The best reason to buy a power sander is to eliminate wood finishing by hand. But, what type of power sander is best for you? Should you purchase an orbital, random-orbital or perhaps a belts sander? Sanding is actually the process for scratching the surface of wood with an abrasive material in a series of moves that reduces the paper grit to a finer grade. Each of the sanders compared below works in different ways.
A belt sander can be compared to a circular saw in that the belt and circular are linear tools. Through using a reciprocity motion that is both circular and continuous, the belt sands while the saw cuts. The belt sander is a much faster machine than an orbital or random-orbital sander. However, speed comes at the expenses of lack of precision control. Improper use of a belt sander can produce gouges, curves and other imperfections you don't want to produce and these imperfections cannot be easily repaired.
Even though you should not use a belt sander on plywood or any other veneer surface, you will find the belt sander as an incredibly useful tool for many of your carpentry and woodworking needs.
A random-orbital sander has a disc that is both freewheeling and orbiting. The speed will vary with whatever pressure is applied. The orbital action is dependent upon the motor's speed. The combination of the 2 actions will produce an irregular, or random, result that in the hands of a practiced user can provide for a very fine finish. It differs from the orbital sander in that it is switched on first while in contact with the wood. This is done to help prevent any gouging from the spinning disc. Using a random-orbital sander will necessitate the use of a hand sander to finish when staining wood.
This is by far the least expensive type of sander and is available in many forms. A popular type is referred to as a palm sander. As stated earlier, orbital sanders are started before the sander is applied to a piece of wood. The less expensive cost aspect is due to use of regular sandpaper sheets that either are bought pre-cut or cut to fit the sander.
Uaing a belt sander is similar to using a wood plane. It can do almost all the same jobs--from sanding door edges to sharpening chisels. However, if you need to simply prepare wood surfaces for finishing with a stain or clear protective coating, use of one of the orbital or ROs (random-orbital) sanders to do the job nicely. You can also use one of these types to remove imperfections, scratches, rough spots and thin finishes.
Check online at Do-It-Yourself for resources to find a bargain on a power sander.