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Screw Threads

Screw Threads. Screw Cutting. Screw Threads. There are 4 basic Thread Forms Vee Threads Buttress Square Trapezoidal. Screw Threads. Vee Thread. Screw Threads. Buttress Thread. Screw Threads. Square Thread. Screw Threads. Trapezoidal Thread (30 ° Angle). Screw Threads.

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Screw Threads

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  1. Screw Threads Screw Cutting

  2. Screw Threads • There are 4 basic Thread Forms • Vee Threads • Buttress • Square • Trapezoidal

  3. Screw Threads • Vee Thread

  4. Screw Threads • Buttress Thread

  5. Screw Threads • Square Thread

  6. Screw Threads • Trapezoidal Thread (30° Angle)

  7. Screw Threads • Thread Terminology • Pitch • Distance from a point on one Thread Groove to the exact same point on the next Thread Groove

  8. Screw Threads • Thread Terminology • Lead • Pitch x Number of Starts

  9. Screw Threads • Thread Terminology • Starts • Grooves running side by side on the same cylinder

  10. Screw Threads • Lead = 12 Lead = 12 Lead = 6 • Pitch = 3 Pitch = 6 Pitch = 6 • Starts = 4 Starts = 2 Starts = 1

  11. Screwcutting • How many Starts? 1 2

  12. Screwcutting • How many Starts? 2 3

  13. Screwcutting • How many Starts? 3 4

  14. Screwcutting • Job 1

  15. Screwcutting • Alternative to Angling Compound Slide Compound Slide moves = ½ Cross Slide Movement

  16. Screwcutting • Methods of Testing Threads • Test Nut

  17. Screwcutting • Methods of Testing Threads • Go – No Go Thread Caliper Gauge

  18. Screwcutting • Methods of Testing Threads • Three Wire Method

  19. Screwcutting • Three Wire Method requires calculating: Best Wire Size = P 2 x Cos 30º (ie.½ included angle)

  20. Screwcutting • Three Wire Method requires calculating: Measurement Over Wires = M = D – 1.5155 x P + 3 x W

  21. Screwcutting • External Threads

  22. Screwcutting • Full Form Carbide Insert

  23. Screwcutting • Internal Thread

  24. Lead of Work Lead of Lead Screw 1 2 3 6 Screwcutting • Tracking Ratio • Tracking Ratio = • Usually expressed as the lowest whole number ratio • Eg. = 1 = Magic # • (The Magic # is used to determine the • Starwheel or Chaser Dial details)

  25. Lead of Work Lead of Lead Screw 1.25 6 5 24 Screwcutting • Tracking Ratio • Tracking Ratio = • Usually expressed as the lowest whole number ratio • Eg. = 5 = Magic #

  26. Screwcutting • Tracking the Thread • Tracking the Thread means to engage into the same Thread groove on successive pass of the tool.

  27. Screwcutting Methods of Tracking the Thread • Starwheel • Chaser Dial • Reversing the Machine • Repeat Distance Method

  28. Screwcutting Starwheel • A thin gear like disc with teeth cut of a size to engage with the Leadscrew of the Lathe

  29. Screwcutting Chaser Dial • Sometimes used in conjunction with a Starwheel to assist correct engagement of the Leadscrew

  30. Screwcutting Chaser Dial Details

  31. Screwcutting Reversing the Machine • Reversing the Spindle is useful where a Thread with an unusual Lead needs to be produced • Usually achieved by reversing the direction of the Lathe spindle without disengaging any of the drive gears

  32. Screwcutting Repeat Distance Method • Repeat Distance is calculated by multiplying the Tracking Ratio by the Lead of the Leadscrew

  33. Screwcutting Threads • Metric Threads available by direct selection

  34. Screwcutting • Change Gears - Simple Gear Train • Standard Leads

  35. Screwcutting Threads • To produce an M40x4 select: • Range II, Lever Position C6

  36. Screwcutting Threads • To produce an M24x3 select: • Range I, Lever Position A1

  37. Screwcutting Threads • Sometimes Threads are NOT available by direct selection, eg. 2.5 mm Lead

  38. Screwcutting Threads • As 2.5 mm is not on the Chart of available Leads we must improvise

  39. D D1 x D2 F F1 x F2 Screwcutting Threads • We can cut Leads not normally available on the chart by using: • Formula

  40. Screwcutting • Compound Gear Train

  41. D Dn x R F Fn x S Screwcutting Threads • We can cut Leads not normally available on the chart by using: • Formula

  42. D 30 x 2.5 F 60 x 3 Screwcutting Threads • To cut a 2.5 mm Lead: • Formula

  43. Screwcutting Threads • To cut a 2.5 mm Lead: • Formula D 30 x 2.5 F 60 x 3 1 x 2.5 2 x 3 2.5 25 6 60

  44. Screwcutting • Change Gears - Simple Gear Train • Change the 30z for a 25z 25 60

  45. Screwcutting Threads

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