Most shops have two types of router bits – dull and sharp ones. It’s easy to tell the difference because the sharp bits ease through the wood while the dull bits labor. Sometimes a good cleaning is all the bit needs. Any good blade solvent will rid bits of pitch and resin.
Once the bit is clean I like to use a fine monocrystalline diamond stone with a couple drops of water to hone the flats of the carbide. Count the number of strokes taken on each flat, then repeat this process with the other carbide surface on the bit. Diamond stones will sharpen carbide or high-speed steel. I only use carbide cutters because they stay sharp longer. Don’t attempt to sharpen spiral router bits – send those to the sharpening shop.– Scott Phillips