MQL (Minimum Quantity Lubrication) for Deep Hole Drilling
MQL uses a small amount of oil or lubricant sprayed as a fine mist instead of flooding the cutting zone with coolant. It is common in conventional machining operations like milling and turning but rare in deep hole drilling. The main challenge is chip evacuation, which in deep hole drilling depends on high-pressure coolant to push chips out of the bore. Recent research on MQL in deep hole drilling (2025 Manufacturing Letters, and a 2023 comprehensive review) confirms that MQL is technically feasible for certain deep hole applications and can actually outperform flood coolant on tool life in some cases. But the data also confirms what I have found in practice — the L/D ratio and material type are the deciding factors. ...