11
PM-30MV v3 2020-10
Copyright © 2020 Quality Machine Tools, LLC
QUILL DOWNFEED
The quill is controlled in two
different ways,
coarse
and
fine
.
In the drilling mode, coarse feed, the mill operates like a stan-
dard drill press with a 3-lever hub; lever action lowers or raises
the quill in the usual way by rack and pinion. Return action is
assisted by a compression spring within the quill and spindle
assembly.
For milling operations the lever hub is not rotated by lever ac-
tion. Instead it is driven by a worm wheel rotated by the fine
control knob. This allows the quill to be driven precisely to
any desired position. The fine control knob, because it drives
through a worm, cannot be back-driven by return-spring force
on the quill (in other words, it stays where it’s put). For milling
operations the quill should be locked by the lever on the left of
the headstock, Figure 3-8.
If you are counting downfeed divisions be aware of
backlash in the worm drive.
QUILL DRO
The quill DRO is in metric mode when switched on. Press the
mm/in button to display inches.
Replace the battery by removing the small molded cover on
the face of the DRO unit. Note that the white dots on cover and
case must be aligned for removal and replacement. Check the
type number and voltage of the installed battery. Replace with
an equivalent silver oxide cell available from local retailers.
Switch off the DRO when not in use!
EDGE FINDING FOR ACCURATE POSITIONING
Why?
On many vertical mills, including the heavier 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 can affect placement of holes drilled
thereafter. To minimize the potential for positioning errors due
to this, consider
lowering the quill using the fine downfeed
control when edge finding
The fine downfeed is worm driv
-
en, so it stays where it’s put without locking.
For edge-finding and table positioning, with
or without DROs, be wary of the quill lock.
Figure 3-11
Workpiece positioning example
1.
Install an edge-finder in collet or chuck (a tip diameter of
0.2” is assumed).
2. Lock the X-axis (optional).
Figure 3-10
Quill downfeed controls
A pinion shaft connects the 3-spoke lever hub (1) to the quill pinion,
which engages a rack on the back side of the quill. When the lever
hub (1) is rotated forward — as in a drilling operation — the quill pinion
drives the quill down. A worm gear sleeve on the pinion shaft is driven
by the fine control knob (2). If the clamp knob (3) is loosened the fine
control knob is free to rotate, doing nothing to the quill. Tightening
knob (3) engages the fine feed by clamping the worm gear sleeve to
the pinion shaft.
Coarse feed
For drilling operations, loosen knob (3); this allows the 3-spoke
lever assembly to directly control the quill.
Fine feed
For milling operations calling for precise, repeatable control of
tool depth, tighten knob (3) to engage the fine control knob (2).
Tighten the Z-axis locks, Figure 3-9.
Rotate the fine control knob (2) to raise or lower the quill. Low
-
er the quill by rotating the fine control knob clockwise, position
-
ing it precisely either by counting divisions on the graduated
collar inboard of hub (1), or by reference to the digital readout
(DRO), Figure 3-1. Use the locking lever left of the headstock
to hold the quill firmly in position.
The quill DRO – which has no backlash issues – offers a much
less laborious way of setting tool height, but note that the quill
is
spring-loaded
. This calls for care when releasing the quill
locking lever. If the fine control knob has been allowed to dis
-
engage (backed off counter clockwise), the quill may jump up
by 0.01” or more. To avoid this, make sure the fine control has
been turned
clockwise
to apply downward pressure on the
quill before the locking lever is released.
In Figure 3-11 a hole is to be drilled exactly 0.25” on the
Y-axis relative to the front edge of a workpiece in a vise, or
otherwise clamped to the table.
TABLE POSITIONING BY COUNTING DIVISIONS