Screwcutting in the Lathe
by Martin Cleeve

Softcover
150 x 210mm
173pp

Published by Special Interest Model Books Ltd, Dorset England

R.R.P.$19.90

ISBN 978-0-85242-838-2

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Extract from back cover of book:

One of the most useful functions of a modern lathe is its ability to cut any form of external or internal thread of any thread form, pitch or diameter within the overall capacity of the machine. Detailed information of a practical nature is, however, not easy to find - a situation that this book will do much to rectify.

About the Author - Martin Cleeve is a very experienced engineer with the capability of converting factual analyses into easily understood forms. His own expertise and the standards to which he works are evident in his writing, and in addition, he is also quite at home with both imperial and metric measures having considerable experience in the conversions required when working in partially metricated areas. This book is not only an invaluable treatise on lathe screwcutting but is also a useful demonstration of working in both imperial and metric standards.

Photos: Black & White

Units of Measurement: Imperial and Metric

Contents

Acknowledgement

SECTION 1 - INTRODUCTION
- Introductory notes
- Conversion notes
- Quick reference thread sizing formulas

SECTION 2 - PRINCIPLES OF LATHE SCREWCUTTING
- 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
- 50-127 translation ratio explained
- Basic conversion formulae
- 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
- 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 -
- 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
- 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)
- Pick- up 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
- 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
- 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 - PRACTICALTHREAD SIZING MEASUREMENT
- Definitions of screw thread terms
- The 3-Wire method of thread checking
- Wire diameters and thread depth
- Three wire formulae for 55 deg. screws
- Checking Whit. thread by metric measure
- One-wire checking
- Pitch diameter calculations
- Acme thread checking
- Summary of formulae for 1-wire checking
- Helix angle of screw threads
- Formula
- Gauging nut threads
- Thread classes
- Threads designated by class.

APPENDIX 1 - LIST OF TABLES