Due to their long length, planer blades cannot be hand sharpened like other types of blades. While the principals are the same, a different method has to be used to ensure that the blades are sharpened evenly. While time consuming, properly-sharpening planer blades can help extend the life of your planer as well as leaving a silky, glasslike finish on your lumber.
Place the planer blade along the edge of a table or bench with the flat face down so that the cutting edge overhangs the surface by no more than 1/16 inch.
Pass a sharpening stone from one end to the other of the blade, applying moderate pressure. Make 10 passes and then stop, taking continuous strokes. Do not stop or lift the stone from the blade mid-stroke.
Flip the blade over so that the flat face of the blade is facing up.
Run the sharpening stone down the length of the flat face. Again, don't stop or lift the stone in the middle of the stroke. Make ten passes.
Continue alternating between sides until the scratches left on the blade by the sharpening stone are uniform in size and coverage.
Repeat the process using a finer-grit sharpening stone, if desired.
Finer-grit stones leave a more honed and razor-like edge.