What a planer does and does not do
A thickness planer makes the two faces of a board parallel and brings the board to a chosen thickness. It does this by pressing the board against a table and cutting the top face with a rotating cutterhead. The key point is that it follows the shape of the board’s bottom face. A cupped or twisted board can pass through, flatten under the feed rollers, and spring back to the same shape afterward. Getting one flat reference face first, usually with a jointer, a hand plane or a sled, is what makes thickness planing accurate.
Planer work also produces a lot of chips, so wear eye and hearing protection, use a dust mask, and connect the machine to a dust collector or shop vacuum if the planer has a port. Always unplug the machine before clearing a jam, changing knives or reaching near the cutterhead, and keep to the instructions in the manual, since adjustments differ by model.
Check the board first
Inspect each board before it goes in. Remove loose knots, check for embedded grit or nails, and look for any metal such as staples. Hidden hardware can damage the knives and throw fragments. Dirt and dried glue also dull knives quickly. A board that is much too short for your planer’s stated minimum length can be unsafe to feed, so check the manual for that limit.
Look at the board’s curvature if it is bowed. Place the concave face down on the table with the ends lifted so it rests on its high points, and the first passes then remove the high spots. If you are unsure how to handle a distorted piece, the issues around board warping are worth reading about before you start.
Choose the feed direction by grain
Look at the edge of the board and notice how the grain lines run. You generally want the knives to cut “downhill” with the grain, so the fibers are lifted and sliced cleanly instead of being pried up. Feeding the opposite way can leave a rough, torn surface, especially on figured or wavy wood. If one direction gives a ragged result, turn the board end for end and try again with a lighter cut. Reading wood grain is a skill that improves with practice and test boards.
Take light passes
Each pass should remove only a small amount. Many benchtop planers handle a maximum cut that is a fraction of an inch, but using the maximum is rarely the best choice. Light cuts leave a smoother surface, put less strain on the motor and reduce tear-out and snipe. A common guide is about a sixteenth of an inch or less per pass, and less for wide boards or hard woods.
Here is a hypothetical example. Suppose you want to take a board from 1 inch to 3/4 inch. That is 1/4 inch to remove, or 0.25 inch. If each pass removes about 1/32 inch (0.03125 inch), you need 8 passes. Many people like to alternate faces in the later passes, which helps balance internal stress in the wood and keeps the board flatter. Measure with calipers or a thickness gauge rather than relying on the depth scale, because those scales are approximate.
Leave a little extra on the thickness if you plan to sand afterward, since sanding also removes material.
Understand and reduce snipe
Snipe is a slightly deeper cut at the start or end of a board, usually because the board tips as it enters or leaves the rollers. It is common on benchtop machines, and it is usually small, but it can matter on a fitted part. These habits often reduce it:
- Support the board with level infeed and outfeed tables or roller stands, set to the planer’s table height.
- Feed boards end to end in a continuous line so the next piece pushes the last one through.
- Use a longer board and cut the ends off afterward, which is one reason to buy stock a bit long.
- Keep the knives sharp, since dull edges tend to make the machine work harder at the end.
- Apply very gentle pressure upward at the board’s tail as it leaves, only if the manual allows it and your hands stay well clear of moving parts.
If a machine consistently produces snipe, check that the tables are aligned and the head lock, if present, is engaged. Some units are better than others at holding the board flat; this is part of why a benchtop planer is often judged by how it handles the ends.
Keep the machine running well
Resin and chips build up on rollers and tables, so wipe them clean and apply a light coat of the lubricant the manufacturer recommends. Sharp knives, or fresh disposable inserts, give much cleaner results than a dull set. Straight-knife and spiral-style heads behave a little differently, so note which one your planer has.
A simple workflow
- Joint or flatten one face, and mark it.
- Plane the opposite face lightly until it is clean.
- Flip and take small, equal passes down toward the target thickness, checking it regularly.
- Finish with a very light pass for the smoothest surface.
Planing wood that has had time to settle to your shop’s humidity helps too, because the board is less likely to move after it is cut. When a project calls for several parts of the same thickness, run them all through the planer at the same setting, which keeps them matched.