What is core drilling
Concrete core drilling (also known as concrete coring) is the mechanical process of drilling a precise circular hole in concrete structures such as walls and floors. It involves the use of a core bit attached to the end of a core drill to perform the cutting. Diamond tipped segments placed at the end of a core bit perform the cutting as the core bit spins or rotates whilst making contact with the surface to be cut.
Core drilling is suitable for drilling holes through concrete, masonry, asphalt, stone, or other solid surfaces. Core holes are able to be drilled horizontally, vertically inverted, or angled.
The core bit removes approximately 4mm of the material which is cut by the segments of the core bit during the drilling process. The inner section that becomes free is known as a core, hence the reason drilling of this nature is known as "core drilling".
Core drilling applications
Common core drilling applications include:
- Safety rails and fencing
- Anchoring bolts, dowel bars and lifting points
- Securing benches and tables in restaurants and locker rooms
- Signage posts, bollards, etc
- Electrical wiring, conduits, ducting, and pipes
- Plumbing, sprinklers systems, and pipes
- And retrieving core samples for analysis of material
- HVAC installations
Benefits of Diamond Drilling
- Unlike percussion tools (like hammer drills), minimal noise or vibration is omitted or transferred to the surrounding area or structure when using a core drill.
- Precise and accurate hole penetration, resulting in minimal if any rectification works post penetration
- Able to cut through steel reinforcement, where required
Core drilling, or the use of a diamond core drill to drill a hole produces a segment of the material being drilled to become separated, this piece left inside the drill bit is referred to as the core.
The water suppression system fitted to core drills, both hand held as well as dedicated drills, is used to not only supress dust but also to cool the core bit (also known as core barrel). Where insufficient water is feed to the core bit, this absence of the water or lack of water resulting in the water getting too hot will see the cutting edges of the diamond glaze over which may also lead to excessive wear and damage to the core bit if ignored for too long. This will become evident with the core bit no longer penetrating any deeper. Other tell tail signs include the water coming our clear (no slurry, lack of colour) when pressure is applied to the drill. A glazed over core bit can be fixed with the diamonds being opened up again by lightly striking the top of the segments to create small dents in the segment thereby allowing the old diamond to fall away and new diamonds to be exposed as the drilling recommences. A file can also be used to expose new diamond. This is also referred to as sharpening a core bit. In general, the harder the aggregate of the material being drilled, the more frequent this may need to be performed. Looking after the core bit will result in a consistent and productive drilling speed being maintained.
The use of a drill rig, or mounting block that supports the attachment of a drill with the drill itself referred to as a dedicated drill. This combination is used where hand drills are no longer able to be utilised, which occurs where the hole size gets too large for a hand drill or the depth of hole is too deep for a hand drill or the surface being drilled is harder than normal or contains excessive steel. In all these situations a dedicated drill mounted on a drill rig is the best way to proceed. The drill rig is first anchored to the surface with the drill then mounted to the drill rig. Levelling bolts as well as the ability to angle the drill stand mast allow for the drill to be set up at the precise angle required. Drill rigs are also available with a vacuum anchor base yet this type of rig will only work on smooth flat surface.
Drilling a hole on a precise angle is best achieved by utilising a dedicated drill mounted on a drill stand. In order to drill a hole on a specific angle, the drill stand post is adjusted to the appropriate angle to suite.
Care needs to be taken when starting the hole as the core bit doesn’t strike the surface perpendicular, rather the segments of the core bit engage one at a time. Do not apply to much pressure at this stage of the drilling process as this is likely to lead to misalignment, jamming up, or segment loss
There really isn’t a limit or fixed to the depth a hole can be drilled. Technology exists to drill as deep as needed. Using a continuous tubing you can just add as many sections of tubing needed to complete the core as long as there is enough power to rotate the drill and water pressure to keep the drill bit or core barrel cool and flushed of debris.
Core bits can be manufactured approximately 1.2 metres in diameter or 120 centimetres. Whilst we ourselves do not have one that large as we haven’t had a client request for this size to date, we have several large size core bits with the largest being 0.9 metres in diameter.
In addition to this, if the hole size needs to be larger and still circular, this can be achieved by stitch drilling the penetration.
Put simply, it represents drilling through a ceiling surface thereby drilling upside down as access from above is either restricted or the holes required only need to be on the underside of the concrete and partially drilled thereby not penetrating through to top side of the surface.
Due to the use of water during the drilling process, the standard electric drilling equipment isn’t suitable. Rather hydraulic or IP rated (waterproof) electric drilling equipment must be used. In addition, a slurry ring is placed around the core bit to capture the waste water generated by the drilling process.
Best suited where a larger style penetration is required in a wall where overcutting the corners is not permitted. Stitch drilling represents the process of linking single core holes together to form a linear line. The holes are drilled such that they overlap slightly in order to achieve a consistent line in the direction and length required for the penetration.
Due to the close proximity of holes needing to be drilled when stich drilling, it is a perfect application for the use of auto-feed drilling rigs, an automation technique where a single core driller can operate multiple drilling rigs at the same time leading to significant advantages including the speed in which the drilling can be completed.
As core drilling is non-percussive it results in minimal vibration and uncontrolled movement. By reducing the amount of vibration, the diamond drill reduces the amount of uncontrolled or sporadic movement when initially penetrating the surface. This results in greater control over the diamond core drill and in turn the precise location of the core bit penetration point.
The combination of water suppression fitted to core drills and the hollow centre of the diamond core bit have been designed specifically to allow water to act as a coolant as well as a suppressant as it passes from the drill through the core bit to the point of contact being drilled. It is for this reason core drilling is sometimes referred to as wet drilling.
The importance of this feature, i.e. the dust suppression, cannot be stressed enough. Crystalline Silica represents a harmful particle substance contained in concrete, sandstone, and other solid surfaces. Inhalation of crystalline silica has the potential to cause various illnesses including asthma, chronic obstructive pulmonary disease and most significantly crystalline silicosis where exposure is significant in nature or prolonged.
The use of water as a suppressant results in the dust generated being kept wet throughout the drilling process thereby preventing the dust particles from becoming airborne. The slurry, or waste generated is then collected using a vacuum called a Wet Vacuum prior to drying.