How Does a Jointer Work?

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A jointer is probably one of the most important tools in a woodworker’s arsenal. This machine essentially makes a board flat on whichever surface you choose. Even though there are alternatives to a jointer, nothing beats its precision and efficiency. So, how does a jointer work? 

How Does a Jointer Work?

The jointer has two sections; the infeed table and the outfeed table. Between them are the jointer blades (which need sharpening more than you might think). You feed the board with defects to the infeed table which then exits to the outfeed table. The outfeed table has the same elevation as the blades on the cutter head which trim the wood to correct any defects. 

To start, find the flattest area on any board you’ll want to flatten by rocking it across the span of the jointer table. Feel the plane and maintain it as you begin the cut. Try not to put downward pressure on the board as you guide it with your left hand against the fence, and push it forward with your right. 

When your left hand is about 18 inches from the cutter head, pause and while keeping firm control of the board, reach for a push block with your right hand, positioning it on the end of the board. Now continue moving the board forward until the end, when the safety guard has closed to the fence.


The end result should be a flatter board without any defects. Let’s quickly look at some of the common board defects that can be corrected using a jointer

Which Wood Defects Can You Correct Using a Jointer?

The three most common types of wood warp that you can correct using a jointer are:

  • Bowing: this happens when a board has a bend and doesn’t lie flat.
  • Twisting: this happens when the board won’t sit flat on all corners, when you press on one corner, the board rocks back and forth.
  • Cupping: with this issue, the board has sides that are lower or higher than the inner part.

Depending on the board you’re working with, it may have either one or more of the defects. If any of the conditions are severe, it can make working with the board very challenging. Lucky for you, you can easily correct these defects using a jointer in combination with a planer.

Common Parts of a Jointer

Knowing all the parts of a jointer can help you understand how it works. Both benchtop jointers and stationary jointers the following important parts: 

  • Handwheels 
  • Levers 
  • Knives 
  • Fences 
  • Infeed table 
  • Outfeed table

Handwheels and Levers

You can adjust the infeed table on a jointer using either a hand wheel or a lever. Handwheels are more precise, with each quarter turn producing a measurable height adjustment. While levers are more subjective, almost all jointers offer a scale to measure the change in height. 

Person pointing the parts of a jointer

Besides, you can’t use jointers to remove exact amounts of material. That means it’s malleable and subject to personal preference.


Knives on the rollerblade of a jointer are usually two, three, or four, depending on the size of the machine. Most benchtop variants have two knives, and the largest of jointers have up to four blades. The more knives that truncate the wood there are in a jointer, the better the finish.

The default knives that come in most jointers are usually high-speed steel. You can go for a similar option or get the more expensive and durable carbide knives. Even though steel does get a great cut, it’s more prone to nicks.

Jointer knives are either set with a magnetic knife-setting jig or jackscrew adjustment. The first option uses a magnet to lift the knife out of the cutter head to the proper height, while the latter uses jack screws under the blade. Both methods are accurate, though most find jack screw adjustment is much easier.


The longer the fence, the better. The fence has to be flat, and not warped or twisted for whatever reason. If it’s not correct, get a replacement, or you won’t get a good trim. 

Fence movement is also important as it should slide easily across the table and adjustable to an angled setting with minimum fuss. Some jointers offer a rack and pinion mechanism for moving the fence, making it easier to quickly adjust the fence location.

How to Operate a Jointer

Start by following the jointer’s directions and make sure you set the outfeed table and knives at the same height. Inspect your board and see which face needs a trim. Run the concave side of the board having a bow above the jointer, to remove off the excess material. 

Man showing how a jointer works

Continue passing the board over the jointer until the majority of the board’s face is clean and flat. Once one face is flat, repeat the basic steps to square one edge of the board to the now flat face. Run the now jointed face against the fence to get a right angle on the edge of the board. 

After attaining a flat face, you can then run the board across the planer to reduce the thickness of the board uniformly. Note that a planer will only make a board thinner, yet still deformed if it’s not flat to its base.

Safety Tips When Using a Jointer

According to a study published on the National Library of Medicine, the highest tool-specific injuries are associated with jointers. If you get sloppy with the machine, the blades can bite you in a hurry and lead to severe injuries.

Follow these basic guidelines as you operate any jointer.

  • Before joining a face or edge, check for knots or defects on the board that could separate from it and cause the board to jump during planning.
  • When face jointing or flattening a thin piece of wood, always use a push block to significantly reduce the chances of injury.
  • Only run stock that’s within the recommended lengths over the jointer. Not too short or too long.
  • The safety guard should always be in place unless face jointing a board wider than the machine’s capacity. 


Many woodworkers can’t get by without a jointer to start their projects. With time and experience operating the machine, operators get more consistent and accurate results. Even though there are alternatives to a jointer, they won’t be as fast or efficient as the machine.

An expert at home repair, remodel, and DIY projects for nearly 40 years. His first experience came in completely restoring an antique home. Completely redone from the inside out, and restored to its original form, the home is a featured design by renowned Southern California Architect Cliff May, considered to be the father of the California Ranch Home. Now Dennis spends his time on fine woodworking projects and tool comparisons.