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G9729 Combination Lathe/Mill
Cutting Threads
1. Set the compound rest to the appropriate
angle for the given thread you want to cut.
For a Unified National Series thread, this is
29º off of vertical to spindle axis.
2. Set the tool tip perpendicular to the
workpiece
and center it vertically.
3. Make
sure the thread dial is engaged with
the lead screw.
If not, use a hex key wrench
to loosen the screw and rotate the thread
dial
until the gear engages with the lead
screw, then tighten the screw to hold the
dial in place.
4. Select the RPM you want to use. A
slower
RPM will give you more time to react espe-
c
ially if threading over a short distance or
threading up to a shoulder.
5. Set the feed direction lever for either
right or
left-handed threads.
6. Examine
the thread charts (inch or metric),
see Figures 46 & 52 , and then set the feed
rate selectors to the appropriate settings.
7. Turn ON the spindle to verify settings.
Check
to see that the lead screw is turning
and verify that the apron moves in the cor-
rect
direction by engaging the half nut lever.
8. Once you
are confident the settings are cor-
rect, disengage the half nut and turn OFF
the
spindle.
G9729 THREAD DIAL
TPI SCALE TPI SCALE
4 1
or 4 27 1-6
4.5 1-6 28 1
or 4
5 1
or 4 30 1-6
6 1-6 32 1
or 4
7 1
or 4 33 1-6
8 1
or 4 36 1-6
9 1-6 39 1-6
10 1
or 4 40 1 or 4
11 1
or 4 42 1-6
12 1-6 48 1-6
13 1
or 4 54 1-6
14 1
or 4 60 1-6
16 1
or 4 66 1-6
18 1-6 72 1-6
20 1
or 4 78 1-6
22 1
or 4 84 1-6
24 1-6 96 1-6
26 1
or 4 120 1-6
Figure 51. G9729 Thread dial chart.
9. Examine
the thread dial chart in Figure 51
to determine which numbers (on the thread
dial) to engage the half nut.
Note: There
are a total of six marks on the
thread dial, ranging 1-6. To maintain accu-
racy and consistency, engage the half nut
on the same mark on each pass. Failure to
start on the same number each time may
lead to cutting off the thread made in the
previous pass.
10. If cutting metric threads, you will not use the
thread
dial. Once the half nut is engaged,
you must leave it engaged until the threads
are
complete.