Before I get into those, however, I want to remind you of a few basic rules for sanding.
1. Always sand with the grain. Most of the fibers in a piece of wood run lengthwise. So you should sand lengthwise to avoid tearing the fibers and creating deep scratches that will either require additional sanding, or will be very visible when the project is finished.
Don't inhale the dust. Get a good dust mask. Those with a built-in vent are easier to breathe through and won't cause your glasses to fog if you wear them.
Use hearing and eye protection when you sand aggressively. You can skip these for hand sanding, but when you fire up a belt sander or a random-orbit sander, you better have them on.
Okay, enough rules,
It's All in Your Head(phones)
Look, I'm not going to try and sell you on the "Zen" of sanding or the romance of becoming one with the wood. Sanding is work, and the payoff isn't immediate. You can sand all day and have seemingly very little to show for it besides a pile of dust. But in the end, your project will look better, the finish will last longer, and there will be no distracting blemishes in an otherwise exceptional project.
Of course, even knowing all that, you probably still dread the time devoted to a thorough sanding job.
The trick is to turn sanding into an exercise you actually look forward to. My secret is a set of noise-canceling headphones with an auxiliary jack. The jack lets me plug in a CD player, iPod, or portable radio so I have something other than the endless drone of the sander to listen to. And since sanding is really pretty repetitive, brainless work, it's easy to get lost in a book-on-tape, podcast, or some good music. It makes the time fly by. And the noise-canceling feature protects my hearing when I'm running a power sander.
Know Thy Grits
Now that you've got your attitude right (thanks to your personal listening choices), it's time to get the right grits for the task at hand. It's important to know where to begin and where to end in your sanding progression.
If you begin with a grit that's too coarse, it can actually make the wood rougher than when you began and create extra work for you in the long run. If you start with a grit that's too fine, your progress will be slow and you may never remove the worst scratches or blemishes.
A good rule of thumb is to begin with 120-grit sandpaper. In most cases, this will be just right. Occasionally, you may need to step back to 100-grit if the wood is especially rough or if there are saw or blade marks that won't smooth out easily with 120-grit.
From there, you should progress through grits in small steps: from 100-grit, go to 120-grit, then to 150-grit.
If the project is getting painted, 150-grit is as fine as you'll have to go. For projects that get a "film-building" finish like a varnish or polyurethane, you can stop at 180-grit. When you're planning on an oil finish, it's best to progress all the way to 180-grit sandpaper.
Sand Before You Assemble
One way to save a ton of time in the long run is to sand all the parts of a project before you put them together. This will give you much better access to all the surfaces, and it eliminates having to sand into corners. So not only will you spend less time sanding, but you also eliminate the likelihood of scarring adjoining pieces, which you will almost certainly do if the project is assembled before you start sanding. And remember, each new scar is just one more thing you need to sand away.
Expose Problem Areas
Looks can be deceiving. So can touch. A board may look and feel smooth to you, but as soon as you apply a coat of finish, tiny mill marks and scratches that you couldn't see or feel stand out like a sore thumb.
You can avoid that headache by wiping each board and each surface with a rag dampened with mineral spirits. The mineral spirits will reveal the same imperfections that a finish will, and then it will evaporate and give you a chance to fix them.
This wiping step also helps remove a lot of the sanding dust that's clinging to the board, just waiting to mess up your finish.
Selecting Your Sander
In addition to your bare hand and a sanding block, there are a number of power sanders that will save you a lot time and energy in achieving that flawless surface. Of course, I'm partial to Skil's line-up of sanders for a number of reasons. But one of the most important qualities of the Skil sanders is there onboard dust canisters. These canisters contain a super-fine filter that traps most of the dust before it ever has a chance to get airborne. That means less clean up and less chance of you inhaling the dust. The canisters snap on and off easily so you can dump out the collected dust and clean the filter every so often.
As for which power sanders you should have on hand, at a very minimum you'll want to have a random orbit sander (ROS) in your arsenal. The model 7490-01 is a great choice. The erratic sanding action of this ROS leaves a pattern of scratches that is almost undetectable, even with mineral spirits. You can use this sander with coarse sandpaper for quick removal of flaws, and with fine paper for a super-smooth surface that's ready for finish in many cases. This is my go-to sander.
When projects require an even finer surface than an ROS can deliver, I reach for my ¼-sheet palm sander (model 7290-01), sometimes called a finish sander. It's called a finish sander because that's what it does — finish the sanding to a super smooth surface that will give luster to any oil finish you wish to apply.
At the other end of the sanding spectrum is the belt sander (model 7500). There's nothing "fine" about a belt sander. This is the meat eater of the group. It removes stock quickly and can level out even the most irregular boards in short order. I save my belt sander for only most demanding jobs and then follow it up with both an ROS and finish sander for the best results.
Just recently, I've added the Skil Octo Multi Finishing Sander (model 7300-01) to my stable. This versatile sander has saved me countless hours sanding intricate projects with a lot of corners and contours. I was able to refinish and entire flight of stair balusters in one weekend using this just this sander to do the prep work. It's an occasional-use sander, but when the work calls for it, there's just no substitute.
And speaking of work, the final piece of advice I'll give you is to let these power sanders do the work for you. Resist the temptation to apply too much pressure to the tool. All you'll accomplish with this is slowing down the sander's pad, reducing its ability to overlap the scratches. Use a light grip and slow movement to get the most out of your sander.
Start to Finish
Clearly, sanding isn't the most exciting part of building a project, but it may be the most important. A thorough sanding job really is the difference between a project being done, or being done well. And by using the techniques and tools I've laid out for you here, you'll quickly see that sanding isn't the drudgery it's made out to be. It's really an opportunity for you to fine-tune each piece of the project and ensure that, once completed, it's the project, and not the imperfections, that the world will see.