Oops! The Sink Won't Fit

The plumbers came out today to install the sink, dishwasher and washer drain. All was well until they attempted to drop in the sink - the cutout wasn't quite large enough. I tried using a belt sander - not so sure that was a good idea...dusty, dusty, dusty- to knock a little off but it didn't work. After the second attempt didn't work, the plumbers decided to come back another day to give me time to make sure the hole was large enough before they had to hoist the sink again - did I mention the sink is cast iron and heavy, heavy, heavy? This time I'm sure it fits. But just to avoid any problems, I also beveled the edge to make sure the brackets wouldn't get in the way. Now it fits perfectly. No, the bottom of the cabinet is not black. That is countertop dust - what a mess.