If you’ve ever bought a two by four at a major hardware store, you know very well that not all timber is straight or flat. Although wood is hard, it can bend, bend, and bend when it dries or is exposed to moisture. Warped wood can be difficult to work with: precision cuts will be more difficult and joints will not be as strong.
Before starting a project with lumber you just bought, you’ll probably need to mill it – woodworkers advocate trimming a plank to a three-dimensional rectangle (aka a cuboid or rectangular prism). This involves flattening both faces, cutting the edges at 90 degrees to those faces and parallel to each other, and trimming each end to the desired length perpendicular to the freshly straightened edges. Once I learned how to properly mill wood, everything I built would fit together better with less effort. It’s time-consuming upfront, but worth it in the end.
Note that the following steps show how to achieve perfectly milled wood with modern power tools. However, it doesn’t always require the utmost precision in your wood, especially if you’re not gluing multiple pieces together or using complex joinery techniques. Consider my current project: a pair of floating shelves that need only be roughly flat and square. Since the wood is too wide for my jointer and too long for my smoothing sled, I used a hand planer to get it flat enough. So before you spend hours trying to get to 1/32 of an inch, think about what level of precision you actually need. Sometimes close enough is good enough.
You can also fully mill wood with just hand tools, although it takes a lot of time and practice to do it well.
Warning: DIY projects can be dangerous for even the most experienced maker. Before proceeding with this or any other project on our site, make sure you have all the necessary safety equipment and know how to use it properly. This includes at least safety goggles, a face mask and/or hearing protection. If you use power tools, you need to know how to use them safely and correctly. If you don’t, or are otherwise uncomfortable with the things described here, don’t attempt this project.
- Time: 1 to 4 hours
- Cost: None
- Difficulty level: medium
1. Acclimate, dry and store your wood properly. Wet wood warps. drying wooden chains. Wood that changes environments warps. If you haven’t dried and stored your wood properly, it doesn’t matter how square you get it. It will be forgiven again.
When you first bring your wood home, test it for moisture content. Ideally, your planks should contain about 9 percent moisture or less. If they are too wet, let them sit until dry. In any case, you should leave the panels in your store for at least a few days to adjust to the temperature and humidity of the new environment.
Do not stack boards directly on top of each other to dry. This traps moisture between them, which can cause additional warping or even cracking. Instead, slide small strips of wood called stickers between each board to allow for proper ventilation. This allows the planks to dry more evenly.
To make my decals, I cut strips about half an inch wide from whatever scrap wood I have lying around.
2. Flatten one side. Once a piece of wood is dry, smooth one of its faces. There are a few ways to do this. It is best to use a floor cutter that was specially developed for this purpose. Slide the board along the tool bed and over the rotating cutting head. Always use pressure blocks to do this, as you don’t want to get your fingers near the blades. It usually takes several passes to make the face completely flat.
If you don’t have a floor saw, you can use a planer to smooth the wood. But you have to build a sled for this. The reason you can’t flatten a board in a plane without a slide is because a plane doesn’t base its cuts on a flat surface. Instead, the slicer follows the contours of the underside of whatever you feed it. So if your board is warped, the planer will cut the top of that piece of wood to follow the warp. By using a slide, you force the planer to follow the milled surface of the slide, creating a nice, flat cut.
- Pro Tip: To see when you’re done, use a pencil to scribble all over the face you’re working on. When all the pencil marks are gone you know the face is flat.
- Note: For those without a planer or planer, you can build a router slide to smooth the faces of your boards, but this is more labor intensive, especially if you’re routing a lot of wood.
3. Join an edge. Now that one side is flat it’s time to trim an edge. The goal is to get this edge perfectly straight and at right angles to the flattened surface. Again, the best tool for this job is a jointer. First, decide which edge to flatten. I usually pick the one that’s already closest to flat. If they’re both wobbly, I cut the one that rides more securely along the bed of my jointers.
Place your board with the chosen edge down and the previously flattened side firmly against the fence on the planer infeed table. Slide the board over the cutting head and trim the edge. Again, this will likely require multiple passes. When you’re done, the edge should be perfectly straight and at right angles to your face.
- Pro Tip: Use a pencil to mark the edge and face you’ve flattened and draw arrows pointing to the 90 degree corner so you don’t lose track of what you did.
- Note: If you don’t have a jointing machine for this step, you can edge joint a board with a table saw.
4. Smooth the second surface. If you have a planer, this is easy. Simply feed the board through the machine, flat side down. Again, scribbling in pencil on the rough side of the board will help you see when you’ve flattened every square inch of the wood.
The planer is the best tool for this job as it cuts parallel to the bottom of the board, giving you an even thickness. You cannot use the jointer for this as it cannot cut parallel to the top. If you try, the board will likely develop a front-to-back taper, defeating the point of milling.
If you don’t have a plane, there are a few other ways to smooth this area. The first is to use a milling slide, which was also an option for step 2. The second is to use a table saw, with the square edge down and the flat side against the fence, but this method only works if the board is small enough for your saw blade to cut through.
5. Cut off the remaining edge. You now have two parallel faces and an edge that is at 90 degrees to both. The next step is to trim the remaining edge on your table saw. Once you know the final width you want the board to be, set your table saw fence to that distance from the blade. Otherwise, adjust the fence to cut off a chunk of that last edge. By only taking a tiny amount of wood you reduce waste and keep the board more versatile for future projects.
[Related: Tune up your table saw the right way]
Feed the board through the saw with one side down and the joined edge against the fence. This creates a cut parallel to that edge, which is also perpendicular to both faces.
- Pro Tip: Every time you use your table saw, check the angle of the saw blade with a digital protractor. For some projects, such as B. cutting boards, there is a noticeable difference between 89.8 and 90 degrees.
6. Cut the ends to length. You can trim the ends of your board with either a miter saw or the miter slide on the table saw. The latter is generally my preference because I have better control with the table saw. Also, clutter piles up near my miter saw and I have to pick it up every time I want to use the tool while my table saw is usually clean.
Place one of the edges against the fence of your slide (if using a table saw) or the fence built into the saw (if using a miter saw). From there, cut off enough wood that the first end is perfectly flat. Then flip the board over and cut it to your preferred length (or just cut enough to flatten the opposite end if you’re not sure what you’re going to use it for).
- Pro Tip: I try to keep the same edge on the fence for both cuts for the sake of consistency, but if you’ve routed the wood properly up to this step it shouldn’t matter which edge you use.
Now your board is perfectly square in all three dimensions, and you’ve opened up a whole new world of woodworking. Go and build.