A coolant-through drill, also known as a through-coolant drill, is a type of drill bit that’s designed with internal channels for coolant to flow directly through the tool and onto the cutting edge.
Coolant-through drills offer many benefits, including:
- Reduce heat buildup and tool wear
- Prevent thermal damage to your workpiece
- Assist with chip evacuation
- Improve cycle times and production rates by eliminating the need for drill peck cycles.
- Increase lubricity for higher speeds and feeds
Coolant-through drills add a ton of value to the machining process, but with one major caveat: they’re expensive.
When to Use a Coolant-Through Drill or a Standard Drill
There’s no mechanical reason to not use a coolant-through drill, unless the hole you’re drilling has dimensions that aren’t compatible with one.
For example, let’s say you need to make a hole that’s .030” in diameter. You can’t use a coolant-through drill because tooling manufacturers don’t make them that small; coolant-through channels weaken a drill, and the tool would break due to the pressure.
So, given that there aren’t any mechanical downsides to using coolant-through drills – they’re just costly – it’s important to know when and when not to use them so you don’t blow through your tooling budget or waste your expensive drills.
Keeping in mind that there are many nuances to consider in any CNC machining project, here are some standard factors to consider when deciding what type of drill would be most appropriate for your project: a coolant-through or a standard.
| Coolant-Through Drill | Standard Drill | |
| Hole Depth |
Deep Holes Ideal for holes deeper than 3x the diameter, as coolant helps evacuate chips and prevent tool breakage |
Shallow Holes Ideal for holes <3 x the diameter; chip evacuation isn’t a major issue |
| Workpiece Material |
Hard or Heat-Resistant Materials Essential for materials where heat buildup is common and could damage the drill or workpiece (i.e., Inconel, titanium, SS, and hardened steels) |
Soft or Easily-Machined Materials Works well on materials where heat buildup isn’t a concern (i.e., aluminum, brass, and mild steels) |
| Production Volume |
High-Volume Reduces tool changes and increases efficiency on cycle times; benefits are most apparent and/or needed with higher volume runs |
Low-Volume For lower volume runs or prototype application, a standard drill is sufficient if the depth of cut and material don’t create chip evacuation or heat buildup concerns |
If you can use a standard drill for your CNC machining project without damaging the workpiece or tool, it’s a great opportunity to lower the cost of that run, spare an expensive tool, and keep your long-term tooling costs low.
Coolant-through drills provide a lot of advantages in CNC machining, and you get the most value out of them when you use them for the right type of cut, on the appropriate material, and for higher-volume runs.
Chris Castaneda
Tre Tiff
Amanda White