There are two large categories of random orbit sanders: electric and pneumatic (compressed air.) Both work well, though you need a fairly large compressor to power a pneumatic sander adequately.
Random orbit sanders are easy to use; you don’t need much instruction. But there are two general rules to keep in mind for achieving the best results:
- Let the weight of the sander do the work. If you press down on it, you’ll leave deeper and more obvious “squigglies” that then have to be sanded out. Simply move the sander slowly over the surface in some pattern that covers all areas about the same.
- Nevertheless, you’ll still leave squiggly marks on the surface. If they aren’t deep, they may not show up under a clear finish, but they will show through a stain. So it’s a good policy to always finish up by hand sanding with the grain using a flat block to back the sandpaper. Use the same grit sandpaper you used last with the sander. You can also use one grit finer, but you’ll need to sand a little longer.