A jointer is a fairly straightforward machine. When everything is adjusted correctly, you feed a board across the cutterhead and end up with a flat face or a straight, square edge.
But a jointer is also a precision machine. Small setup errors can show up immediately on the workpiece as a taper, snipe, scallops, ridges, or an edge that simply refuses to come out square.
The good news is that the symptoms often provide clues to what's wrong. Before you start making random adjustments, take a close look at the cut and use it to narrow down the problem.
RELATED ARTICLE: How to Flatten a Board with a Jointer
Problem 1: The Jointer Is Cutting a Taper
If repeated passes across the jointer produce a board that gets progressively narrower from one end to the other, start by checking the relationship between the cutterhead and outfeed table.
A common cause is an outfeed table that's slightly higher than the jointer knives. As the board crosses the cutterhead, the high table lifts the workpiece slightly. The error may seem insignificant on one pass, but it becomes increasingly noticeable after several passes.
Check the Outfeed Table Height
With the machine disconnected from power, place an accurate straightedge on the outfeed table so it extends over the cutterhead.
Rotate the cutterhead by hand until a knife reaches its highest point. Adjust the outfeed table until the straightedge just contacts the knife at top dead center.
If the knife and outfeed table are properly aligned but the machine still produces a taper, the infeed and outfeed tables may not be coplanar. We'll check that later.
Problem 2: Snipe at the End of the Board
A low outfeed table creates essentially the opposite problem.
The board may cut normally for most of its length, but as the trailing end leaves the infeed table, the workpiece can drop toward the lower outfeed table. The knives then remove more material from the final few inches, leaving jointer snipe.
The Fix
Use the same straightedge test to compare the outfeed table with the knives.
If the table is too low, raise it until its surface is correctly aligned with the cutting height of the knives.
This is why getting the outfeed table right is so important:
Too high → tapered cuts
Too low → snipe
Problem 3: Scallops or Ripples on the Surface
A properly adjusted jointer should leave a relatively straight, smooth surface. If you're seeing a repeating pattern of scallops or ripples, there are several things to investigate.
Start with the Feed Rate
Each knife removes a small, curved shaving as the cutterhead rotates. During a normal cut, those cuts overlap closely enough to produce a smooth surface.
Feed the workpiece too quickly and the individual cuts become more pronounced.
The simplest test is also the easiest fix: slow down your feed rate and make another pass.
Check the Knife Heights
If slowing the feed doesn't solve the problem, check the knives.
One knife sitting higher than the others can take a slightly deeper cut each time the cutterhead rotates, creating a repeating pattern on the board. The source method uses a straightedge and feeler gauges to identify the high knife before readjusting it.
Problem 4: The Jointer Won't Produce a Square Edge
One of the jointer's main jobs is creating an edge that's both straight and square to the adjacent face. If you're getting a straight edge that's consistently out of square, look at the fence first.
Use an accurate square to check the fence against the tables at several points along its length.
If it's out of square, adjust the fence stops according to your jointer's instructions.
What if the Fence Isn't Flat?
A more troublesome problem is a twisted or warped fence. A minor bow or crown may not have much effect, but a twisted fence makes it difficult to consistently produce a square edge.
One solution is an auxiliary fence face.
Cut a piece of 3/4" plywood or MDF slightly larger than the existing fence and fasten it securely to the fence. Paper or cardboard shims can then be placed behind the auxiliary face as needed to bring it square with the tables.
Problem 5: A Raised Ridge Along the Board
A long, narrow ridge running down a freshly jointed surface points toward a different problem: a nick in one or more jointer knives.
If you're edge-jointing narrow stock, the easiest temporary solution may be moving the fence so the workpiece passes over a different section of the knives.
For wider face-jointing operations, that's not always possible.
Offset the Knives
On a conventional straight-knife cutterhead, slightly shifting one knife sideways can stagger the locations of small nicks. Since the defects no longer line up, one knife removes the ridge left by another.
Woodsmith Tip: If you use your jointer's rabbeting ledge, remember that shifting the knives can affect the width and accuracy of rabbets cut on the machine.
When the Quick Fixes Don't Work: Check the Tables
If you've checked knife height, outfeed-table height, feed rate, and fence alignment but still aren't getting good results, it's time to investigate the basic geometry of the machine.
The infeed and outfeed tables need to be coplanar. If they're out of alignment, the jointer can produce tapered, concave, or convex cuts.
How to Check Jointer Table Alignment
You'll need a long, accurate straightedge.
First, check each table individually. Lay the straightedge along the length of the table, across different areas, and diagonally. You're looking for evidence that either casting isn't flat.
Next, raise the infeed table until it's level with the outfeed table.
Place the straightedge across both tables. Check along the outer edges, through the center, and diagonally. The straightedge should maintain consistent contact rather than revealing gaps between it and the table surfaces.
Clean Before You Adjust
Don't immediately assume that a gap means the machine needs a major adjustment.
Debris packed into the dovetailed ways can interfere with table alignment. Lowering the tables and cleaning these areas with a nylon or brass-bristle brush may be enough to solve the problem.
Correcting Jointer Table Alignment with Shims
Older jointers can develop table sag over time. If the castings themselves are sound, the tables may be brought back into alignment with thin shims.
Use brass shim stock or thin aluminum placed between the table casting and dovetailed ways. The table needs to be shimmed on both sides, and shim position determines which portion of the table is raised.
Because jointer designs vary, use your machine's manual as the primary guide before making this type of alignment adjustment.
Jointer Troubleshooting at a Glance
Start with the Symptom
The easiest way to troubleshoot a jointer is to avoid changing several adjustments at once. Look closely at what the machine is doing, identify the symptom, and start with the simplest likely cause.
A straightedge and an accurate square can tell you a lot. Check the outfeed table against the cutterhead, verify the fence, inspect the knives, and only then move on to the more involved job of checking the tables for coplanar alignment.
A jointer that's properly dialed in should reward that effort with what you're after in the first place: straight, flat, square stock that's ready for the next step of the project.
Keep Your Table Saw Running at Its Best
A well-tuned jointer is only part of an accurate woodworking setup. Your table saw also needs regular attention to stay smooth, safe, and precise. From cleaning and lubrication to checking alignment and inspecting wear points, a little routine maintenance can prevent problems before they affect your cuts.
TABLE SAW MAINTENANCE TIPS → Table Saw Maintenance: Cleaning, Lubrication & Rust Removal
