This is a new oscillating sander that I bought yesterday. The spindle not only revolves, it travels up and down in a linear motion. I have never had much luck getting smooth inside corners on my aluminum fabrication work for small engines. I have tried filing, wrapping sandpaper around a dowel, even sanding drums mounted in my milling machine, but non of it gave really great results. This machine comes with five different size arbors, from 1/4" up to and including 2" diameter. Hopefully, this is going to improve the quality of some of my work. It was on sale for $160 off the regular price, so I dug deep into the Rupnow fortune and bought it.---Brian