Threads & Fasteners

1. Threads & Fasteners Competency: D505.00 Describe various types of thread and fastener representations and their annotations.

2. Threads & Fasteners Objective: D505.01 Specify threads and fasteners on a technical drawing.

3. Basic Applications of Threads How are threads used? • Hold parts together • Adjust parts • Transmit power

4. the string represents the general form of a HELIX . • Another example of a HELIX curve is a coiled spring All screw threads wind around a shaft in a curve called a HELIX

5. Tapping A Small Hole Tap Tool - is a small fluted cutting tool with cutting teeth shaped to form small internal threads.

6. External threads are formed by cutting helical grooves around the shaft on a lathe. The Lathe can produce large internal threads by using a boring tool Cutting Large Threads

7. Thread Terminology

8. Thread Forms • Sharp V or Sellers Thread • First U.S. Standard Thread • Now used on brass pipe work

9. Thread Form Unified Thread • Adopted by the U.S., British, and Canada after World War II as an ANSI standard. • Mainly used for fastening and adjusting

10. Thread Form • Metric Thread • Adopted in 1946 by the International Organization for Standardization (ISO)

11. Thread Form Square Thread • Theoretically the ideal thread for power transmission • Tough to cut the threads because of the 90° angles

12. Thread Forms ACME Thread • Modification of the square thread • Stronger and easier to cut than the square thread • Also used to transmit power. • Better know as a worm thread.

13. Thread Forms • Whitworth Thread • First standard in England • Has been replaced by the Unified thread

14. Thread Forms • Knuckle Thread • Typically rolled from sheet metal • Sometimes is formed by casting • Used in light bulbs, sockets, and jar & bottle tops

15. Thread Forms • Buttress Thread • Designed to transmit power in one direction • Used on large guns, screw jacks, and Bumper Jacks.

16. Thread Representation Most Common Practice Of The Two Symbolic Method Is used for all forms of thread forms

17. Thread Representation INTERNAL THREADS EXTERNAL THREADS Detailed Method Primarily used for threads 1” and larger.

18. Conventional Practices SIMPLIFIED TECHNIQUES FOR A THROUGH HOLE

19. Conventional PracticesSIMPLIFIED SYMBOL Blind Hole The tapped hole as it would appear on a drawing

20. Conventional PracticesSIMPLIFIED SYMBOL Blind Hole A BLIND TAPPED HOLE AS IT WOULD APPEAR ON A DRAWING IF TAPPED TO THE BOTTOM OF THE HOLE

21. Can You Identify The Following Conventions Within The Sectional View? • Major diameter • Thread Axis • Minor diameter • Thread depth

22. Can You Identify The Following Conventions Within The Elevation View? • Tapped hole • Major diameter • Thread depth • 30 degrees

23. Annotations For Unified Thread Major diameter of threads Number of threads per inch Unified National Coarse Class ofFit Internal thread

24. Example Of A Screw Thread Table

25. Annotation For Metric Threads Metric thread Major diameter Separation Thread pitch M10 X 1.25

26. Example Of A Metric Screw Thread Table

27. Left Hand Threads Advances Counterclockwise Right Hand Threads Advances Clockwise

28. Other Types Of Threaded Fasteners • Bolt & Nut • Cap Screws • Machine Screws • Set Screws • Wood Screws

29. CAPSCREWS • Used to fasten parts together. • Have a naturally bright finish to match the machined part. • Chamfer to the depth of the first thread

30. Cap Screw Types (a) Round, (b) Pan, (c) Oval, (d) Hex, (e) Socket, (f) Flat, and (g) Phillips

31. Standard Dimensions Used In Drawing The Cap Screw D = Diameter of the shaft.

32. Cap Screws & Bolts • What is the difference between a cap screw and a bolt? • Cap screws fasten into a threaded blind hole. • Bolts are usually accompany by a Nut to fasten parts together.

33. Hex Socket Cap Screw IsBEST used with a counterbored hole

34. Flat Head CapScrew Countersinking is the BEST type of machined hole to accept a FLAT HEAD cap screw.

35. Set Screws • There are generally two types: square-head and headless. • Because of safety issues the headless setscrew would be best for rotating parts.

36. Set Screw Used to hold the collar to the shaft This type of set screw would be a safety issue if the assembly had a rotating motion.

37. Fasteners For Wood • Wood Screws – create their own thread when you drive them into soft woods such as pine and spruce. • Cone shaped shafts for easy entry into the wood. • Hard woods, such as maple or oak, may require drilling a pilot hole. • Wood screws have flat, round, or oval heads with slotted or Phillips head configurations.

38. Wood Screw Head Types (a) Round, (b) Flat, (c) Oval, (d) Phillips

39. Non-Threaded Fasteners • Keys & Keyways • Rivets • Cotter Pins

40. Are used to prevent relative movement between, wheels, pulleys, gears, cranks, and similar parts to a shaft. Keys

41. Identification

42. Square Key – Design is used for heavy-duty functions. Sometimes referred to as a flat key.

43. Gib Head Key – It is exactly the same as the square key except that it has a gib head, which provides for easy removal.

44. Pratt & Whitney Key – is rectangle in shape with semi-cylindrical ends.

45. Woodruff Key – is semicircular in shape and is often used in machine-tool work. The bottom of the key fits into a semicircular key slot cut with a Woodruff cutter and the top into a rectangular slot.

46. Stock Key Size Based On The Diameter Shaft

47. Use pins when the need for disassembly of parts by hand or tools. Use where appearance is not critical (pins need to protrude). Types of Pins Clevis pin Straight pin Taper pin Cotter pin

48. Rivets • Rivets – are regarded as permanent fasteners. • Generally used to hold sheet metal or rolled steel shapes together. • The shaft of the rivet is inserted into the aligned holes of the matting parts and then formed to create a head on the opposite end of the shaft, establishing a permanent assembly.