On the rare occasions when I have to do something remotely like that, I use multiple heavy pipe stands and clamp a tube with ID no more than 2X the bar OD to all the stands. Effectively, this builds a crude bar feeder, drastically limits the bar deflection, and stops the positive feedback at an early stage. Simply supporting the free end of the bar, as in the original posting video, does nothing to control the whap-whap-whap.
In fact, this is how I set up my DV-59 for (manual) bar feed, since I am too cheap and too cramped to get an actual bar feed. Of course, DV-59 won't eat anything over 1.06" OD, so rather different world than 3" bar stock.
