Finishing router bits produce a smooth and visually appealing surface finish on the material. They work best when following a roughing cutter.
Up cut refers to the direction of the flute. As the router bit grooves, slots and cuts the chips are forced upwards. Therefore, the best finish is on the underside of the cut part. Up cut spirals are not recommended for softer materials such as MDF as the finish on the top surface is often ragged. Up-cut spirals can run at higher speeds but require good quality suction on the table to prevent material tug.
One flute router bits are recommended for plastics, also softer materials can be run at higher feed rates.