How to Check a Jointer’s Infeed and Outfeed Tables for Coplanarity
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A jointer’s infeed and outfeed tables do not sit at the same height during normal use. The infeed table is lowered to set the cut, while the outfeed table must meet the knives at the correct height. “Coplanar” means the two table surfaces lie in the same plane from side to side and along their length when checked together—not that they are always at the same elevation during a cut.
Contents
Why Coplanarity Matters
If the tables are twisted or tilted relative to each other, the jointer will not produce a reliably flat face. A board may rock on the infeed table, climb onto the outfeed table, or leave with a taper. You may also see snipe-like dips at the beginning or end of the cut, even when the knives are sharp and correctly set.
Common symptoms include a board that is flat near one edge but not the other, a visible gap under a straightedge, or a cut that becomes deeper as the board crosses the cutterhead. A table that is high at one corner can also make stock difficult to push and can encourage you to press down harder than necessary—a poor and potentially unsafe workaround.
Tools Needed
You need a genuinely straight reference, not a framing level or an ordinary board. A machinist’s straightedge is the best choice. A verified jointer straightedge or a high-quality precision rule also works. For occasional setup work, a long, known-straight aluminum rule can be adequate, but check it against a flatter reference before trusting it.
Useful additions are a set of feeler gauges, a bright inspection light, a small combination square, and a marker. A machinist straightedge is more useful for this job than a long spirit level because it is designed to reference a surface rather than indicate level.
Disconnect the jointer from power before placing anything near the cutterhead. Remove the fence if it blocks access, and make sure the cutterhead cannot rotate. Wear eye protection when cleaning the tables, but do not run the machine during measurement.
Clean and Position the Jointer
Wax, pitch, rust, and packed dust can create gaps that look like alignment problems. Scrape off residue and wipe both tables clean. Do not use a thick paste wax immediately before checking; even a small lump can change the reading.
Put the jointer on its normal floor location. If the machine has adjustable feet, level or stabilize the stand first. A badly twisted stand can distort a cast-iron table or change the relationship between table supports. Lock the fence out of the way, raise the infeed table to its highest position, and lock both table mechanisms if your machine provides locks.
Check with a Straightedge
Lay the straightedge lengthwise so it bridges the infeed table, cutterhead area, and outfeed table. Take readings along the left edge, center, and right edge of the tables. Do not force the straightedge down. Let it rest naturally, then use a feeler gauge to measure any gap.
Next, check across the width. Position the straightedge across the infeed table, then across the outfeed table, checking near the front, center, and rear of each surface. Finally, place it diagonally across both tables. A diagonal check often finds twist that a simple front-to-back check misses.
Record the largest gap and where it occurs. On a typical woodworking jointer, a few thousandths of an inch is a meaningful error. A gap of roughly 0.002 inch may be acceptable for less demanding work if the error is consistent and the machine cuts well. A 0.005-inch gap, a visible rocking straightedge, or a change in gap from one side to the other warrants adjustment before accurate surfacing.
Check the Outfeed Table Against the Knives
Table-to-table coplanarity is only part of the setup. The outfeed table must also be aligned with the highest point of the knives or cutterhead inserts. Rotate the cutterhead by hand only after confirming the machine is unplugged. Bring one knife or insert to top dead center, where its cutting edge is highest.
Place the straightedge over the outfeed table and extend it slightly over the cutterhead. Gently rotate the cutterhead by hand. A correctly set knife should just touch the straightedge and move it slightly, without lifting it substantially. If the knife passes under the straightedge, the outfeed table is too high or the knife is too low. If the knife pushes the straightedge up noticeably, the outfeed table is too low or the knife is too high.
Repeat across the cutterhead width and check every knife or insert. A knife that is higher on one side can produce ridges, chatter, or a board that is cut more deeply at one edge. Do not use this test with loose knife hardware. Tighten and secure the cutterhead according to the manufacturer’s instructions before rotating it.
Interpreting the Error
| Observed condition | Likely cause | Typical result |
|---|---|---|
| Same gap along both tables | Reference or table height issue | Usually consistent and easier to correct |
| Gap changes from left to right | Table twist, uneven support, or damaged surface | Tapered cuts and uneven faces |
| Outfeed matches on one side but not the other | Knife height varies or cutterhead is misaligned | Ridges, chatter, or edge-to-edge thickness changes |
| Tables rock under the straightedge | Debris, loose hardware, or worn adjustment mechanism | Unrepeatable setup and snipe |
How to Correct It
Start with the simple causes. Clean the mounting pads, check that table-lock bolts are tight, and inspect the gibs, dovetail ways, or parallelogram supports for looseness. A loose table can appear aligned when stationary but shift under feeding pressure.
Use the machine’s built-in table adjustment if available. Many jointers allow the outfeed table to be raised or lowered at several points; others require shimming or careful adjustment of the support mechanism. Make small changes—about 0.001 to 0.002 inch at a time—and recheck every direction after each change.
For a jointer without fine adjustment, thin metal shims can correct a low corner, but this is a careful repair rather than a casual shortcut. The shim must remain captive, not interfere with the table lock, and not create a rocking support. If the cast iron is visibly warped or a dovetail way is damaged, replacement parts or professional machining may be cheaper than chasing the error.
What to Buy for Future Checks
If you maintain one stationary machine, a basic feeler gauge set and a reliable straightedge are enough. A machinist-grade setup is worth buying if you own several jointers, planers, or table saws and want repeatable measurements. A digital level is not a substitute for a straightedge; it measures angle to gravity, not whether two surfaces share the same plane.
After adjustment, make a test cut on straight, reasonably wide stock. Use light, even pressure and inspect the face with a straightedge. If the cut is still tapered, recheck table coplanarity, knife height, fence squareness, and the machine’s stability in that order. The measurement is only useful if the jointer remains locked and stable while you feed the board.
