How a Jointer Works: Setup and Usage

A jointer does one thing: it flattens one face and straightens one edge of a board. Every other milling operation depends on this reference surface.

How It Works

The jointer has two tables—infeed and outfeed—with a rotating cutterhead between them. The outfeed table sits exactly level with the top of the cut. The infeed table sits lower by whatever amount you want to remove.

Push a board across and the knives shave off the high spots. Make enough passes and you get a flat face. Flip the board on edge, reference that flat face against the fence, and you get a straight, square edge.

What Size Jointer

Jointers are sized by the width they can flatten. A 6-inch jointer handles boards up to 6 inches wide. For furniture work, 8 inches provides more flexibility. Professional shops often run 12-inch or larger machines.

Bed length matters too. Longer beds produce flatter results on long boards. Short benchtop jointers work for small parts but struggle with anything over a couple feet.

Setting Up

Outfeed table height is critical. Too high and the board lifts off the cutterhead mid-cut, creating a taper. Too low and you get snipe at the end of the cut. Dead level with the knives at top of rotation is the goal.

Check this setup with a straightedge. Place it on the outfeed table extending over the cutterhead. Rotate the cutterhead by hand—the knives should just kiss the straightedge without lifting it.

Using the Jointer

Face jointing comes first. Put the concave side down—the board should rock, touching at the ends. Make passes until the rocking stops and the entire face touches the table.

Edge jointing follows. Press the flat face firmly against the fence. Concentrate on maintaining that pressure throughout the cut. A square edge depends on consistent fence contact.

Common Problems

Snipe—a deeper cut at the board’s end—usually means the outfeed table is too low or the board lifted slightly. Check table alignment and apply firm downward pressure through the entire cut.

Twisted results suggest a twisted board or inconsistent technique. Check your stock with winding sticks before blaming the machine.