12 years ago
Another chapter in the unfolding saga of my education as a machine tool tech.
While using the Millrite MVI to mill the ends of mild steel bars off square, I
noticed something odd. When moving the table in and out in the Y direction
(closer and farther from the column) with the table clamped in the X-axis
direction, cutting would happen only in the conventional-milling direction, and
no cutting would happen in the climb-milling direction, unless I moved the table
in the X-direction (side-to-side).
The bar is held in a milling vise, the bar being parallel to the T-slots in the
table, with the left end being presented to the side of the cutter (6 helical
flutes, 1" in diameter).
As I'm cranking the table in and out I'm wondering what could cause that.
Clearly, there is some unintended X-axis motion due to the intended Y-axis
motion, despite the X-axis being clamped. So, I used the Skoal optical
centering scope to test the
theory, finding that reversing Y-axis direction causes a ~0.0028" X-axis motion.
That's a lot, and certainly explains why the mill would cut only in one
direction, and also why I had some difficulty cutting the bars to a specified
Cause? The Y-axis feedscrew is on the right side of the saddle, so if the
saddle-to-knee gib is loose the saddle will cock one way when being cranked
closer to the column and will cock the other way when being cranked away from
the column. So, time to adjust the saddle-knee gib. This was easily done, and
eliminated the X-axis motion due to Y-axis motion. I wonder when that gib was
What I have not yet done is to tighten the table-saddle (X-axis) gib, as this
requires removal of the table-saddle assembly from the mill to get access to the
adjustment screws and setscrews. Given the difficulty, I bet this gib has never
been adjusted. The X-axis feedscrew is in the center, so cocking would be more
random and thus more confusing than in the Y-axis. Table removal isn't
difficult, but requires a small hoist. I don't have the space to store such a
hoist, but they can be rented from the local Taylor Rentals place.
Or, I can hang the table from the ram with welded-link chain and quick links
eyebolts bolted to the table, undo and remove the saddle-knee gib, and crank the
knee down leaving the table-saddle assembly dangling from the ram. Perhaps I
can then tighten the table-saddle gib on the dangling assembly. I'll have to
work out the details of how this would be done safely. And the Y-axis DRO will
have to be removed. I already have the eyebolts and matching thick washers and
T-nuts, bought precisely to allow secure attachment for safe lifting of the