Get some R8 collets for that machine! A cheap 3-jaw chuck is horrible for milling with because it offers no lateral support, although I am impressed with the work you were able to accomplish with it. Using collets will reduce chatter & vibration, the cutter will run truer, and just overall perform better because you will be running the cutter much closer to the spindle bearing support. You will also be able to take larger & deeper cuts. Kudos on the setup though, those are fairly decent little mills.