How to Use a Jointer for Face Flattening Before Planing
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Contents
Why flatten one face before planing
A thickness planer makes the opposite face parallel to the face riding on its bed. It does not reliably straighten a board that rocks, bows, or twists. Put a twisted board straight into a planer and the rollers can press it flat for the cut, then let it spring back afterward. The result may be thinner, but it will still be twisted.
A jointer makes one face flat. Once that face sits steadily on the planer bed, the planer can cut the other face parallel to it. This two-machine sequence is the standard way to prepare rough lumber. It works best when the board is long enough to control safely and wide enough to fit the jointer without balancing on its edge.
Check the board and the machine first
Inspect the lumber for nails, grit, loose knots, and checks that could open during cutting. Remove metal and brush off dirt; embedded grit can damage knives. Check the jointer’s maximum width and the board’s length. A 6-inch jointer cannot flatten a board wider than 6 inches in one pass, and trying to balance an overwide board on the cutterhead is not a safe workaround.
Use push blocks, keep hands away from the cutterhead, and stand out of the likely kickback path. Follow the machine manual for guard use, workpiece limits, and feed direction. If the board is too short to control with the machine’s recommended minimum length, or badly cupped, split, or unstable, don’t force it through. Crosscut it into shorter usable pieces if appropriate, or flatten it with a safer method.
For boards wider than the jointer, a planer sled can carry the board without rocking while shims support its twist. That takes more setup and can be slower, but it avoids buying a wider jointer for occasional wide stock. A planer sled is a useful option when the planer is already available and the board fits its capacity.
Set up the jointer
Unplug the machine before inspecting or adjusting it. Make sure the tables are clean, the fence is square to the outfeed table, and the cutterhead guard moves freely and returns to cover the knives. A straightedge across the tables can help reveal a step or dip; consult the manual for adjustment procedure and tolerances. Dull or nicked knives leave ridges and make flattening take longer, so check the knives if the finish is consistently poor.
Set a shallow cut. For a first pass on ordinary stock, about 1/32 inch is a practical starting point; use less for figured, brittle, or difficult grain. Deeper cuts remove material faster but increase tear-out and the chance of kickback. Don’t try to erase a deep hollow in one aggressive pass. A face with 1/8 inch of cup may need several cuts, and the board’s final thickness must allow for the wood removed during flattening.
Before cutting, identify the board’s high spots and the direction of its bow or twist. Mark the face you intend to flatten with a pencil. This makes it easier to see where the machine is cutting and helps prevent accidentally working the wrong face.
Flatten the face in controlled passes
Place the board with its most stable face down on the infeed table. For a lengthwise bow, orient the concave side down when possible so the ends make contact rather than rocking on a high center. For twist, locate the high corners; the goal is to remove those high points while keeping the board supported, not to press the twist out by force.
Feed the board steadily in the direction shown on the machine, keeping it flat against the table and fence as appropriate. Apply pressure over the infeed table at the start. As the leading end reaches the outfeed table, shift pressure gradually to the newly cut section there. This supports the reference face as it is created. Don’t push down hard on the trailing end: that can lift the leading end and produce a tapered cut.
After each pass, check the face with a straightedge and inspect the pencil marks. Continue with light cuts, concentrating on high areas until the full face has been cleaned up and the board no longer rocks. If only one edge or a few strips show cuts, the face is not yet flat. Stop if the board shifts, chatters, or requires you to reach close to the cutterhead. Reassess the setup rather than trying to muscle it through.
Jointer and planer: different jobs
| Machine | What it establishes | Best use in this process | Main limitation |
|---|---|---|---|
| Jointer | A flat face or straight edge | Make a stable reference face before planing | Width capacity limits the board; it does not make opposite faces parallel |
| Thickness planer | A face parallel to the face resting on its bed | Bring the board to consistent thickness after flattening | Can preserve twist or bow if the board is unstable on the bed |
| Planer sled | Supports a twisted or cupped board in a planer | Flatten stock wider than the jointer, within planer capacity | Requires shimming and setup; does not make the sled unnecessary to check |
Plane the opposite face
Once one face is flat, mark it clearly and place it down on the planer bed. Take light passes until the opposite face is clean, then flip the board and alternate faces as needed to reach the target thickness. Removing material from both sides can help reduce uneven moisture-related movement, though it cannot guarantee a board will stay straight after machining.
Measure the thickness at several points with calipers or a reliable rule. If the board is already close to its target, don’t remove more than necessary; flattening the first face may have taken away more stock than expected. Leave extra thickness if the lumber may move after machining and you can let it rest before a final cleanup pass.
A bench jointer is not essential for every shop. If you flatten rough lumber often, a jointer sized for your typical stock saves time and makes the process more repeatable. For occasional projects, especially with wide boards, a planer and sled may be the more economical choice. Compare capacity and footprint before shopping for a woodworking jointer; a wider machine costs more and takes more space, and is worthwhile only if its capacity matches the lumber you actually use.
