This example shows how to refinish a cedar chest, but the technique is the same for any wooden furniture. I've also included a lot of information about other techniques, and their pros and cons, as well as some tips I've found for making the job easier.

My grandpa found this old cedar chest (I think at a garage sale) a few years ago. He planned on refinishing it and giving it to my wife as a wedding present. Then he was hit head-on by a drunk driver. Countless surgeries and several years later, his back and leg still aren't up to the manual work of refinishing. So he gave the cedar chest to me and instructed me on how to refinish it. With his help, and with some research of my own, I've managed to finish the job (get it? aha-ha-ha?).

What you will need:

Sandpaper (~ 10 sheets of 150 grit, ~3 sheets of 220 grit, 1-2 sheets of 320 grit).
Clear Varnish (a small can of General Finishes water-based polyacrylic).
A Paint Brush (a 3-inch wide synthetic brush from Home Depot).

FOR REFERENCE: Notes on Alternative Refinishing Methods, Brush Types, Finish Types, etc.
There are lots of ways to refinish. People use stains, shellacs, varnishes, lacquers, waxes, oils... it's a little overwhelming. Searching online gives you a lot of people that swear their way is the only right way. But after a lot of searching, and some conversations with my grandpa, I think I have a decent handle on what's what.

In this instructable, I'll be using clear finish only. I'm not coloring the wood at all (with stains or oils). For cedar, this looks pretty nice, because the wood has a lot of color of its own, and the clear finish really brings it out. On the other hand, when I've done the same thing on pine, the results are pretty boring. It depends on your wood, and your desired look. TIP: If you want to know how your wood will look with just a clear finish, use water. Just smear some water on the wood with a paper towel. The way the wood looks wet is approximately how it will look with a clear finish.

Clear finishes generally provide a protective coat on top of the wood.They might bring out the color of the wood (think increasing saturation, if you're a photographer), but they don't really change the color.

But what type should you use? Here are the options:

Types of Clear Finish

Shellac: Shellac comes in anything from a spray-can at a craft store to fancy flakes that you can mix into a liquid and apply with a brush or sprayer. It has a stigma of being kind of a cheap-and-easy solution. It can be brittle, is not very water resistant, and can yellow with age.
Lacquers: Lacquers can give a very high gloss. They are hard to apply with a paint brush, and less durable than some other types of finish. Some have yellowing problems.
Epoxies: Epoxy is normally used as glue, but there are types you can use for finishing. You mix two parts together, pour them onto a flat surface, spread with a disposable brush, and let set. You get an extremely durable, thick finish (I think this is what a lot of restaurant tables have), but the epoxy is more expensive and complicated to apply, especially to non-flat, non-horizontal surfaces.
Varnishes: These are probably the most popular. Polyurethane and Polyacrylic (or Polycrylic) are examples. These are very durable and can be applied with a brush, sponge, or even a cloth. However, since they are so common, there are a lot of options out there that deserve some de-mystification.

Varnishes: De-mystification

Polyurethane or polyacrylic? This is the question of the ages. I've searched for info on which is better. There are some who swear by one, some who swear by the other. Polyurethane seems to be the more common, by a hair. Other than that, I can't say I've found a difference. I used polyacrylic because the guy at the Woodcraft store handed me a can and said it was good.
Matte, Satin, Semi-Gloss, Gloss? The obvious answer is that the matte is less shiny than the gloss, and the others are in between. What was news to me was some advice from the guy at the Woodcraft store. He said always use gloss for most of your coats. If you want the final finish to be matte, then still use gloss for all but the final coat. Why? Because multiple coats of matte will start to cover up the wood and make it hazy. Better to build up clear, then finish with your desire shiny-ness.
Water-Based or Oil-Based? Both polyurethane and polyacrylic come in water-based and oil-based varieties. The water / oil is what carries the solids in the finish. The solids are what is left when the finish is dried. Why use one or the other? Well, there are pros and cons to each.
- Water-Based Pros:
  - Dries more quickly (2 hours vs 4-6 hours between coats).
  - Doesn't stink as much when you're applying it.
  - Easy clean-up (you can just rinse your brush out in 30 seconds under the faucet).
- Water-Based Cons:
  - Coats go on thinner, so more coats are required (3-5 instead of 2-3).
  - Some people find it harder to apply with a brush.
  - Can be a little more expensive.
  - You can't use a natural-fiber brush.
  - It "raises the grain" (makes the wood swell a little, so the surface becomes a little rougher. I didn't notice this at all, but if you do, you can brush plain water on the wood and sand it while the grain is raised before you apply the finish).
- Water-Based Facts: This can be either a pro or a con, but water-based finishes don't change the color of the wood at all. They bring it out, but they don't give it an amber tint (think no white-balance change, if you're a photographer). Some people like the amber tint, and think the wood looks cold without it. Some people think it looks more natural without the amber tint.
- Oil-Based Pros:
  - Goes on thicker, so fewer coats are required (2-3 vs 3-5).
  - Some people find it easier to brush.
  - You can use a natural-fiber brush, if you like.
- Oil-Based Cons:
  - Lots of fumes when you're applying it.
  - Difficult to clean up (you need solvents, like paint thinner, to clean your brush).
  - Takes longer to dry (4-6 hours vs 2 hours between coats).
- Oil-Based Facts: Again, this can be either a pro or a con, but oil-based finishes give the wood an amber tint. Think changing the white balance from day-light to shade, if you're a photographer. Some people like this, some don't.

Other Questions:

Bristle brush, Foam brush, or Cloth? You can use any of them. I haven't been able to find any pros and cons of one over the other. The guy at Woodshop said to use a cloth. A few articles online say to use a foam brush. I used a bristle brush, because that seemed the easiest way to have good control.
Natural bristle or synthetic bristle? If you're using an oil-based finish, you can use either. Natural fiber brushes are apparently preferred. If you're using a water-based finish, you have to stick with synthetic bristles. The natural ones will soak up the water and get sticky / soggy / hard to use.
What about stains? Stains add a color to the wood. Unlike paint, they are not opaque. They're more like applying a color filter to a photo, or looking at the wood through tinted glasses. Sometimes they can look really nice. Other times they look artificial. If you put an oak-color finish on pine, for example, the combination of a very open grain (pine) and a dark oak color (when oak usually has very fine grain) will look pretty unnatural (see this toy sword I made, where I did exactly that). If you do apply a stain, you do it after sanding and before the clear finish.
What about oils and waxes? Oils (like linseed oil, tung oil, teak oil, or butcher block oils), soak into the wood rather than coating it. They increase the wood's natural color (the same way a clear finish would) and often give it an amber hue (like an oil-based clear finish would). Usually you have to keep reapplying them every couple years, but they're easy to apply (you just rub them in and then wipe off the excess). Gun stocks are finished this way a lot of the time. Collectors pay a lot for the patina of a gun stock that has been oiled for the last hundred years. However, oiled wood is pretty vulnerable. You can wax it to add some shine and protection, but it's not a tough protection, and it has to be reapplied periodically too. This is more of a purist approach, and some people like the look better, but it's also more work and less durable.

That's about it. Now, on with the instructable.

Step 1: Start Sanding the Big Flat Areas

You can get fancy chemical finish removers, but one of the only ways that's guaranteed to work is sanding... a lot of it. I started with 150 grit on an orbital sander to remove the finish on the big, flat areas.

(General Tips on Sanding, if you're not familiar with the basics)

Sand paper grits tell you how rough the sandpaper is. 60 grit is really rough. 80 is less rough, but still really rough. 100 is less rough, 150 even less rough, and so on. 220 is pretty smooth... just about as smooth as you need to go before applying your clear finish. 320 is really smooth; this is what you'll use between coats. For 400 plus, it's almost hard to tell that it's sandpaper at all.
Start with rough grits. To remove a really thick finish, you could start with an 80 or 100 grit. Just remember that the really rough grits will remove material faster, but they'll also leave deeper scratches that you'll have to sand out later.
Work your way up to finer grits. Don't do this until you've finished with the current grit. 90% of the work is usually done with the first grit you use. After that, you're just getting rid of the sanding marks you left with the last grit.
Go with the grain, when you can. If you sand against the grain (not parallel to the lines in the wood), it'll look weird and scratched. Sometimes you have to, like in a corner, but try to avoid it.
Be patient. Sanding is a lot of work, but it's also magical. You really get to see a lot of improvement during this step.

Step 2: Sand the Curved Areas by Hand

This is where you can employ your sanding-with the grain technique. Pay special attention to these areas; it can be easy to get lazy and skip them, but they make all the difference.

Tip: If you have a really crazy edge, say the edge of a table with curves and cutouts, you can make a custom sanding block to make your life easier.

Use plastic wrap (or your sandpaper) to cover the edge you want.
Make sure the plastic wrap conforms to the edge well.
Cover the plastic wrap with some kind of putty or foam (the triple expanding insulation from Home Depot might work well)
When the putty/foam dries, you have a sanding block that is the exact shape of the edge you're trying to sand.

(Disclaimer: I haven't actually tried this, because my edge was pretty simple, but I read the tip in a book from the library, and it sounds awesome.)

Step 3: Finish Sanding With 150 Grit, Then Re-Sand With 220 Grit

Once you've removed all the finish with 150 grit sandpaper, re-sand the whole thing with 220 grit. Don't worry, this second sanding will only take about 10% as long as the first. I used 7 or 8 sheets for the first sanding, and only 1/2 sheet for the second sanding.

Step 4: Fix Any Broken Spots

If your furniture has broken areas, now is the time to fix them.

For cosmetic fixes (like the big splinter that had broken off of the leg on this chest), wood glue is great. It's very strong, especially if you can keep the gap between pieces of wood as thin as possible. Apply the glue, use a clamp, and wipe away the excess glue before allowing to dry. After 24 hours, you'll have a very strong bond. You can lightly sand the area to remove excess glue and bring everything flush.

Step 5: Remove All Saw-Dust From the Chest

If you have a blower or vacuum, clean the sanded wood thoroughly. Then wipe the whole thing down with damp paper towels. You'll be surprised at how much wood dust clings to the furniture.

When I initially started, I didn't wipe down the chest good enough. As I was applying finish, I noticed tiny little flecks of sawdust on the wood, and saw that my brush was turning brown with sawdust it was picking up. I had to periodically clean my brush. On the remaining coats, I was careful to wipe everything down first, and had no problems.

Step 6: Prepare Your Finish

Stir the Polyacrylic with a paint stirring stick. Don't shake or stir too vigorously (this can create bubbles). If you do create bubbles, wait a while and they'll go away.

Step 7: Start Your First Coat on a Non-Descript Area

I decided to flip the chest upside down and apply finish to the bottom first. The bottom wasn't very well sanded, and didn't really need finishing, but I figured if I messed up here, it wouldn't be as important.

The Technique:

The instructions for polyacrylic aren't very helpful. They say not to "over-brush" and to apply several coats. What exactly is over-brushing? It seems to be something that come with experience. My policy was to brush as little as possible. Following some unnecessarily long video tutorials I found online, I followed this procedure:

Dip the brush about 1/2" into the finish.
Spread the finish on the wood, not worrying about brush strokes or going with the grain. Just get good coverage and use the brush to work the finish into all the pores and crevices.
Finish by "tipping off": making long, soft brush-strokes over the area you just covered. Go in the direction of the wood grain. This will smooth out any puddles, drip marks, etc.

Step 8: Finish Applying First Coat

Finish applying your first coat to the entire project. Check back over everything you've done to find and fix any possible drips, runs, puddles, or thin spots. Move your head around to see things in reflected light.

When you're satisfied, let the coat dry for the recommended time (2 hours for my water-based polyacrylic).

Step 9: Sand the First Coat With 320 Grit Sandpaper

Once the first coat has dried, sand it very lightly with 320 grit sandpaper. This will help smooth out any runs you missed and help the second coat stick.

Once you've sanded, don't forget to wipe everything down with damp paper towels or a damp cloth to remove all sandpaper.

NOTE: The first coat may have "soaked in" and disappeared almost completely, so that the wood looks like it did before applying any finish. That's ok. The second and third coats will soak in much less.

Step 10: Apply a Second Coat

Apply a second coat in exactly the same way as you applied the first.

Step 11: Repeat for Up to Five Coats

Allow second coat to dry.
Sand with 320 grit sandpaper.
Wipe off sawdust.
Apply third coat.

Repeat for a fourth and fifth coat if you like (I did 5 coats).

TIPS:

In the later coats, it becomes more difficult to see where you have applied finish and where you haven't. Use reflected light.
Check for runs or drips that have collected. Fix them by tipping off before you allow the finish to dry.

Step 12: Re-Assemble and Admire

Some people like to sand the final coat with 400 grit (or finer) sandpaper. I thought it looked really nice without a final sanding, so I left it.

Let the final coat dry for longer to completely harden (24 hours to a week), then re-assemble your furniture and enjoy it!

Keep reading for a few helpful tips I discovered.

Step 13: Tip 1: Use Water to "Preview" a Clear Finish

If you're not sure whether to use stain or not, you can use water to see how your wood will look with clear finish on it. Just get a paper towel or sponge wet and put some water on the wood. The wet portion will look really similar to what the wood will look like with a clear finish on it.

Step 14: Tip 2: on Prolonging Sand Paper Life

This tip is from my grandpa: You may notice melted finish building up on your sand paper. If you want to prolong the life of the sandpaper, you can use a knife or razor blade to pop off the finish so you can keep sanding.

Step 15: Tip 3: How an Orbital Sander Vibrates

This really doesn't have any bearing on how to refinish old furniture, but I think it's fascinating. When you turn an orbital sander on, it vibrates. The whole time I sanded, I thought it was vibrating back and forth from front to back, so I tried to go with the grain when I could. Then I took some slow motion video, and realized that the sander actually vibrates in a circle. That's why they call it an orbital sander, I guess.