As far as metals go, cast iron is not very hard. So drilling into cast iron is not as challenging as you might expect it to be. The positive thing about it is that you do not have to spend a lot of time choosing the appropriate drill bit. Basically any drill bit intended for drilling through metal will also drill through cast iron. The crucial thing is that you drill patiently and slowly and to avoid overheating of the drill bit.
What do you need?
Well, first you need to know that cast iron has a high content of carbon which acts as a lubricant and therefore it is often acceptable to drill iron without the lubricant. On the other hand, oil or a water-based coolant can cool the drill bit and the metal which helps in preventing cracking or the drill bit to wear out. To sum it up, if you are drilling one or two hole, you can get by without the lubricant, but if you are drilling more please apply a few drops of cutting oil or spray lubricant before each drilling.
As far as drill bits, the best drill bit for cast iron is a cobalt brass-colored bit with a 135-degree point angle. The angle is sharper than that on a conventional bit, making drilling quicker and more precise. The second best thing is an all-purpose bit, a gold-colored titanium nitride drill bit which is intended for metal and because of that suitable for cast iron. The only drill bits you should not use to drill cast iron are those intended for wood or masonry only.
When it comes to speed, if you are drilling a hole which is ½ inches, your speed should approximately be 1,146rpm – this is the middle speed on most drills. If you are drilling hard cast iron reduce the speed by half.
The drilling into cast iron is very simple. Grab a drill, put the correct drill bit, mark the place you will be drilling and start. Drill slowly with or without a lubricant depending on how many holes you are making.
How to drill a cast iron pipe
When drilling a cast iron pipe you need to know that you can’t drill with just one drill bit. An array of drill bits needs to be at your disposal if you want to get the desired size of the hole.
The trick is to gradually increase the dimension of the hole. You will need gloves and goggles which you will put on, electric drill and drill bits. Hold the drill firmly and start drilling. Increase the size of the hole by changing the drill bits from the smallest to the largest. This will slowly enlarge the size of your hole in the cast iron pipe. Repeat this process until you have the hole which you desired.
How to drill a cast iron sink
The things you will need to get this job done are: a permanent marker, a masking tape, a variable speed drill, ¼” porcelain drill bit, a small paintbrush, carbide diamond bit, round metal file and lubricating oil or a container of water.
First you locate the place of your future hole in the cast iron sink and place some masking tape on that spot. Use a permanent marker to place a dot on the masking tape. Take the porcelain drill bit and put a drop of oil on the tip to keep the friction from burning it. If you don’t have oil, have a container of water nearby to cool the bit as you go. This drilling through porcelain serves to get to the cast iron part. You use if you need it.
When you get to the cast iron, remove the debris with a paintbrush and take a carbide diamond drill bit and continue drilling. Remember that you must stop every few seconds to cool your bit with lubricating oil or water from the container. When finished with making your holes, use a round metal file to smooth the edges of the holes you have made.