4
PM-236 v4 -207.indd
Figure 3-
Carriage feed gearbox
CARRIAGE FEED GEARBOX
The rate of power feed relative to spindle speed is set
by the four shifter knobs below the main control panel,
Figure 3-.
The
S-M
knob at right determines which is the driven
shaft, leadscrew (M) or carriage feed (S).
Unliike speed and feed direction changing at the main
control panel, there is no need to stop the motor while
selecting a different carriage feed. The same applies to
switching between M and S.
In the table on the following page, Figure 3-3, the ex-
ternal "change gears" are 24T and 48T, Figure 3-2 (24T
is the output from the headstock, 48T the input to the
carriage feed gearbox). This is a frequently used setup
for these two reasons:
Figure 3-9
Cross slide and compound dials
TAILSTOCK
The tailstock leadscrew is 0 TPI, with a travel of 4
inches. Like the compound, the tailstock has two gradu-
ated collars, one reading 0.00”/division, the other 0.02
mm/division. To remove tooling from the tailstock taper
(MT3) turn the handwheel counter-clockwise (handle
end view) until resistance is felt, then turn the handle a
little more to eject the tool. Conversely, to install a taper
tool make certain that the quill is out far enough to allow
firm seating.
For taper turning the tailstock may be offset by adjusting
the set screws on either side, arrowed in Figure 3-0.
To move the tailstock to the rear, for instance, the screw
on the lever side would be unscrewed, then the oppos-
ing set screw would be screwed in to move the upper
assembly.
Figure 3-0
Tailstock
A visual indication of the offset is provided by the scale,
but this is not a reliable measure for precise work. In
practice, the only way to determine the offset precisely
is to "cut and try' on the workpiece, homing in on the cor-
rect degree of offset in small increments.
The same issues arise when re-establishing "true zero"
of the tailstock, in other words returning it to the normal
axis for routine operations. One way to avoid cut-and-try
is to prepare in advance a bar of (say) " diameter qual-
ity ground stock, with
precise center drillings
at both
ends (do this by indicating for zero TIR in a 4-jaw chuck,
not in a 3-jaw unless known to be equally accurate). The
prepared bar can then be installed between centers and
indicated along its length.
