[jakemestre]

Based on the time it is taking to cut such a small amount of material, it could well be that you are feeding way too slowly. Speeding that up might well get rid of all of the screech and chatter. Also, you don't mention what tooling you are using.
Normally I would have suggested flex in the tool post on a 9x20 lathe as that is a crippling weak link on the machine as I am sure you know, however you have clearly upgraded that weakness very nicely already. Impressive sheet metal work too.

Thanks for the suggestion LongRat. I did forget to mention the tooling. I'm using a Sandvik CCMT3251 PF 4215 grade insert. It's in a 1/2" holder that's choked all the way up in the toolpost. I started with the recommended feeds and speeds off the box at .014" radial depth of cut, .004"/rev and 1500SFM. My machine about exploded with chatter with these values so I took it down to the absolute minimum of .004"DOC, .002"/rev and 1500SFM. Still lots of chatter. The spindle is moving relative to the cross slide, but I tightened every bolt and even built some L brackets to help stabilize the headstock.
The only way I can stop the chatter is at 200SFM, .01"DOC and .oo2"/rev. The part takes 26min at that speed, and I need to make it in 3. The insert is rated to 1950SFM(15500RPM at .472"diameter), .079" radial depth of cut, and .009"/rev. The insert will get me there even for a finishing mid grade insert, it's the machine that won't.