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Cheap sandpaper will do it because it will have one or two pieces of grit on it that are too large and cause the scratches.
A cheap random orbit sander won't oscillate enough to hide the swirls.
-Rob
*keep the sander flat, don't put too much back into it and maybe move a little slower.
*How fine a paper are you using, what kind of wood?? What kind of sander?
*bosch, 80 grit, oak and poplar
*That 80 grit probably cuts pretty fast but you have to go much finer than that to get less scratching. Like Chuck Crawford said, don't skip any grits. From 80 you should go to 100, 120, 150, maybe even to 180. Sometimes I skip 120, but then it takes longer with the 150.
*we take everything to 220 or 240 depending on what's available.If the swirls are somewhat continuous, like a spirograph, then it's probably cheap paper.I suspect with the 80 grit, you have the other problem - lots of minute, non-desript scratches. Difficult to notice, unless you do alot of that work.Why are you starting with 80 grit. For items that we do, if they have been planed we start at 180. If they came of the big sander (36in 100 grit) we start with 100.-Rob
*I've also found that hooking my RO up to a vacumn gives a much better finish. I believe that it's from removing the dust before it loads up the sandpaper and the grain. I also never use anything under 180--it just tears down the wood too quickly, paritcularly on veneers.
*Rob, In this area (st.louis) most of the stair builders generally use 80 grit paper in carving fittings, cleaning up tread returns and etc. If the painters want a slicker finish they usually hand sand it down to a finer finish. Also it depends on how dark the stain color is, it seems thedarker the stain the smoother the surface needs to be.
*Some of the obvious causes of big swirls have been dealt with, such as a stray piece of large grit, or bearing down too hard, moving too fast, etc.. But I find it odd that anyone would expect a machine that operates in a random rotary swirl pattern would leave anything other than, well,.....random rotary swirls. They all do, and any finish over the top of something prepared with a random orbital sander only highlights the swirls, particularly on something horizontal, like a table or cabinet top. Maybe I'm particularly pernickety, because I build furniture rather than trim houses, but a swirl, is a swirl, is a swirl, and I can always see them in furniture prepared for polishing with one of these machines, even when taken down to 320 grit and beyond. It may be small, but I can still see it.I guess I'm being pedantic and nitpicking, and if so I apologise to everyone for being so, but I'm only stating what my eyes can see as plain as day.
*Had a big problem with swirl patterns on mahogany panels with dark stain applied...looked like someone set down a wet coffee cup in the work piece. Nasty part was the wood looked completely smooth and uniform until the stain went on. We were able to minimize the swirling by starting up the sander before contacting the work surface, and breaking in any new sanding disks for a couple of seconds on a bench top suface to reduce its aggressiveness.
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