13
PM 25MV v9 2021-12
Copyright © 2021 Quality Machine Tools, LLC
not been moved before – the paint seal may let go with-
out warning. (First-time tilting may also call for unusual
effort on the wrench.)
Set the headstock to the desired angle by reference to
the tilt scale on the headstock base casting, then re-
tighten the nuts. The tilt scale is typically good to within
± 1/4
o
. A more accurate means of angle measurement
will be needed if the project calls for greater precision.
Figure 3-9
Headstock nuts
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 sur
-
facing a workpiece with a large-radius fly cutter, greatly
exaggerated in Figure 3-11.
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 3-12 shows a typical shop-made holder; it has a
threaded arbor allowing the choice of two radius arms, 6
and 10 inches measured from spindle centerline to indi-
cator tip. A collet is used to hold the arbor, in this exam
-
ple 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 establishing tram:
1. Disconnect power.
2. Install the dial indicator.
Figure 3-11
Head tilt can affect surface flatness
REMOVING THE HEADSTOCK
If you wish to remove the headstock be aware that it
may — depending on the date of manufacture — be se-
Figure 3-10
Safety groove in headstock base casting
cured to the base casting by set screws in addition to the
nuts shown in Figure 3-9. The set screws, if installed,
are in a threaded hole on the 3-spoke handle side (right
hand) of the headstock casting. The screws are installed
in line, with the inner screw seated in a “safety groove”
in the base casting, Figure 3-10. The outer screw locks
the inner screw.
