Figure 6-11.--Quick-change gear box.
shifting appropriate levers or knobs. An index plate or
QUICK-CHANGE GEAR MECHANISM
chart mounted on the gear box indicates the position for
placing the levers to get the necessary gear ratio to cut
To do away with the inconvenience and loss of time
the thread or produce the feed desired.
involved in removing and replacing change gears, most
modern lathes have a self-contained change gear
mechanism, commonly called the quick-change gear
box, showing the arrangement of gears. Splined shaft
box. There are a number of types used on different
F turns with gear G, which is driven by the spindle
lathes but they are all similar in principle.
through the main gear train on the end of the lathe.
Shaft F in turn drives shaft H through tumbler gear T,
The mechanism consists of a cone-shaped group of
which can be engaged with any one of the cluster of
change gears. You can instantly connect any single gear
eight different size gears on shaft H by means of lever
to the gear train by moving a sliding tumbler gear
C. Shaft H drives shaft J through a double clutch gear,
controlled by a lever. The cone of gears is keyed to a
which takes the drive through one of three gears,
shaft that drives the lead screw (or feed rod) directly or
depending on the position of lever B (right, center, or
through an intermediate shaft. Each gear in the cluster
left). Shaft J drives the lead screw through gear L.
has a different number of teeth and hence produces a
different gear ratio when connected in the tram. The
Either the lead screw or the feed rod can be
same thing happens as when the screw gear in the gear
connected to the final drive shaft of the gear box by
train is changed, described previously. Sliding gears
engaging appropriate gears.
also produce other changes in the gear tram to increase
Twenty-four different gear ratios are provided by
the number of different ratios you can get with the cone
of change gears just described. All changes are made by