Trace around your faucet or other accessories to make a template. Lay the accessory on a piece of paper and draw around the perimeter of the insertion point with a pencil. Cut the template out of the paper with a scissors.
Place your template on the cast iron sink where you'd like to cut out the hole. Trace around the outside of your template with a marking pen.
Place a pilot drill over the hole you drew. Drill a 1/4-inch hole through the sink in the center of your template shape. This will be your cutting guide.
Cut through the porcelain surface of your sink with a porcelain saw. Apply cutting oil in the area and cut around the shape you drew on the sink. Cut a smooth, beveled groove through the porcelain until you reach the metal base.
Cut through the metal base of the cast iron with a finish hole saw. Follow the hole you cut in Step 4.
Place your sink fixtures into the hole you cut to check the fit.