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.

Edit:
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.

 

The 505 is used a lot for flat work. Good sanders just awkward to use other than flat...

 

the half-sheet sanders are highly valued when finishing flat panels.
it's back and forth motion does not leave swirl marks like a Random Orbit sander will.
flat sheet sanders come in 1/4 sheet palm sanders, and 1/3 & 1/2 sheet are bigger.

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The 505 will swirl....

 

you are correct - I will add that when I use the half-sheet sanders,
the swirl marks (to me) are not as noticeable as a Random Orbit.
which varies greatly with the type of wood being sanded and the operator (as with all tools).

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......if you press on a corner it will leave curly-Q's...

 

The PC 330 is well known I cabinet shops for sanding seal coats in cabinet door corners...

Block sanders were put in the closet for main sanding when the PC 332 came out...

The PC 332 and 333 hit shops like a blessing....

Today shops just buy a profile sander and throw under the table...

Tools like these made PC....belt sander , ROS, 690 routers,etc...

 

The PC 330 is well known I cabinet shops for sanding seal coats in cabinet door corners...

Block sanders were put in the closet for main sanding when the PC 332 came out...

The PC 332 and 333 hit shops like a blessing....

Today shops just buy a profile sander and throw under the table...

Tools like these made PC....belt sander , ROS, 690 routers,etc...

Maybe so, but I love my 330s. As long as I can get them repaired, I will keep using them. Better fit in my hand, more control due to better grip. For me, anyway. But I did love that 505 when I worked in a cabinet shop in the early 80s. And as for swirls, by the time I'm done with the 330, any swirls are so fine that they cannot be seen with the naked eye.

 

this is my old workhorse half-sheet finish sander for flat work - and I like it a lot.
I have two round disk random orbital sanders, and they remove a lot of material faster.
I guess you would have to have used both in order to form a personal opinion.
(note: this is a home-made PVC attachment as the factory bag hung out of the
back - pretty cumbersome to me. the shop vac also attaches to the PVC as well).
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There is a single trick to getting defect free sanding from any of these orbital/random orbital sanders. Move the sander at speed of one inch per second. No faster. Let the sander do the work like it is supposed to. I learned that in issue #60 of FWW.

 

a tool I really miss is the all plastic Black & Decker half-sheet sander from the 1980s.
it had a switch that you could choose between inline and orbital.
I don't know why it was discontinued. (or even if it was - I just haven't seen one like it since).

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