Before sanding, skilled carpenters had to use planes and scrapers to smooth out a piece of wood they were working on. This is why there’s so much old woodwork around in which you can still see cutting marks. Unless it was necessary, the time consuming process of smoothing out a surface was seen as an unnecessary cost.
Sanding has made it possible for anyone to properly finish a project, giving a smooth, even surface to finish. When electric sanders came along, that just made it possible to finish off workpieces all that much easier. For people who don't have a lot of patience for sanding (like myself), having a sander or two (or three) around makes projects much more enjoyable.
The trick is figuring out the type of sander you need in order to provide the finish you’re looking for. While the grit of the sandpaper has a lot to do with the finish a sander gives you, so does the type of sanding action said sander provides.
While we could break down the types of sanders there are into a wide range of specialties, there are seven basic categories of portable power sanders.
Types of Portable Sanders
Belt Sanders
Belt sanders, whether portable or hand-held, are designed for taking off a lot of material quickly. This makes them perfect for final shaping of workpieces, before finishing sanding. However, the same thing that makes them good for taking off a lot of material quickly makes them a poor choice for finishing sanding. Even with a fine sanding belt, a belt sander will reshape material quickly and possibly destroy it if you’re not careful; you’re really not going to get a smooth finish with a belt sander either.
Palm Sanders
Palm sanders fall into two sub-categories; quarter sheet sanders and "mouse" sander with both operating the same way, being vibratory sanders. That means the motor is attached to an eccentric cog, which is in turn attached to the sanding pad. This creates the vibratory action which cuts the material. This is a fairly typical sander for wood working and probably the most common one you'll find in a woodworker's shop. It is not used for metalwork at all.
The basic difference between the two types of palm sanders is their shape. Quarter-sheet sanders are designed to use a quarter sheet of sandpaper. There’s a clamping system used to hold the sanding sheets in place but they’ll also work quite well with self-stick sanding disks which stick directly to the pad without having to use the clamps. The mouse style usually uses sanding sheets that stick with Velcro. The biggest advantage of these types is they’re extremely good for getting into inside corners.
Detail Sanders
Detail sanders are the new kid on the block, stealing that title from the mouse style palm sanders. They’re based on the oscillating tools that perform so many tasks and in fact, many are the exact same thing. Like the palm sander they work by vibration; however, the vibration in a detail sander is much finer which helps eliminate scratch marks from the sanding medium. The sanding pad is smaller on these tools so they don't take off a lot of material at any one time.
There are also a few unusual detail sanders which still fit best in this category rather than any other. These would include pneumatically driven sanders and pencil sanders. These don't operate the same way as the oscillating ones do but still designed for detail-oriented work.
Finish Sanders
In reality, all of the sanders we’re talking about can be called finish sanders because that's what they’re used for. However, we are actually referring to a specific type of sander when we talk about finish sanders, either the 1/3 or 1/2 sheet sander. These are essentially the big brother to the quarter sheet palm sanders and have clamps to hold the sanding sheet as well.
These sanders have two main advantages over the quarter sheet sander. First of all the larger pad size means you can cover more territory at a time, speeding up the sanding process. To speed it up even more, they operate at a faster speed. These sanders are usually heavier, meaning you don't need to provide as much pressure when sanding horizontal surfaces; but you might want to have a quarter sheet sander available for sanding vertical surfaces.
Orbital Sanders
Orbital sanders fall somewhere in between the extremes of being a fine finish sander and taking off material like a belt sander will. They can take off material much faster than vibratory sanders, while providing a much better finish than belt sanders can. Originally, orbital sanders were developed for auto-body work, but woodworkers are starting to use them as well, especially for use with tight grained hardwoods. The caution that needs to be taken when using orbital sanders with wood is sanding isn’t done across the grain.
Orbital sanders almost exclusively use self-stick sanding disks, although Velcro sanding disks are gradually replacing them. These higher quality disks will last a long time if used correctly.
Dual Action Sanders
Random orbital sanders, a sub-category of orbital sanders combine the orbital pattern with a second rotating pattern, eliminating the possibility of causing a swirl pattern in the surface being sanded. This is especially good for fine finish work, whether in wood or metal.
Dual action sanders allow you to choose between normal orbital action and random orbital. This allows you the faster cutting of the orbital pattern and then you can switch over to the random orbital for the fine finish work.
What to Look for in a Sander
The first thing is always to select the type of sander you need for the work you’re going to do. Don't be surprised if you can't find one sander to do everything as most people end up with multiple sanders.
When looking at sanders, the issue isn’t power but rather control. Being able to accurately control the sander, especially for finish sanding, is a major issue. Sanders operating at a higher speed will cut faster and provide a smoother finish along with less swirl than slower operating ones.
Operator comfort is a major issue with any sort of sanders. Both vibratory and orbital sanders shake constantly which contributes to operator fatigue. Rubber over-molded handles, shock-mounted mechanisms, and dual hand grips all help in dealing with operator fatigue.
Many vibratory and orbital sanders now use self-stick sanding sheets. These can either be adhesive or hook & loop. The added convenience of self-stick sheets is time since changing sanding sheets is limited to a few seconds, rather than several minutes of struggling with latches and trying to make the sanding sheet smooth. Although costlier, these very convenient self-stick sheets really pay for themselves.