The 505 is an orbital sander, complete different animal than a Random Orbit sander, yes there is a difference.
I was curious, so I did a web search on the Porter-Cable 505. It is called a finish sander.
I have an old Craftsman sander that looks similar to it. It has a switch for two modes. One has an "orbital motion" that removes material faster, but leaves circular scratches. The other has a "back and forth" motion that is less efficient, but sands with the grain as long as you align it correctly on the wood.
If the Porter-Cable 505 is a "finish sander", how can it be an "orbital sander"? Wouldn't it leave ring scratches on the wood? Could it be that the ring scratches are expected but very fine, and then the owner does a quick and easy hand-sanding before applying finish?
I always assumed that a "finish sander" has a back-and-forth motion, but perhaps I am wrong. Maybe @shoot summ
or someone else can clarify it for me.
Asked and answered. See the posts above. Posts that "crossed in the mail."
P.S. I gotta get that old Craftsman sander out, give it a try, and see if I might like it more now. There is one thing I remember about it: It was a pain to change sandpaper, and you had to change the sandpaper often.