I am relatively new to machining. 2 years on Mazak QT28 w/T32 Control.
I am having hell with this job on my bench. 64pc flex shafts. ~40" lg pin x box with a deep undercut 1" OD 27" lg right in the middle.

I've center drilled and with tailstock no luck in turning the entire undercut all together. Shortened up the part to cut half of the undercut and still chatter on rough and finish.

Changed to a 1/64" nose radius insert on VNMG to reduce tool pressure and also played with tailstock pressure high and low. Even tried roughing a 1/4 of the 1/2 that's hanging out of the chuck then profiling the entire part all together. Still chatter like none other... No steady rest on the machine either...

Any ideas or advice?