Screw Threads Screw Cutting. Screw Threads There are 4 basic Thread Forms Vee Threads Buttress Square Trapezoidal.
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Screw ThreadsScrew Threads
Screw CuttingScrew Cutting
Screw ThreadsScrew Threads
There are 4 basic Thread FormsThere are 4 basic Thread Forms
Vee ThreadsVee Threads ButtressButtress SquareSquare TrapezoidalTrapezoidal
Screw ThreadsScrew Threads
Vee ThreadVee Thread
Screw ThreadsScrew Threads
Buttress ThreadButtress Thread
Screw ThreadsScrew Threads
Square ThreadSquare Thread
Screw ThreadsScrew Threads
Trapezoidal Thread (30Trapezoidal Thread (30° Angle)° Angle)
Screw ThreadsScrew Threads
Thread TerminologyThread Terminology
PitchPitchDistance from a point on one Distance from a point on one
Thread Groove to the exact Thread Groove to the exact same point on the next Thread same point on the next Thread GrooveGroove
Screw ThreadsScrew Threads
Thread TerminologyThread Terminology
LeadLead
Pitch x Number of StartsPitch x Number of Starts
Screw ThreadsScrew Threads
Thread TerminologyThread Terminology
StartsStarts
Grooves running side by side Grooves running side by side on the same cylinderon the same cylinder
Screw ThreadsScrew Threads
Lead = 12 Lead = 12 Lead = 6Lead = 12 Lead = 12 Lead = 6 Pitch = 3 Pitch = 6 Pitch = 6Pitch = 3 Pitch = 6 Pitch = 6 Starts = 4 Starts = 2 Starts = 1Starts = 4 Starts = 2 Starts = 1
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How many Starts?How many Starts?
21
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How many Starts?How many Starts?
32
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How many Starts?How many Starts?
3 4
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Job 1Job 1
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Alternative to Angling Compound SlideAlternative to Angling Compound Slide
Compound Slide moves = ½ Cross Slide Movement
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Methods of Testing ThreadsMethods of Testing Threads
Test NutTest Nut
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Methods of Testing ThreadsMethods of Testing Threads
Go – No Go Thread Caliper GaugeGo – No Go Thread Caliper Gauge
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Methods of Testing ThreadsMethods of Testing Threads
Three Wire MethodThree Wire Method
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Three Wire Method requires Three Wire Method requires calculating:calculating:
Best Wire Size = Best Wire Size = P
2 x Cos 30º
(ie. ½ included angle)
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Three Wire Method requires Three Wire Method requires calculating:calculating:
Measurement Over Wires = Measurement Over Wires =
M = D – 1.5155 x P + 3 x W
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External ThreadsExternal Threads
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Full Form Carbide InsertFull Form Carbide Insert
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Internal ThreadInternal Thread
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Tracking RatioTracking Ratio
Tracking Ratio =Tracking Ratio =
Usually expressed as the lowest whole Usually expressed as the lowest whole number rationumber ratio
Eg. Eg. == 1 = Magic #1 = Magic #
Lead of WorkLead of Work
Lead of Lead ScrewLead of Lead Screw
11
22
33
66
(The Magic # is used to (The Magic # is used to determine the determine the
Starwheel or Chaser Starwheel or Chaser Dial details)Dial details)
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Tracking RatioTracking Ratio
Tracking Ratio =Tracking Ratio =
Usually expressed as the lowest Usually expressed as the lowest whole number ratiowhole number ratio
Eg. Eg. == 5 = Magic #5 = Magic #
Lead of WorkLead of Work
Lead of Lead ScrewLead of Lead Screw
1.251.2566
55
2424
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Tracking the ThreadTracking the Thread
Tracking the Thread means to engage Tracking the Thread means to engage into the same Thread groove on into the same Thread groove on successive pass of the tool.successive pass of the tool.
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Methods of Tracking the ThreadMethods of Tracking the Thread
StarwheelStarwheel Chaser DialChaser Dial Reversing the MachineReversing the Machine Repeat Distance MethodRepeat Distance Method
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StarwheelStarwheel
A thin gear like disc with teeth cut of a A thin gear like disc with teeth cut of a size to engage with the Leadscrew of size to engage with the Leadscrew of the Lathethe Lathe
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Chaser DialChaser Dial
Sometimes used in conjunction with a Sometimes used in conjunction with a Starwheel to assist correct engagement Starwheel to assist correct engagement of the Leadscrewof the Leadscrew
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Chaser Dial DetailsChaser Dial Details
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Reversing the MachineReversing the Machine
Reversing the Spindle is useful where a Reversing the Spindle is useful where a Thread with an unusual Lead needs to Thread with an unusual Lead needs to be producedbe produced
Usually achieved by reversing the Usually achieved by reversing the direction of the Lathe spindle without direction of the Lathe spindle without disengaging any of the drive gearsdisengaging any of the drive gears
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Repeat Distance MethodRepeat Distance Method
Repeat Distance is calculated by Repeat Distance is calculated by multiplying the Tracking Ratio by the multiplying the Tracking Ratio by the Lead of the LeadscrewLead of the Leadscrew
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ThreadsThreads
Metric Threads Metric Threads available by direct available by direct selectionselection
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Change Gears - Simple Gear TrainChange Gears - Simple Gear Train
StandardStandard
LeadsLeads
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ThreadsThreads• To produce an M40x4 select:To produce an M40x4 select:
• Range II, Lever Position C6Range II, Lever Position C6
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ThreadsThreads• To produce an M24x3 select:To produce an M24x3 select:
• Range I, Lever Position A1Range I, Lever Position A1
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ThreadsThreads• Sometimes Threads are NOT available Sometimes Threads are NOT available
by direct selection, eg. 2.5 mm Leadby direct selection, eg. 2.5 mm Lead
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ThreadsThreads• As 2.5 mm is not on the Chart of As 2.5 mm is not on the Chart of
available Leads we must improviseavailable Leads we must improvise
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ThreadsThreads• We can cut Leads not normally We can cut Leads not normally
available on the chart by using:available on the chart by using:
• FormulaFormulaD D1 x D2
F F1 x F2
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Compound Gear TrainCompound Gear Train
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ThreadsThreads• We can cut Leads not normally We can cut Leads not normally
available on the chart by using:available on the chart by using:
• FormulaFormulaD Dn x R
F Fn x S
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ThreadsThreads• To cut a 2.5 mm Lead:To cut a 2.5 mm Lead:
• FormulaFormulaD 30 x 2.5
F 60 x 3
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ThreadsThreads• To cut a 2.5 mm Lead:To cut a 2.5 mm Lead:
• FormulaFormulaD 30 x 2.5
F 60 x 3 1 x 2.5
2 x 3 2.5 25
6 60
ScrewcuttingScrewcutting
Change Gears - Simple Gear TrainChange Gears - Simple Gear Train
Change Change
the 30zthe 30z
for a 25zfor a 25z
25
60
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ThreadsThreads
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