12
PM 25MV v9 2020-10
Copyright © 2020 Quality Machine Tools, LLC
For all spindle positioning operations, with
or without DROs, avoid using the quill lock.
POSITIONING BY COUNTING X / Y DIVISIONS
Why?
On practically all vertical mills, including the heavi-
er knee mills, locking the quill may offset the spindle by a
few thousandths of an inch. If the edge of the workpiece
has been “found” in the quill-locked condition, this will af-
fect placement of holes drilled thereafter. Instead,
lower
the quill with the fine downfeed
control. This is worm
driven, so it stays where it’s put without locking.
Figure 3-8
Workpiece positioning example
TAPPING OPERATIONS
When threading a drilled hole it is essential to align the
threading tap properly in the bore. The mill is often used
for this purpose, ideally with a dedicated (non-slip) tap
holder or, for production work, an auto-reverse tapping
attachment. A drill chuck can be used instead for sizes
up to (say) M6 or 1/4”, beyond which the chuck may
not grip tightly enough to avoid slippage. Tapping can be
done under power, or by hand turning the chuck.
I
n this illustration a hole is to be drilled exactly 0.25” on
the Y-axis relative to the front edge of a workpiece in a
For either method, it is essential to use a tapping fluid.
Any cutting oil is better than none, but most users find
Castrol’s Moly Dee the most reliable for threading in
steel.
If power tapping bear in mind that the spindle does not
stop instantaneously, so be careful tapping blind holes.
Be sure the quill locking lever is free, and start trial
work
with the lowest spindle speed.
TILTING THE HEADSTOCK
In routine operations the user relies on squareness of the
spindle relative to both axes of the table. Front-to-back
squareness is set at the factory, and is not adjustable
by everyday methods. In the other plane the headstock
can be set to any angle up to 90 degrees either side
of the normal vertical position. Because re-establishing
true vertical (tramming) on any mill is a time consum-
ing process, most machinists look first for other ways of
handling a project instead of tilting the head.
The headstock is secured by three nuts spaced 120 de-
grees apart, one underneath and one either side, Figure
3-9. The headstock is top-heavy, and may swing sud
-
denly to either side unless a helper is on hand to restrain
it. Testing for moveability as you go, carefully loosen the
nuts by degrees. Be especially careful if the head has
vise, or otherwise clamped to the table, Figure 3-8.
1. Install an edge-finder in collet or chuck (a tip diam
-
eter of 0.2” is assumed).
2. Lock the X-axis (optional).
3.
If the reference edge is already to the back the spin-
dle centerline, do nothing; if not, rotate the Y-axis
handwheel clockwise to send the workpiece back-
wards (toward the column).
4. Engage the fine downfeed, Figure 3-7.
5.
With the spindle running, lower the quill as neces-
sary using the fine downfeed control, then bring the
table forward (counter-clockwise), stopping at the
point where the edge-finder just makes contact (the
tip jumps out of line). Stop the spindle.
6. While holding the Y-axis handwheel to prevent rota
-
tion, zero the Y dial.
7.
Raise the quill, then rotate the handwheel one exact
full turn counter-clockwise (0.1”) to bring the refer
-
ence edge to the spindle centerline.
8.
Rotate the handwheel 2-1/2 turns counter-clockwise
to bring 50 on the dial opposite the datum; the spin-
dle is now 0.25” to the back of the reference edge.
