Setting Jointer Knives

Like cleaning your home’s gutters or giving the dog a bath, changing jointer knives can be a chore you keep putting off (maybe even hoping someone else will do it). But these knives need periodic resharpening to ensure clean cuts and prevent strain on your jointer’s motor. Here’s how to make the job quick and easy.

Never sharpen or adjust jointer knives again-for a price

Bypass sharpening and resetting jointer knives by replacing them with Dispozablade Self-Set knives. These disposable knives have two edges (just like those on a benchtop planer). The knives register to pins on a magnetic metal holder that rests in the cutterhead channel on locator tabs, as shown right. A starter set for a 6" jointer with three-knife cutterhead costs $239; replacement knives are $28 for a three-pack. Costs increase for wider jointers and those with four knives. You secure the knife and holder in place with the jointer’s gibs. Learn more at dispozablade.com, or call 800-557-8092.
Remove the dull knives

Unplug the machine, remove the cutterhead guard, and move the fence clear of the knives. Lower the infeed table ¹⁄₈ " or so, but do not lower the outfeed table; it serves as the point of reference for installing the sharp knives. To keep the cutterhead from rotating, lightly tap a pair of small wedges between the cutterhead and each table, as shown below.
Loosen the big bolts.

Tip! Keep a second set of sharpened knives on hand to avoid jointer downtime.

Loosen the gib bolts, then remove the knife and gib. If you’ll remove all knives to sharpen and replace later, remove the jackscrews (or springs, if so equipped) too, so they don’t fall into the machine when you rotate the head to access the next knife. If you’re installing a backup set of knives, leave the jackscrews in place and simply install a new knife on top of them.
Clean the knife

A jointer knife rests on jackscrews. Adjusting these up or down determines the knife’s height on the cutterhead.

Clean the knife, gib, and knife slot using a wire brush and mineral spirits or lacquer thinner. Wipe dry with a rag. Repeat for each knife location.
Install the sharp knives

Clamp or tape a square or 90° drafting triangle to the outfeed table as shown, and reinstall the wedges. Insert the jackscrews, gib, and knife for one channel. Snug up the outer gib bolts to hold the knife in place, but just loose enough to allow adjustments. Remove the wedges.
Finish up

Place a scrap of lightweight wood or MDF over the cutterhead and against the triangle. Rotate the cutterhead by hand. When the knife moves the block about ¹⁄₈ ", as shown, without lifting it off the table, you have the correct knife-height setting. Repeat this procedure for the other end of the cutterhead. When finished, tighten all the gib bolts. Repeat for all knives. Reset the infeed table to your desired cut depth.