Wrought iron is a form of metal work that involves pulling hot, soft pieces of iron to create forms and decorative shapes. Wrought iron is featured in practical elements such as door hinges, as well as decorative fixtures such as lanterns and fences. In each case, drilling through wrought iron to affix it or install additional elements can present challenges.
One of the biggest problems with drilling through wrought iron is the material's hardness. Many types of drill bits, including general multi-use bits, will break or quickly become dull from working with wrought iron. Specialty bits made from cobalt alloys or those specifically rated for working with steel and other hard metals will be able to cut through wrought iron, provided the bits are sharp. These bits are more expensive than general-purpose bits.
Wrought iron is prone to rust unless treated with a sealant or paint. Drilling through a treated piece of wrought iron will expose the vulnerable iron content inside, which will need further treatment to avoid rust. For example, if you drill a hole in a wrought iron fence to install a mailbox, you'll need to paint the inside of the hole before you install mounting screws, which won't keep moisture out well enough to avoid eventual oxidation. Refinishing rusted wrought iron is a time-intensive process that involves removing fixtures and working with harsh chemicals.
Because it is so hard, wrought iron presents a problem for workers attempting to drill at precise positions. Beginning to drill without assistance from clamps can make it difficult to produce a hole that is both straight and on-center. Removing wrought iron fixtures to clamp them to a drill press is the best option. If this isn't possible, you can drill a small hole to serve as a guide for a larger hole. This will prevent the large drill bit from shifting during drilling and producing a hole in an incorrect position.
Drilling wrought iron also raises several safety problems. Even with the right tools, drilling can create metal shards that the drill ejects at high speeds. These shards can cause eye damage, which makes eye protection a necessity. Rough edges are another danger, which workers can safeguard against by wearing gloves and filing down the drilled area to reduce the chance of lacerations.