Go to a hardware store and get the size bit you need that is made for metal. Most cast iron isn't really hard unless it is white cast iron. If the hole is over 3/16, pre-drill it with a small bit first. It might be a good idea to use some cutting oil to.
For more info, see the section on calcium absorption. High calcium foods include dark leafy greens, cheese, low-fat milk and yogurt, bok choy, fortified tofu, okra, broccoli, green beans, almonds, and fish canned with their bones. The daily value (DV) for calcium is 1000mg.
  Another one of the most beneficial 3 food sources of calcium is fish. Sardines, tuna and salmon are considered to be rich in calcium and provide many health benefits. 1-2 cups or 5-6 ounces of these fish, with or without bones, are enough to provide up to 300 mg of calcium.You can also buy canned salmon and enjoy a healthy meal full of nutrients.   The last of our 3 food sources of calcium is calcium fortified orange juice.-2 cups or 5-6 ounces of these fish, with or without bones, are enough to provide up to 300 mg of calcium. You can also buy canned salmon and enjoy a healthy meal full of nutrients.   The last of our 3 food sources of calcium is calcium fortified orange juice.