Orbital Sander Tips

Cabinetmakers give advice on avoiding swirl marks. July 22, 2005

My orbital sanders leave hundreds of scalloped marks (half-moons) all over the wood surface. How can I prevent this? I've tried different types of paper, different brands, but to no avail. I use and electric sander, not an orbit sander.

Forum Responses
(Cabinetmaking Forum)
From contributor S:
A few of the more common responses that I've seen are:

1. Lighten up on the pressure, let the sander / paper do the work.
2. Don't take too big a step between grit sizes.

One thing I've noticed on my 6" Dynabrade is that since the rubber backer is slightly convex shaped, if I leave the sander balanced in the center I get more swirl marks. If I lean it slightly off to one side or the other so that the edge is doing more of the work, the swirls are almost eliminated. If I had to guess, I'd say it's because the random motion is more pronounced at the edge than it is in the center.

From contributor J:
Air line size was my fix when I had same problem. I now use 3/8" and it seems to do it for me.

From contributor R:
These days I think a few small marks are normal, not perfect but normal. I think it is a good trade off, compared to the alternative.

From contributor F:
Since you didn't say random orbit, Ill assume you have a plain orbital sander. If that is the case, then pushing down too hard is probably the main problem. Pushing down too hard with a soft padded sander will also give you rounded edges on narrow stiles and rails. It is better to change your sand paper more often than to press hard to try and get more work from a dull sheet of paper.

From contributor S:
Are you using an electric sander or air? I've found that there are a few answers to this problem. The most common two seem to be applying too much pressure on the sander and skipping grits. I have also had problems with electric sanders with brakes. This feature slows the sander down when it isn't on the surface. Manufactures put this feature on the sander to keep it from freewheeling and gouging the material when the sander is first put onto the work piece.

The brakes seem to wear out and I'm not exactly sure why this happens (heat may distort the rubber brake). I haven't had this problem with the Dynabrade air sanders, although we only use the 5" 3/8" orbit.

I have also noticed small swirls on the material due to the pad being out of balance or distorted. In this scenario replacing the pad has solved the problem. Yet another reason why you may be getting swirls is that you are not vacuuming or blowing off your surface between grits. If you don't clean the surface, the dust and ground grit from the previous sanding will get trapped under the pad and leave tiny gouges on the surface.

From contributor W:
Ive found that slower passes with lighter pressure will allow the sander to smooth out the scallop marks.

From contributor T:
I agree with the previous responses. I'll add that keeping a small pad of Berber carpet handy to clean the disks often while sanding will help a lot, and increase the life of the paper. Dustless sanders do better too. Make sure to apply light pressure, slightly tilt the sander, keep the disk clean, and don't skip steps when changing grits.

From contributor T:
Also, with air sanders the pad needs to always rotate in a clockwise direction. We have tick marks on all of our sanders so the guys can see the rotation. It doesn't have to rotate fast, but if it stops or goes counterclockwise you will have swirl marks.

From contributor B:
I've had the same problem and tried lots of the things mentioned here. What worked best for me was to follow Troy's advice. Now all the sanders I use are marked and I haven't had the problem unless I really bare down on the sander.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor G:
It is more so the paper that you are using. You would need to switch to a paper that does not have the grit breaking away from the paper. Once the grit breaks off the paper on the side, there are only two places for it to go - under the sander or off the wood. What goes under the sander is what would cause that type of scratch pattern.