To make furniture that fits together like Legos, you need to know the ins and outs of milling lumber.

The milling process is how you make boards flat, straight, and square — and it’s the crucial first step to any woodworking project.

If you don’t do it right, your measurements won’t be accurate, your joinery won’t quite fit, and boards that were once straight will turn into hockey sticks over time.

It’s a pretty straightforward process. But there are a few things to know to get it right — not just for making boards square, but for keeping them that way.

This is a guide to how almost every professional woodworker mills lumber, using a jointer, planer, and table saw.

Yes, you can do your milling entirely with hand tools. But it requires quite a bit of skill, a lot more time, and bucketfuls of elbow grease.

If you’re ok with using modern machinery, this is the process to follow.

So throw on your safety goggles and ear protection (this will get loud) and let’s get to it.

Here’s a few points to keep in mind before, during, and after milling.

To get clean, tearout-free edges and faces on your boards, you need to pay attention to grain direction.

Feeding a board through a jointer or planer against the grain can chip off pieces of wood instead of cleanly severing the fibers.

Think of it like petting a cat. Pet it in the direction the fur lies, and it stays flat. But pet against the fur, and that cat will look like it’s coming out of a three day catnip bender.

Run boards through your jointer and planer so the cutterheads “pet” the grain down.

Keep in mind the cutterhead on a jointer is below a board, while on a planer it’s above. On either, the part of the cutterhead that cuts spins the opposite direction the board is moving.

To identify grain direction, look at the grain lines on the side perpendicular to the side you’re about to cut.

If the grain lines are angled, feed that board so the cutterheads lay the grain down.

If the grain lines go straight along that entire edge, you can probably get away with feeding the board either direction.

Here’s a great video all about grain direction.

Wood is constantly absorbing and releasing moisture from its surrounding environment — which causes it to expand and contract (a.k.a. wood movement).

That means boards can start to warp when moved from one location to another.

The lesson?

When you buy lumber, let it acclimate to your shop for a couple days.

I know it’s tempting to get home, mill up your new boards, and start building a project right away. But you’ll pay the price when those perfectly straight table legs suddenly aren’t straight.

Milling also exposes the inner, more moisture-laden parts of a board. And as that newly exposed moisture is released… yup — the board will warp.

So even after boards are acclimated to your shop, you should do a “rough” milling one day, then a final milling a day or two later.

This gives boards adequate time to shift so they’ll stay square for your project.

Pencil lines are an excellent gauge of when boards are flat.

Before running a board through your jointer or planer, scribble pencil lines over the side you’re cutting.

As you make multiple passes (which you should always do), any remaining pencil lines will show the low/high spots that haven’t yet been cut.

Once all the pencil lines are gone, you’ll know a board is flat and you're ready to move on to the next step.

I also recommend labeling the faces and edges you’ve already milled. It’s easy to get confused — especially if you’re milling multiple boards at once.

You need to know how to properly set up and use your tools. Not just for good results, but for safety too.

If the outfeed table on your jointer is too low or high, you won’t get a flat face — even if you follow proper technique.

And if you try to take too much material at once with a planer, you can damage a board, or even your machine.

I’ll cover the most important points below, but here’s a few resources for you to get a solid understanding of the tools involved in the milling process:

• How to Tune Up a Table Saw
• How to Set Up and Use a Jointer
• How to Set Up and Maintain a Planer

Don’t have a jointer? Here’s how to joint a board without a jointer.

Before anything else, you need to pick up some lumber.

But if you want to make table legs that are 1 ½ inches thick, don’t buy a 1 ½ inch board.

Account for losing ¼ inch to ½ inch of material to milling — so buy boards at least ¼ inch thicker than the final dimensions you're after.

Obviously, this depends on how flat a board is. But remember: Even a super flat board can warp when you bring it to your shop.

Also, most lumber is actually thinner than the labeled thickness.

For example, 4/4 (four quarter) lumber is theoretically 1 inch thick. But it’s really around ¾ inch thick.

You should generally assume:

• 4/4 = ¾ inch thick
• 5/4 = 1 inch thick
• 6/4 = 1 ¼ inch thick
• 7/4 = 1 ½ inch thick
• 8/4 = 1 ¾ inch thick

This of course depends on where you buy lumber, so take a measuring tape to be sure.

Then there’s rough vs pre-milled lumber.

The varying degrees you’ll usually find are:

• Rough lumber: Squarish boards straight off the mill. These haven’t been surfaced on any side, and are the cheapest option.
• S1S (surfaced on one side): Boards that have one face planed.
• S2S: Boards that have one flat face and a square, jointed edge
• S3S: Boards that have two surfaced faces and one square edge.
• S4S: Fully milled boards with all faces and edges planed and jointed. The most expensive option by a longshot.

If you own all the machinery needed for milling, I’d go with rough lumber.

The problem with pre-milled lumber is you’re almost always going to have to mill it anyway.

Since the moisture levels between the lumber yard and your shop are probably different, the boards will likely warp when you bring them home.

And what’s the point of spending all that extra money when you’ll have to mill it anyway?

The last tip here is to let boards acclimate to your shop.

As mentioned above, changes in location can change the shape of boards. Let them sit a few days before milling to save you from trouble later on.

Once your board is acclimated, it’s time to run it through the jointer and flatten one face. Remember to pay attention to grain direction.

As you feed the board over the cutterhead, put all the pressure on the outfeed table as soon as possible. This will keep you from cutting a curve into the board.

Don’t take off more than ⅛ inch in a single pass. You can learn more about jointer technique in this video.

If you marked the face with a pencil, make multiple passes until all the lines are gone.

For smaller boards, you can also use the “suction trick” to test flatness.

No, don’t start sucking on the board. Set the face you just flattened on the outfeed table. If you feel slight suction as you lift it, you know it’s dead flat.

Mark this flattened face as “Side 1,” and you’re ready for the next step.

Now you’ll use the jointer to cut one edge square to Side 1.

First, make sure your jointer fence is square to the outfeed table.

When you push the board over the cutterhead, keep it flat against the fence while putting pressure on the outfeed side.

Make sure the face you flattened is the side against the fence (the photo above was just a demonstration — Side 1 should face the other way).

Again, use pencil lines to gauge when the edge is flat. When all the pencil’s gone, mark it “Side 2.”

Use your most trusted square to check that Side 1 and Side 2 are at 90° to each other.

If they are, turn off the jointer and move on to the planer.

You’ll now run the board through your planer with Side 1 (the flattened face) facing down.

Mark pencil lines all over the top face and start running that sucker through.

Take off around 1/16 inch of material at a time and make multiple passes until the pencil lines are gone.

Once they are, flip the board over so Side 1 is facing up and take another pass.

As you keep making passes, alternate which side is facing up to help keep things even.

If this is Day 1 of milling, don’t go to your final thickness yet.

Leave an extra ⅛ inch of material for milling to your final dimensions the next day (remember, wood movement).

Now we move on to the table saw.

With the jointed edge (Side 2) against the table saw fence, cut the board to its rough width. Leave a bit of material for final milling the next day.

As long as your table saw is properly tuned, this creates a clean edge that’s square to the rest of the board.

For rough dimensioning, a combination or general purpose blade works great.

But if you’re milling a bunch of lumber, or want ultra-clean edges, a dedicated ripping blade is the way to go.

Read more about table saw blades here. And be sure to follow all the steps for avoiding kickback.

Your board is now milled flat, straight, and square.

But that’s not necessarily the end of the process.

Rough milling exposes moisture within a board — and that can cause a board to warp overnight.

That’s why you should come back the next day for a final milling to get your board to its final working dimensions.

You can also save yourself from wood movement by properly storing milled boards.

Make sure they’re lying on flat surfaces, and use either weight or clamps to keep them flat.

If you’re stacking boards, “sticker” them by laying equally thick strips of wood between each board. This lets air circulate around them so moisture can escape evenly.

Also keep in mind that the thinner a board, the more susceptible it is to wood movement. Clamps might be the move here.

Resawing — where a board is cut into two equally wide boards — is a special case.

With all the moisture trapped in the middle, the two sides are guaranteed to cup towards each other.

You’ll more than likely have to re-mill resawn boards. But you can clamp them together overnight with the newly cut faces facing out. This should help mitigate the cupping.

As the first step of almost any woodworking project, milling can make or break your build.

But overtime, you’ll have no problem quickly getting boards straight, flat, and square…

So you can move on to the fun parts — and know your builds will stand the test of time.

Got any of your own milling tips? Leave them in the comments below!

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And as always, STAY SAFE IN THE SHOP!