The cutting was going well until we hit a piece of sand or a stone in the aluminum which destroys the edge of the HSS cutter. You can see the defect in the middle of the casting - the small black dot in the middle. You can also see the smooth finish on the left and the rough finish on the right which was after the cutter edge was ruined. We try switching to a tougher carbide bit, but it does not have enought relief clearance and the bottom edge drags on the metal, cutting poorly.
We end up digging the stone out with a pointed chisel which allows us to finish the work with the resharpened HSS cutter.
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