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PM-727MV v6 2020-10
Copyright © 2020 Quality Machine Tools, LLC
Tramming calls for patience! Expect to tighten
and re-check at least three times (simply tight-
ening the bolts can itself aect the tram).
Figure 3-14 Indicating the vise
The tip of a standard dial indicator, arrowed, rides along the
face of a ground reference bar
5. Remove the vise, if installed, and clean the table
surface. If there are noticeable grooves or dings,
atten the surface with a diamond lap or ne-grit
stone.
6. Set a 1-2-3 block (or other precision-ground block)
on the table under the indicator probe.
7. Switch on the DRO.
8. Using the ne downfeed lower the spindle to give an
indicator reading of about half-scale.
9. Note both the dial indicator and DRO readings, then
back o the ne downfeed at least a couple of turns
to avoid collision when sweeping.
10. Reposition the 1-2-3 block to the opposite location
on the table.
11. Swing the indicator holder to the new location, then
lower the spindle – ne downfeed again – to give
the same dial indicator reading as in step (7).
If the headstock is perfectly trammed – highly unlikely
at the rst shot – the DRO reading should be as in step
(9). If not, loosen the nuts just enough to allow the head-
stock to be tapped a fraction of a degree in the direc-
tion called for, then re-tighten the nuts. The “tap” can be
anything from a gentle slap of the hand to a rap with a
dead-blow mallet.
Repeat steps (8) through (11) until satised with the
tram, tightening the nuts as you go. This will likely call
for several iterations. There is no “right” tram; the ac-
ceptable dierence in side-to-side readings depends on
project specs. As a starting point, aim for ± 0.001” on a
sweep radius of 5 or 6 inches.
A similar procedure may be used to check tram in the
Y-axis, front to back. The dierence here is that there is
that Y-axis tram is established in manufacture, and can
be adjusted by one of two methods:
1. Shimming between the dovetailed base casting and
the headstock itself. It is more likely that the head-
stock is nodding forward rather than leaning back-
ward, so start with (say) a 2 mil shim in line with the
underside (central) headstock nut. This is a tempo-
rary x that will need to be checked if the headstock
is tilted again.
2. Shimming between the underside of the column and
the main base casting. This is a long-term x. It is a
two-person procedure, requiring an engine hoist or
some other means of un-weighting the headstock
(see Section 2, Installation).
INSTALLING & INDICATING A VISE
For routine milling operations the workpiece is held in a
precision vise. For the PM 727M a 4” vise is most suit-
able. “Indicating” means checking the alignment of the
xed (back) vise jaw relative to the axis of table motion.
Install the T-bolts and align the vise by eye. With one of
the clamp nuts snug, but not tight, tighten the other one
just short of fully-tight (but tight enough so the vise won’t
budge without a denite tap from a dead-blow mallet).
A typical setup for indicating is shown in Figure 3-14.
There is no spindle lock, but you need to make sure
that the spindle does not rotate throughout the pro-
cedure. It helps to set the gears for the lowest spindle
speed (L-1). Take up any backlash by pushing against
the indicator holder. Set the indicator tip against the up-
per edge of a precision reference bar or, if not available,
use the front face of the xed jaw of the vise instead
(check for dings, hone if necessary). Adjust the Y-axis to
pre-load the indicator to mid range at the tightly-clamped
side of the vise, then lock the Y-axis.
Note the indicator reading, then watch the indicator as
you traverse the table slowly toward the loosely clamped
side. Ideally, there should be no discrepancy between
the indicator readings at the two ends — unlikely at the
rst attempt. Return the table to the starting point, then
repeat the process, tapping the vise in as you go. Re-
peat the process as often as necessary for the desired
accuracy, progressively tightening the “looser” nut. Now
fully tighten both nuts, and re-check again (tightening a
nut can itself introduce signicant error). An established
routine like this – tight to loose – can save a lot of time.
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