Sanding is an important process in any lumber project because it prepares the wood by opening it's natural pores to accept finishes and stains. It also removes any residue left over from planer blades when the wood was processed. Not just any sander or sandpaper will do though. You must first choose the correct grade of sandpaper and type of sander for the job you are working on or you might damage your wood project.
Sanders use sandpaper which come in various different grits (degrees of abrasiveness). The lower the amount of abrasive particles per square inch, the higher the course of the grit. Course sandpaper has 40-60 grit and is used for removing previous finishes or quickly removing unwanted wood. Medium grit sandpaper has a grit of 80-120 is good for removing scratches and rough spots in the wood. Fine grit sandpaper has a grit of 150-180 and is used for finishing sanding and smaller fine projects. Sandpaper also comes in Very Fine (220-240), Extra Fine (280-320) and Super Fine (360 and up). These are all used to continue to remove very small scratches left by previous sanding. You would want to keep sanding your lumber project with finer grit sandpaper until you reach your desired appearance.
After choosing the correct sandpaper for your project you want to choose the right sander
appropriate for the job. If you have a small project that needs to be handled with care you might want to hand-sand the wood or use a small hand-sander such as a mouse sander. A rotary sander or palm sander would be used for larger, flat surfaces and a belt sander would be used for a large job such as hardwood floors. It is important to note that belt sanders are powerful and often cause more scratching so use it on big, tough surfaces. Taking the time to do a little research on what type of lumbar you are using, the different types and grits of sandpaper and choosing the proper sander will help you achieve a finished project you can be proud of in the end.