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enough to avoid unexpected headstock movement.
3.
Remove the vise and clean the table surface.
4.
Set a -2-3 block (or other precision-ground block)
on the table under the indicator probe.
5.
Switch on the quill DRO.
6.
Lower the spindle using fine downfeed to give a half-
scale indicator reading (exact location isn't impor-
tant, but remember the reading).
7.
Note both the dial indicator and DRO readings, then
back off the fine downfeed at least a couple of turns
to avoid collision when sweeping.
8.
Set the spindle drive to H-3 (this will allow you
to sweep the indicator holder easier from side to
side).
9.
Reposition the -2-3 block to the opposite location
on the table.
0.
Swing the indicator holder to the new location, then
lower the spindle – fine downfeed again – to give the
same dial indicator reading as in step (7).
If the headstock is perfectly trammed – highly unlikely at
the first shot – the DRO reading should be as in step (7).
If not, loosen the nuts just enough to allow the headstock
to be tapped a fraction of a degree in the direction called
for, then re-tighten the nuts. (The "tap" can be anything
from a gentle hand-slap to a rap with a soft-face dead-
blow mallet).
Repeat steps (4) through (0) until satisfied with the
tram, tightening the nuts as you go. This will likely call
for several iterations. There is no "right" tram; the ac-
ceptable difference in side-to-side readings depends on
project specs. As a starting point, aim for ± 0.00" on a
radius of 5 or 6 inches.
A similar procedure may be used to check tram in the
Y-axis, front to back. The difference here is that there
is that Y-axis tram is established in manufacture, and
can be adjusted only by shimming the column-to-base
interface. This is a two-person procedure, requiring an
engine hoist or some other means of un-weighting the
column and headstock (see Section 2, Installation).
Tramming calls for patience on any mill! Expect
to tighten and re-check at least three times (sim-
ply tightening the bolts can affect the tram).
PM-940M 0-206 v.indd
INSTALLING & INDICATING A VISE
For routine milling operations the workpiece is held in a
precision vise. For the PM 940M a 4" vise is highly suit-
able. "Indicating" means checking the alignment of the
fixed (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 definite tap from a dead-blow mallet).
A typical setup for indicating is shown in Figure 3-2.
You need to make sure that the spindle does not ro-
tate throughout the procedure. There is no spindle lock,
but set the gears for the lowest spindle speed (L-), then
take up any backlash by pushing against the indicator
holder.
Figure 3-2 Indicating the vise
The tip of a standard dial indicator, arrowed, rides along the side face
of a ground reference bar (or the front face of the back jaw).
Set the indicator tip against the upper edge of a preci-
sion reference bar or, if not available, use the front face
of the fixed 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
first 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 significant error). An established
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