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.
Other foods that are high in calcium include: 1  Spinach. 2  Kale. 3  Okra. Collards. 4  Soybeans. White beans.  Some fish, like sardines, salmon, perch, and rainbow 1  trout. Foods that are calcium-fortified, such as some orange juice, oatmeal, and breakfast  cereal.
Other food sources are more absorbable like bone broth, dark leafy greens, fish with bones, and even carrots. Some foods like spinach, which is often suggested as a good dietary source of calcium, are only 5% absorbable, which make them great for other nutrients but not a good source of calcium. Bottom line: We need about 300-400 milligrams of absorbed calcium per day from food sources and not much more than that.