: uhmmm... so if someone invented a 4 action sander we would be using an 80
: grit and end with a glass smooth surface""

If it eliminated "all" distance between scratches would'nt it do the job?
The surface would be smooth as glass...the depth of amount of material removed would be more than if 400 grit was used is all. I think a DA sander could be considered a 4 way sander...i mean what other action could you add...jackhammer?

...still looking for a shootdown on the statement that 220 grit with a DA sander is same 400 grit by hand.

I suppose i should just walk out in the garage and try it.