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Screw Threads Screw Cutting. Screw Threads  There are 4 basic Thread Forms  Vee Threads  Buttress  Square  Trapezoidal.

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

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? 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

34 Screwcutting  Change Gears - Simple Gear Train  Standard Leads

35 Screwcutting Threads To produce an M40x4 select:To produce an M40x4 select: Range II, Lever Position C6Range II, Lever Position C6

36 Screwcutting Threads To produce an M24x3 select:To produce an M24x3 select: Range I, Lever Position A1Range I, Lever Position A1

37 Screwcutting Threads Sometimes Threads are NOT available by direct selection, eg. 2.5 mm LeadSometimes 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 improviseAs 2.5 mm is not on the Chart of available Leads we must improvise

39 Screwcutting Threads We can cut Leads not normally available on the chart by using:We can cut Leads not normally available on the chart by using: FormulaFormula D D 1 x D 2 F F 1 x F 2

40 Screwcutting  Compound Gear Train

41 Screwcutting Threads We can cut Leads not normally available on the chart by using:We can cut Leads not normally available on the chart by using: FormulaFormula D D n x R F F n x S

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

43 Screwcutting Threads To cut a 2.5 mm Lead:To cut a 2.5 mm Lead: FormulaFormula D 30 x 2.5 F 60 x 3 1 x x

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

45 Screwcutting Threads


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