How to Use a Jointer for Preparing Glue-Joint Edges
What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
A jointer makes a board’s edge straight, square to its face, and clean enough for a strong glue joint. It does not automatically make a twisted board straight, and it cannot correct poor stock preparation on its own. The quality of the finished edge depends on machine setup, feed technique, and choosing boards that are suitable for the job.
Contents
What a jointer does for a glue joint
A jointer has an infeed table, a cutterhead, and an outfeed table. The infeed table sets the depth of cut. The outfeed table supports the board after the knives remove material. For edge jointing, you place the board’s face against the fence and run its edge across the cutterhead.
The goal is a flat edge with a consistent 90-degree relationship to the reference face. Two properly jointed edges should meet with no visible gap when placed together. The joint should not require heavy clamping pressure to close it. If it does, the edges are likely bowed, tapered, out of square, or cut with a poor technique.
A jointer is different from a thickness planer. A planer makes the opposite face parallel to the face already riding on its bed; it does not reliably straighten a crooked edge. For rough lumber, flatten one face first, then joint one edge, and only afterward rip the board to width on a table saw.
Prepare the machine before cutting
Unplug the jointer before checking anything near the cutterhead. Confirm that the knives or inserts are sharp, even, and installed at the correct height. Dull knives leave burn marks, fuzzy grain, and ridges that make a glue joint look closed until pressure is released.
Set the outfeed table level with the highest point of the knives. A straightedge spanning the outfeed table and cutterhead should just touch the knife at top dead center. If the outfeed table is too low, the board drops after passing the cutterhead, producing a snipe-like dip at the trailing end. If it is too high, the board catches on the table and the cut becomes uneven.
Set the fence square to the outfeed table using a reliable square. A fence that is only slightly out of square can produce a joint that closes on one side but leaves a gap on the other. Check the fence at both the front and rear of the cutterhead. Make sure the guard returns freely and covers the exposed cutterhead when the board is not over it.
For most glue-joint edges, start with a light cut of about 1/32 inch. A 1/16-inch cut is useful for removing a damaged edge or correcting a moderate bow, but it demands more feed force and increases the chance of tear-out. Take several light passes rather than one aggressive pass, especially with a small jointer.
How to joint a straight, square edge
-
Mark the edge you intend to cut with a pencil or chalk. The marks show where material is being removed and help reveal high spots.
-
Place the board’s best face firmly against the fence. Keep the edge being cut over the cutterhead, but keep your hands on the stock and out of the guard opening.
-
Start the machine and let it reach full speed. Put the board on the infeed table with moderate downward pressure near the front, then feed it steadily.
-
As the leading portion reaches the outfeed table, move your forward hand onto the outfeed side. Keep pressure over the outfeed table so the freshly jointed section stays flat.
-
Continue feeding at a consistent rate. Do not stop over the cutterhead, and do not force the board sideways into the fence. Use the fence as a reference, not as a lever.
-
Inspect the edge after each pass. Stop when the pencil marks are gone and the edge is straight from end to end. Use a straightedge and square rather than relying only on appearance.
For a final pass, some woodworkers joint with the board’s show face against the fence and others alternate faces to balance minor imperfections. Keep the same reference face against the fence throughout a matching pair of boards. If you change references randomly, the edges may be square individually but fail to align as a pair.
Check the edge before applying glue
Put the two boards together as they will be assembled. Hold them against a bright background and look for light between the edges. Check the first few inches, the center, and the last few inches. A small hollow in the center can sometimes close under clamps, but a large gap is not a substitute for a properly jointed edge.
Use a straightedge to identify a hollow or crown. A simple edge test also helps: place the boards together, then gently squeeze one end. If the opposite end opens, the edges may be slightly bowed in opposite directions. This can be corrected with another light pass, but avoid repeatedly jointing until the boards become noticeably narrower.
| Symptom | Likely cause | Practical correction |
|---|---|---|
| Gap at the trailing end | Outfeed table too low or pressure shifted incorrectly | Level the outfeed table and keep pressure on the outfeed side |
| Gap at the leading end | Infeed pressure or board support is poor | Support the board at the front and use a steady feed |
| Edge is not square | Fence is out of square or board is tilted | Square the fence and keep the reference face flat against it |
| Fuzzy or torn edge | Dull knives, excessive cut, or difficult grain direction | Sharpen or rotate knives and reduce the cut depth |
| Burn marks | Slow feed, dull knives, or a dirty cutterhead | Feed consistently and service the cutterhead |
Choosing the right jointer
Jointer width determines the maximum face width you can flatten, but it also affects edge-jointing capacity and machine stability. A 6-inch jointer handles most furniture boards and is usually the sensible cheaper option for a home shop. An 8-inch machine gives more room for wide stock and is generally more stable, but costs more and needs more floor space.
Benchtop jointers are compact and can prepare narrow boards, but their short tables make long, bowed boards harder to straighten. A floor-standing jointer is easier to use on long stock and typically has a better fence and more substantial tables. If you mainly edge-joint boards already flattened by a woodworking table saw, a benchtop machine may be entirely adequate.
Consider a 6-inch floor-standing jointer when you routinely process rough lumber, need to flatten faces, or work with boards longer than 6 feet. A spiral or helical cutterhead can reduce tear-out and noise, but it is not essential for producing straight glue edges. Sharp straight knives on a correctly adjusted machine are enough for many projects.
Safe working practice
Use push blocks or push pads, eye protection, and hearing protection. Keep hands away from the cutterhead and never reach over it to retrieve stock. Joint short pieces only when the machine’s manual permits it; very short or narrow work can be difficult to control. Do not joint stock with loose knots, embedded metal, or severe splits.
Provide outfeed support for boards longer than the tables. Without it, the board can tip as its center of gravity moves off the machine, ruining the cut or pulling your hands toward the cutterhead. Disconnect power before clearing chips, changing knives, or making table and fence adjustments.
