Preventing Swirl Marks from Orbital Sanding

Advice on how to minimize swirl marks from a random orbital sander. June 17, 2009

Recently I have been sanding doors with 150 grit sandpaper on a bi orbital sander. I noticed that there are consistent swirl marks after sanding is completed. I always hold the sander the right way. Is there anything i can do to prevent this?

Forum Responses
(Finishing Forum)
From contributor B:
You should not be getting swirl marks with 150 grit. If your down to 150, maybe youíre using too much pressure. Is the wood real soft or is dirt collecting on the sandpaper? Other than that its usually bad sanding technique that does it.

From contributor G:
Some people hand sand with paper one grit coarser after orbital sanding to cure that very problem. Try orbital sanding to 180, then hand sand with 150. That way you get rid of the swirls and still maintain your finish sanding schedule. Use quality sandpaper.

From contributor J:
A few things to think about regarding swirl marks: all orbital sanders will make swirl marks but not all sanders have the same size orbit pattern. A sander with a large orbit pattern will be more aggressive and efficient at removing a lot of stock but will leave heavier swirls. A sander with a smaller orbit will be less aggressive and produce smaller swirls even with the same grit paper. A sander with a thicker, softer pad also helps.

Not all sandpaper is the same. 150 grit from one manufacture will be slightly more or less coarse than 150 from a different manufacture. Even within the same brand, different types of paper can vary in actual coarseness for the same number grit. Technique has as much to do with swirl marks as anything else.

The biggest mistakes people make when sanding are going too fast, using too much pressure and tilting the sander off level. All of these mistakes can cause sanding marks that may not be evident until after staining and finishing.

Finally, knowing what grit is the best for the wood you are using also helps. 150 is a good all around choice but it can be overkill for some hardwoods like ash and hickory, while other woods seem to like a finer grit. For instance, I go all the way to 180 or even 220 with walnut. It seems to show marks from anything coarser, especially when stained.

From contributor R:
Try a different sander if youíre getting swirl marks. Has someone dropped it one too many times? I have the Porter Cable 1/4 sheet sander and the 1/2 sheet one as well and both have a 1/32 swirl to them.

The only times I seem to get swirls is if I sand too fast. I like the 3M silicon carbide paper for both raw wood sanding and sealer sanding. Iíve been sanding sealer coats with 280 for quite awhile and it seems to work for me. With raw wood I might use150-180 and like contributor J I like 220 on walnut.

From the original questioner:
Yes my men have dropped the sanders a couple of times; however they cost 350 dollars. I can't see buying new ones if they get dropped?