Why is my thickness planer leaving rough cuts?

Repeated lines or grooves often point to a nick or buildup on a cutter. Unplug the planer before opening it, then inspect the cutters and rollers for damage or stuck resin. The edges are sharp, so follow the manual and handle them carefully.

Before blaming the machine, check the board. A twisted or cupped piece can shift as it feeds, and taking too much off at once can make a small planer struggle. Try a straight, clean board with very shallow passes, and feed it with the grain where you can.

Try one known-straight test piece and see whether the same marks appear in the same pattern. If they do, inspect the cutter edges. If the cut is uneven from side to side even on that test, check the setup and feed rollers according to the manual. For a recently purchased machine, warranty service may be a better move than guessing at adjustments.