Two videos in a playlist on a good way and a better way to flatten a wide board.
OFFICIAL TRANSCRIPT:
If you don't have a jointer or you want to joint boards that are wider than your jointer, then typically you can use a planer sled to joint one face of a wide board with a planer.
I've never made one of these because it requires wedging the board here and there, and quite a bit of setup time, and while they work, I just haven't wanted to go through the hassle.
Instead of going with something like that, today I'm going to show you how to joint a board wider than your jointer with both a jointer and a planer.
Before getting started I just want to show you that this board—is not flat.
Because the board is wider than the jointer, it is too wide to pass through the cutter head guard, so that has to be removed. Any time you remove guards like this its obvious that you have to be careful. If you are uncomfortable doing this, then absolutely do not do it.
Once the guard is removed, the board can be jointed as normal taking as many passes as necessary to get the jointed section actually flat and jointed.
I'm back at the thickness planer now and this is the eight-inch wide section that was jointed flat to the jointer. And the overhang that needs to be removed so that it is down nice and flat with this.
You can remove this with hand tools, but I know that if I jointed one face, odds are that I'm going to be using the planer to make the opposing face flat and parallel to it. So why not use the planer for all of this and skip hand tools on this step?
Basically, you need to have a flat surface that can extend the jointed surface along its length, such as a piece of half-inch plywood. If you put it on the bottom side here, and make sure the flat face references off the thickness of the plywood, which will extend down to the bed of the planer, then you can run this setup through the planer like so and it will plane the top side parallel to the flattened face that we flattened at the jointer.
The only thing you need to make sure of is that the bottom surface of the plywood has less friction than the top surface of the plywood touching the actual wood itself.
With the opposite side flattened and parallel to the jointed face, the board can be flipped back over and planer can be used to remove the material that the jointer left behind.
Both the twist and cup have been removed from this board, both faces are flat and parallel, and it was extremely easy to do. If you don't have a jointer, then obviously a planer sled will do you wonders but if you do have a jointer and want to joint something wider than the jointer, I find this method to be so easy to do, you don't have to use any hand tools, and you're already setting up the planer anyway, so you might as well use it to do the rest of the process.
All you need to have is something that is a consistent thickness, such as plywood, acrylic, or plastic.
UPDATE:
After posting this great little video tip, @JayBates86 came up with an even better way to do it. So we made a playlist and embedded it up top.
—Jay Bates is a woodworker and YouTuber based in Starkville, MS