So I’m having some major trouble with slop in my Z axis, regardless of how tightly I’ve cranked down the gib adjuster.   While what follows may not be the best test setup, I wanted to at least come up with some way of showing what I’m seeing.  I attached the magnetic base to the head, on the left hand side near the front edge. I set up the dial indicator to indicate off of the surface of the table. I then apply upward force on the front edge of the head, causing it to “tip back.”

I can feel the head wobble in the ways as I do this, and the dial indicator moves ~0.030″ typically, though I’ve seen it jump as much as 0.040″.

Here’s a video which shows this test.

I haven’t yet pulled the gib out to see how badly formed it may be.  I’ve read at least one forum post where someone has had roughly the same experience, and they indicated that their gib was really badly made.  Some folks suggest making a new gib out of brass to solve this problem.  I don’t know how difficult this will be just yet…