I cut a 18" crab apple log in half, sketched out an 12" circle on each, and
roughly trimmed it with the chainsaw. Unfortunately it was way too big to
fit on my bandsaw, but it would have bound anyhow.

I screwed a faceplate to the flat surface and ran the tail piece into it.

Well, the lathe shook like crazy, and thunked pretty badly each time a high
spot hit the gouge. (400 rpm, the lowest setting on the machine) I have
roughed out both the outside and the inside and the lathe seems to be okay;
once I got them balanced they spun just fine.
But I wonder if a lathe is designed for that? Without a really big bandsaw
I am not sure what I could have done to make it any better.

On a completely different issue, the crapapple has pretty streaks of red
running though it, mixed with brown and white. Is that going to last?