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Model G8688 (Mfg. 3/09+)
-27-
For example if you wanted to cut a
1
⁄4" x 20
thread on a piece of round stock.
1. UNPLUG THE LATHE!
2. Remove the gear cover.
3. Loosen the adjuster to disengage the gears
from each other.
4. Remove the gears in place and replace with
the 40, 65, & 55 tooth gears in the called out
positions.
Note: The C combination gear is not
required.
5. Remove the bushing from the D shaft and
engage D gear directly to B gear.
6. Slip the bushing back over the shaft to hold D
gear in position.
7. Position the adjuster so the gears mesh.
Cutting Threads
G8688 THREAD DIAL
TPI SCALE
12 1,3,5,7
13 1
14 1 or 5
16 1 – 8
18 1 or 5
19 1
20 1,3,5,7
22 1 or 5
24 1 – 8
26 1 or 5
28 1,3,5,7
32 1 – 8
36 1,3,5,7
38 1 or 5
40 1 – 8
44 1,3,5,7
48 1 – 8
52 1,3,5,7
Figure 28. G8688 Thread dial chart.
6. Once you are confident the settings are cor-
rect, disengage the feed lever and turn the
spindle Off .
7. Examine the thread dial chart in Figure 28 to
determine which numbers (on the thread dial)
to engage the feed lever.
Note: There are a total of eight marks on the
thread dial, ranging 1–8. 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.
To cut threads:
1. Set the compound rest to the appropriate
angle for the given thread you want to cut.
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.
4. Examine the thread charts and select the
gear ratios you need (see Figures 25 & 26).
5. Turn the spindle ON and select the RPM you
want to use. Check to see that the lead screw
is turning and verify that the apron moves in
the correct direction by engaging the feed
lever.