It is proved experimentally in this paper that the plowinggroove on the machined surface is cut by the bue built-up edge overhang. The cross section profile of the plowing-groove may keep unchanged in a cutting path of 150-310mm or longer. Experimental result shows that the stability of the bue is over one hundred times higher than that of the scale. The experimental observation on the formation of a scale has been done by the present author, who noticed that the discontinuous chip, the bue and the rounded ...