Square Floor Sander Leaving Swirl Marks?!?!

[decker 14]

Using a 12x18 square floor sander on PT and it's leaving swirl marks. Have tried, 60,80 and even 120 grit. No idea why this is happening. Tried it on multiple PT decks all with the same result. I tried it on cedar and it was much better, but still left some marks. Really weird.

Any ideas on why this is happening?

[bigchaz 157]

For one thing you shouldnt be using 120 on PT. The bearings could be going bad maybe causing it to wobble too much? Never had swirls on mine so not sure

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[decker 14]

Ya, the 120 was just out of curiousity. No idea what's going on with the machine, except this is damn annoying.