How To Care for Your Core Drills

Diamond Drills in The Stone Industry

There are many variables involved in drilling stone and other hard surfaces. We are often asked by customers "how many holes will this drill make?". Unfortunately, there is no accurate answer to this question due to all the possible variations that affect the lifespan of diamond drills. There are, however, care guidelines and tips to help improve drilling techniques, that will improve the life of the drill itself.

The following advice is designed to help you optimise drilling stone, with the aim to increase tool life, reduce damage to materials and ensure you get the best cutting ability possible from your core drills.

If you need further specialist advice that was not covered by this article please contact us here.


Choosing The Right Diamond Technology For The Application

The first thing to check is to make sure that you are using the right kind of drill for the material. Hardness and the level of abrasion of the material need to be assessed to match the tool to the application.

We supply three main types of diamond core drill. Sintered diamond drills have diamond grits suspended in a metal matrix that wears away as the drills cuts. They are designed for hard materials and feature thick diamond segments on the cutting crown. The electroplated kind is designed for soft stones and they have a very fine layer of diamond that ensure smooth, chip-free results on soft materials. Vacuum brazed drills feature a coarse coating of diamond grit on their cutting rims. This exposed diamond makes them fast cutting and able to drill a wide range of materials.

The table below will help you to choose the correct type of diamond core drill based on the material you are cutting for optimum results.


Diamond TechnologyOptimum Results For
Sintered SegmentedGranite, quartz, sandstone, terazzo, brick, terracotta
Sintered Continous RimPorcelain, ceramics
ElectroplatedMarble, limestone, travertine, oynx
Vacuum BrazedSlate, terazzo, crystalised stone, Ultra Compact Surfaces

Calculate the Correct RPM Speed for The Material and Core Drill Diameter

One of the main ways to care for your core bit is to use it on a machine capable of running on the settings needed for the tool. The best drilling results and tolerances are only guaranteed with Computer Numerical Control Machines (CNC). Manual drilling is more common with machines like pillar drills and rigs, SDS drills and angle grinders. The critical factor is to ensure that the machine has enough power to use the drill at the correct rotation speed for the diameter and material being cut.

If the diamond tool rotates too slowly, it drags on the surface and creates heat. If it spins to fast, it causes friction, will not cut and also generates heat. Excessive heat is a major problem for diamond tools of any kind. With sintered core drills, the metal bond that the diamonds are surrounded by must wear away to continuously keep re-exposing diamonds grits for the tool to continue cutting. If the tool becomes overheated, the metal bond does not wear away, instead, it covers the diamond, meaning the drill does not cut and the diamond has become "glazed".

It is sometimes thought that the faster the drill is rotated the faster it will cut or that larger drill diameters need to be rotated faster than smaller drill diameters. For example, a 35mm diameter core drill cutting granite should be rotated at approximately 350rpm while a 100mm diameter size should be rotated at 190rpm. Generally, the speed should decrease as the hardness and abrasiveness of the material increases and/or the diameter increases in size.

The article below contains further details on rpm speeds for drilling stone.


Rotation Speeds for Drilling Stone

Below are some examples of the types of hand machines core drills are commonly used with



Maintaining Diamond Drills

Using a sharpening block

If the tool does become glazed, this means that the metal bond has become the cutting element rather than the diamond. It will not cut the material or will take excess pressure to do so - as it has become "blunt".

At this point, the drill needs to be reconditioned by redressing the diamond cutting tips. Make 3-5 drill holes in an abrasive stone such as sandstone using plenty of water. Alternatively, you can use an aluminum oxide sharpening block to do this. Doing this several times should be enough to wear away the metal carrier to expose a fresh layer of diamond to cut the material. Now test the core drill on a regular stone material. If done correctly, the drilling performance will be improved and the drill will be able to cut the surface.

Ultimately, sintered diamond core drills are able to be used until the segment wears to the barrel - if the core stops cutting then follow this advice.

Using a waterfeed for drilling stone

As the core drill cuts the stone, material, and debris is released. This needs to be removed immediately by an internal water feed to avoid overheating. If this is not practical due to the application (in-situ or horizontal drilling) then water can be directed at the drilling zone with an external hose or a sprayer bottle.

Using an uninterrupted internal water feed at high pressure with your core drills is very important. It helps:

  1. To reduce frictional heat generated at the diamond tip cutting the stone. Excessive heat can destroy the diamond crowns and the weld points of the segments resulting in segment loss
  2. To reduce the wear rate of the tool. Abrasive stone pieces are removed by water and are not left to grind against the cutting tips which will damage them. This will also increase the speed of cut
  3. To wash out material that becomes lodged in the center of the core drills. A drilled core held in the center of the drill can restrict water flow and prevent cooling the diamond tips adequately
  4. To keep the drilling edge clean to ensure precise and accurate results

Consider using a water feed, like the one below to help prolong the cutting life of the drill and avoid damage to the segments or segment loss. They can be mounted on SDS Drills as well as pillar drills.



Why Use Dust Supression With Core Drills?

Sometimes it is not possible to use an internal waterfeed with diamond core drills. Usually, this is due to the application - if the workpiece is in-situ or horizontal drilling is required. On-tool dust suppression (or local exhaust ventilation) helps to reduce the wear rate of the tool as abrasive stone pieces are removed from the working area and are not left to grind against the cutting tips.


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