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Copyright © 2021 Quality Machine Tools, LLC
PM-1340GT v8 2021-04
FEEDSHAFT CLUTCH
The clutch shown in Figure 3-12 disengages the pow-
er feed if the carriage or cross slide hits an obstruction
when power feeding, thus minimizing the potential for
damage. This could be the result of either an accidental
event, or deliberately stopping the carriage at a precise
location set by a micrometer stop fixture, if installed, Fig
-
ure 3-13.
The clutch comprises a pair of spring loaded steel balls
bearing on a detent disc driven by the carriage feed gear-
box. Spring pressure is adjusted by two set screws on
either side of the feed shaft, arrowed (1) in Figure 3-12.
Setting the spring pressure is a process of aiming for the
best compromise between too high — damaging feed
pressure — and too low, which might mean unexpected
stopping for no good reason. Setting the clutch to work
reliably with a micrometer carriage stop is a good exam
-
ple of such a compromise: start with low spring force,
then work up in small increments until the carriage stops
in the same location (say ± 0.002”, assuming a constant
depth of cut and feed rate).
ENGAGING THE POWER FEED
Power feed controls are located on the apron, Figure
3-11. The split-nut lever engages the
leadscrew
, typ-
ically used only for thread cutting (rotary knob on the
gearbox clockwise), described later.
The power feed lever is active only when the keyed
feed shaft
is rotating (rotary knob on the gear box coun
-
terclockwise). In its neutral (detent) position the lever
pinion is captive, a safety measure to avoid accidental
engagement of the power feed unless the lever is first
shifted to the left or right.
Figure 3-11
Power feed levers on the apron
Carriage feed
("Longi") — lever
right & up
Cross slide feed
— lever
left & down
To engage either power feed move the power feed lever
gently
, feeling for the gears to mesh as you go. If the
gears don’t engage at the first try, use the appropriate
handwheel to jiggle the carriage or cross slide, whichev-
er one you wish to move under power.
Figure 3-9
Carriage and cross slide lock screws
Figure 3-10
Compound lock screw
