A thickness planer makes both faces of a board parallel and brings the entire piece to a consistent target thickness.
The machine solves the problem of lumber that is twisted, cupped, or uneven — not by flattening from scratch, but by machining one side parallel to the other so every inch of stock is the same thickness.
How a Thickness Planer Works
The board rests on a flat steel bed. Rotating cutterhead knives remove thin slices from the top surface while rubber or steel rollers feed the stock through at a steady rate. The operator sets the desired final thickness using the height adjustment mechanism; the cutterhead then shaves the board until it matches that setting.
The process only works when the board has one flat reference face to ride against the bed. That face is created first on a jointer. The planer does not flatten a board — it makes faces parallel. Sending a cupped or twisted board through without a flattened bottom produces a board that is still cupped or twisted, just thinner.
What a Thickness Planer Can (and Cannot) Do
The planer is a powerful time-saver but has clear limits. The table below separates what it handles well from what belongs on another machine.
| Task | Planer Does This? | Notes |
|---|---|---|
| Make both faces parallel | Yes | Core function — the bed provides the reference plane |
| Bring stock to final thickness | Yes | Set the depth stop; use light passes |
| Flatten a warped board | No | Requires a jointer first to create one flat face |
| Remove sawmill roughness | Yes | Rough-sawn boards benefit from an initial face jointing first |
| Work against the grain | Poorly | Causes tear-out and rough patches; always feed with the grain |
| Handle long boards | Yes, with support | Unsupported long boards cause snipe and tipping |
Key takeaway: a healthy workflow is jointer first, planer second. Joint one face flat, then feed that face down through the planer to make the opposite face parallel and bring the board to the needed thickness.
Thickness Planer vs. Surface Planer vs. Thicknesser: Same Machine, Different Name
In the United States and Canada this machine is almost always called a planer or thickness planer. In the United Kingdom, Australia, and New Zealand it is nearly always called a thicknesser. Historically, “planer” once referred to a long-bed machine for surfacing and jointing, so “thicknesser” avoided confusion. Today the terms are interchangeable, and “thickness planer” is the descriptive cross-regional name.
Search “thickness planer” in North America and “thicknesser” across the pond — you will see the same type of machine under either name.
Using a Thickness Planer the Right Way
The machine is straightforward, but a few habits separate a clean result from a frustrating one. Follow these guidelines on every board:
- Flatten one face first. Joint one face, then thickness the other.
- Set the machine to the target thickness while it is off. Adjust the height mechanism so the cutterhead stops slightly above the desired final dimension, then fine-tune after the first pass.
- Wait for the machine to reach full speed before feeding. Pushing stock through before the cutterhead is up to speed produces a poor finish and can be hazardous.
- Feed with the grain direction. Inspect grain lines and feed so knives cut into the grain rather than lifting it. This cuts tear-out dramatically.
- Remove material with several light passes. A heavy single pass strains the motor, risks kickback, and leaves a worse surface. Gentle passes yield better results and are safer.
- Support the outfeed end of long boards. Letting a board drop as it exits causes snipe — a deeper cut at the trailing end. An inexpensive roller stand solves this.
Most planer manuals recommend taking off no more than 1/16 inch per pass on softer woods and half that on hardwoods.
Common Mistakes Beginners Make
The most frequent error is expecting a thickness planer to act as a surfacing machine on a badly warped board — it cannot. The second is removing too much material at once. Feeding against the grain and failing to support long workpieces round out the top four mistakes; each is easy to avoid once you know it is a problem.
If you are shopping for your first planer and want a solid model that will not blow your budget, check our roundup of the best budget thickness planers on the market to see which matches your shop space and typical stock.
FAQs
Can a thickness planer flatten a warped board?
No. A planer makes both faces parallel but cannot fix cupping, twisting, or bowing. A jointer creates the flat reference face first; the planer mirrors that flatness onto the opposite side at the target thickness.
What is the difference between a jointer and a planer?
A jointer flattens one face of a board and squares one edge. A thickness planer then takes that flattened board and makes the opposite face parallel at a consistent thickness. Most woodworking shops own both for complete lumber preparation.
Do I need to flatten both faces on a jointer before using the planer?
Only one face needs to be flat. That flat face rides on the planer bed, and the machine cuts the top face parallel to it. If neither face is flat, the planer produces a board that is thinner but still twisted or cupped.
References & Sources
- Wikipedia. “Thickness planer.” Covers regional naming differences and core function.
- BC Campus Open Publishing. “Woodworking Machinery: Planer.” Details correct workflow, light-pass advice, and grain-direction feeding.
- Harvey Mudd College Machine Shop. “Planer.” Documents step-by-step standard operating procedure and safety precautions.