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Copyright © 2021 Quality Machine Tools, LLC
PM-1340GT v8 2021-04
Figure 3-13
Micrometer carriage stop
Figure 3-12
Feedshaft clutch
Pressure adjusting screws are arrowed (1). Arrow (2) is the
leadscrew shear pin, brass or similar soft material.
COMPOUND SETUP FOR THREAD CUTTING
Threa
d cutting on the lathe is unlike most other turning
operations, for two reasons: 1. The cutting tool must be
precisely ground with an included angle of 60 degrees
for most American and Metric threads, and; 2. It is pref
-
erable to feed the tool into the workpiece at an angle
so it cuts mostly on the left flank of the thread. The cor
-
rect angle relative to the cross slide (zero degrees) is a
subject of debate — should it be 29, 29-1/2 or 30 de
-
grees? Many machinists use 30 degrees, others prefer
29 degrees, because it holds the cutting tool marginally
clear of the right flank of the thread — close enough for
cleanup of the flank, while at the same time avoiding
appreciable rubbing.
Figure 3-14
Compound set for 30
o
infeed
For 29 degrees estimate an additional 1 degree clockwise be-
yond the engraved scale.
