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Threads, Fasteners, and Springs

Threads, Fasteners, and Springs. Chapter 11. Objectives. Define and label the parts of a screw thread Identify various screw thread forms Draw detailed, schematic, and simplified threads Define typical thread specifications. Objectives (cont.).

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Threads, Fasteners, and Springs

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  1. Threads, Fasteners, and Springs Chapter 11

  2. Objectives • Define and label the parts of a screw thread • Identify various screw thread forms • Draw detailed, schematic, and simplified threads • Define typical thread specifications

  3. Objectives (cont.) • Identify various fasteners and describe their use • Draw various screw head types • Draw springs

  4. Understanding Threads and Fasteners • There are three basic applications for screw threads: • To hold parts together • To provide for adjustment between parts • To transmit power

  5. Screw Thread Terms

  6. Screw Thread Terms • Screw thread – a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder • External thread – a thread on the outside of a member • Internal thread – a thread on the inside of a member

  7. Screw Thread Terms • Major diameter – the largest diameter of a screw thread • Minor diameter – the smallest diameter of a screw thread

  8. Screw Thread Terms • Pitch – the distance from a point on a screw thread to a corresponding point on the next thread measured parallel to the axis • Pitch (P) equals 1 divided by the number of threads per inch

  9. Screw Thread Terms • Pitch diameter – the diameter of an imaginary cylinder passing through threads where the widths of the threads and the widths of the spaces would be equal • Lead – the distance a screw thread advances axially in one turn

  10. Screw Thread Terms • Angle of thread – the angle between the sides of the thread measured in a plane through the axis of the screw • Crest – the top surface joining the two sides of a thread • Root – the bottom surface joining the sides of two adjacent threads

  11. Screw Thread Terms • Side – the surface of the thread that connects the crest with the root • Axis of screw – the longitudinal centerline through the screw • Depth of thread – the distance between the crest and the root of the thread measured normal to the axis

  12. Screw Thread Terms • Form of thread – the cross section of thread cut by a plane containing the axis • Series of thread – standard number of threads per inch for various diameters

  13. Screw Thread Forms • Typical thread forms include: • Sharp-V thread (60 degrees) • American national thread • Unified thread • Unified extra fine thread series • Metric thread • Square thread • Acme thread

  14. Screw Thread Forms • Typical thread forms (cont.) • Standard worm thread • Whitworth thread • Knuckle thread • Buttress thread

  15. Screw Thread Forms

  16. Thread Pitch

  17. Right-hand and Left-hand Threads

  18. Single and Multiple Threads • Single threads are composed of one ridge and the lead is equal to the pitch • Multiple threads are composed of two or more ridges running side by side

  19. Single and Multiple Threads

  20. Thread Fits • ANSI has established 3 classes of fit: • Class 1 – when clearance between mating parts is essential • Class 2 – high quality for the bulk of interchangeable screw thread work • Class 3 – exceptionally high quality recommended only when high cost of precision is warranted

  21. Thread Fits • Some specialized metric thread applications are specified by: • Tolerance grade • Tolerance positions • Class • Length of engagement

  22. Methods for Drawing Thread • There are three methods of representing screw threads on drawings: • Schematic • Simplified • Detailed

  23. Methods for Drawing Thread

  24. Methods for Drawing Thread

  25. Methods for Drawing Thread

  26. Thread Notes • ASME/ANSI Y 14.6-2001 “Screw Thread Representations” is a standard for representing, specifying, and dimensioning screw threads on drawings • These same notes or symbols are used in correspondence, in records, and in specifications for parts, taps, dies, tools, and gages

  27. Thread Notes

  28. Thread Notes

  29. External Thread Symbols

  30. Internal Thread Symbols

  31. Detailed Representation

  32. Detailed Representation

  33. Use of Phantom Lines

  34. Threads in Assembly

  35. Pipe Thread Representation

  36. Bolts, Studs, and Screws

  37. Types of Screw Heads

  38. Tapped Holes • The bottom of a drilled hole formed by the point of a twist drill is cone shaped • The thread length is the length of full or perfect threads • The tap drill depth does not include the cone point of the drill

  39. Tapped Holes

  40. Standard Bolts and Nuts • Standard bolts and nuts have characteristics determined by: • Bolt types • Finish • Proportions • Threads • Thread lengths • Bolt lengths

  41. Specifications • In specifying bolts, the following information must be covered in order: • Nominal size of bolt body • Thread specification or thread note • Length of bolt • Finish of bolt • Style of head • Name

  42. Locknuts and Locking Devices

  43. Standard Cap Screws

  44. Standard Machine Screws

  45. Standard Set Screws

  46. Standard Wood Screws

  47. Miscellaneous Fasteners

  48. Keys • Keys are used to prevent movement between shafts and wheels, couplings, cranks, and similar machine parts attached to or supported by shafts

  49. Keys

  50. Machine Pins • Machine pins include taper pins, straight pins, dowel pins, clevis pins, and cotter pins

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