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can see that the burge is being removed as the sander flattens the work progressively. This part coud have been chucked or pushed onto an offset mandrel I guess and faced, but I took the esay route.
One thing I'm noticing about parting off large diameters is that as the as you lengthen the cut-off bar to reach the center of the piece, the thin blade tends to flex to the left enlarging the part with a bulge