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Turning 3 NM27. Screw Threads  There are 4 basic Thread Forms  Vee Threads  Buttress  Square  Trapezoidal.

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Presentation on theme: "Turning 3 NM27. Screw Threads  There are 4 basic Thread Forms  Vee Threads  Buttress  Square  Trapezoidal."— Presentation transcript:

1 Turning 3 NM27

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? 21

12 Screwcutting 3 2

13 Screwcutting 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 – x P + 3 x W

21 Screwcutting  External Threads

22 Screwcutting  Full Form Carbide Insert

23 Screwcutting  Internal Thread

24 Screwcutting  Tracking Ratio  Tracking Ratio =  Usually expressed as the lowest whole number ratio  Eg. =1 = Magic # Lead of Work Lead of Lead Screw 1236 (The Magic # is used to determine the Starwheel or Chaser Dial details)

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

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


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