A rotatable cutting tool for machining of a honeycomb core includes a front end; a rear end; a peripheral surface extending between the front and rear ends; a set of helical flutes formed in the peripheral surface at a first helix angle 45°≤α≤65°, having a first depth; and a set of helical ridges. At least one helical groove formed in the peripheral surface at a second helix angle 90°<β≤100°, has a second depth, which is smaller than the first depth. The at least one helical groove intersects the helical ridges so that a plurality of cutting teeth are formed on each helical ridge. Each cutting tooth includes a second ridge formed in a transition between two lands, a cutting edge and a clearance edge join in a tooth tip constituting the radially outermost point of the cutting tooth.

A cutting tool includes a shaft portion and a plurality of edge region groups. The ridgeline between the first rake face portion and the first flank face portion constitutes a first cutting edge portion. The ridgeline between the second rake face portion and the second flank face portion constitutes a second cutting edge portion. As seen from the direction perpendicular to a plane tangent to the outer peripheral surface, in a state where the central axis overlaps a first end on the front end side of the first cutting edge portion, the inclination angle of the first cutting edge portion relative to the central axis is larger than the inclination angle of a straight line relative to the central axis, the straight line connecting the first end to a second end on the front end side of the second cutting edge portion.

A rotatable cutting tool for machining of a honeycomb core includes a front end; a rear end; a peripheral surface extending between the front and rear ends; a set of helical flutes formed in the peripheral surface at a first helix angle 4565, having a first depth; and a set of helical ridges. At least one helical groove formed in the peripheral surface at a second helix angle 90<100, has a second depth, which is smaller than the first depth. The at least one helical groove intersects the helical ridges so that a plurality of cutting teeth are formed on each helical ridge. Each cutting tooth includes a second ridge formed in a transition between two lands, a cutting edge and a clearance edge join in a tooth tip constituting the radially outermost point of the cutting tooth.

A cutting tool includes a shaft portion and a plurality of edge region groups. The ridgeline between the first rake face portion and the first flank face portion constitutes a first cutting edge portion. The ridgeline between the second rake face portion and the second flank face portion constitutes a second cutting edge portion. As seen from the direction perpendicular to a plane tangent to the outer peripheral surface, in a state where the central axis overlaps a first end on the front end side of the first cutting edge portion, the inclination angle of the first cutting edge portion relative to the central axis is larger than the inclination angle of a straight line relative to the central axis, the straight line connecting the first end to a second end on the front end side of the second cutting edge portion.