| i use rhe fiberglass reinforced cutoff discs...
i draw my circle, the draw as large a square as possible inside the circle.
cut out the square...remove any extra possible with the cutoff disc, then i switch to a hard sanding head to remove the remainder.make sure to sand the edge too, to remove any burrs, and you may want to try to round the edge to prevent cuts. If you plan on using a rubber gasket to line your hole, this is an absolute must.
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