Thanks for your efforts Julien. I have tweaked your process and got results I am fairly happy with. I did 2 things different than you. I ran at 10k rpm at 80ipm feed and 60 ipm plunge, but at a doc of 0.005" due to some other info I read online. I also did a second pass, but I did that pass at full depth. This got rid of any visible cut lines on the walls, not that there were many with the step down. This left some very thin wisps of material along that bottom that got easily blown out with compressed air. I might mess around a little with this in the future, but for now this recipe seems to work quite well.