(2) The thickness of copper layer is generally around 0. 1mm, and the copper layer is too thick, resulting in unnecessary waste; The copper layer is too thin, so it is easy to inject during electric carving.

(3) The hardness of copper layer should be controlled at 180 ~ 220 HV, which is too high and easy to be injected during electro-carving; The hardness is too low, and the dot is easy to deform, which is not conducive to the reduction and reproduction of hue.

(4) The chamfers at both ends of the drum are smooth without burrs and pits.