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What causes swirl scratches?9/3/17
What actually causes swirl scratches when using a random orbit sander? Pressing down to much or not enough? Going over the wood to fast or to slow? We are using a ceros sander with 120 grit. I don't do the sanding but the guy that is has been with me for years. Doesn't happen all the time but certain stains tell on us.
With an pneumatic sander the first thing to look at is low pressure. Electric... not sure pressing to hard. Cheap paper that has "big grit" mixed in. Dirty disk under the paper. Lots of things can cause it.
Go down to 150 or do you always stop at 120? 120 is too rough.
I've used disks from industrial abrasives for years, best I've found. I think it's Indasa or something like that, got a rhino on the box I think. I do stop at 120 grit and have for the last 20 years mainly because when you go finer the wood is more likely to repel stain than soak it up. Hard to achieve a rich dark color. By the time I'm through the schedule my finishes are slick.
I always look at the speed I moving the sander. Sometimes moving to slow with the sander causes it along what has always been said.
Good info above.
Some sanders seem to be worse than others. I'm happy with Dynabrade air sanders but there are so many types of electrical sanders that I cannot recommend one over the other. Except, quit using electric lol.
My most common problem is the paper. I've found a small handful of brands that give me good results (usually the green emerald colored pads) on Dynabrades. Using a good quality paper has been our #1 way to stay consistent.
But like said above-- using excess pressure will do it. Sanding in a dusty environment will do it (we use downdraft tables, which is a huge help). Having a worn velcro or PSA pad will do it. Getting a lump of dust under your velcro or PSA pad will do it.
On oak, it can be really tricky to hide them even on the best days with the best equipment.
Im pretty sure that Indasa does NOT have a multi hole disc (Multi hole being a LOT of really small holes ) If you are only using a 5 or 8 hole then that causes dust collection to not be very good.
The no. 1 cause is going back and
From my experience, two things cause swirls: moving too fast and/or tipping the sander causing it to sand on the out edge of the abrasive.
along with the above suggestions; when I was a corian certified installer we were told it was inconsistent grit in the sanding paper which is why the micron graded sandpaper was recommended.
All good responses. 120 grit an in between paper as far as aggressiveness. We all sand by the numbers. Our schedule is typically 100/150/180 for stain grade. In order to eliminate the previous depth of cut you need to sand to that depth to get rid of that scratch.If you skip one spot depth wise you will be left with swirls typically from when the sander initially touches the surface. The random orbit sander initially is a rotary sander until it makes that first cut then switches to true random orbit on the next rotation or two.
My first suggestion would be to wipe the entire surface with denatured alcohol after finish sanding to see if you missed a spot. This is common practice for our stain jobs.