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Chapter 5 Threads and Fasteners

Chapter 5 Threads and Fasteners. Topics Exercises. Threads & Fasteners: Topics. Summary 5.1) Fasteners 5.2) Screw Thread Definitions 5.3) Types of Thread 5.4) Manufacturing Screw Threads 5.5) Drawing Screw Threads 5.6) Unified Threads 5.7) Metric Threads

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Chapter 5 Threads and Fasteners

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  1. Chapter 5Threads and Fasteners Topics Exercises

  2. Threads & Fasteners: Topics Summary 5.1) Fasteners 5.2) Screw Thread Definitions 5.3) Types of Thread 5.4) Manufacturing Screw Threads 5.5) Drawing Screw Threads 5.6) Unified Threads 5.7) Metric Threads 5.8) Drawing Bolts 5.9) Bolt and Screw Clearances

  3. Threads & Fasteners: Exercises Exercise 5-1: Screw thread features Exercise 5-2: Unified national thread note components Exercise 5-3: Unified national thread note Exercise 5-4: Metric thread note components Exercise 5-5: Metric thread tables Exercise 5-6: Fastener tables and clearance holes

  4. Threads and Fasteners Summary

  5. Summary • What will we learn in Chapter 5? • How to represent fasteners and threads on an engineering drawing. • How to calculate bolt and screw clearance holes. • Key points • Threads are represented by thread symbols, not by a realistic drawing.

  6. Threads and Fasteners 5.1) Fasteners

  7. Fasteners • Fasteners include: • bolts and nuts (threaded) • set screws (threaded) • washers • keys • pins • Fasteners are not a permanent means of assembly such as welding or adhesives.

  8. Fasteners • Fasteners and threaded features must be specified on your engineering drawing. • Threaded features: Threads are specified in a thread note. • General Fasteners: Purchasing information must be given to allow the fastener to be ordered correctly.

  9. Threads and Fasteners 5.2) Screw Thread Definitions

  10. Thread Definitions • Screw Thread:A ridge of uniform section in the form of a helix.

  11. Thread Definitions • External Thread:External threads are on the outside of a member. • A chamfer on the end of the screw thread makes it easier to engage the nut. Chamfer

  12. Thread Definitions • External Thread: • An external thread is cut using a die or a lathe.

  13. Thread Definitions • Internal Thread:Internal threads are on the inside of a member. • An internal thread is cut using a tap.

  14. Thread Definitions • Major DIA (D):The largest diameter (For both internal and external threads). • Minor DIA (d):The smallest diameter. • Depth of thread:(D-d)/2 • Pitch DIA (dP): The diameter at which a line cuts the spaces and threads equally.

  15. Exercise 5-1 Screw thread features

  16. Skip to next part of the exercise Identify the Major,Minor & Pitch diameters and the Thread Depth. 3 2 1 4 5 8 7 8 6 10 9

  17. Identify the Major,Minor & Pitch diameters and the Thread Depth. 3 2 1 4 Thread Depth Majorn 8 Pn Minorn 10 9

  18. Thread Definitions • Crest:The top surface. • Root:The bottom Surface. • Side:The surface between the crest and root.

  19. Skip to next part of the exercise Identify the Crest, Root and Side. 3 2 1 4 Thread Depth Majorn 8 Pn Minorn 10 9

  20. Identify the Crest, Root and Side. Crest 2 1 Root Thread Depth Majorn 8 Pn Minorn 10 Side

  21. Thread Definitions • Pitch (P):The distance from a point on a screw thread to a corresponding point on the next thread (in/Threads). • Angle of Thread (A):The angle between the threads.

  22. Thread Definitions • Screw Axis:The longitudinal centerline. • Lead:The distance a screw thread advances axially in one turn.

  23. Identify the Pitch, Screw Axis and Thread Angle. Crest 2 1 Root Thread Depth Majorn 8 Pn Minorn 10 Side

  24. Identify the Pitch, Screw Axis and Thread Angle. Crest Pitch Axis Root Thread Depth Majorn 8 Pn Minorn Angle Side

  25. Thread Definitions • Right Handed Thread:Advances when turned CW. (Threads are assumed RH unless specified otherwise.) • Left Handed Thread:Advances when turned CCW.

  26. Application Question 5-1 • Name an example of a left handed thread. Left peddle of a bike

  27. Threads and Fasteners 5.3) Types of Thread

  28. Types of Thread • There are many different types of thread forms (shape) available. The most common are; • Unified • Metric

  29. Types of Thread • Thread form choice depends on; • what it will be used for • length of engagement • load • etc…

  30. Types of Thread (Form)

  31. Types of Thread (Form)

  32. Threads and Fasteners 5.4) Manufacturing Screw Threads

  33. Manufacturing Threads • Internal Threads • First a tap drill hole is cut with a twist drill. The tap drill hole is a little bigger than the minor diameter. Why?

  34. Manufacturing Threads • Internal Threads • Then the threads are cut using a tap. Incomplete threads The tap drill hole is longer than the length of the threads. Why?

  35. Manufacturing Threads • Internal Threads • Chamfers are sometimes cut to allow for easy engagement.

  36. Manufacturing Threads • External Threads • You start with a shaft the same size as the major diameter.

  37. Manufacturing Threads • External Threads • The threads are then cut using a die or on a lathe.

  38. Threads and Fasteners 5.5) Drawing Screw Threads

  39. Drawing Screw Threads • There are three methods of representing screw threads on a drawing. • Detailed • Schematic • Simplified • Screw thread representation present in this chapter is in accordance with the ASME Y14.6-2001 standard.

  40. Detailed Representation • A detailed representation is a close approximation of the appearance of an actual screw thread.

  41. Detailed Representation • Pros and Cons? Pro: Looks good and clearly represents a thread. Con: Takes a long time to draw.

  42. Schematic Representation • The schematic representation uses staggered lines to represent the thread roots and crests.

  43. Schematic Representation • Pros and Cons? Pro: Nearly as effective as the detailed representation and easier to draw. Con: Still takes some time to draw.

  44. Schematic Representation • Rules of use for Schematic threads • Should not be used for hidden internal threads or sections of external threads.

  45. Simplified Representation • The simplified representation uses visible and hidden lines to represent the major and minor diameters.

  46. Simplified Representation • Pros and Cons? Pro: Simple and fast to draw. Con: Doesn’t look like a thread.

  47. Simplified Internal Threads

  48. Simplified Internal Threads

  49. Drawing Screw Threads • Thread tables in the appendix can be used to look up value for the; • Pitch • Minor diameter • Tap drill diameter • If screw thread tables are not available, the minor diameter can be approximated as 75% of the major diameter.

  50. Threads and Fasteners 5.6) Unified Threads

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