How to Adjust a Jointer

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A jointer is highly recommended for jobs when you will be working with rough lumber. In fact, it’s often recommended as the first tool you should purchase to upgrade your workshop. A jointer’s purpose is to straighten and flatten boards for woodworking. The process of preparing a rough-hewn board for woodworking projects is called ‘milling’.

Why Do You Need a Jointer?

Home improvement centers sell pre-milled stock, known in the business as S4S lumber. S4S stands for ‘smooth all four sides’.

While the lumber you buy may be smooth on the surface, warping, cupping, and uneven sides are common. Not to mention, the only thickness available at most home centers is ¾ of an inch, which significantly restricts the projects you can take on. 

The other option is purchasing rough-hewn lumber and milling it yourself. This will require several different tools. 

For jobs that require straight and even stock, a jointer starts the process by straightening one edge of the board, and squaring up the adjacent edge. To do this, it must be set up properly.

Jointer

The best jointers make short work of straightening boards. Read on to learn how to adjust a jointer before using it to straighten and flatten boards.

Jointer Adjustment for Milling Stock

  1. Unplug the jointer. The process of adjusting your jointer requires you to remove the cutterhead guard, making this a dangerous project. Navigating around exposed blades is risky enough without the chance that they will accidentally be turned on and start spinning unexpectedly. Always turn off the power to your jointer and unplug it before making any adjustments. 
  2. Clean the machine and assemble your tools. Use mineral spirits and steel wool to remove any rust or residue. Apply paste wax for protection and enhanced friction control. Grab a long straightedge (at least 36 inches) and an accurate square.
  3. Remove the fence and cutterhead guard. The fence is an adjustable, vertical guide to the right of the cutterhead, used to guide the plank or board as it moves through the jointer. The cutterhead guard sits over the blades and prevents you from losing a fingertip, so once the knives are exposed, take extra caution. Always follow safety recommendations for using a jointer
  4. Check that your tables are parallel. A jointer has two tables that support the boards as it moves across the cutter head, one to either side. The infeed table is on the right, and the outfeed table is on the left. Once your fence has been removed, temporarily adjust the infeed table to be even with the outfeed table. Place a straightedge on the infeed table, extending over the outfeed table. Press down on the straightedge and take a peek. If there are any gaps or light is showing underneath the straightedge, adjust the height of the tables until it disappears. Reattach the cutting guard and fence.
  5. Eliminate snipe. The outfeed table is level horizontal surface that supports stock during and after introduction to the blade. When the outfeed table is lower than the infeed table, the board ‘drops’ as it passes over the cutterhead, removing more material than you intended. This creates an unevenness in the trailing end of the board, called ‘snipe’. Adjust the infeed table to the desired depth and joint just a few inches of a scrap board. Then, turn off the jointer and place the jointed portion of the board over the cutterhead. Observe the gap between the board and the outfeed table. Raise the outfeed table until it is just touching the bottom of the board. This will ensure adequate support as you feed the board through the machine, eliminating snipe. 
Person adjusting his jointer knives
  1. Check your knives. A typical cutterhead is a cylinder with two or three notches. A jack screw or a spring sits in each notch, and a knife blade rests on top of that, held in place by a locking bar and screw. These blades provide the cutting action as the board is fed through the machine from right to left, shaving off excess wood and creating a perfectly straight and flat edge. Visually inspect the surface of the knives for nicks, dents, divots, and rust. 
  2. Remove and clean the blades. For the best end result, the knives should be sharp and clean. First, you’ll want to find top dead center — the highest point the blades reach as the cylindrical cutterhead rotates. To find the top dead center, tape a piece of paper to your fence. Using a combination square hung from the fence and rocking the cutterhead back and forth, lower the blade of the square until the knife edge barely grazes it. Run a pencil along the straightedge to mark the spot on your paper.  Align the knife with your mark and wedge wood in the gaps between the cutterhead and the tables, to prevent rotation. You can then loosen the screw that holds the locking bar in place, and remove both the knife blade and the locking bar. Clean both with mineral spirits and steel wool. If needed, you can also sharpen the jointer blade.
  3. Replace the blades. If your blade is past cleaning up and sharpening, then you’ll need to start anew. Insert a fresh, sharp blade into the notch and hold it in place by inserting the locking bar and gently tightening the screw that holds it in place. Adjust the spring or jack screw underneath the blade until the tip of the blade is level with the mark you made earlier at top dead center. When the blade is in place, fully tighten the outermost screw. 
  4. Test the adjustments. Joint two boards about six inches wide and 36 inches long. Place the jointed faces together. If the jointer has been properly adjusted, there will be no gaps between the boards. If you see tiny gaps at the end of the boards, adjust the outfeed table and try again. 

Conclusion

A jointer is a cutting tool used to straighten and flatten one edge of a board, and to perfectly square up one adjoining edge. Before using a jointer to square edges or flatten boards, you must adjust the settings. Make sure you are using sharp, clean knives. 

Your infeed and outfeed tables must be parallel when at the same height. Lower the infeed table to dictate how much wood will be removed. Ensure your cutterhead guard and fence are locked down before jointing.

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.