Took this info off another site and have found this info very helpful. Baily, this may help you too. Concise, no opinion "it works for me and should work for you response"
It is important to consider some different factors whenever you are sanding. In no particualr order, here are some:
Wood species: Walnut is more forgiving than maple, oak sands different than cherry, and the technique you use on straight grain will not work on figured wood. Employ the technique, sander and abrasive germane to the species.
Technique: On an orbital sander you must always keep the sander moving to convert those tiny orbits into long ellipses which line up with the grain and disappear. If you are having trouble with your random orbital sander, try moving it in the same fashion, with a light hand in long, brisk strokes. Scratches are usually made in the coarser grits, deep below the surface. They are often not detected until the sanding done, with the assumption that they were caused by the final passes in the finer grits. Spend more time sanding with the coarser grits employing good technique, careful not to push the sander and dig deeply. Woodworkers generally tend to push with the coarser grits and lighten up on the fine ones. If anything, the opposite approach is be better. The pad must always spin freely for optimal results. Different sanders require different technique. If you are used to using one type of sander and have changed machines, you will need to employ different technique. Experiment and see what achieves best results. Some wood workers dampen the surface with water to raise the grain prior to the final pass.
Sander: Festool sells a dozen sanders for good reason, so you will always have the right sander for the job and achieve best results. It may be that the sander is not best suited to the task. It may be that using a different sander, or using different sanders at each stage creates better results faster. The amount of suction by the vac affects sander performance and surface quality. The 125 is a fairly small pad and the CT at full suction can make that pad tend to stick to the workpiece. I know, you are not using the sander, only the small paper filter bag supplied with the sander. That dc is powered by the sander's fan and is not efficient in removing all the dust off the workpiece. I have used that filter bag less than a handful of times in all the years I am using the sanders - to me it's to be used only when there ain't no room to use a vac - and it doesn't have to be a Festool vac either. Always use the optimal sander for the task, along with good technique, and you are assured excellent results.
Abrasive: Rubin has a thicker backing than Brilliant, and so is stiffer. It has a heavy top coat which prevents wood fiber from attaching, which helps it to cut better. But that irregular surface can be less forgiving than the more uniform Brilliant. You can sand pine or walnut with the open-coated Cristal and achieve a good surface quality, but to use Cristal on maple or cherry would create deep scratches which would require bringing the entire surface down to disappear. If you are having trouble with Rubin, try Brilliant, and visa versa. Matching the abrasive to the application is key. When the abrasive is caked up, get rid of it.
Overusing a disc will burnish the surface. A contaminated disc will deface. Fresh paper creates fine results. Most important, don?t skip grits. When you are sanding, you are creating a finer and finer scratch pattern. Each step is necessary for perfect results. When you skip grits you are not effectively covering your tracks, and it will show in the results. Working successively through the grits, you will not only achieve better results, but you will spend less time sanding in the end.
Finish: Using a dark stain on a light wood species will bring out any surface imperfections. While a clear coat on the same surface won?t show a sign. If you want to go dark, start dark, you will achieve better results. Not all stains are created equal; always use the finest products for best results. Finishes have a shelf life, too. Surface contamination can create problems. How about trying a sanding sealer to reduce surface imperfections? Never apply finish before you test the surface, you can wipe it down with alcohol or paint thinner or water first, and that will reveal any scratches. It is also good to use a side light, a strong light cast at a low angle which will also show you any surface irregularities. Correct as you go.
Having said all of the above, this doesn't mean that any sander (even Festool sanders) can't develop problems, or have a problem to start with (countrweights/brakes, brushes, etc.), but you have plenty (at least 30 days) of time to use the tool and if you sense their is a problem, or something ain't right, call your dealer or give Festool's Service Department a holler. They are always ready to help in any way they can, but no one can help, if they are unaware of the possible problem/issue you have.
Bob
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bob marino
www.bobmarinosbesttools.com
Terry
my fair share actually.
