Loading...03 – Screwcutting In The Lathe
قطع القلاووظ على المخرطة
من سلسلة
Workshop Practices Series
Martin Cleeve
CONTENTS
Acknowledgement 8
SECTION 1 INTRODUCTION
Introductory notes- Conversion notes- Quick
reference thread sizing formulas
9
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.
16
ECTION 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.
40
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.
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.
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 4 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.
117
SECTION 5 71
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 threadnotes-Generalobservations:
Thread crest radii- Taper threads- Improvised cutting
method- Screwcutting speeds- Lubrication- Effect of
coolant on light cuts- Screwcutting troubles, possible
causes.
136
SECTION 6 100
SECTION 9 PRACTICAL THREAD 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.
159
APPENDIX 1 LISTOFTABLES 173
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