Engineering Drawing MECH 211/2 YLecture #10 Dr. John P. Peach

2 Screws, Nuts and Bolts Used to assemble machine partsUsed to transmit power / motion The threads are cut or rolled Bolts and nuts must be matched

3 Screw and Thread TerminologyScrew Thread - A ridge of uniform section in the form of a helix on the external or internal surface of a cylinder. Major Diameter - The largest diameter of a screw thread. Minor Diameter - The smallest diameter of a screw thread.

4 Screw and Thread TerminologyAxis – the longitudinal center line of the original work (blank) or hole Chamfer – the angular relief at the beginning or end of the thread to allow easier engagement with the mating part Crest – the peak of the top of a thread Depth – the distance between the crest and the root

5 Screw and Thread TerminologyExternal thread – the screw thread on the outside of a cylindrical surface Internal thread – the screw thread on the inside of a cylindrical surface Lead – the distance that a screw will travel along the axis when turned by 360°

6 Screw and Thread TerminologyPitch – the distance between corresponding points on adjacent thread forms, measured parallel to the axis expressed in 1 divided by the number of pitch in one inch Pitch diameter – the diameter of an imaginary cylinder that is located equidistant between the major and the minor diameter

7 Screw and Thread TerminologyRoot – the bottom of the screw thread cut in a cylinder Thread angle – the angle between the surfaces of two adjacent threads Thread series – the number of threads per inch for a given diameter

8 Tap and Die

9 Thread Specifications – Imperial SystemANSI Y Thread form Thread series Major diameter Class of fit Threads per inch

10 Screw Thread Forms Imperial & Metric have same proportionSharp V was original American national thread American National now has flattened root and crest to increase strength Unified thread is agreed as standard in US, Canada and Britain, the crest may be flat or rounded but the root is rounded. Otherwise similar to American national

11 Screw Tread Forms ISO Metric is the most common of all. The depth is smaller than that of Unified National thread Knuckle thread is rolled or cast (used in light bulbs and sockets) Square and Acme threads are used for transmitting power Buttress thread takes pressure on one side ( to the axis). Unidirectional motion.

12 Power Transmission & Measurement ScrewsControls and positioning applications

13 Measuring Thread PitchPitch is the distance along the axis between corresponding points in adjacent threads (i.e crest to crest or root to root) Metric: Measured in millimeters (i.e. M10 X 1.5) Imperial: Measured in threads per inch Thread Pitch is measured with scale or a thread pitch gage

14 Unified National Thread SeriesSeries: Varies with the pitch and the major diameter of the thread Coarse Series (UNC) General purpose usage Fine Series (UNF) Used when a great deal of force is necessary Extra Fine Series (UNEF) Used when the length of engagement is short and there is a high degree of stress 8-Pitch (8UN), 12-Pitch (12UN), 16-Pitch (16UN) Does not depend on the diameter

15 Metric Thread Series Simplified compared to Unified SeriesOnly two series Coarse (General Purpose) Fine

16 Left & Right Handed ThreadsThreads are assumed to be right handed (RH) A nut advances when turned clockwise Left handed (LH) threads turn counter clockwise to tighten

17 Single and Multiple Thread Forms

18 Thread Symbols Three Types: Simple, Schematic or DetailedFor major diameters >1” Detailed is preferred

19 Simplified & Schematic Internal Symbols Normal & Section Drawings

20 Unified Thread Class of FitLoose fit where quick assembly is required and play between parts is acceptable Class 2 High quality general purpose commercial class of fit for bolts, nuts and screws used in mass production Class 3 Very high quality threaded fasteners with a close fit used for precision assembly subjected to vibrations A is for external threads and B is for internal threads

21 Metric Thread Class of FitTolerance grade 3 to 9 for external threads 4 to 8 for internal Tolerance position Letter between A and H Capitals for internal threads and lowercase letters external threads Tolerance Class Tolerance grade plus a tolerance position, First for the pitch diameter Second major diameter Example, “4g6g”

22 Imperial Thread Notes

23 Metric Thread Note Thread form symbol – M Nominal size Pitch sizeTolerance Class

24 Basic Metric Thread Note

25 Complete Metric Threading NoteFor example, grade 4 < grade 6 < grade 8 tolerances In addition to the tolerance grade, a positional tolerance is required For external threads: Tolerance position e (large allowance) Tolerance position g (small allowance) Tolerance position h (no allowance) For internal threads: Tolerance position G (small allowance) Tolerance position H (no allowance)

26 How to Represent a Threaded Hole

27 Threads Per Inch for Various FormsANSI

28 Screws, Nuts and Bolts

29 Screws, Nuts and Bolts Large variety of bolts (dimensional, head shape, etc.) Material, quality, finishing Grade

30 Finished and Unfinished BoltsUnfinished bolts are not machined anywhere except for the thread portion Finished bolts have machined face for washer holding or flush location on parts

31 Fastener Locking

32 Fastener Locking Durlock nut Castellated nut Jam nut

33 Standard Cap Screws Head can have different shapesPass through a clearance hole to screw into member Socket screws are used while in crowded condition

34 Standard Machine ScrewsSimilar to cap screws but smaller in size. General diameters between .06 to .75 inches Hex head (not shown here) may be slotted if desired Other heads are available as either slotted or recessed Generally used for screwing into thin materials

35 Bolt Representation

36 Cap Screw Representation

37 Screw Assembly Representation

38 Screw Assembly Representation

39 Screw Assembly Representation

40 Screw Assembly Representation

41 Screw Assembly Representation

42 Bolt Assembly Representation

43 Non-Permanent Fasteners Snap Rings

44 Non-Permanent Fasteners Pins

45 Permanent Fasteners Once assembled, the parts of the assembly (including the fastener) would be destroyed to disassemble the assembly. Rivets, soldering, brazing, welding

46 Rivets Used to permanently fasten mechanical components

47 Riveting process

48 Fastening With Rivets The headless end of the rivet is plastically deformed such that keeps together two components

49 Fastening With Rivets

50 Fastening With Rivets

51 Fastening With Rivets

52 Fastening With Rivets

53 Fastening With Rivets

54 Fastening With Rivets

55 Common Riveted Joints

56 Self-Piercing Rivets Blind rivets

57 Blind Rivets

58 Soldering, Brazing & WeldingJoining of two part using a third component – filler that joins the parts when in liquid state Soldering and brazing – low temperature binding materials – Sn-Pb, Cu-Ag alloys Limited capability to face thermo-mechanical loading

59 Welding Very well regulated activity It requires license to practiceWelders bear significant responsibility The activity is based on rigorous rules and regulations Designer prescribe welding based on mechanics of materials calculations Symbols indicate the type of welding

60 Basic Welding Note

61 Basic Welding Symbols

62 Basic Welding Symbols

63 Basic Welding Symbols

64 Springs Designed to store energy when deflected and return the same amount of energy when released Basically divided as Helical and Flat springs Helical springs are sub divided as Compression Springs Extension Springs Torsion Springs

65 Helical Springs Compression, Extension & Torsion

66 Spring RepresentationDetailed representation Working drawing of a compression spring Schematic representation

67 Gears

68 Gear Nomenclature

69 Gear Representation A table containing cutting data must accompany the representation This gear is not sectioned unless something inside should be shown

70 Gear Representation A table containing cutting data must accompany the representation

71 Gear Representation

72 Rack and Pinion Rack representation (the cutting data is included)Transmission of liner motion to circular or vice versa

73 Worm Gear Worm and Gear representationTransmission of motion between out of plane, perpendicular axes

74 Bevel Gear Bevel Gear representationTransmission of motion between perpendicular axes

75 Cam and Follower

76 Clutch Reduce the high stress when power is coupled to an idle shaft

77 Ball Bearings

78 Ball and Roller Bearings

79 Ball and Roller Bearings

80