The present invention relates to a router bit. A router bit used for chamfering and finishing the butt end and side of a board is available in two types, i.e. a straight tooth type and a helical tooth type. Usually, a router bit of the helical tooth type is provided with an even number of cutting edges having helix angles in the same hand or direction with respect to the axis of rotation of the cutting edges. The conventional router bit of this type is liable to form burrs at the side of board when a board material containing fiber reinforced plastics is chamfered or finished. This is true particularly in chamfering or finishing FRP board or FRP-clad board in which fluffy fibers remain on the finished surface because the fibers are much stronger than the matrix resin. Such rough finish brings about delamination, corrosion, a decrease of strength, and breakage. This is quite different from problems involved in chamfering or finishing metal materials.
The object of the present invention is to eliminate the drawbacks of conventional technology as mentioned above, and is the result of observation of mutual actions of cutting edges and the material being cut.