Bits ‘n Pieces – The Driller’s Blog

At the Bottom of the Bore Hole: How Not to Ruin Your Core Bit

Posted by Rod McCoremick on Jun 20, 2017 10:00:00 AM

In this blog, our last installment on handling core bits, we look at problems that can happen at the bottom of the bore hole when you’re adding or changing a new core bit. I always say that choosing the right core bit and bit configuration is one of the most important decisions you have to make to ensure you get the best drilling performance. You also need to make sure you handle them properly so that they get to the drill the ground they were chosen for.





In previous blogs we’ve looked at potential problems above ground and on the way down to the bottom of the borehole. Today we’ll focus on the bottom of the bore hole, where it is often hard to know what is going on.


Take your time

As is the case above ground, and on the way down, many problems can be avoided by not rushing, Yes, I know that time is money and good diamond drillers want to get the most meters per shift, but rushing can lead to problems that will take even more time to fix. When lowering your drill rods, take your time so you don’t slam into the bottom of the hole. The crown of yourbit can be easily damaged if trying to rush, and you will have to deal with the mess of having to change the bit again. Lowering your rods too fast is risky and can also cause your equipment
to jam.


Know where the bottom is

As mentioned in the point above, you don’t want your equipment to slam into the bottom of your borehole. If you know exactly where the bottom is, it is much easier to avoid this. Keeping your log book up to date with detailed and precise information is the key. Check the log book and make sure you always stop a few feet before the bottom of your bore hole. Learn more about keeping a great log book here.


Always re-drill

An experienced diamond driller knows that you can lose diameter at the bottom of the bore hole. This is why stopping before you hit the bottom is so important. The outer gauge of the bit and the reaming shell wear out as you drill, often at the same time. If they have reached the end of their life, they will not be able to maintain the desired gauge of the bore hole. Forcing a new core bit into this funnel-shaped bottom will lead to the fragile ends of the matrix crown to pop off. It is a drilling best practice to always re-drill the bottom of the bore hole to make sure you maintain the right diameter.



What goes on at the bottom of a bore hole is always a bit of a mystery because you can’t see. By following these simple tips, you can change up your bit and shell with less chance of damage. A really good core bit that was designed for a particular type of ground can be expensive so you want to make sure you extend its life and get as many meters as possible. Our goal is to help drillers improve their performance. Knowing how to handle your bits, as well as other equipment such as drill rods, will lower your operational costs, improve your drilling performance and help make you an “All Pro Driller”.


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Topics: Tips on common drilling issues, Basic drilling information

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