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.