Putting a straight, square edge on a board may be the first job that comes to mind when you think about a jointer. But there's another operation that's even more fundamental: flattening the face of a board.
A flat face gives you the reference surface you need for nearly everything that follows. Once one face is flat, you can plane the opposite face parallel, joint an edge square, rip parts accurately, and cut joinery with greater confidence.
The process isn't complicated. The key is learning to read the board and adjusting your technique to match the problem you're trying to correct.
Start by Reading the Board
Before turning on the jointer, take a good look at the lumber. You're checking two things: grain direction and the overall shape of the board.
Grain direction matters because feeding a board against the grain can cause the jointer knives to lift and tear the wood fibers rather than slice them cleanly. When possible, orient the board so the grain runs up and away from the jointer table in the direction of feed.
Light cuts help, too. A cut of roughly 1⁄32" to 1⁄16" is usually all that's needed. Several light passes give you more control than trying to flatten a board with one aggressive cut.
Use the Outfeed Table as Your Reference
Your hand pressure is just as important as the depth of cut.
As the leading end of the board passes over the cutterhead, transfer your left-hand pressure to the portion resting on the outfeed table. Your right hand should primarily move the board forward. The goal isn't to force the board flat against the tables. You're gradually creating a flat reference surface.
WOODSMITH TIP: Let the jointer remove the high spots. Excessive downward pressure can temporarily flatten a warped board while you're cutting it, only to have the board spring back when you release it.
Identify Cup, Bow & Twist
Most rough lumber won't start out perfectly flat. The three common problems you'll encounter are cup, bow, and twist.
Each requires a slightly different approach at the jointer.
How to Flatten a Cupped Board
Cup is a curve across the width of a board.
Place a cupped board on the jointer with the hollow, or concave, side facing down. This puts the two outside edges against the jointer table and gives the board a stable stance.
Then make a series of light passes.
The important part is resisting the temptation to push down hard in the center. Doing so can flatten the board against the table while you're making the cut. Once the pressure is released, the cup may simply return.
Instead, use only enough pressure to control and feed the workpiece.
Consider Ripping a Severely Cupped Board
A wide board with a pronounced cup can require removing a surprising amount of material before the entire face becomes flat.
In that situation, consider ripping the board into narrower pieces first. Narrowing the stock reduces the amount of cup across each piece, so less material needs to be removed during jointing.
That can leave you with considerably thicker finished stock.
How to Flatten a Bowed Board
Bow is a curve along the length of a board.
As with cup, start with the hollow side facing down. But the technique is a little different.
Initially, the board may contact the jointer table primarily near its ends. Those are the high areas you want to remove first.
Concentrate your pressure near the portions of the board that are already touching the tables and avoid pushing down in the middle. Pressing the center flat can cause you to simply reproduce the bow rather than eliminate it.
As material is removed from the high spots, more of the board will contact the tables. Continue making light passes until you've established a continuous flat face.
How to Remove Twist with a Jointer
Twist can look intimidating because the four corners of the board don't sit in the same plane.
Set a twisted board on a flat surface and it rocks from corner to corner. At the jointer, you may initially have only two opposing corners making solid contact with the tables.
The solution is to work gradually.
Concentrate pressure on the high corners that are contacting the jointer tables. As those high areas are removed, the other corners will begin to come into contact and the board will become increasingly stable.
Once you've removed most of the twist, you may discover that the board also has some cup or bow. From there, use the same techniques described above to finish flattening the face.
WOODSMITH TIP: Don't chase a warped board by pressing it flat. Let the board rest naturally on the jointer and remove the high spots progressively.
Know When the Face Is Flat
You're finished when the face makes consistent contact with the jointer tables and you've established a continuous reference surface.
It doesn't necessarily need to look like a finished surface straight from the jointer. What matters is that it's flat enough to serve as the reference face for the next milling operation.
From there, you can move to the planer to make the opposite face parallel and bring the board to final thickness.
Flat Lumber Is the Foundation for Accurate Woodworking
Face-jointing only takes a few minutes, but it affects nearly every operation that follows.
Establishing one reliable flat face gives you a reference for thickness planing, edge jointing, ripping, crosscutting, and joinery. Instead of trying to make accurate parts from warped lumber, you're starting with stock that's flat, stable, and ready for precise work.
And when something doesn't look right coming off the jointer, don't assume your technique is the problem. The machine itself may need a little attention.
Is Your Jointer Cutting Correctly?
Tapered cuts, snipe, scalloped surfaces, ridges, and edges that aren't square can all point to setup or alignment problems. Our Jointer Troubleshooting guide walks through the common symptoms, likely causes, and what to check before your next cut.
TROUBLESHOOT YOUR JOINTER → 5 Common Jointer Problems & How to Fix Them
