If you've ever held a solid carbide drill bit and noticed tiny holes running through it, you’ve probably asked yourself: How do they actually make those coolant holes? After all, carbide is an extremely hard material, and drilling holes inside a drill seems like a serious manufacturing challenge.
In this post, we’ll walk you through how coolant holes are made in modern drill bits, why the process is so precise and specialized, and what this means for quality and performance in CNC machining.
Coolant holes—also called internal coolant channels—are small, precision-engineered passages inside the body of a drill bit. They allow cutting fluid (coolant) to flow directly to the drill’s cutting edge, which helps with:
Heat dissipation
Chip evacuation
Improved surface finish
Longer tool life
These holes are essential in high-speed and deep-hole drilling, where external coolant can’t reach effectively.
Creating internal holes in a solid carbide drill isn’t as simple as drilling into steel. Carbide is extremely hard and brittle. It can't be drilled using regular methods once it's sintered (hardened). That’s why the process to create coolant holes has to be done before the tool reaches its final hardness.
Carbide tools begin as a mixture of tungsten carbide powder and a binder material (usually cobalt). This powder is pressed into a soft, chalk-like shape called a “green body.” At this stage, the material is soft enough to be machined or drilled.
During pressing or pre-sintering, thin rods (often made of steel or graphite) are inserted into the green compact to form the desired coolant channel shape. These rods stay in place as the rest of the tool is formed.
Alternatively, high-precision gun drilling or electrical discharge machining (EDM) is used at this stage while the carbide is still soft.
Once the coolant holes are formed in the green state, the tool goes through sintering, a high-temperature process (often over 1400°C) that bonds the carbide particles together. During sintering:
The soft green body shrinks and becomes dense and hard
The rods used to create the holes are either burned away or removed
The holes remain intact as precision channels
This results in a solid carbide drill bit with internal coolant holes that are capable of handling high pressure and temperature during CNC machining.
In indexable drills or larger multi-flute tools, the coolant holes are often made using gun drilling machines or EDM if the material permits. For steel-body tools, internal channels may be drilled after the body is forged or machined, sometimes using angled approaches to reach near the tip.
In advanced applications, additive manufacturing (3D printing) using metal powders is now being used to create complex internal coolant channels that cannot be machined using traditional methods.
Why is this process so critical?
If the hole is too small, coolant flow is restricted.
If it’s misaligned, it won’t reach the cutting edge.
Poor surface finish inside the hole can create turbulence, reducing cooling efficiency.
That’s why top manufacturers invest in ultra-precise tooling and inspection systems—to ensure coolant delivery is optimized and consistent.
Tools with properly designed coolant holes offer:
50–100% longer tool life (source: Sandvik Coromant)
Better chip evacuation, especially in deep holes
Cooler cutting temperatures, which reduces thermal cracking
Higher productivity, as you can increase feed rates confidently
Internal coolant holes are more than just a clever design feature—they are the result of advanced engineering and manufacturing. If you’re using solid carbide or indexable drills with internal coolant, you’re relying on a process that took decades of development to perfect.
At Amony, we manufacture and supply high-performance drills with through-coolant holes, engineered for maximum durability and precision. If you're looking to improve your CNC drilling efficiency, don’t hesitate to contact us for the right tool recommendation.
Contact our experts today for a free quote or technical consultation.