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PM-1440BV v3 2020-10
Copyright © 2020 Quality Machine Tools, LLC
Figure 3-13
Threading dial
CROSS SLIDE & COMPOUND
The cross slide and compound have 10 TPI leadscrews, with
100-division graduated collars, Figure 3-14. Each division rep-
resents a “true” motion of 0.001”. On the cross slide dial, only,
this shows as 0.002” per division, meaning that a 0.001” depth
of cut reduces the diameter of the workpiece by 0.002”.
The collars also have 127-division metric graduations, display-
ing "true metric" motion of 0.02 mm per division on the com-
pound, 0.04 mm on the cross slide.
Figure 3-14
Cross slide and compound dials
TAILSTOCK
The tailstock leadscrew has a 10 TPI thread, with 4 inch travel.
Inch and metric graduated collars on the tailstock handwheel
read 0.001” and 0.02 mm per division. A transverse slot at the
narrow end of the internal taper (MT4) provides clearance for
drills and other devices with tang ends. To remove tooling from
the tailstock taper turn the handwheel counter-clockwise (han
-
dle 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 set
screws on either side, Figure 3-15. To move the tailstock to
the back, for instance, the screw on the lever side would be
unscrewed, then the opposing set screw would be screwed in
to move the upper assembly. A clamp screw holds the tailstock
firmly against a transverse rib in the base casting. Loosen it if
necessary to allow offsetting.
A visual indication of the offset is provided by a scale on the
back surface, 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, or scrap stock, homing in
on the correct 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 rou-
tine operations. One way to avoid cut-and-try is to prepare in
advance a bar of (say) 1" diameter quality 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
predictably accurate). The prepared bar can then be installed
between centers and indicated along its length.
Figure 3-15
Tailstock
LOCKING THE SLIDES
When face-cutting large diameter surfaces, for instance, it is
often desirable to lock the saddle. Less frequently it can be
helpful to lock, or at least stiffen, sliding motion of the com
-
pound, Figure 3-16.
If a DRO system is installed, the Y axis scale blocks access to
the cross slide lock screw.
