Bits ‘n Pieces – The Driller’s Blog

Core Matrix Troubleshooting: Overly Exposed Diamonds

Posted by Rod McCoremick on Feb 13, 2017 10:30:00 AM


We’ve talked a lot in previous blogs about the importance of choosing the right core bit and the right core bit configuration, so I think it is time we talk about getting the most out of your core bit. There are many variables that can cause a really good core bit to underperform. It can be a change in ground conditions, drilling parameter or simply lack of experience.  One of the best ways to determine what is off is to examine the wear profile of your bit crown and change drilling parameters if necessary.

We should keep in mind that the ideal wear on a core bit is attained when the wear on the diamonds and matrix is balanced and even, and the full depth of impregnation is evenly consumed.  This allows the driller to get as much footage as possible on the bit, before it is retired.  In comparison, below, we will look at some consumed core bits with wear patterns that are less than ideal, some reasons for this and possible solutions to improve on the correct bit selection.


As you can see in the photo, the matrix wore out before the diamonds were worn out. This results in the diamonds popping out prematurely, which reduces the life of the bit. A few things can lead to this happening.

Matrix is too soft

If the matrix is wearing out too quickly, it could mean that it is too soft for the type of ground in which you are drilling. You must determine the hardness of the ground before you choose your core bit. An easy way to do this is with a scratch test and hardness kit. Watch this video to see how easy this is.

The solution to this problem is change the bit to a lower series, meaning one with a harder matrix. You should refer to a matrix selection chart to guide your choice.

Water flow is too low

The water flow should be as high as possible but must be related to the bit size and type of rock to be drilled. If your matrix is wearing out too quickly, your water flow is probably too low.

The simple fix is to increase your water flow. You can always refer to recommended water flow charts such as the one found in this guide.


Bit pressure too high

Drilling pressure that is too high for the speed of rotation can also cause premature wear of the core bit and other equipment, as well as other problems like hole deviation. Bit pressure, or the force applied on the bit, plus the weight of the rods that are being used, this must be adjusted to achieve better performance.

To remedy this problem, increase the speed of rotation and reduce the drilling pressure. You should put only as much pressure on the bit as needed to advance. You can refer to this guide for more information.


Examining the wear patterns on your bit crowns is an excellent way to improve your drilling performance. In upcoming blogs we will look at other common issues such as burnt bits, polished bits, inside and outside diameter gauge loss, and more.

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Topics: Tips on common drilling issues, Basic drilling information

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