Machinery Repairman

slide is securely bolted to the cross-feed nut that
moves back and forth when the cross-feed screw is
turned by the handle. The micrometer dial on the
cross-feed handle is graduated to permit accurate
infeed. Depending on the manufacturer of the lathe,
the dial may be graduated so that each division
represents a 1 to 1 or a 2 to 1 ratio. The compound
rest is mounted on top of the cross-feed slide.
The carriage has T-slots or tapped holes for
clamping work for boring or milling. When the lathe
is used in this manner, the carriage movement feeds
the work to the cutting tool, which is revolved by the
headstock spindle.
You can lock the carriage in any position on the bed
by tightening the carriage clamp screw. Use the clamp
screw only when doing such work as facing or
cutting-off, for which longitudinal feed is not required.
Normally, keep the carriage clamp in the released
position. Always move the carriage by hand to be sure
it is free before you apply the automatic feed.
APRON
The apron is attached to the front of the carriage.
It contains the mechanism that controls the movement
of the carriage for longitudinal feed and thread cutting
and controls the lateral movement of the cross-slide.
You should thoroughly understand the construction
and operation of the apron before you attempt to
operate the lathe.
In general, a lathe apron contains the following
mechanical parts:
A longitudinal feed handwheel for moving the
carriage by hand along the bed. This
handwheel turns a pinion that meshes with a
rack gear secured to the lathe bed.
Gear trains driven by the feed rod. These gear
trains transmit power from the feed rod to
move the carriage along the ways and to move
the cross-slide across the ways, thus providing
powered longitudinal feed and cross-feed.
Friction clutches operated by knobs on the
apron to engage or disengage the power-feed
mechanism. (Some lathes have a separate
clutch for longitudinal feed and cross-feed;
others have a single clutch for both.) (NOTE:
The power feeds are usually driven through a
friction clutch to prevent damage to the gears if
excessive strain is put on the feed mechanism.
If clutches are not provided, there is some form
of safety device that operates to disconnect the
feed rod from its driving mechanism.)
6-7
A selective feed lever or knob for engaging the
longitudinal feed or cross-feed as desired.
Half-nuts that engage and disengage the lead
screw when the lathe is used to cut threads.
They are opened or closed by a lever located on
the right side of the apron. The half-nuts fit the
thread of the lead screw, which turns in them
like a bolt in a nut when they are clamped over
it. The carriage is then moved by the thread of
the lead screw instead of by the gears of the
apron feed mechanisms. (The half-nuts are
engaged only when the lathe is used to cut
threads, at which time the feed mechanism
must be disengaged. An interlocking device
that prevents the half-nuts and the feed
mechanism from engaging at the same time is
usually provided as a safety feature.)
Aprons on lathes made by different manufacturers
differ somewhat in construction and in the location of
controlling levers and knobs. But, they all are designed
to perform the same functions. The principal difference
is in the arrangement of the gear trains for driving the
automatic feeds. For example, in some aprons there are
two separate gear trains with separate operating levers
for longitudinal feed and cross feed. In others, both
feeds are driven from the same driving gear on the feed
rod through a common clutch, with one feed at a time
connected to the drive by a selector lever. The apron
shown in figure 6-9 is of the latter type.
Figure 6-9.—Rear view of a lathe apron.