LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
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.
(d) A selective feed lever or knob
is
provided
for
engaging
the
longitudinal feed or crossfeed as desired.
(e) Half-nuts are used to engage and disengage the lead screw when the
lathe is used to cut threads. They are opened or closed by a lever that is
located on the right side of the apron. The half-nuts fit the thread of the
lead screw which turns then 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.)
(f) The manufacturers of lathe aprons differ somewhat in their
construction and in the location of the controlling levers and knobs.
However, they are all designed to perform the same function. The principal
difference is in 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 crossfeed. In others, both feeds
are driven from the same driving gear on the feed rod through a common
clutch; they have a selective lever for connecting the drive to either the
longitudinal feed or the crossfeed.
(7) Feed Rod.
(a) The feed rod transmits power to the apron to drive the longitudinal
feed and crossfeed mechanisms.
The feed rod is driven by the spindle
through a train of gears, and the ratio of its speed to that of the spindle
can be varied by
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