Hi,
Yes, exactly. Many people do not realise just how significant the rotating mass is to the overall momentum. As of a couple of years ago I assumed the rotational inertia was just a small detailTwisting a very heavy large diameter ball screw takes much more force than turning a narrower one. Given the numbers it appears the weight of the X axis gantry may not have as much bearing on the acceleration force needed as it is divided up into small increments by the threads on the ball screw. You may have a very valid point.
compared to the massive gantry....but no that is definitely not the case. That discovery has changed my entire appreciation of machine mechanics.
Craig