How to use a thickness planer — why you must flatten one face first, beating snipe, avoiding tearout, and why moisture content matters.
A thickness planer is a wonderful machine. Feed a rough board in one end and a smooth, accurately dimensioned board comes out the other. It turns cheap rough-sawn timber into stock you can actually build with, and it pays for itself quickly if you buy lumber rough.
But there is one thing about it that catches almost everyone, and it causes more disappointment than any other woodworking misunderstanding:
A thickness planer does not flatten a board. It makes the top face parallel to the bottom face.
Think about what happens inside. Rollers press the board down onto the bed as it passes under the cutterhead. If the board is bowed or twisted, those rollers flatten it temporarily while the knives cut. Once it comes out the other side and the pressure is released, the board springs back to exactly the shape it was — just thinner, with two parallel curved faces.
So the first job is always flattening one face some other way. Get that right and everything else in this guide is straightforward. 💡
Alt text: “Board feeding into a benchtop thickness planer with roller stands supporting it at both ends”
- What a planer does — and does not — do
- Flattening one face first
- The correct milling order
- Snipe and how to beat it
- Depth of cut
- Grain direction and tearout
- Moisture content
- Step by step
- Limits: length, thickness and what not to feed it
- Dust and chips
- Common mistakes (and how to fix them)
- Pro tips worth knowing
- What I recommend
- Frequently asked questions
- Your final checklist
What a Planer Does — And Does Not — Do
| Task | Thickness planer | Right tool |
|---|---|---|
| Make a board a consistent thickness | ✅ Yes — its job | Planer |
| Make two faces parallel | ✅ Yes | Planer |
| Smooth a rough-sawn surface | ✅ Yes | Planer |
| Flatten a cupped or bowed board | ❌ No | Jointer, router sled or hand plane |
| Remove twist | ❌ No | Jointer or hand plane |
| Straighten an edge | ❌ No | Jointer or table saw |
| Make a board narrower | ❌ No | Table saw or band saw |
Put a banana-shaped board through a thickness planer and you get a thinner banana with beautifully parallel curved faces. The machine did exactly what it is designed to do. It just is not the machine that fixes bananas.
Flattening One Face First
You need one genuinely flat reference face before the planer can do anything useful. There are several ways to get it.
A jointer
The traditional answer, and the fastest. A jointer’s beds are in the same plane, so it cuts a flat face rather than following the board. Take light passes with the concave side down and stop as soon as the whole face is clean.
A router sled
The best option if you do not own a jointer. Build a flat frame, sit the board inside it shimmed so it cannot rock, and run a router with a wide flattening bit across it on rails. Slow but genuinely accurate, and it handles boards far wider than most home jointers. See our guide on using a router.
Hand planes
Entirely viable, and quieter. Work across the grain with a scrub or jack plane to remove the high spots, check with winding sticks and a straight edge, then refine. Our guide on using a hand planer covers technique, and you will want sharp irons — see sharpening plane blades.
Planer sled
A workaround that lets a thickness planer flatten a face. Sit the board on a flat sled with shims underneath so it cannot rock or flex, hot-glue or wedge it in place, and run the whole assembly through. The sled becomes the flat reference, so the knives cut a flat top face. Once one face is flat, remove the sled and plane normally.
The Correct Milling Order
Rough timber becomes square, accurate stock in a fixed sequence. Doing it out of order is why boards end up out of square.
- Rough-cut oversize. Cut boards slightly longer and wider than final size — a bowed long board is much harder to flatten than two shorter ones.
- Let it acclimatise. Sticker the boards in the shop for a while so they reach the moisture level of the room. See below.
- Flatten one face. Jointer, router sled, hand plane or planer sled.
- Thickness plane the second face parallel to the first, flat face down on the planer bed.
- Straighten one edge square to the flat face, on a jointer or with a table saw sled.
- Rip the second edge parallel on the table saw.
- Crosscut to final length — see using a miter saw.
Take material off both faces where you can. Wood has internal stresses, and removing a lot from one side only can make a board cup as those stresses rebalance. Alternating faces as you approach final thickness gives a more stable result.
Snipe and How to Beat It
Snipe is the shallow dip planed into the first and last few inches of a board. It is the most common complaint about thickness planers and it is largely fixable.
Why it happens: a planer has a roller before the cutterhead and another after it. In the middle of a cut, both rollers grip the board and hold it firmly against the bed. But at the very start, only the infeed roller is engaged — and at the very end, only the outfeed roller. With just one roller holding it, the board can tip slightly toward the cutterhead, and the knives take a deeper cut for those few inches.
| Fix | How well it works | Notes |
|---|---|---|
| Support the board level, both ends | ✅ Biggest single fix | Roller stands at bed height |
| Lift the board slightly as it enters and exits | ✅ Very effective | Gentle upward pressure on the free end |
| Feed boards end to end | ✅ Very effective | Each board backs up the next |
| Leave sacrificial length | ✅ Reliable | Cut the sniped ends off afterwards |
| Lock the cutterhead | ✅ Good | If your machine has a head lock |
| Very light final passes | Helps | Less depth means shallower snipe |
| Adjust the tables level | Good | Check the manual for your machine |
The most practical combination for a home workshop: leave a few extra inches on each board, support both ends properly, and feed boards nose-to-tail so each one supports the next. Then trim the sniped ends off when you cut to length. That removes the problem entirely rather than fighting it.
Depth of Cut
Light passes. This is the general rule, and it matters more than people expect.
- Take small increments — a fraction of a millimetre at a time on wide or hard boards.
- Wider boards need lighter cuts. A cut that a narrow board takes easily will bog the motor on a wide one, because there is far more material being removed per pass.
- Hardwood needs lighter cuts than softwood.
- Figured wood needs the lightest cuts of all, to control tearout.
- Listen to the motor. If it bogs down, you are taking too much. Back off.
- Finish with a very light pass on both faces for the best surface.
Heavy cuts cause everything bad: motor strain, more tearout, worse snipe, faster knife wear, and a rougher surface. There is no prize for finishing in fewer passes.
Grain Direction and Tearout
Tearout is where the knives lift and tear chunks out of the surface instead of slicing it cleanly. It happens when the cut runs against the grain.
Reading grain direction
Look at the edge of the board. The grain lines run at a slight angle to the face — like the tiles on a roof. You want to plane “downhill”, in the direction the grain slopes away from the surface, so the knives cut the fibres cleanly rather than lifting them.
The practical test: run your hand along the face. One direction feels smooth, the other slightly rough — plane in the smooth direction. If a pass tears, flip the board end for end and try again.
When the grain changes direction
Figured, curly and interlocked timbers have grain that reverses within the same board. There is no “right” direction, because both directions are wrong somewhere.
| Approach | Effect |
|---|---|
| Very light final passes | ✅ The main defence — less to tear |
| Feed the board at a slight angle | ✅ Shears the fibres rather than lifting |
| Slow the feed rate | ✅ More cuts per inch |
| Dampen the surface lightly | Softens fibres — use sparingly |
| Sharp knives | ✅ Dull knives tear rather than cut |
| Helical / spiral cutterhead | ✅ Best solution — an upgrade, not a technique |
| Finish with a scraper or sander | ✅ Accept some tearout and remove it |
For badly figured timber, accept that the planer will not give you a finished surface. Take it close, then remove the last fraction with a card scraper or a random orbital sander. Fighting the planer on curly maple is a losing battle.
Moisture Content
This is the part people skip, and it undoes all the careful work.
Wood shrinks and swells as its moisture content changes to match the air around it. If you plane a board that is wetter than your workshop, it will keep drying afterwards — and as it dries, it shrinks, cups and twists. Your perfectly flat, perfectly parallel board will not be flat or parallel in two weeks.
What to aim for: the target moisture content depends on your climate and whether the piece will live indoors or out. Indoor furniture in a heated home generally needs drier wood than outdoor work. The reliable approach is not a fixed number but a stable one — measure over several days and mill when the reading stops moving.
How to acclimatise properly:
- Sticker the stack. Thin spacers between boards so air reaches every surface.
- Keep it off the floor, especially a concrete floor, which is a moisture source.
- Store it where the piece will live, not in an unheated garage if the furniture is for a heated house.
- Give it time. Thicker stock takes considerably longer than thin.
- Measure rather than guess. A moisture meter turns this from folklore into a number.
Step By Step
Step 1 — Acclimatise and check moisture
Stickered, in the right space, measured until stable.
Step 2 — Inspect the board
Check for nails, screws, staples and embedded grit. Reclaimed timber is the usual culprit. A single nail destroys a set of knives.
Step 3 — Flatten one face
Jointer, router sled, hand plane or planer sled.
Step 4 — Set up support
Roller stands at exactly bed height, both infeed and outfeed.
Step 5 — Connect dust extraction
Not optional — see below.
Step 6 — Set the first cut
Measure the thickest point of the board and set the machine just under it, so the first pass only touches the high spots.
Step 7 — Feed flat face down, correct grain direction
The flat face rides on the bed; the knives cut the top.
Step 8 — Support the board in and out
Slight upward pressure on the free end as it enters and leaves, to reduce snipe.
Step 9 — Take light passes, alternating faces
Flip the board between passes as you approach final thickness.
Step 10 — Finish with very light passes
On both faces, for the cleanest surface.
Step 11 — Trim the sniped ends
When you cut to final length.
Limits: Length, Thickness and What Not to Feed It
Other limits worth knowing:
- Minimum thickness. Below the machine’s stated minimum the board can chatter or break up. Use a sled and a backing board for thin stock.
- Maximum width. Obvious, but boards close to the limit need much lighter cuts.
- No metal, ever. Nails, screws, staples, old hardware. Check reclaimed timber with a metal detector.
- No embedded grit. Timber that has been on the ground or sanded picks up abrasive particles that dull knives fast. Brush it off.
- No plywood or MDF. The glue lines are extremely abrasive and will ruin knives quickly.
- Nothing wider than it is long, and nothing that can twist sideways in the machine.
Dust and Chips
A thickness planer produces more waste volume than any other workshop machine, by a wide margin. Planing a few boards fills a large bag with chips remarkably fast.
- Connect extraction before you start. Without it, chips pile up inside the machine, get pressed into the board surface by the rollers, and leave dents.
- A shop vacuum struggles. The volume is high even though the chips are large — a dust extractor moving more air is far better suited than a high-suction, low-volume vacuum.
- Empty it often. A full bag backs up into the machine.
- The fine fraction still matters. Big chips are not the health risk — the invisible dust is. See our guide on wood dust safety.
- Chips are useful. They compost, mulch and make good animal bedding, so they need not be waste.
Common Mistakes (And How to Fix Them)
Mistake 1 — Expecting the planer to flatten a board
The fix: flatten one face first. The planer only makes the second face parallel to the first.
Mistake 2 — Milling wood that has not acclimatised
The fix: sticker it in the right space and measure until the reading is stable.
Mistake 3 — Heavy cuts
The fix: light passes. Heavy cuts cause tearout, snipe, motor strain and knife wear.
Mistake 4 — No infeed and outfeed support
The fix: roller stands at exactly bed height. This is the biggest single snipe fix.
Mistake 5 — Planing against the grain
The fix: read the grain on the edge, or feel the surface. Flip the board if it tears.
Mistake 6 — Feeding boards that are too short
The fix: check the minimum length. Short boards can be thrown.
Mistake 7 — Hidden nails in reclaimed timber
The fix: metal detector on anything reclaimed. One nail ruins a set of knives.
Mistake 8 — Taking everything off one face
The fix: alternate faces. Uneven removal lets internal stress cup the board.
Mistake 9 — Running without extraction
The fix: connect it. Chips get rolled into the surface and dent it.
Mistake 10 — Fighting figured wood
The fix: get close with light passes, then scrape or sand the last fraction.
Pro Tips Worth Knowing
- Wax the bed. Paste wax dramatically reduces feed resistance and helps prevent snipe. Do not use silicone-based products — they contaminate wood for finishing.
- Mark the board with a pencil scribble before each pass. When the scribble is gone, that surface is fully planed.
- Cut long boards in half first where the project allows. Shorter boards are far easier to flatten and mill accurately.
- Mill everything for a project at once. Boards milled weeks apart in different humidity will not match.
- Leave stock slightly thick, then final-pass everything together at the very end so all parts are identical.
- Keep a spare set of knives. A nail strike mid-project is far less painful with replacements on the shelf.
- Rotate or reposition knives slightly if your machine allows, so a single nick does not leave a permanent line on every board.
- Never reach into the machine while it is running, and unplug it before clearing a jam or changing knives.
- Ear protection. Planers are among the loudest machines in a workshop.
- Consider a helical cutterhead upgrade if you work figured timber often — it is expensive, but it transforms tearout, noise and knife maintenance.
What I Recommend
The most common way careful milling gets wasted is not a technique error — it is planing wood that was still drying. The board comes out perfect and moves within a fortnight. A moisture reading turns that from guesswork into a number.
General Tools MMD4E Digital Moisture Meter
🏆 Best Value MeterA pin-type digital moisture meter with a backlit display and audible alert. Press the pins into a board and you get a reading in seconds — which tells you whether timber has finished acclimatising, or whether milling it now means watching it move next month.
- ✅ Tells you when timber has stopped moving — take readings over several days and mill when stable
- ✅ Prevents the classic disappointment of a perfectly milled board cupping a fortnight later
- ✅ Pin type reads inside the wood, not just the surface
- ✅ Backlit display and audible alert for reading in a dim workshop
- ✅ Useful around the house too — damp walls, leaks, firewood readiness
Prices and availability change often — check Amazon for the current price. Pin meters leave small holes, so read on a face that will be cut away or hidden.
Frequently Asked Questions
Why is my board still bowed after planing it?
Because a thickness planer does not flatten wood — it makes the top face parallel to the bottom face. The feed rollers press a bowed board flat against the bed while the knives cut, then it springs back to its original shape once the pressure is released. You have to flatten one face first using a jointer, a router sled, hand planes or a planer sled, and only then thickness the second face.
What causes snipe and how do I stop it?
Snipe is the shallow dip at each end of a board, caused by only one feed roller gripping it as it enters and leaves — the board tips slightly and the knives cut deeper. Support the board level at both ends with roller stands at exactly bed height, apply gentle upward pressure on the free end as it enters and exits, and feed boards nose-to-tail so each supports the next. Leaving a few extra inches to trim off afterwards removes the problem entirely.
How deep a cut should I take?
Light passes — a fraction of a millimetre at a time, especially on wide boards, hardwoods and figured timber. Wider boards need lighter cuts because far more material is being removed per pass. Listen to the motor; if it bogs down, you are taking too much. Heavy cuts cause tearout, worse snipe, faster knife wear and motor strain, and there is no advantage to finishing in fewer passes.
Can I plane reclaimed or old timber?
Only after checking it thoroughly with a metal detector. A single hidden nail, screw or staple will destroy a set of planer knives instantly, and embedded grit from timber that has sat on the ground dulls them fast. Brush the surface clean, scan both faces and the edges, and if there is any doubt, take the surface down with a hand plane or belt sander first — a cheap blade is easier to replace than planer knives.
How dry does wood need to be before milling?
The target depends on your climate and whether the piece lives indoors or outside, so rather than chasing a fixed number, aim for a stable reading. Sticker the timber where the finished piece will live, with spacers so air reaches every face, and measure over several days. When the reading stops changing, it has acclimatised. Milling before that means the board keeps drying and will cup or twist afterwards.
Why is the surface torn and rough instead of smooth?
Usually planing against the grain, dull knives, or too heavy a cut. Read the grain direction on the edge of the board and feed so the knives cut downhill, or flip the board end for end if a pass tears. On figured or interlocked timber the grain reverses within the board, so take very light passes, feed at a slight angle to shear the fibres, and accept that you may need to finish with a card scraper or sander.
Your Final Checklist
- Acclimatise the timber and measure until the reading is stable
- Check for nails, screws and grit — especially reclaimed stock
- Flatten one face first — the planer will not do it
- Rough-cut oversize before milling
- Roller stands at exactly bed height, both ends
- Dust extraction connected before the first pass
- Set the first cut just under the board’s thickest point
- Flat face down, grain running the right way
- Light passes — lighter still on wide, hard or figured stock
- Alternate faces as you approach final thickness
- Support in and out to reduce snipe
- Respect the minimum length — short boards can be thrown
- Ear protection on
- Very light final passes on both faces
- Trim the sniped ends when cutting to length
Next in this series: how to use a hand planer and how to use a band saw.
