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Figure 3-7 Headstock tilted 45
Figure 3-8 Headstock tilt nuts (two of three)
TRAMMING THE HEADSTOCK
"Tram", short for trammel, means accurate alignment
— in this case adjusting the headstock tilt to bring the
spindle to a known angle — usually 90 degrees — rela-
tive to the table.
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, 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-radius fly cutter, exaggerated in Figure 3-9.
PM-940M 0-206 v.indd
o
counter clockwise
Figure 3-9 Head tilt can affect surface flatness
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 3-20 Sweeping holder for dial indicator
This example shows a rectangular section aluminum bar with
threaded holes allowing the choice of two sweep diameters, 6"
and 0", measured from spindle centerline to indicator tip. The
smaller sweep can be used for front-to-back tramming, also
left-to-right as here. For more sensitive left-to-right tramming,
use the larger sweep.
Figure 3-20 shows a typical shop-made holder; it has a
threaded arbor allowing the choice of two radius arms,
6 and 0 inches measured from spindle centerline to in-
dicator tip. A collet is used to hold the arbor, in this case
5/8" diameter. The dimensions are arbitrary, but note that
the indicator must be firmly attached, and the arm rock-
solid relative to the indicator spring force (which can be
considerable on plunger-type indicators).
A suggested procedure for re-establishing tram:
.
Disconnect power.
2.
Set the headstock to the approximate zero degree
position on the tilt scale, then tighten the three nuts
9
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