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

Screw ThreadsScrew Threads

Screw CuttingScrew Cutting


There are 4 basic Thread FormsThere are 4 basic Thread Forms

Vee ThreadsVee Threads ButtressButtress SquareSquare TrapezoidalTrapezoidal


Vee ThreadVee Thread


Buttress ThreadButtress Thread


Square ThreadSquare Thread


Trapezoidal Thread (30Trapezoidal Thread (30° Angle)° Angle)


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



LeadLead

Pitch x Number of StartsPitch x Number of Starts



StartsStarts

Grooves running side by side Grooves running side by side on the same cylinderon the same cylinder


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

ScrewcuttingScrewcutting

How many Starts?How many Starts?

21



32



3 4


Job 1Job 1


Alternative to Angling Compound SlideAlternative to Angling Compound Slide

Compound Slide moves = ½ Cross Slide Movement


Methods of Testing ThreadsMethods of Testing Threads

Test NutTest Nut



Go – No Go Thread Caliper GaugeGo – No Go Thread Caliper Gauge



Three Wire MethodThree Wire Method


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)


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


External ThreadsExternal Threads


Full Form Carbide InsertFull Form Carbide Insert


Internal ThreadInternal Thread


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)


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


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.


Methods of Tracking the ThreadMethods of Tracking the Thread

StarwheelStarwheel Chaser DialChaser Dial Reversing the MachineReversing the Machine Repeat Distance MethodRepeat Distance Method


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


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


Chaser Dial DetailsChaser Dial Details


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


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


ThreadsThreads

Metric Threads Metric Threads available by direct available by direct selectionselection


Change Gears - Simple Gear TrainChange Gears - Simple Gear Train

StandardStandard

LeadsLeads


ThreadsThreads• To produce an M40x4 select:To produce an M40x4 select:

• Range II, Lever Position C6Range II, Lever Position C6


ThreadsThreads• To produce an M24x3 select:To produce an M24x3 select:

• Range I, Lever Position A1Range I, Lever Position A1


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


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


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


Compound Gear TrainCompound Gear Train


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


ThreadsThreads• To cut a 2.5 mm Lead:To cut a 2.5 mm Lead:

• FormulaFormulaD 30 x 2.5

F 60 x 3


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


Change Gears - Simple Gear TrainChange Gears - Simple Gear Train

Change Change

the 30zthe 30z

for a 25zfor a 25z

25

60


ThreadsThreads

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

Documents

leadscrew slide

angle slide

lathe slide

cross slide movement

cylinder slide

thread groove slide

screwcutting external

screw threads screw