Random Orbital SanderThe most common type of sander found on store shelves today - and easily the most versatile. The "orbital" part of the name comes from the action of the sanding disk. The "random" part comes from the elliptical motion the disk makes in addition to the orbit. The Black & Decker Mouse is probably the most prominent example of a random orbital sander.
Why You Want to Use One: Prevents scuffing and scarring the wood if you happen to go against grain.
What to Use it For: Fine projects, chairs, tables, or trim and baseboards where surface condition is highly important.
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Belt SanderA belt sander is any kind of sander, handheld, table-mounted, or on the floor, which has a continuous loop of sandpaper running through the machine.
Why You Want to Use One: Great for ripping off the rougher, initial stages of any sanding project.
What to Use it For: Removing exterior paint, hitting high spots on wood flooring, removing extraneous wood material, etc. Due to space limitations, not good for getting close to walls.
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Orbital SanderWhy You Want to Use One: A handheld machine. Removes a lot of product fast, and allows you to get right into edge spaces.
What to Use it For: Hitting wood flooring right near the baseboards. It is also possible to rent large orbital floor sanders to prepare the finish of wood floors.
Drum SanderWhy You Want to Use One: Technically part of the belt sander family, this is a specialized sander that must be obtained from rental yards.
What to Use it For: Wood flooring only.
Spindle and Disk SandersWhy You Want to Use One: Tablemounted machines allow for greater stability than with handheld machines. Spindle sanders have the sandpaper on a tube-like base. Disk sanders have the sandpaper on a disk, much like the handheld orbital sander.
What to Use it For: Woodworking projects.