How to Square a Board With a Jointer

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You’ve got a new woodworking project and are excited to get started. You head to the home improvement store and stock up on the lumber you need. Then back in your workshop, you notice the stock you purchased has problems. Cupping, twisting, uneven edges — the pre-milled stock for sale at big centers is notorious for not laying flat. 

That’s where the jointer comes in. You can salvage the workable pieces of wood, remove cupping, correct twisting, and create a perfectly square board with just a few steps. Learn how in this article.

Once you’ve got the basics of squaring boards with a jointer, you’ll be able skip the home improvement center altogether and purchase rough-hewn stock from a lumber yard for your next project. 

Using a Jointer to Square Boards

Before we delve into the step-by-step instructions, let’s review some terminology and parts of the jointer. Picking the best jointer for your project helps to make your cuts accurate and precise.

Cutterhead

The cutterhead is a cylindrical part of the jointer, located in the middle, between the infeed and outfeed tables. Jointing involves passing the board over the cutterhead in a controlled fashion. The cutterhead has two or three notches, inset with knife blades. These blades must be clean and sharp for effective jointing

Cutterhead Guard

A piece of metal or plastic that covers the cutterhead. It protects fingertips or dangling items from being sliced off by the sharp, spinning blades. 

Jointer

Fence

The fence is a removable bar that sits on top of the jointer, spanning the infeed and outfeed tables. It’s purpose is to help guide the board evenly over the cutterhead, and it can be adjusted to suit the width of the board in question

Infeed and Outfeed Tables

These are simply the surfaces on which the board will rest as it is being jointed. Infeed is on the right, that’s where the un-jointed board goes. As it is passed over the cutterhead, it is supported by the outfeed table on the left. 

Tip: If you don’t have a jointer, you can use these methods to square boards.

Squaring Boards With a Jointer

Most of the steps for squaring wood are spent setting up the jointer properly. Once you have the tool dialed in, the process is very simple.

  1. Check the size of the wood against your jointers capability. The most common jointers have a cutterhead that measures six inches wide, meaning it can handle boards up to six inches across. Never joint pieces of wood less than twelve inches in length. The length of the board that can be jointed is determined by the total distance from one end of the infeed table to the opposite end of the outfeed table. The jointer should be able to handle boards that are no more than twice the total length of the tables. 
  2. Check that your infeed and outfeed tables are in the same plane by bringing them up to their maximum height, removing the fence and cutterhead guard, and pressing a straightedge across the surface. For precision work, there should be no detectable gap between the tables and the straightedge. Use shims cut from aluminum cans to make minute adjustments, if necessary. 
  3. Adjust the height of the outfeed table. The outfeed table has a very important job. It needs to adequately support the board after it passes over the cutterhead. If the outfeed table is too high, the board will simply bang into it and not move any further. If the outfeed table is too low, the board will drop as it comes off the cutterhead, leading to hollow gouges in the end of the wood known as ‘snipe’. Perfect adjustment of the outfeed table includes ensuring it is level with the highest point that the blades reach during rotation, otherwise known as ‘top dead center’. 
  4. Adjust the height of the infeed table. The height of the infeed table determines how deep the cut will be. It should sit slightly below the cutterhead. It’s better to remove material a little at a time than all at once. You can give a board another pass with the jointer, but you can’t reattach wood once it’s been shaved off. 
Person showing how to square a board while using a jointer
  1. Inspect the board to be flattened and squared. Hold it at one end and look down the length of the board for bowing, crooking, cupping or twisting. It helps to close one eye. If the board has severe issues, cut it into smaller pieces and joint them individually. This will not only be easier, but will also preserve more of the material. Check the grain of the board. When you place it on the jointer, the grain should slope down and away. If you orient the board with the grain sloping up, tear out can occur. 
  2. Ensure your safety. Personal protective equipment should include safety glasses for eye protection and earmuffs for hearing protection. Never use a jointer without the cutterhead guard in place. Securely attach the fence to the table before beginning work. Put the board on the infeed table and set two push blocks with handles on top of it. Turn the jointer on. 
  3. Flatten one face of the board. Use two push blocks with handles to guide the wood. Start with pressure on the infeed table. Transfer that pressure to the outfeed table as the board passes over the cutter head, keeping the board as flat as possible. When the entire board has been run through the jointer, it should have a perfectly flat face. You may need several passes to flatten severely warped boards. 
  4. Square the adjoining edge. Once one face of the board is flat, you can use the jointer to square up an adjoining edge. Simply flip the board onto its edge and press the flat face firmly against the fence. Keeping your hands well away from the cutterhead, feed the board through the jointer.  Before you leave the jointer, mark the face and edge that have been perfectly squared. Use carpenter’s orientation marks to keep track of where you are in the finishing process. Finishing the board to be square on all four sides will require feeding the opposite face and edge through a planer and using a table saw to trim. 

If your project involves smaller pieces of wood, you can probably get by with a good benchtop jointer. Otherwise, larger pieces require a larger tool.

Conclusion

When perfectly square boards are needed, a jointer is the right tool for the job. While there are methods for squaring a board without a jointer, they are not as precise or foolproof. Knowing the parts and limitations of your jointer will help you get the most out of it.

Always adjust your settings before jointing, and wear hearing and eye protection to keep yourself safe.

Ellenkate grew up on job sites run by her family’s construction company. She earned her theater degree from The Hartt School, a prestigious performing arts conservatory in Connecticut. Her design and DIY work from her Chicago loft was featured in the Chicago Reader and on Apartment Therapy.