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.
Probably the best source of dietary calcium is fat-free organic Greek yogurt. 1  It gives you 450 mm of calcium per serving, plus vitamin D and protein, and two servings fulfill your calcium needs for a full day. Other sources of calcium include: 2  Leafy green veggies like spinach and kale. 3  Legumes and beans. 4  Sardines.