The Different Types of Sanders
Belt sanders are probably the most common thing people have in mind when they think of a sander. They have a looped pieced of sandpaper fitted around two wheels, which spin the sandpaper around at a very fast speed. This is probably the most heavy-duty of the hand-held power sanders, and should be used at the very beginning of a rough sanding project. Some examples of times to use a belt sander would be removing lots of old paint or stain, basically preparing a surface for more detailed work by removing the old. These sanders are very aggressive and can remove a lot of material in a hurry, so be sure to pay attention while you are using them, especially on softer woods. If this worries you, then a belt sander with a variable speed adjustment is for you.
You may have also heard of a narrow belt sander. This is just a normal belt sander that is not as wide, making it useful for smaller hard to reach areas.
Palm sanders are also sometimes called finish sanders, or pad sanders. They have a small rectangular pad on the bottom, which usually takes a 1/4 or 1/3 sheet of sandpaper. It vibrates in a somewhat circular pattern, and must be moved along the wood in the same circular motion to avoid scratching. When used correctly, they provides a nice smooth finish on flat, easy to access surfaces. This would be a perfect sander to use after the belt sander does the heavy-duty work.
Detail sanders (sometimes called a contour sander) are smaller than other handheld sanders, and are used for getting into tight spaces and sanding odd shapes that other sanders cannot handle. The pad is usually triangle shaped, but many of these sanders come with multiple attachments to aid in reaching even the smallest of spaces. These tools are usually used for small craft projects and even mill working, such as window and door casings.
Random Orbit Sander
Random orbit sanders are probably the most versatile sanders around. They are great for jobs big and small, and they are small enough to get into most tight spaces. These sanders have a round pad that moves in a circular motion, with a little bit of random variation to prevent swirl marks on your piece. They also feature variable speed control, which is great when you are working with soft wood, or you are getting to the end of your sandpaper. Dust collection is built into the random orbit sander, usually coming with a dust collection bag, but sometimes with a vacuum hose attachment. There are small holes on the circular pad that sucks up the sawdust as it is created. Because of these holes, special sandpaper specific to random orbit sanders must be used. This sandpaper also has holes that line up with the dust collection holes. If you are looking for an all-around sander that is great for multiple purposes, the random orbit sander is for you.