I ran a compressed air powered vibrator (little eccentric spinner) attached inside a laundry tub to provide vibration and foam in a process to wash oil from closely spaced plates. Keep a lid on the sink and it works pretty well!

Where are the pictures to "watch" ?

Very interesting! A couple of comments:

First, it's not ultrasonic, unless some components have harmonics in the ultrasonic range, or the relationships between the two kinds of motion in the sander result in ultrasonic movements.

Second, I was not familiar with the term "DA sander", and had to look it up. I gather that DA is synonymous with Random Orbital...

In any case, that's all semantics; if it works as shown, then I don't want to knock it!

I have a 40+ yr old Craftsman, all aluminum housed, "DA" sander. It stands for Dual Action. There's a lever on the side of the base that will switch it from straight linear stokes to orbital strokes.

Thanks. My all aluminum Craftsman tool is either just over 50 years old, or just under 60; I can't remember which of two possible times I could have purchased it. It is sort-of Dual Action; the motor has two heads: a drill and an orbital sander; no linear motion on the sander. My wife just used that sander to refinish her park bench a couple of months ago.

When I did a search for "DA sander", most of what appeared were random orbital sanders, plus one that appeared to be a disc sander, but was labelled DA. I presume that last one also had some form of vibratory motion.