Thanks for walking through the setup of a 4 jaw. Some people, including myself years ago, are afraid of them and don’t realize how precise you can dial in a part with a 4 jaw vs a 3.
yknow, it makes me realise... everytime i use a 4-jaw, i wanna modify the damn thing... throw in a set of gears and have two screws on one side so you can adjust the rear jaw without rotating would be an interesting project actually... i reckon most of them have the meat to throw a pair of shafts across in there... make sure theyre not intersecting. and clear the bore... um. youre meant to indicate in at the chuck, out at the end, and keep doing both ends... you only indicated the portion of shaft youre indicating for concentricity, you didnt ensure its parallel.