Table of Contents
Acknowledgment 8
Section 1 Introduction 9
Introductory notes
Conversion notes
Quick reference thread sizing formulas
Section 2 Principles of Lathe Screwcutting 16
Altering the pitch
Calculations
Simple and compound gear trains
Schematic gear train presentation
Calculations for mixed number TPI
Equal ratio setting
Threads designated by lead
Proving gear trains
Self-act feeds from leadscrews
Diametral pitch worms
Formula for worms by DP
The DP formula
How evolved
Proving worm thread gearing.
Section 3 Gearing an English Leadscrew for Metric Threads 40
50-127 translation ratio explained
Basic conversion formula
Checking metric gear trains
Modified gearing systems for metric pitches with an English leadscrew
Reduced pitch translators
Alternative translation gearing
The 2-21 (63-160) method
Checking the 2-21 gearing
13-33 translation gearing and 15-38
Worms sized by module
Gearing an English leadscrew, practical examples.
Section 4 Lathes With Metric Leadscrews 58
Probable standard pitches for metric leadscrews
Screwcutting calculations
Gearing for English threads with a metric leadscrew
Disadvantages of 127-50 step up
Disadvantages overcome by alternative translation ratios
Very small pitch errors
Proving metric
English gear trains
Finding exact pitch given
Quick checking for nominal pitch
Worms for gears sized by module: gearing with metric leadscrew
Worms sized by DP: gearing with metric leadscrew
Change gear calculations by approximation.
Section 5 Problems and Analysis of Repeat Pick-Up 71
Meaning of pick-up
Examples
The thread dial indicator or leadscrew indicator
Action of English indicator
Metric threads: pick-up
Geared leadscrew indicators
Special application of leadscrew indicator: How to pick-up for short metric threads being cut from an English leadscrew
Leadscrew indicator for metric leadscrews
Pick-up when gearing is approximate
Repeat pick-up from chalk marks
Repeat pick-up: electrical indication
Pick-up with dog-clutch control
Advantages and theory
A little-known method for obtaining even faster screwcutting with dog-clutch control
Calculating metric pick-up.
Section 6 Multiple-Start Threads 100
Automatic start indexing (by dog-clutch control)
Designation of multiple start threads
Feasibility test (to ascertain whether or not any given leadscrew is suitable for indexing a required number of starts automatically)
Pickup for automatic multiple start indexing
Metric multiple start threads from an English leadscrew
Automatic start indexing possibilities by dog-clutch control explained
Automatic start indexing of metric multiple-start threads from metric leadscrews
Special leadscrews for auto-start indexing
Special leadscrew design formula: For metric working, for English working
Example of lathe with dog-clutch control to the leadscrew drive.
Section 7 Single Point Lathe Threading Tools 117
Various single point threading tools discussed
High speed steel
Stellite
Blackalloy
Tungsten Carbide
Carbon steel
Cutting angles
Internal threading tools
Inserted bit tools
Internal thread tool bit fitted by brazing, a tested design
Thread tool sharpening and grinding
A simple jig for the production of accurate angles and a new design retractable, adjustable height, swing-clear, general purpose and threading toolholder
The thread tool grinding jig described
Sharpening external and internal threading tools of various types: solid-with-shank and inserted bit.
Section 8 Practical Aspects of Lathe Screwcutting 136
Four ways of depthing a screw thread
Five ways of depthing a nut thread
Square thread cutting
Acme thread cutting
Nut threads: notes on bore sizing
The percentage approach to bore sizing for nuts
Tap finishing
Special tap making
Multiple-start threads
How cut in lathe without dog-clutch control
Multiple-start nut threading
How cut in lathe without dog-clutch control
Multiple start thread indexing by use of leadscrew indicator
Multiple-start worm thread notes
General observations: Thread crest radii
Taper threads
Improvised cutting method
Screwcutting speeds
Lubrication
Effect of coolant on light cuts
Screwcutting troubles, possible causes.
Section 9 Practical Thread Sizing Measurement 159
Definitions of screw thread terms
The 3-Wire method of thread checking
Wire diameters and thread depth
Three wire formula for 55 deg. screws
Checking Whit, thread by metric measure
One-wire checking
Pitch diameter calculations
Acme thread checking
Summary of formula for 1-wire checking
Helix angle of screw threads
Formula
Gauging nut threads
Thread classes
Threads designated by class.
Appendix 1 List of Tables 173
