Being able to quickly plane boards flat, smooth and to the exact thickness you need all make the thickness planer one of the most important machines in any workshop's power tool arsenal. But a planer is only useful if it's kept in good running condition. Some of the regular maintenance tasks you need to do include cleaning and lubricating the planer's bed and running gear, keeping its knives sharp, and adjusting its extension tables, depth stop and cutting thickness scale.

Cleaning and Lubricating

While shop machine cleanliness is next to, well, you know, cleaning might be more important for thickness planers than for any other shop machine. The reason is that a planer with a dirty bed and sticky feed rollers may cause stock to not feed smoothly--or not to feed at all. An accumulation of fine sawdust can make it difficult to raise and lower the cutterhead, and chips trapped inside the planer can jam up the entire machine.

Start cleaning your planer by first unplugging it from power and then raising the head assembly all the way up. Use your shop vacuum to clean sawdust from the bed and every nook and cranny inside the body. A crevice tool (an accessory nozzle that comes standard with many shop vacuums) can be very handy for getting dust and chips that are stuck inside the planer.  If the area around the cutterhead is packed with chips, remove the dust shroud and vacuum that area thoroughly.

Once all the loose dust is gone, do a quick visual inspection of the planer's bed and all components that serve to raise and lower the planer's head assembly (or, on stationary models, the bed). Clean dust and dirt that's accumulated on any gears, screwposts, chains, etc. by first spraying them with a cleaning solvent, then using a brush and rags to remove as much of the grime as possible.  Spray the planer bed with solvent, too, if there's accumulated pitch or other deposits. Use a ScotchBrite™ pad to remove hardened deposits or corrosion (DO NOT use an abrasive pad if your planer's bed is covered with a thin chromed steel sheet; the abrasive will only scratch it and reduce its slickness). If you use a water-based cleaner, such as Simple Green, be sure to dry all surfaces with a few blasts of compressed air, to remove any remaining moisture that could trigger rust.

Next, inspect the planer's infeed and outfeed rollers, and clean off any stuck-on deposits using alcohol and a clean rag. You can also use a cleaner like Simple Green® and a ScotchBrite pad to remove stubborn deposits — just stay away from cleaning solvents, such as naptha or paint thinner, as these could harm rubber- or plastic-coated rollers. To access the entire roller, clean one section, then briefly plug the planer back in and flip the on switch for just a second, until the rollers rotate around slightly. Then unplug the machine and continue cleaning. Be VERY careful to keep your fingers away from the cutterhead during cleaning; alternatively, you could clean the rollers with the planer's knives removed.

If the rollers are clean and you still notice stock slipping during planing, check to see if the rubberized surfaces of the rollers look shiny and glazed. You may be able to temporarily improve their grip by sanding their surfaces slightly. But eventually, such rollers will need to be replaced or recovered.

If you wish to lubricate any of your planer's internal parts, make sure to use ONLY a dry lubricant, such as Boeshield T-9®. Wet lubricants like oil or penetrating sprays such as WD-40 will attract dust and cause more problems than they solve. Before spraying, it's important to cover rubber feed rollers with paper or rags, as coating them with lubricant will cause them to slip and not feed stock effectively.  Finally, don't try to lubricate your portable planer's cutterhead bearings; these are permanently sealed and lubricated. If they're making rumbling or grinding noises, they're likely worn out—oiling them won't help.

To keep stock sliding smoothly through a planer, it's most important to keep its bed and extension tables well lubricated, either by spraying them with dry lubricant such as TopCote®, or applying a coat of paste wax. If you choose waxing, apply only a light coat of wax, let it dry until it hazes over, then buff off the excess with a clean rag. I prefer liquid automotive waxes, as I find that they're easier to apply and last longer than traditional carnuba paste waxes. Cleaning and lubricating the bed/tables is a maintenance task that may need to be done quite often, especially if you often plane sappy woods such as pine.

SIDEBAR: How Do You Know When Your Planer Knives Are Dull?

The length of time it takes fresh, sharp planer knives to dull depends on a myriad of factors: the hardness of the steel the blades are made from (and how sharp they were to begin with), the hardness of the wood you're planing and how deep a cut you take, the planer's feed speed, and, naturally, how many board feet of wood have been run. There are several telltale signs that your planer's blades need changing.

If the blades have been nicked, you'll notice small ridges forming on the surface of planed boards (to deal with these, see the section "Changing the Knives" below). Somewhat dulled knives tend not to cut as cleanly, especially on figured woods. If you notice more tearout on such boards, it's likely your knives need freshening. Really dull planer knives will actually burnish the surface of plain-grained boards. If board surfaces look somewhat shiny after planing, check by putting some water on the board (use an open-pore, not-too-dense wood, like oak or mahogany, for this test — not hard, resinous woods like teak or rosewood).

If the water instantly forms small beads, it's likely the knives are really dull and have burnished the wood. This can be a real problem, as a burnished surface will actually repel water-based glues and finishes.

Changing the Knives

When your planer is no longer producing clean, flat planed surfaces (see the sidebar, above), it's time to refresh its knives. Fortunately, this process is very easy for modern benchtop planers, which use reversible, disposable knives that mount onto registration pins that automatically set each knives cutting depth. (If you own an older or stationary model planer which uses single-edged knives that require individual adjustment, consult your machine's manual for removal and resetting procedures).

After making sure your machine is disconnected from power, remove the planer's dust collection shroud or chip chute, and any other body panels that cover or limit access to the cutterhead. Once the cutterhead is fully exposed, rotate it until one of the knives is facing fully upwards.

If your planer has an automatic cutterhead lock, you'll have to depress it before turning the cutterhead.  It will automatically engage when the knife is in the optimal position. Now, either using the wrench that came with your machine or one that fits, loosen all the bolts that secure the knife and its holder to the cutterhead.

What you do next depends on what shape your knives are in: If the knives are only nicked (see the sidebar, above), don't remove the knife, but simply remove the knife cover and slide the knife slightly to the left. Then clean the cover with a rag.

Refit the cover, then replace and carefully tighten all the bolts. Advance the cutterhead to the next knife. Loosen its retaining bolts, slide this knife slightly to the right, and re-secure the cover and bolts. If there's a third knife, leave it alone. Shifting the knives will offset the nicks and let you get a little more life out of the set before it needs to be reversed or replaced. 

Dull knives must be changed. For this process, lift the knife out and either reverse it (if the opposite edge hasn't been used yet) or replace it with a fresh knife. Some planers come with special magnetic knife removal tools, which let you handle the knife out without risking slicing up your fingers.  If yours doesn't have one, you can use a small horseshoe or bar magnet to do the job.

When refitting the knife onto the cutterhead, take care to make sure that the small slots in the knife slip onto the cutterhead's registration pins correctly. Before rebolting the knife, use a little solvent to clean the knife holder of any dirt or grime, and clean any bolts that are dirty as well.

If you've reversed your knives, use a felt-tipped pen to mark each knife's used edge, so you'll know not to reverse them next time. Reinstall the holder and tighten the bolts, and repeat the process with each knife.

TIP: If you really hate changing planer knives, one way to extend their life is to make sure that each board you run is clean of mud and dirt and free of staples, tacks or other metal fasteners.

Check the Belt and Chains

Before buttoning your planer's covers back up, it's a good idea to check the condition of the motor's drive belt, if it's visible. If the belt shows excessive wear or is damaged in any way, replace it.

If your planer uses a chain-driven mechanism to raise and lower the cutterhead assembly, clean the chain and lubricate its links lightly with a drying lubricant. If the chain has an accessible tensioning mechanism, tighten the chain up if it's noticeably loose.

When you're done, replace the cutterhead cover, shroud, and/or dust chute.

Leveling the Extension Tables

One of the ways to combat planer "snipe" (where the ends of a board end up with a depression or are planed thinner than the rest of the board) is to make sure that your planer's extension tables are level and in line with the bed. Most portable planers have fold-down extensions that are adjustable via a pair of small bolts or screws under their outside edges. To check the level of your planer's tables, slide a long carpenter's level or straightedge into the planer so that it lies on edge across the bed and extension tables. Sight across each extension table, to see if there's a gap at any point between the table and straightedge. If necessary, tweak the table's adjustment bolts/screws until the straightedge sits in full contact with the bed and table.

If the outfeed table can be adjusted up and down, it's a good idea to set it just a fraction lower than the planer bed. This prevents the lower edge of a planed board from catching on the outfeed table. Once all table adjustments are made, be sure to tighten the locking nut at the base of each adjusting bolt.

Set the Depth Stops and Thickness Scale

Every planer has a scale and cursor to show just how thick a board will be after planing. But if the cursor setting is off, then you run the chance of ending up with stock that's planed too thick or thin. Many modern portable planers also have a depth stop feature that allows you to easily and accurately set the cut thickness to one of several common sizes: 1/2 in., 3/4 in., etc. To check the accuracy of the stop mechanism, set it to one of the middle settings, say 3/4 of an inch, and then plane a board. Use a dial caliper to check the board's thickness.

If it's greater or less than 3/4 in., readjust the stop's depth rod. Recheck the stop's accuracy as before, and tweak it as needed until it's dead-on. 

Now, without changing the planer's depth of cut, reset the planer's cursor, to read the same thickness on the scale as your planed board (in this case, 3/4 in.). It's especially important to check and reset the cursor after changing knives, especially if your planer has older style knives that lack registration pins in the cutterhead.