The jointer requires sharp tooling and precision set-up to perform the work it is designed to do. Perhaps more than any other woodworking machine, maintaining and adjusting the jointer is an art that requires a thorough understanding of the mechanics involved and the skill to dial in the correct adjustments. Every jointer is a little different, it takes experience to know a particular machine and how to set it up to perform well.
Adjusting the outfeed table
Occasionally, the jointer will not produce straight, flat faces and edges. Instead, it cuts a taper, or snipes the end of the piece. These can easily be corrected by adjusting the outfeed table height with respect to the knives.
- Lock out the power to the machine.
- Using a quality straight edge such as a steel ruler placed on edge on the outfeed table, observe the position of the table in relation to the cutterhead. Rotating the cutterhead by hand will reveal if the knives are not touching the ruler (table too high), or lifting the ruler off the table (table too low). This observation will help you determine how far the table needs to be adjusted.
- Unlock the outfeed table and adjust. Use the steel ruler on edge to check the location.
- Lock the table, power up the machine and make a few test cuts.
- Keep making adjustments until the jointer is cutting properly.
Changing straight knives
Changing knives in the jointer can be an art. Different methods have been developed for getting the knives at exactly the correct height which is necessary for the machine to perform properly. It is often necessary to readjust one or all the knives multiple times to get them set properly. The method used will also depend on the exact configuration of the jointer as they have different means of adjusting the height of the knife.
Follow these general steps to change straight knives. Also refer to the machine manual if it is available.
To remove the knives:
- Lock out the machine.
- Unlock the fence and move it to the far right position on the machine bed to allow full access to the cutterhead.
- Loosen the gib screws for one knife. Carefully remove the knife out of the cutterhead, and remove the gib.
- Be aware that when rotating the cutterhead without the knife and gib installed, the jack screws and/or springs may be loose and can fall into the base of the jointer. Change one knife at a time unless you are sure there are no loose parts.
- Clean any pitch or sawdust from the surfaces of the cutterhead and the gib using mineral spirits or strong citrus cleaner. Check the gib for any sharp edges or burrs, lightly file if necessary to remove them.
To reinstall the knives:
- Use mineral spirits to clean the knives of any oil or contaminants. Hone the back of the knives to be installed with a flat, fine water stone to remove any burrs and dry thoroughly.
- Position the gib in the cutterhead, and slide the knife into place. Turn the gib screws until there is no play between the knife, gib, and cutterhead. The knife should still be able to move.
- If the jointer uses a spring under the knife, lay a flat, heavy block of wood on the outfeed table. Press the block into the knife while it is at the top dead centre of its rotation. This positions the knife at the correct height. Tighten the gib screws just enough to keep the knife in place when the wooden block is removed. It is important to tighten the gib screws in sequence a little at a time to help prevent the knife from shifting. After the initial tightening of the screws, check the height of the knives with the block again to see if they have shifted. Adjust if necessary, and tighten all screws one last time.
- If the jointer uses jack screws, use a narrow block of wood or a steel ruler as a gauge. Turn the jack screw until the edge of the knife at top dead centre of its rotation makes contact with the block or ruler. Do this on either end of the knife where the jack screws are located until the knife touches equally. It may be necessary to use a wooden block to tap the knife back down if it has been raised too far. Tighten the gib screws just enough to keep the knife in place. Check alignment and adjust if necessary, and tighten all screws one last time.
- Check the height of the knife. Place a thick ruler on edge or block of hardwood on the far right side outfeed table so that it hangs just past the knife. If using a wooden block, make a reference pencil mark on it at the edge of the outfeed table. If using a ruler, place the ruler a set distance past the outfeed table.
- Slowly and gently, rotate the cutterhead by hand. The knife should pick up the block or ruler, move it forward and set it down. If it does not pick up, lower the outfeed table slightly until it does. Note the distance it moved. If using a wooden block, make another mark at the edge of the outfeed table. The distance the block or ruler moves should be the same left to right, and for all the knives. Adjust as necessary until the block or ruler travels the same distance.
- Install all the knives using the steps above.
- The distance the block moves is not initially important for setting the knives, it only ensures they are all the same height. Once this step is complete, the outfeed table can be calibrated to the knives. It should be adjusted so that the ruler or block moves about 3 mm or ⅛″, which will mean the knives are about 0.003″ above the outfeed table. This distance accounts for the peaks left by the circular cutting motion of the knives.
- Use a piece of scrap wood to test the knives and the height of the outfeed table. If required, adjust the outfeed table until the jointer is neither sniping nor cutting a taper. Check by making passes on both the left and right side of the table.
Magnetic knife setting jigs are available to assist in set up. They sometimes come with the machine, or can be purchased as an aftermarket accessory. They use magnets to hold the jig securely to the table, and to hold the knives at the correct height. Once the jig is in place on the table, the magnets hold the knives while the gib screws are tightened. If using a knife setting jig, it is still necessary to check the knives for alignment as the jig does not guarantee the knives are perfectly set.
Changing carbide insert cutters
Changing insert cutters is simple, with no need to adjust the individual cutters to height or adjust the outfeed table. Using the correct tool, such as a Torx™ drive, the inserts are unbolted from the cutterhead. If damage has occurred, a single cutter can be rotated to a fresh cutting edge. If the entire head is to be changed, the cutters are all rotated in the same direction to keep track of which edges are fresh and which are used. A paint pen can be used to mark the cutters which are used or new, and the direction of rotation for the next change.
When the cutters are tightened, care must be taken to exert the correct torque on the cutters. If they are under-tightened they can potentially vibrate loose, while over-tightening can shatter the brittle carbide. A should be always be used to tighten the machine screws.
Cleaning and lubricating the tables
The tables and fence on a jointer should be kept clean and free of pitch and contaminants. Follow the procedure for cleaning and waxing the table saw.
In addition, the pivot points on the fence should be kept lubricated. Use a few drops of light machine oil to keep the fence moving easily. The mating surfaces of the fence and table where the fence slides should also be kept clean and lubricated. White lithium grease works well for this and lasts longer than paste wax.
A torque wrench is a tool used to apply a specific torque to a fastener such as a nut, bolt, or lag screw. It is usually in the form of a socket wrench with special internal mechanisms.