A core drill is a drill bit which cuts large holes from masonry and concrete removing the centre part of the hole (core) as it drills.
There are many core drill sizes and each one is manufactured to represent the size of a commonly used pipe, cable or duct.
Before you start your drilling you should always make sure there are no cables or pipes hidden in the wall. You can never take for granted that work hasn't been done by someone else in this area before. A cable and pipe detector can be used to scan the wall area for any hidden items. Clicking on any of the tool images below will take you through to the tool store where you will be able to buy a pipe and cable detector as well as the core drills and accessories themselves.
You will need a high powered SDS drill. Most SDS drills come with built in clutches which are highly recommended for this process of hole drilling. Core cutting SDS kits are easily available and are not really that expensive for what you get (£100 - £120). If you plan to be using this process of cutting a lot, it will end up being cheaper than hiring. All hire companies will have a suitable drill for you to hire, if purchasing a drill is deemed too expensive. Remember you will also be charged for the amount of wear on diamond tipped bits.
A core cutter, once within the hole it is cutting can snag or grab at any moment without any warning. You will be surprised how easily your wrist or arm can be harmed in this way.
If you are fitting a new bathroom you may need to drill at least 3 holes; 117mm for your toilet waste, 55mm for your bath and shower waste and possibly 40mm for your basin waste. These are hole sizes, not pipe sizes, and they allow for movement of the pipe.
A core cutter will always have a removable guiding drill bit which acts as a pilot hole to guide the drill.
The drill bit itself has no shaft like a normal drill bit. The connection to the drill is made via an arbor. The arbor screws into the core bit and then slots into the SDS chuck of the drill. When hiring or buying a core bit always make sure you have the correct sized arbor.
Never use hammer action when core drilling. The drilling action needs to be as smooth as possible and the jerky action of the hammer can snap expensive diamond teeth very easily.
If you are able to drill right the way through the wall in one go, the core drill will remove the core at exit. If however the depth of the hole is longer than the drill bit you will need to withdraw the drill bit and chop out the core with a hammer and bolster.
When you have repeated this process a few times you will be near the other side of the hole you are cutting, now is the time to decrease your pressure! If you keep forcing the core cutter through, when you actually break through you will force a large amount masonry away from the outside of the hole. For the neatest cut it is advisable to allow the drill guiding bit to penetrate the wall, then finish the hole from the other side. This guarantees a neat entry and exit hole.
As always at DIY Doctor we advise the use of purpose built tools for DIY use. Safety must always come first. Wear the appropriate safety equipment, gloves, dust masks and eye protection.