Pump-Maintenance

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. ...

The coolant pump is the heart of any deep hole drilling system, and I have seen more production downtime from pump failures than from spindle issues. The pump must deliver consistent pressure and flow at the tool tip, and the maintenance approach is completely different from the standard sump pump on a CNC lathe. Pump Selection Criteria The pressure and flow required depend on the drilling method, tool diameter, and depth. For gun drilling, the rule of thumb I use is 800 to 1,200 psi (55 to 83 bar) for diameters under 20 mm, and 400 to 800 psi (28 to 55 bar) for diameters above 20 mm. BTA drilling typically runs at lower pressure, 200 to 500 psi (14 to 35 bar), but requires two to three times the flow rate. ...

Problem Description A coolant pump that can’t maintain pressure makes deep hole drilling impossible. I’ve had jobs where the pump dropped from 80 bar to 40 bar mid-cycle and the chips stopped flowing. The drill packed up and snapped within 10 seconds of the pressure drop. Pump problems show up in three ways: low pressure at the outlet, fluctuating pressure during operation, or no pressure at all. Each pattern points to a different root cause. I follow a systematic approach rather than guessing. ...