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Copyright © 2020 Quality Machine Tools, LLC
PM-835S v3 2020-10
Figure 3-17 is an example of Y-axis positioning. A hole is to be
drilled 0.25” on the Y-axis relative to the front edge of a work-
piece in a vise, or otherwise clamped to the table:
1.
Install an edge-finder in collet or chuck (a tip diameter of
0.2” is assumed).
2. Lock the X-axis by tightening both levers.
3. If the reference edge is already to the back the spindle
centerline, do nothing; if not, rotate the Y-axis handwheel
clockwise to send the workpiece backwards (toward the
column).
4.
Engage the fine downfeed.
5. With the spindle running, lower the quill with the downfeed
handwheel to bring the tip of the edge-finder just below the
top of the workpiece.
6. 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.
7. While holding the Y-axis handwheel to prevent movement,
zero the dial.
8. Raise the quill, then rotate the Y-axis handwheel one ex-
act full turn counter-clockwise (0.1”) to bring the reference
edge to the spindle centerline.
9. Rotate the handwheel 2-1/2 turns counter-clockwise to
bring 50 on the dial opposite the datum; the spindle is now
exactly
0.25” behind the reference edge.
Figure 3-17
Spindle positioning example
both axes, 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, high
-
ly exaggerated in Figure 3-18.
Figure 3-18
Head tilt can affect workpiece surface flatness
This shows the effect when fly-cutting if the head is tilted left or right
(clockwise/counter-clockwise). Front to back tilt causes a similar scal
-
loping effect in the other axis of the workpiece.
Figure 3-19
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 10”, mea
-
sured 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.
X & Y-AXIS POSITIONING BY COUNTING
DIVISIONS
Note:
The following procedure shows how to eliminate the
leadscrew backlash factor when dead reckoning. This also ap-
plies to the knee: when counting divisions on the knee dial, the
knee must be traveling in the
same direction
when approach-
ing a point of reference, then onward by a specific number of
divisions to the desired location.
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 — relative to the table. This
is essential for routine operations in which the user relies on
squareness of the spindle relative to both axes of the table.
Unless it was swiveled 90 degrees for compactness in ship-
ping, the head is usually installed accurately enough for initial
out-of-the-box test drillings, etc. If the head was swiveled, it
can be zeroed with ± 0.25
o
accuracy by reference to the at-
tached scale. For more demanding project work thereafter, the
spindle needs to be precisely set at 90 degrees to the table in
Tramming is the process of 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 3-19 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 case 5/8” diameter. The dimen-
sions 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 a factor with plunger-type indicators).
A suggested procedure for establishing tram in the X axis:
1. Disconnect power.
2. Set the headstock to the approximate zero degree posi-
tion on the tilt scale, then tighten the three nuts enough to
avoid unexpected headstock movement.
3. Remove the vise and clean the table surface.
