There are many core drill sizes and generally each size is manufactured to represent the size of a commonly used pipe, cable or duct so that once the hole is drilled, the object in question passes through with ease. For example, smaller holes up to 30mm in diameter can be drilled at up to around 3000 rpm whereas large holes around 400mm should be drilled at speeds as low as 300rpm. Drilling a 6mm hole in the wrong place can easily be rectified, but trying to fill in a 4 inch hole is not an easy job at all. If however the depth of the hole is longer than the drill bit you will need to withdraw the core bit when you hit a depth of about 125-130mm and chop out the core with a hammer and bolster, or in some cases you can lever it out. As we have already stated but will do so again, 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. Mark the Exact Drilling Spot

There are a few different types of core bit and the best one to use will very much depend on the size and depth of hole you’re drilling and the type of material you are drilling through. Once the core bit is attached to the arbour insert the pilot or guide drill into the arbour, pushing it in until it goes tight. In the majority of domestic cases the largest hole you will need to drill will probably be around 6 inches in diameter through a standard cavity wall which will be around 300mm in depth. For anything up to this size a dry cutting diamond core bit will be more than up to the job.

If in any doubt always refer to the manufacturers instructions for your particular power drill and also for the core bit you are using. In both cases, each set of instructions should state the correct drilling speed you should be using. Preparing for Drilling Holes Using a Core Drill In general, a corded drill is the best to go for as it will produce power at a more constant rate, but if funds are available, the more expensive and higher quality cordless drills (minimum 24v) from brands such as DeWalt, Makita, Milwaukee etc should provide more than enough grunt. With everything assembled it’s time to start drilling your hole. Position the tip of the guide drill on your drilling mark and start the drill slowly, increasing speed slightly until the pilot drill starts biting into the wall. If you are able to drill right the way through the wall in one go, the core drill will remove the core at exit. When drilling your hole, always hold the drill and core bit dead level. You do not want to drill in at an angle and cause the hole to slope up or down!

Corded power drill with safety clutch and variable speed ideal for use with a core drill How Fast Should you Drill When Using Core Bits? The drill bit itself features carbide “teeth” that surround the circumference of the drill bit. Once rotating, these teeth bite into the surface you’re working on and cut their way through creating the required hole. As well as wearing the drill bit out much faster, the hammer action also creates a lot of vibration whilst drilling often leading to the hole ending up larger than intended. Once you have cut 25-30mm into the surface you are working on, you can withdraw the core bit and remove the guide drill and carry on without it.

How Fast Should you Drill When Using Core Bits?

Most domestic use diamond core cutters will always have a removable guiding drill bit which acts as a pilot hole to guide the core drill. There are in fact two different types of diamond core bit – wet cut and dry cut. Essentially, wet cut diamond core bits use water to cool them while drilling and dry diamond core bits are just used dry.

As we have briefly touched on, a core drill is a drill bit which cuts large holes through masonry and concrete removing the centre part of the hole (core) as it drills and cuts its way through. When using dry cutting bits it is essential that they are kept as cool as possible. To do this they should be used in short bursts and the whole bit should be regularly withdrawn from the hole and exposed to the air to disperse any heat. Despite this, dry cutting diamond core bits don’t have to be used dry you can also use them wet. Trying to drill more dense objects such as solid concrete will in most cases cause the bit to heat up, wearing it out even faster. Diamond core drill and correct sized arbour What Type of Power Drill do you Need for Core Drilling?Generally, the guide or pilot bit is just used to get you started and keep the actual core bit in position whilst cutting into the surface of the wall. 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, making a total mess of it all. Again, as we have also touched on above, there are several different types of core bit available and depending on the object you are drilling through and the size of hole you need to create will ultimately depend on what type of core drill your should use. Carbide Core Drill Bits 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 at all times.

Before you start any drilling, the first job is to measure and mark the exact spot that you want to drill your hole so there isn’t any mistakes. When hiring or buying a core bit always make sure you have the correct size and type of arbor for not only the core bit your are using but also for the type of drill you have e.g. SDS, spline, straight shank etc. Although it is not recommended, many use hammer action with these drill bits to increase their cutting speed and ability. This will ultimately wear the core bit out much faster, but as they are generally cheap this is not often seen as a major concern. You can never take it for granted that work hasn’t been done by someone else in this area before and it has not been recorded.The best tool to use for this is a cable and pipe detector. You simply pass it over the surface of the wall and if any items such as these are found, lights and/or a buzzer indicate their presence. How to Drill a Hole using a Core Drill A core drill should always be used with a power drill, at minimum around 800 watts and at maximum somewhere around 1300 watts. Your chosen drill should also have a variable speed function (somewhere between 100 and 300 rpm) and it must also have a safety clutch! As this point it’s a good idea to ask someone to stand on the other side of the wall and let you know as soon as the guide drill breaks through and when it does, stop drilling.