A grinding head for a grinding machine is disclosed in which the axial bore of the head is provided with flutes of variable width. The dimension of the flutes from an upstream location to a downstream location of the head is variable to provide different effects in operation of the grinding machine. Flutes may be wider in areas of the head where greater shear is expected or may be narrower in width to decrease backpressure. Flutes may be primarily located adjacent to or along an increased diameter area of the head and may be constructed by casting.