A heater tube is provided for use in a method of producing a diamond or cubic boron nitride (CBN) tipped cutting tool by sintering a mass of crystalline particles to a metal carbide. The heater tube has a cylindrical shape and is comprised of a plurality of windings of an expanded graphite foil which are compressed together. In the method, a heater tube assembly is formed which comprises the metal carbide substrate positioned within the heater tube and a mass of diamond or CBN particles positioned within the heater tube adjacent the substrate. The method includes simultaneously applying sufficient levels of pressure to the heater tube assembly and sufficient levels of electrical current to the heater tube assembly for a sufficient amount of time to cause sintering of the crystalline particles and bonding to the substrate to form a diamond or CBN tipped cutting tool.