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PM-30MV v3 2020-10
Copyright © 2020 Quality Machine Tools, LLC
Tramming is done by fine-tuning the headstock tilt angle. Tram
is typically checked by attaching a dial indicator to some form
of “sweepable” holder installed in the spindle, the aim being to
adjust tilt for the same reading on either side of the X axis. The
longer the radius arm, the greater the sensitivity.
Figure 3-17 shows a typical shop-made holder; it has a thread-
ed arbor allowing the choice of two radius arms, 6 and 10 inch-
es measured from spindle centerline to indicator tip. A collet
is used to hold the arbor, in this example 5/8” diameter. The
dimensions are arbitrary, but note that the indicator must be
firmly attached, and the arm rock-solid relative to the indica
-
tor spring force (which can be considerable on plunger-type
indicators).
A suggested procedure for establishing tram:
1. Disconnect power.
2. Install the dial indicator.
3. If the headstock has been tilted, reset it to the approximate
zero degree position on the tilt scale, then tighten the three
nuts enough to avoid unexpected headstock movement.
4. Remove the vise, if installed, and clean the table surface.
If there are noticeable grooves or dings, flatten the surface
with a diamond lap or fine-grit stone.
5. Set a 1-2-3 block (or other precision-ground block) on the
table under the indicator probe.
6. Switch on the quill DRO.
7.
Using the fine downfeed lower the spindle to give an indi
-
cator reading of about half-scale.
8. Note the dial indicator
and
DRO readings, then back off
the fine downfeed at least a couple of turns to avoid colli
-
sion when sweeping.
9. Reposition the 1-2-3 block to the opposite location on the
table.
10. 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 (8).
If the headstock is perfectly trammed – highly unlikely at the
first shot – the DRO reading should be as in step (8). 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
slap of the hand to a rap with a dead-blow mallet.
Repeat steps (7) through (10) until satisfied with the tram,
tightening the nuts as you go. This will likely call for several
iterations. There is no “right” tram; the acceptable difference in
side-to-side readings depends on project specs. As a starting
point, aim for ± 0.001” with a sweep radius of 5 or 6 inches.
Figure 3-17
Shop-made indicator holder
Figure 3-16
Head tilt can affect surface flatness
Figure 3-15
Headstock tilted 45 degrees counter-clockwise
TRAMMING THE HEADSTOCK
As shipped, the mill is set to zero tilt, squared accurately
enough for initial out of the box test drillings, etc. For more
demanding project work thereafter, the spindle needs to be
set at precisely 90 degrees relative to the table, in other words
trammed. “Out of tram” may show up as an offset of a few
thousandths between entry and exit of a deep hole, or as a
scalloped effect when surfacing a workpiece with a large-radi
-
us fly cutter, greatly exaggerated in Figure 3-16.