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G4002/3 Gear Head Lathes
Half Nut Lever - This lever compresses and
releases the half nut that engages the leadscrew.
See Figure 16. The lever is only engaged while
turning threads in stock. A lockout device fea-
tured in the lever mechanism engages when the
feed selector is used.
Threading Dial Indicator - The indicator tells
you when to engage the half nut to begin the
threading process. See Figure 16.
The Threading Dial Indicator has 8 lines and four
numbers printed on the dial. An indicator mark is
positioned near the rim of the dial. The dial is
mounted on a shaft that has a worm gear mount-
ed at its opposite end.
Figure 16. Threading dial and half nut lever.
NOTICE
Do not simultaneously engage the feed lever
and the threading lever. Doing so will damage
the lathe.
NOTICE
The threading dial cannot be used when cut-
ting metric threads. Once the half nut has been
engaged, it must remain engaged throughout
the threading process.
16b. Dial indicator chart.
Lever
Dial
These rest in a housing that pivots so that the
gear can be engaged or disengaged. An Allen
®
head cap screw is located on the side of the
housing. Loosen this screw to change the posi-
tioning of this housing.
When engaged, the dial will turn when the spin-
dle is turning. If the dial does not turn, readjust
the housing.
When the half nut is engaged the dial stops turn-
ing. By carefully engaging the half nut as the
appropriate line or number passes by the indica-
tor mark, a thread can be established and the
lead maintained through the multiple passes that
are required to cut a thread to the finished depth.
The chart listed in Figure 16b shows a system
for using the threading dial indicator while cutting
inch threads.
Example:
To cut 11 threads per inch engage the half nut
when the 1 or the 3 is on the indicator mark.
Determine the length of the thread to be cut.
Make a cut along the part and disengage the half
nut. Return the carriage to the beginning of the
cut. Watch the dial and when the 1 or the 3
comes around to the indicator mark engage the
half nut. Repeat this process until the desired
depth of cut has been achieved.