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

[Bill Dufour]

I try to never use brand new paper on a finished project. Put it on the sander then a few seconds on a back side or scrap to knock off any high spots of grit then onto the project. When you are talking about several thousand pieces of grit what are the possibilities that at least one ended up clumped on top of another and glued there. It only needs to be 1/1000 of an inch higher to be visible.
Note that your swirl marks are not evenly spaced and all over. They are separate small single individual swirls caused by one individual grit randomly spaced. They may even be loose grits that shifted and re embedded in the paper. Or I suppose small shavings of wood like a planer may mark the surface with if dust collection is poor.
Bill D.

[Jim Becker]

Aside from the comments already stated, check your pad on your sander to make sure there's not a spec of dirt on it between the pad and the abrasive disk. It happens...

Also, Rotex isn't a "one hand" tool like the regular Festool ROS so you need to keep that in mind so it stays balanced. Rotex is designed to err toward the rotary motion and heavy stock removal and that's a two-handed process for control. ROS mode is a bonus, but the balance of the tool still prefers both hands, um...handling it.

[Dan Friedrichs]

Also, Rotex isn't a "one hand" tool like the regular Festool ROS so you need to keep that in mind so it stays balanced. Rotex is designed to err toward the rotary motion and heavy stock removal and that's a two-handed process for control. ROS mode is a bonus, but the balance of the tool still prefers both hands, um...handling it.

I have noticed that

Jim, I think you have a Rotex? Do you keep it in rotary mode all the time, or do you find the ROS mode useful in any way?

I tried prepping a sample board using only rotary mode from 80, 100, 120, 150, 180, 220, and there's still some swirls visible. I ordered some 380 and 400 to see if that makes them disappear, though.

[Jeff Ramsey]

Here's an alternative approach. I typically reach for my LN 85 scraping plane (or a Stanley 85) in lieu of coarse/fine sandpaper, with several grain-raising sessions. Then I leave my Festool ROS and Vac in the corner, and with 400 grit and a block I finish up (and only stop at 400 if it's a satisfactory finish, which it often is). Less noise and great results.

https://www.lie-nielsen.com/product/...aper?node=4075

[Jason Lester]

I have noticed that

Jim, I think you have a Rotex? Do you keep it in rotary mode all the time, or do you find the ROS mode useful in any way?

I tried prepping a sample board using only rotary mode from 80, 100, 120, 150, 180, 220, and there's still some swirls visible. I ordered some 380 and 400 to see if that makes them disappear, though.

I don't have a Rotex but I'm pretty sure you'll need to switch it to ROS to get a smooth surface with no visible swirls. Rotary is used for stock removal and quick cutting. ROSS is for a uniform scratch pattern that will disappear under the finish.

[Phil Mueller]

In a word, no. Pretty much any finish is going to accentuate scratches, dents, and other flaws. With penetrating finishes, I usually wet sand up to 800 grit. With film forming finishes, I sand to at least 320. I typically follow up a ROS with a quick hand sanding. And even then, I wipe the whole thing down with DNA looking for anything I’ve missed. A finish is only as good as the prep.

[mreza Salav]

I do minimum 180 (typically 220 grit). Hand sanding with the grain is needed IMO if you want to truly get rid of the ROS marks. No matter what good of a sand paper you have I think a light hand sand with the grain and with the same final grit of ROS helps a lot.

[Alan Lightstone]

I put 120 grit on my Rotex, and place it gently down on the workbench. Then I put 120 grit on my 150/3, and do all my sanding with that, up to 220.

The Rotex is a beast in my hands. Exhausting and way too much vibration. I basically never use mine. On the other hand, I use the 150/3 on virtually all projects.

Not sure this helps you at all, but it's my experience.

[roger wiegand]

Another possibility:if you started at a coarser grit (or sandpaper with a few bigger particles) you may not have gotten the deeper sanding marks out as you went from 80, say to 120. Those swirls will then persist, even if you go to 1200 grit. It's critical to completely eliminate the sanding marks from the prior grit before moving on, let they be permanently enshrined in your final project. (You can, of course, sand them out with a finer grit, but it takes forever.)

[Jim Becker]

I have noticed that

Jim, I think you have a Rotex? Do you keep it in rotary mode all the time, or do you find the ROS mode useful in any way?

I tried prepping a sample board using only rotary mode from 80, 100, 120, 150, 180, 220, and there's still some swirls visible. I ordered some 380 and 400 to see if that makes them disappear, though.

I do have a Rotex, but it's the larger 150. I rarely use it in "ROS" mode because my primary sander 98% of the time is my 150/3. I did use it for my recent "kitchen continent" project to "level" the top as it was too big for anyone's wide-belt. (I should have kept it in two sections for that) I really don't understand why you're getting so much swirling. Any time I've had that problem, it was the result of debris under the disc or a piece of some kind of grit getting caught on the business side of the disc.

[John K Jordan]

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

I didn't take time to read all the posts so this may be covered. I do several things when sanding. (Most of my use is with small pneumatic random orbital sanders on woodturning - usually with a Grex.)

One, I sand by hand after each of the coarser grits with the same grit and take out any cross scratches, sanding with the grain with a soft backing pad. My theory is that if I can't get a 320 scratch out with 320 paper it will be very difficult or impossible to get it out with 400 or 600. Hand sanding after every grit also eliminates the unpleasant discovery of scratches from a much coarser grit. If I see any of those, I'll drop back and re-sand with the coarser grits. I don't find the hand sanding tedious if done at each step. Maybe it's a zen thing.

Two, intermediate scratches are far easier to see with a good glancing light AND after wiping on a liquid. I use naptha for this since it dries so quickly. A sopping wet surface will let me see what the figure and color will look like after applying oil, but as the wet gloss evaporates (or after wiping with a slightly damp cloth) is the perfect time to look at the surface from different angles with the glancing light. Scratches that are invisible on the dry wood will be quite obvious.

I use small diameter light sources instead of broad, diffuse sources like indirect lighting or long fluorescents high overhead. A bright hand-held light works well. The glancing angle puts the scratch in a dark valley, made even darker with the liquid.

Also, it may have been mentioned but the quality of the sandpaper can make a big difference. Some cheap paper is poorly graded and may contain a few particles of coarser grit. Nothing worse than a few coarse scratches in a 400 grit sanded surface. Don't forget to carefully clean the surface before each grit to remove any stray particles that may have broken off the coarser paper. I used compressed air followed by wiping with a damp cloth. (I used to grind and polish metal samples in a metallography lab and I have experience with what a single stray particle of grit can do!)

BTW, this may not apply to your work but with most woodturnings I rarely start with coarser than 320 or perhaps 220 grit because I usually remove tool marks with hand scrapers first. Also, with walnut and other open-grain wood, if I'm finishing with oil I usually wet sand with the oil at the coarser grits to help fill in the pores. On large, flat surfaces a grain filler would probably be easier and a quicker.

JKJ

[Ole Anderson]

I typically use 120/220 to remove planer marks and other imperfections, but then I don't use an oil finish either. On bigger projects I use my 5" PC angle grinder style of ROS with the dust vacuum kit added. I found it jumped around a lot when holding the disc flat so I tended to hold the disc at an angle and use the edge. When I went to the vac kit, I got a 6" disc for it and now it sits flat and doesn't jump around. Go figure... I believe the 5" PC has a smaller orbit than the 6" so it is less aggressive and you get a finer finish. Sorry this a bit off topic, but it may be useful to someone.

[Dan Friedrichs]

Very useful, Ole. So you stop at 220?

[Ole Anderson]

Very useful, Ole. So you stop at 220?

My discs stop at 220. Lately that seems all I need. Lately I have worked with oak, hickory and aromatic cedar. I typically finish with four wiped on coats of P&L 38 satin mixed 50/50 with naptha. I never see any swirl marks. I hit the dist nibs lightly with a 400 grit block sand by hand only after the last coat.

[Dan Friedrichs]

Thank you all for the replies. I think I've figured it out!

I was previously annoyed by the slowness of ROS mode on the Rotex. Turns out, you don't need to use the slow mode if you don't want to Using only rotary mode, I went from 80-100-120-150-180-220-320 and the final board had only slightly visible swirls. I should say, the swirls were still very obvious at 180 and 220 - it was going to 320 that was really quite key.

I think I could safely finish at that point, but a very quick hand sand at 320 really eliminated any last vestige of a swirl mark.

I'll try omitting a few of the intermediate grits (150, 220) in the future.

Thanks, guys! I used to HATE sanding (mostly because the amount of hand sanding I was doing was an extreme amount of labor, and because it never felt like I was sure the sander was "doing" anything), but now I'm just so tickled at how well this works that I don't mind it.