Cannot figure out how to Random Orbit Sand (I must be stupid)

[Dan Friedrichs]

Trying to improve my sanding technique...

Festool Rotex 5", with a new pad, a new piece of Granat P120 paper, Festool dust extractor...

Piece of walnut, fresh from the planer (which has sharp knives and leaves a nice surface, to being with)

Set the sander to ROS mode (not rotary mode), turn the vacuum suction way down, lightly place the sander on the work, let the weight of the sander do the work (no pressing down). For this board, which is ~6"x8", I spend maybe 30 seconds sanding, until there is a uniform scratch pattern all over.

Wipe some BLO on, and there are little spiral marks visible.

I just don't get it. For the last several projects, I've taken to hand sanding with P120 paper after the ROS, because at least then, I can get rid of the spiral marks, but it's a HUGE amount of work. It's almost less work to NOT use the ROS, and just hand sand everything!

What am I doing wrong?

[Grant Aldridge]

I'm not familiar with that brand of paper but it sounds like you just need a finer grit. I like to use a 180 or 220

[Lee Schierer]

120 grit paper should not be you final grit before finishing. You need to go to at least 220 and maybe to 320. Even so, in some woods you will see the swirl marks even from a ROS. For a piece that small, you could easily hand sand it going with the grain to eliminate the marks.

[Robert LaPlaca]

120 is not a fine enough for a oil finish, keep going till 220.. the oil is basically magnifying the swirl marks..

[Matt Day]

It’s the sander. My Bosch doesn’t do that, but since I really want you to succeed, i’ll trade sanders with you.

[Dave Cav]

Pretty much what everyone else said. You're stopping too soon. For my normal furniture work I go to at least 220, for table tops and other large flat surfaces, 320 or higher. Lately I have been making a bunch of natural finish door and window trim and I take it to 180.

[Brian Henderson]

120 grit is not nearly enough, I never stop before 220 and often go higher, depending on the wood and/or the project. In fact, 120 is often where I START sanding, assuming the wood is generally well-prepared before that.

[Marc Rochkind]

I agree with what everyone else said (especially Matt). My understanding is that the initial coarse grade is to remove machine marks, and it sounds like you don't have any. If the surface is as perfect as you say it is, you might start with something even finer than 120.

But definitely, as everyone else says, end up with something 180 or higher, depending on what finish you're applying. Probably the walnut won't be stained, so maybe finer than 180.

[Prashun Patel]

In fact, you may find that even with a good sander like your Rotex, you have sanding swirls at 180 or 220. I like to go higher to 400 or 600. By then the scratches get quite small to see.

Many people recommend sanding by hand lightly with the final grit to remove those scratches. I will do that when I want to be extra sure.

[Leo Graywacz]

If you are oiling wood you need to sand much higher. 600-800 grit. 320 is about the minimum you should stop at.

[ernest dubois]

But lets face it, it is the sander. Finer grit just means smaller tears, small enough that they are no longer so irritating to look at granted but even at that scale they leave their effect and you end up with... an orbital sanded surface.

[Mike Cutler]

I gotta agree with the others Dan, 120 is too soon to stop for a "softer" wood like walnut.
I have four DeWalt Orbitals set up as follows; 150,220,320,400 and above, grit.
Festool has an instructional video for using their sanders. It might be worth a look.

https://www.youtube.com/watch?v=rZZyypf-Qqk

[Dan Friedrichs]

But lets face it, it is the sander. Finer grit just means smaller tears, small enough that they are no longer so irritating to look at granted but even at that scale they leave their effect and you end up with... an orbital sanded surface.

I think this is it. From 5' away, the surface looks fine - I'm getting picky, and I guess that means this is the problem.

I prepped another test board, and did sections where I stopped at 100, 120, 150, 180, 220, and a section where I hand sanded at 120. It's obvious that the swirls just get less noticeable as grits progress, but are still visible.

Though, if I'm topcoating with a film-forming finish, it seems silly to sand the wood to 220+ just to avoid swirl marks, doesn't it? Seems like it makes more sense to use the ROS to get most of the machine marks gone, then hand sand at ~120 grit in the direction of the grain?

[Dan Friedrichs]

I gotta agree with the others Dan, 120 is too soon to stop for a "softer" wood like walnut.
I have four DeWalt Orbitals set up as follows; 150,220,320,400 and above, grit.
Festool has an instructional video for using their sanders. It might be worth a look.

https://www.youtube.com/watch?v=rZZyypf-Qqk

Mike, this was SUPER useful!

For those of you who have Rotex sanders: do you leave them in Rotary mode all the time (like is done is this video)? I was under the impression that rotary mode was for rough use, and the ROS mode was for "finishing" use (>120 grit-ish) - is that incorrect?

[Bob Varney]

Dan,

I use my rotex for the lower grits, my rotex has a 5mm swirl, then use my its 150 with a 3mm swirl. For a really smooth surface.

Bob