15
PM-1228VF v3 2021-05
Copyright © 2021 Quality Machine Tools, LLC
EXTERNAL GEAR SWAPPING
Key fact ...
For all thread cutting, with a single exception, the middle
gears are
always
86T and 91T, and the lower gear is
al-
ways
90T. The one exception is 13 threads per inch (TPI).
Non-metric applications
Most users find that the machine as supplied, with 30T
upper gear, meets all typical needs without alteration —
all fine-pitch threads up to 10 TPI, plus feed speeds from
0.0016” to 0.0115” per revolution of the spindle. Coarser
threads need a different size of upper gear; this in turn calls
for the change gear “quadrant” to be repositioned. The pro-
cedure for this is:
1. Loosen the M10 socket head screw securing the change
gear quadrant; swing the quadrant down.
2. Remove the M6 socket head screw and washer from the
upper gear spindle.
3.
Exchange the upper gear (see the table of UNC/UNF
threads later in this section). Be sure the shaft key en
-
gages both the 65T inner gear and the selected upper
gear.
4. Replace the M6 screw and washer.
5. Swing the change gear quadrant up to mesh the 91T
gear with the new upper gear. Tighten the M10 screw.
6. Lubricate the gears.
How to gauge “correct mesh”
Many users go by feel and
intuition, others use a paper feeler gauge. The mesh is good
if a scrap of 0.004” printer paper can be run between the
gears with definite resistance.
Metric applications
For metric thread cutting the gearbox is driven slower than
for US threads. This is done by driving the gearbox with the
86T
translating gear
instead of the 91T gear, which usu-
ally serves only as an idler. Depending on the thread pitch
called for, the upper gear may also need to be changed (see
the table of Metric threads later in this section). Changing
the upper gear is described above. To reconfigure the other
gears the procedure is:
1. Remove the M8 socket head screw and washers from
the gearbox input shaft (grip the Vee belt pulley to stop
the gear rotating).
2. Remove the keyed spacer bush followed by the 90T
gear. Be sure the key stays in place on the gearbox shaft.
3. Re-install the keyed spacer bush, followed by the 90T
gear. The 90T gear should now be in line with the 86T
translating gear.
4. On the gearbox input shaft replace the cup washer, the
plain washer and M8 screw.
5. Using a 19 mm or 3/4” wrench loosen the middle gear
axle post.
6.
Mesh the 86T gear with the 90T gearbox input gear (see
”How to gauge correct mesh” above), then re-tighten the
axle.
7. Exchange the upper gear if necessary, see above.
8. Swing the change gear quadrant up to mesh the 91T
gear with the upper gear, see above.
9. Lubricate the gears.
Figure 3-23
Feedshaft clutch
Hold the clutch body with one of the two supplied rods. Use the oth-
er rod to rotate the outer bobbin — forward to reduce feed pressure,
backward to increase. Several turns of the outer bobbin may be need-
ed to achieve the desired result.
Saddle and cross-slide power feeds are both controlled by a
single lever at right of the apron. The split-nut lever on the front
of the apron is used only for thread cutting with the leadscrew.
It is interlocked with the power feed lever, meaning that when
the split-nut is engaged, the saddle/cross-slide power feed is
disabled, and vice versa, Figures 3-25 and 3-26.
Before engaging the power feed, be sure there are no
clamps or obstructions to impede motion! Select a low
spindle speed for initial tests!
Figure 3-24
Saddle stop
If using the stop with power feed, be sure it is clamped
firmly enough to trip the feedshaft clutch reliably no matter
what feed pressure has been set, Figure 3-23. If the stop
tends to slide, try inserting a shim between the clamp plate
and underside of the bed.
SETTING UP THE POWER FEED
(continued)
