How frequently do you change ROS sandpaper discs? (and other dumb sanding questions)

[Dan Friedrichs]

I'm finding my sanding skills/results lacking, and wonder if I'm doing something fundamentally wrong.

Some questions:
1) Say you've got a 5 or 6" ROS with excellent dust collection and high-quality paper (Mirka or Festool, etc). Assume you're sanding a large table top (or something where 100% of the sandpaper is contacting the work). How much time do you put on a sanding disc before you consider it "worn out"? (Seems like a new disc quickly loses a bit of sharpness, but beyond that, is it usable for 30 seconds or 30 minutes?)

2) How thoroughly do you vacuum/brush off a surface when switching between grits? Is it: "Not at all - the (Festool) dust extractor gets it all", or a "I spend several minutes with the air compressor blowing every last remnant of the last grit off"?

3) How much time do you spend with each grit? Say you were sanding a completely-flattened coffee table top (~2'x4') through 120, 150, 180, 200.... is that a multi-hour procedure or a ~15 minute procedure?

4) Finally, would you do any hand sanding of a flat surface, or is the ROS the last step? Even using what I think are "best practices", a sideways-aimed flashlight shows sanding scratches that I'm worried will show up after finishing, so I end up using a sanding block to do the final sanding "with the grain". Is that normal/necessary?

[Charlie Jones]

I probably change the ROS paper to often. I would rather waste a little than spend more time sanding. That is my least favorite woodworking task. I start at 80 for most surfaces. I use 80 to get rid of defects then switch to 150 to take out the 80 scratches. Then 220. Sometimes 150 will do.
I brush and vacuum the surface between grits. When I think I may be done, I wipe the surface with mineral spirits. That will tell you if your done or need to go back and sand some more. If I am aiming for A
high gloss finish I may ROS to 220 then block sand with 220. If the finish is oil or matte I may stop at 150.

[Charlie Jones]

Oh, and I use Klingspor disc's.

[Ole Anderson]

I just refinished an old Lane cedar hope chest. All aromatic cedar. I used 80 grit 6" discs on my 6" PC ROS with the dust collection kit. The finish and wood clogged the paper so bad I went through probably 6 discs. And I turned to the belt sander with 80 grit to finally get down to real wood which still clogged the paper with resin. Used two belts. Hit it with 120 then 220 on the ROS. All PC stick on discs. Four layers of satin P&L 38/naptha 50/50 wiped on. Block sanded out the dust nibs with 400 grit on a foam auto style block only after the last coat. Just like my kitchen cabinets, it looks and feels like raw wood, no plastic look built up finish. Smooth as a baby's skin.

Edit: To answer some of your questions, 1. if they are just wearing out (no clogging) I keep using them for probably 15 minutes of sanding, Although I leave my 80 grit on my 6x48 belt sander months until it breaks, by then it feels like there is no grit left. 2. I generally brush between grits and vacuum after the final grit 3. on a 2'x4' oak machine planed surface I would be less than 5 minutes per grit usually using 120 then 220, but then my PC is pretty aggressive, it is actually the 5" sander with a 6" disc. 4. I might go over everything, particularly the corners, with 400 grit folded in half, by hand. I have a roll of 180 and a roll of 400 2.5" sticky back from the auto parts store. Fold it adhesive to adhesive side and you get grit on both sides. Highly recommended for hand or block sanding.

[Matt Day]

1). If I had to guess I’d say 5-10 minutes of continuous sanding. After a few minutes of sanding I check the wear of the sanding disc visually and by feel. I try not to get to the point where it’s a noticeable difference when I put a new disc on.

2). A few brushes stokes or usually a microfiber wipe down.

3). Generally I spend the most time with 80, as I’m removing planer/jointer marks and it takes the longest to get a consistent scratch pattern. Probabaly 5 minutes on a 2x4 top. Then I go to 120 then 180 then 220 or something like that. Time with each is say 3, 3, 2 minutes, respectively.

4) ROS is the last sanding step for me. Hand sanding, especially a panel is easy to get a long straight scratch pattern going. The random pattern is much cleaner. I wipe down with a rag and DNA to clean dust and mimic what it will look like with finish.

[glenn bradley]

I'm a bit of a broken record on this . . . trying to wring more life out of your abrasives is a false economy. When your abrasive stops doing what you expect it to do (that is; what it was doing when you started using it new) then change it. Quality abrasives like Klingspor, Industrial Abrasives and others are a whole different level than anything you find at the Home Center. Once you make the transition you will wonder why you waited so long to get such an increase in performance for such a small cost (different from price) increase.

[johnny means]

I think of a single disc as being good for approximately the surface of a sheet of plywood. I do three passes of each grit after the initial flattening. If a disc is showing wear, it's way past due, abrasives should still look new when discarded.

[roger wiegand]

The fellows at our turning club constantly say "use sandpaper as if someone else is paying for it". That said I probably use mine too long, I'd guess 20-30 min of sanding time. Typically when I change I get the feeling that the new piece is much faster, which probably means the old one was worn. I have typically spent a long time on the first grit (80), getting the entire surface flat and uniform in its scratch pattern. Subsequent grits I do only until the scratches from the previous grit are gone, maybe 20% the time of the first grit. At the end (180 or 220) I dampen the surface to raise grain and make another very quick pass with the final grit. I never skip a grit, that's the quick way to swirl marks visible only after you apply the finish. I do as much as possible through the SuperMax at 80 grit, then RO at 80 to take out the parallel sanding marks from the drum.

Since I finally (after 40 years of woodworking) learned to sharpen and setup my planes I've found that I can plane the surface flat to a near finished surface and start sanding at 150 or 180. Maybe if I can improve my technique I will reach the nirvana of skipping the sander!

[Dan Friedrichs]

When your abrasive stops doing what you expect it to do (that is; what it was doing when you started using it new) then change it.

Oh, I agree, Glenn. But with a Festool "dustless" sander, I'm having a hard time telling when it stops doing what I expect!

Seems like a new piece of paper is "really sharp" for about 10 seconds, then feels about the same for....a really long time? I'm usually throwing paper away when I bump the edge of the ROS into something and it tears a piece off, but otherwise, I can't really tell when I should be changing it...

[Matt Day]

With Norton abrasives it's pretty easy to visually tell as the blue wears away. Not sure about Festool.

[Jim Becker]

I change the disc when it's either clogged with something that doesn't clean off or when there's enough noticeable wear to warrant the change. In many cases, they are still usable for hand sanding at that point. I use compressed air to clean most of the time and sometimes try a gum-rubber sandpaper cleaning stick. I do use Festool and the excellent dust collection absolutely helps prolong abrasive disc life, especially because of that center hole.

[Wayne Lomman]

Change the disc based on a combination of how well it is cutting and is it heating the surface. Remember also that the paper should be doing the work. If you are leaning heavily on the machine it is definitely time to change. There is no set time though. This is different for every timber or timber product. Cheers

[Sam Murdoch]

Never thought about "time" as regards to the use of an sanding disc. I too, likely throw them out early - before they are done, but would rather sand effectively than just go through the motion. Still, I would expect to be able to strip the finish off an entire 48" round table top (normal refinish of a dining table) with one grit before tossing and moving on to the next.

For finishes I have found the Mirka Abranet Mesh far exceeds the Festool papers. It goes at least 5 times, possibly more, without clogging. To the point that I now use it nearly exclusively in my Festool ROs. I still like the Brilliant II for wood or between coats of fresh paint, or Granat for coarse sanding but if I have the Mesh on hand I use that first.

[Jim Becker]

Remember also that the paper should be doing the work. If you are leaning heavily on the machine it is ...

...going to toast the pad on the sander prematurely from heat. Leaning also slows the sander down. Excellent point, Mr. Lomman!

[Andrew Joiner]

Oh, I agree, Glenn. But with a Festool "dustless" sander, I'm having a hard time telling when it stops doing what I expect!

I test with light pencil marks on the wood. The rate they sand off is visible. I'm usually surprised how long disks last.