Workshop Practice Series 03 Screwcutting in the Lathe

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Workshop Practice Series 03 Screwcutting in the Lathe

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CONTENTS

Acknowledgment
SECTION 1
SECTION 2
INTRODUCTION
Introductory notes – Conversion notes – Quick
reference thread sizing formulas
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 lead screws- Diametral pitch worms – Formula
for worms by DP – The DP formula- how evolved- Proving
worm thread gearing.
GEARING AN ENGLISH LEADSCREW FOR METRIC
THREADS
50- 12 7 translation ratio explained- Basic conversion
formulae – Checking metric gear t rains- Modified gearing
systems for metric pitches with an English leadscrewReduced
pitch translators- Alternative translation gearing The
2-21 (63- 160) method – Checking the 2-21 gearing__:_
1 3-33 translation gearing and 15-38-Worms sized by module
– Gearing an English leadscrew, practical examples.
SECTION 4 LATHES WITH METRIC LEADSCREWS 58 SECTION 7 SINGLE POINT LATHE THREADING TOOLS 117
Probable standard pitches for metric leadscrews – Various single point threading tools discussed – High speed
Screwcutting calculations – Gearing for English threads with steel – Stellite – Blackalloy-Tungsten Carbide- Carbon
a metric leadscrew – Disadvantages of 127-50 step up – steel – Cutting angles- Internal threading tools – Inserted
Disadvantages overcome by alternative transl~tion ratios. bit tools – Internal thread tool bit fitted by brazing, a tested
Very small pitch errors- Proving metric – Engltsh gear trams design- Thread tool sharpening and grinding – A simple jig
– Finding exact pitch given – Quick checking f~r non:inal for the production of accurate angles and a new design
pitch-Worms for gears sized by module: ge~n n g ‘:””th . retractable, adjustable height, swing-clear, general purpose
metric leadscrew – Worms sized by DP: geanng w1th metnc and threading tool holder – The thread tool grinding jig
leadscrew- Change gear calculations by approximation. described- Sharpening external and internal threading tools
of various types: solid-with-shank and inserted bit.
SECTION 5 PROBLEMS AND ANALYSIS OF REPEAT PICK-UP
Meaning of pick-up – Examples – The thre~d dial indi ca~or or SECTION 8 PRACTICAL ASPECTS OF LATHE SCREWCUTTING 136
lead screw indicator – Action of English indtcator- Metnc Four ways of depthing a screw thread – Five ways of
threads: pick-up – Geared leadscrew indicators – Special depthing a nut thread- Square thread cutting- Acme
application of leadscrew indicator: How to pick-up for short thread cutting – Nut threads: notes on bore sizing – The
metric threads being cut from an English leadscrew – percentage approach to bore sizing for nuts-Tap finishing –
Leadscrew indicator for metric leadscrews- Pick-up when Special tap making – Multiple-start threads – How cut in
gearing is approximate- Repeat pick-up from ch_alk marks – lathe without dog- clutch control – Multiple-start nut
Repeat pick-up: electrical indication – Pick-up wtth dog- threading – How cut in lathe without dog-clutch control –
clutch control – Advantages and theory – A little-known Multiple start thread indexing by use of leadscrew indicator
method for obtaining even faster screwcutting with dog- – Multiple-start worm thread notes – General observations:
clutch control – Calculating metric pick-up. Thread crest radii – Taper threads – Improvised cutting
method – Screwcutting speeds – Lubrication – Effect of
SECTION 6 MULTIPLE-START THREADS coolant on light cuts- Screwcutting troubles, possible
Automatic start indexing (by dog-clutch control) – causes.
Designation of multiple start threads – Feasibility test (to
ascertain whether or not any given leadscrew is suitable for SECTIION 9 PRACTICAL THREAD SIZING MEASUREMENT 159
indexing a required number of starts automatically) – Pick- Definitions of screw thread terms – The 3-Wire method of
up for automatic multiple start indexing- Metric m~lti ple thread checking – Wire diameters and thread depth – Three
start threads from an English leadscrew – Automattc start wire formulae for 55 deg. screws – Checking Whit. thread by
indexing possibilities by dog-clutch control explained – metric measure – One-wire checking – Pitch diameter
Automatic start indexing of metric multiple-start threads calculations – Acme thread checking – Summary of
from metric leadscrews- Specialleadscrews for auto-start formulae for 1-wire checking- Helix angle of screw threads
indexing- Specialleadscrew design formula: For r:netric – Formula- Gauging nut threads – Thread classes – Threads
working, for English working- Example of lathe w1th dog- designated by class.
clutch control to the leadscrew drive.