Bob Engelhardt fired this volley in
:

I measured it to see just how much more to remove (.067 IIRC) &
advanced
the cross feed .025 (same feed & speed). It hardly cut at all!! .005
maybe. Whaaat??? I had set the cross feed dial to zero after the first
cut & to .025 for the second, so I knew that I hadn't lost track of it.
The bit was tight in the tool holder, the chuck tight, etc.

OK, I tried again ... same thing! A cut very much smaller than the
advance. ???


Heh! You got bit by "lost motion". There's backlash in the cross-feed,
and the gibs are probably not as tight as need be for that hearty a cut.

The bit got sucked into the work as far as the backlash would permit by
the back rake of the bit.

LLoyd