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Internal coolant (through-coolant) VS external coolant (flood-coolant) drill bits

Internal coolant (through-coolant) VS external coolant (flood-coolant) drill bits

2025-09-09

Internal Coolant vs External Coolant Drill Bits

Type	Advantages	Disadvantages	Suitable Applications
Internal Coolant (Through Coolant)	1. Coolant reaches the cutting edge directly, providing better cooling. 2. Extends tool life. 3. Helps with chip evacuation.	1. Higher cost. 2. More complex drill design.	Deep-hole drilling, hard materials, difficult-to-machine materials (stainless steel, alloy steel).
External Coolant (Flood Coolant)	1. Simple structure. 2. Lower cost.	1. Cooling is less effective. 2. Deep holes may clog with chips.	Shallow holes, ordinary steel machining.

Selection Tips

Deep holes / hard materials → Internal coolant drill bits
Shallow holes / ordinary steel → External coolant drill bits
For high-speed machining or materials prone to chip adhesion, internal coolant is preferred to protect the tool and improve efficiency.