How to Use a Thickness Planer | Flatten Boards The Right Way

Using a thickness planer correctly means jointing one face flat first, feeding the board with the grain, and taking multiple light passes until you hit the target thickness.

For the full breakdown, see our best Budget Thickness Planer guide.

A thickness planer turns rough, uneven lumber into boards with a consistent thickness across the entire length. But it is not the first step in the process — the planer references the face that rides against the table, so if that face is warped or cupped, your “finished” board will be too. The sequence matters more than the machine settings, and getting it right keeps you safe and saves you from wasting expensive wood.

What To Do Before You Feed The First Board

Set yourself up properly and you’ll avoid the two disasters that ruin planer work: tear-out and kickback. Begin by inspecting every piece of stock. The manufacturer manuals agree that removing nails, dirt, glue, paint, loose knots, and cracks is mandatory before anything goes near the cutterhead.

Next, check that your lumber meets the machine’s minimum size. Many benchtop models require a piece at least 12 inches long, and several guides specify a minimum thickness around 5 mm. Feeding short or thin offcuts through a planer is how boards get thrown back at you — there simply isn’t enough material for the feed rollers to grip.

Finally, measure the thickest point on the board. Set the planer to that thickness minus your planned depth of cut. For the first pass, keep the cut shallow — the instruction sheets recommend a cut of about 1 mm so the gauge reads roughly one millimeter less than the stock thickness.

The Correct Feeding Sequence

With the stock inspected and the depth set, the feeding routine determines whether you get a clean board or a ruined one. Follow this order every time:

1. Put the jointed, flat face down on the planer table so the machine references that stable surface.
2. Orient the board with the grain, not across it — feeding across the grain increases tear-out and the risk of kickback.
3. Stand to one side of the machine, turn it on, and let the cutterhead reach full speed before you feed anything.
4. Let the feed rollers pull the board through on their own. Do not push or force it; your job is to guide, not drive.
5. Support long workpieces at the same height as the planer table, using stands or a helper so the board doesn’t dip or bind.

When the board emerges, check the surface and measure the thickness. Then reset the depth and make another light pass. Multiple shallow cuts beat one heavy pass every time — deep cuts strain the motor, leave chatter marks, and increase the chances of the board catching and kicking back.

What Not To Do With A Planer

The single most common mistake is planing stock that doesn’t belong in the machine. Painted, varnished, or dirty boards dull the blades fast and can hide nails that will destroy the cutterhead. The manufacturers are explicit: these planers are for clean, defect-free wood only.

Beyond bad stock, watch your hands and your patience. Keep your fingers off the infeed and outfeed tables and never reach into the throat or near the feed rolls while the machine is running. If a board jams or you need to clear shavings, shut the machine off and wait for every part to stop moving before you reach in.

Eye protection is not optional here — multiple manuals require it — and hearing protection is strongly recommended since planers run loud enough to damage hearing over a long session.

Setting The Right Depth For Your Project

Depth of cut is where beginners push their luck. The smarter approach is to work down in small increments — the manuals suggest a shallow first pass, then a series of light passes that each remove a little more.

For a board that needs 3 mm removed, take six passes of 0.5 mm rather than two heavy cuts. The result is a smoother surface that needs far less sanding, and the machine stays cooler and safer to operate.

When you finish the final pass, shut the planer down and wait for the cutterhead to stop completely before leaving the machine or clearing the dust. A planer that has stopped spinning is a tool; a planer that is still winding down is a hazard.

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