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.
The most healthful calcium sources are greens and beans. Green leafy vegetables are loaded with calcium. One cup of collard greens has 226 milligrams of calcium. Whatâs more, the calcium in most green leafy vegetables is more absorbable than the calcium in milk.