Still woodturning :
this is a sanding gouge.
The head is in two parts, glued together. They hold together a ball bearing (salvaged from rollerblades).
The articulated shaft is ended by a piece of threaded rod, attached to the ball bearing with two nuts.
The sand paper is attached via a velcro interface (salvaged from the the sole of an oscillating sander).
With this kind of tool, you simply need to apply it on the turning piece and it is self powered.
You don't even need to cut round pieces of sand paper, you can leave them square.