It may not be the most versatile machine in the shop, or be capable of doing fancy cutting or shaping jobs. But without a jointer to put flat faces and straight edges on the lumber we build with, most of our other machines wouldn't be worth their weight in sawdust. We need true edges and faces on our stock that will ride solidly, smoothly and safely on our machines' tables and against their fences.
Since a jointer performs a fairly simple task, it isn't that difficult to keep this machine in top form. There are only a few regular maintenance tasks that you need to stay on top of. These include: Checking and adjusting the parallelism of the tables, changing the knives when they become dull or damaged, setting the height of the outfeed table level with the knives, setting the fence angle stop(s), setting the spring tension of the cutterhead guard, and checking the motor drive belt and pulleys.
For safety's sake, ALL of the tune-up procedures described in this article (aside from taking test cuts) MUST be done with the jointer unplugged from electrical power. To make adjustments easier and less messy, clear any chips left in the jointer's dust chute. Use a shop vacuum to suck up chips stuck up around the machine's cutterhead, as well as from its tables and base. You'll also want to use a small clamp to prop open the jointer's guard and keep it out of the way for most of the steps described in this article.
Checking Parallelism of Tables
To do its job correctly, a jointer's infeed and outfeed tables MUST be parallel to one another. If your jointed boards are coming out with either a convex (humped) or concave (hollowed) edge instead of straight, it's possible that your tables aren't truly parallel. To check this, use a straightedge with a dependably straight, preferably ground edge that will make firm contact with the table's machined surfaces. Better still, I recommend using a long, high quality carpenter's level, say four or five feet long. Unlike a straightedge, the edge of a level will sit flat and not fall over.
After repositioning the fence so it's clear of the tables, set your straightedge or level across both jointer tables. Raise the height of the infeed table up to the level of the outfeed table. Now tap on the ends of the level to see if it rocks back and forth, an indication that the tables have drooped, and they are lower at the ends than in the middle. If the level doesn't rock, check to see if there's a gap under the level near the cutterhead ends of both tables. Check the gap using the thinnest leaf in a feeler gauge set (typically .0015 in. thick). If you don't have feeler gauges, a piece of regular paper will work. If the feeler gauge reveals a gap, it's an indication that the tables are lower in the middle than the ends.
In either case, you can usually return the tables to parallel by adjusting the screws that press on the gibs in the jointer's dovetailed ways. The ways are the joints that connect each table to the base and allow it to slide up and down. If one or both tables have drooped, tighten the gib screws nearest to the outer ends of the table. If the tables sag in the middle, concentrate on the screws near the cutterhead end of each table (for more information on gib adjustments, consult your machine's manual).
Changing and Setting the Knives
No amount of jointer tune-up is going to give you good cutting results if the machine's knives are dull. Generally, dull knives tend to produce more tearout when jointing figured woods. Really dull knives can even burnish the wood to the point where it won't readily absorb water-based glues, which can lead to gluing failures.
The first step in changing knives is to remove them from the cutterhead ... very carefully. Start by hand-turning the motor's drive pulley until one of the knives is centered between the jointer's tables. Loosen the bolts or screws on the gib that secures the knife in the cutterhead. Once all bolts all loose, carefully lift the knife and gib up and out of its slot. I prefer to wear gloves and use a magnet for this job, as even a dull knife can render a nasty gash! Now clean out the cutterhead slot by brushing off any caked-on dust with a stiff-bristled brush, then blowing the slot clean with compressed air. Also carefully clean any dust and grime from the gibs and the knives themselves with a rag (definitely wear gloves for this task!). To loosen tough grime, you may need to use a little cleaning solvent, such as naphtha. A penetrating lubricant, such as WD-40, can also serve as a solvent for grime.
Ideally, you'll have a second set of sharp jointer knives on hand to install immediately. This saves the waiting period that it takes for the dull knives to come back from being sharpened (some jointers, including models with helical heads, use reversible, disposable knives; consult the machine's manual for information).
If one of your jointer's knives has been nicked due to accidentally encountering a nail or screw in a board, you can temporarily save the trouble of changing out the knives by sliding the affected knife (or knives) slightly sideways in the cutterhead, thus offsetting the nicks.
When you're ready to install new or newly sharpened knives, don a pair of work gloves and carefully lower a knife and gib pair into a cutterhead slot - use the magnet again if you wish. Make sure that the cupped edge of the gib faces up and that the beveled side of the knife faces towards the outfeed table. Tighten each gib bolt just enough to put very light pressure on the knife. Now slide the knife sideways so that it extends past the outboard edge of the cutterhead by 1/32-in. It's important to set all the knives that way, in order to get a clean, straight cut when using the jointer's rabbeting ledge.
The next job is to raise or lower the knife so that its cutting edge is both level with and parallel to (widthwise) the outfeed table. Fortunately, the majority of jointers have leveling screws in their cutterheads designed to help accomplish this task (for those with leveling cams, consult the machine's manual). Most require an Allen wrench to turn the screw at each end of the cutterhead to raise or lower each end of the knife. The idea is to turn the screw a very small amount at a time, say an eighth of a turn, then check to see whether or not the knife is level with the outfeed table. Some woodworkers like to use a dial indicator or a special jig to check knife height. A lower-tech approach is to use a small straight edged wood stick I call a drag block. Set the block over the outfeed table and cutterhead, then rotate the cutterhead a little. The goal is to raise each end of the knife so that it makes light contact and just "ticks" against the block as the cutterhead turns. First check one end of the knife, then the other. Readjust the leveling screw until the block makes the same amount of contact with the block at both ends of the knife. If the knife is set too low, turn the screw some more; if it's too high, back off on the screw a little, then gently tap the knife back down with the end of a wood scrap. Once the knife is level and parallel with the outfeed table, tighten the gib bolts fully, starting with the bolts in the middle, then the ones at the edges.
Unfortunately, there's a bit of a rub: Tightening these bolts tends to make the knife raise up just a little, so you'll need to check its height settings again. If the knife has, indeed, raised up a bit, it'll pull the drag block forward as the cutterhead is hand turned. That's actually OK, as long as it drags the block forward by the same amount when you check at each end of the knife. You can accurately gauge the amount of drag by putting a few marks on the lower edge of the block, say 1/32-in. apart. As long as the block moves the same amount at each end of the knife, its height is fine. When you repeat the installation and leveling process on the jointer's other knives, be sure they're all set with the same height and drag the first knife. Finally, check the tightness of all the gib bolts/screws again, just in case you missed completely tightening any (we don't want any flying bolts or knives, now do we?).
Leveling Outfeed Table to Knives
Once the knives are leveled and secured, it's time to set the jointer's outfeed table exactly level with the top of the knives' cutting arc. First, set a short wood block with a straight, flat edge on the outfeed table with one end overhanging the cutterhead. After loosening the lock knob or screw that secures the outfeed table's setting, turn the hand wheel and lower the table a little while slowly rotating the cutterhead by turning on the jointer's motor pulley or by pulling on the drive belt. Lower the outfeed table until the knives just make very light contact as the cutterhead is rotated. If the knives drag the block forward, raise the table. A very slight "ticking" sound as the knives hit the block will tell you the setting is just right. Tighten the outfeed table's locking knob and recheck the setting once again.
Now run a test board over the jointer and check its edge to make sure there are no signs of sniping - an area near the end of the board that's cut a little deeper than the rest of the edge. Snipe at the board's front end indicates that the outfeed table is higher than the knives. In worst cases, the table's height will actually stop the work from being pushed past the cutterhead. Snipe at the back end of the workpiece means that the table is set lower than the knives. Reset the outfeed table and recheck it as necessary.
Setting Jointer Fence Stops
Now that the cutterhead and tables are in tiptop shape, it's time to give some attention to the jointer's fence. Since we usually depend on this machine to produce edges that are not only straight but square, it's important for the fence to be properly set. Start by using your largest and most accurate try square to check the fence for squareness to the jointer's tables. If the setting is off, reset the fence to 90 degrees.Back off the fence stop (or swivel it out of the way) if it interferes with resetting. With the fence locked down, adjust the stop bolt and secure its locknut. To confirm your stop adjustment, reset the fence to 90 degrees using only the stop to set it, then lock the fence in place. Now joint the edge of a wide board and check it for square using a reliable try square. Reset the stop and recheck the setting as necessary. If your jointer has a 45 degree stop, repeat this procedure, using a miter or combo square to check the setting.
Adjusting Cutterhead Guard
Next, check the cutterhead guard and make sure it's operating properly. Its spring should have enough tension to quickly snap the guard back against the fence and fully cover the cutterhead after it's been pivoted open during use. If the action is sluggish, increase the guard's spring tension following the directions provided in your jointer's manual.
A Few More Details...
In order for you to accurately set your jointer's depth of cut, the cursor/pointer on the infeed table needs to be set so that it reads "0" when the two tables are level with each other. Typically, the pointer is held in place with a small screw that simply needs to be loosened before resetting the pointers position. To confirm the adjustment, set the jointer for say a 1/16-in. deep cut, then measure the exact width of a board before and after taking a pass.
It also pays to take a moment and check your jointer's drive belt and pulleys. Replace any belts or pulleys that are excessively worn - excessive vibration or reduced cutting power may be a symptom of this. Also, check the belt's tension: You should just be able to deflect the belt a little when you pinch it together in the middle. If it's too loose, tighten it as necessary.
Sandor Nagyszalanczy is a furniture designer/craftsman, writer, photographer and regular contributor to Woodworker's Journal. His books are available at: www.sandorsworkshop.com