In the cutting of aluminium and its alloys, the surface finish is often inferior, and the variation of cutting forces is considerably large. In this paper, the relation between the variation of cutting forces and overcutting phenomenon is described. Then the cause of overcutting is experimentally discussed. Some results obtained in this paper are as follows:
(1) In the repeated orthogonal cutting of pure aluminium (1100) at low speed, the cutting forces vary in each cutting.
(2) The finished surface is deeply overcut without a built-up edge. The depth of overcutting becomes often comparable with the depth of cut.
(3) There exists the explicit relation between the cutting forces and the actual cutting area, i. e. the actual cutting area is consistent with the cutting forces.
(4) The cause of overcutting is the friction on the rake face, which restrains the chip flow.