[Geof]

Question for you:

The floor toolpaths that show the tight little swirls, are they trochoidial paths? (I don't think my spelling is correct.)

[Aquatic]

Question for you:

The floor toolpaths that show the tight little swirls, are they trochoidial paths? (I don't think my spelling is correct.)

No. Straight lines.
Coming from the right on the right hand side. straight - 20° left - straight - 110° left - straight

And even adding a small radius at the junctions doesn't make a difference.

[haastec]

What was tested to make you say "spindle and head are good" and how?
What did the ballbar test reveal?

[Aquatic]

What was tested to make you say "spindle and head are good" and how?
What did the ballbar test reveal?

I wasn't present when the spindle was tested. So can't answer the how.
The shudder is there when running a program with the spindle off.
It's not the spindle!

Ball bar test should be today I think. I will post results when I get them.