Pressure-Drop

I have seen this pattern more times than I can count. A shop is running 12mm gun drills with no coolant issues. Then they switch to a 6mm job and the pump starts making a rattling noise, the pressure gauge oscillates, and coolant flow becomes erratic. The diagnosis is almost always the same: the pump is cavitating because the small drill restricts flow more than the pump can tolerate. Why Small Drills Cause Cavitation A centrifugal pump needs a minimum flow rate to operate correctly. When the flow drops below this minimum, the pump recirculates fluid internally, heats up, and vapor forms at the impeller inlet. Those vapor bubbles collapse violently — that is the rattling noise you hear. ...

Piping design is where most coolant system installations go wrong. I have walked into shops with a $50,000 high-pressure pump and $300 worth of undersized pipe fittings that turned the whole investment into a 600 psi system instead of the designed 1,000 psi. The piping carries the coolant, but it also creates pressure losses that compound with every fitting, bend, and length of tube. Pressure Drop Fundamentals Every component in the coolant path adds resistance. The pressure drop through a system is proportional to the flow rate squared. Doubling the flow quadruples the pressure loss through the piping. This matters enormously in deep hole drilling because the flow rates are high and the pressure requirements are tight. ...

I was running a job that still haunts me a little when I think about it. Forty titanium shafts, aerospace grade Ti-6Al-4V, each one needed a 14mm hole drilled 600mm deep. The material alone was worth about eight hundred dollars per shaft, and the customer had a delivery date that did not have any slack. The machine was a UNISIG BTA system with a 200-gallon coolant tank and a pump rated at 2000 psi. The gauge on the pump console read 1500 psi steady, which was right where it should be for that diameter and depth. Everything looked good on paper. ...