Coolant-Pump

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 largest energy consumer on a deep hole drilling machine, typically using 60 to 70 percent of the total machine power. I have spent considerable effort optimizing pump energy consumption because the savings add up quickly on machines that run multiple shifts. The key is reducing energy use without affecting the coolant pressure and flow that the drilling process requires. Energy Consumption Baseline Before optimizing, I measure the baseline energy consumption of the coolant pump under different operating conditions. The baseline measurement identifies the largest opportunities for savings. ...

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. ...

The coolant pump is the heart of a deep hole drilling machine. The right pump delivers adequate pressure and flow for the drilling application. The wrong pump causes chip evacuation problems, poor surface finish, and tool breakage. I have specified pumps for eight deep hole drilling systems, and I have made both good and bad choices that taught me what matters. Pump Types by Drilling Method For gun drilling, a positive displacement pump is the right choice. It delivers consistent pressure regardless of flow demand. The two most common types are piston pumps and progressing cavity pumps. Piston pumps use reciprocating pistons to pressurize the coolant. They deliver pressure up to 3000 psi with good efficiency. Progressing cavity pumps use a rotating helical rotor inside a stator to move the coolant. They deliver pressure up to 2000 psi with less pulsation than piston pumps. ...

We had a machine that had been losing coolant pressure for about three months. Not dramatically, but steadily. The pressure at the tool had gone from 1200 psi down to about 900 psi, and it kept dropping a little more every week. I had changed the filter elements. I had checked the pump motor current. I had inspected the pressure relief valve. Nothing helped. The machine was still making good parts, so the slow pressure loss got treated as a low priority. The operators adjusted their peck cycles to compensate for the reduced chip clearing. The production schedules got padded to account for the longer cycle times. Everybody just worked around it. ...

Coolant pump motors on deep hole drilling machines need properly sized starters and drives to operate reliably. A pump that starts and stops frequently under high pressure draws significant current during startup, and the starter must handle this without tripping or welding its contacts. I have seen coolant pump motors fail prematurely because the electrical system was undersized or improperly configured. Motor and Starter Sizing Guidelines The motor full-load current is listed on the motor nameplate, and this is the starting point for sizing the starter and protective devices. I follow standard electrical engineering practice with some specific adjustments for coolant pump applications. ...

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. ...

I maintain the coolant system regularly because it causes the most problems. Roughly 60% of the unplanned downtime I have seen on deep hole drilling machines traces back to the coolant system. The coolant system is the heart of a deep hole drilling machine. Without it, the machine cannot function. The coolant flushes chips, lubricates the cutting zone, and controls temperature. A poorly designed system causes scrapped parts, broken tools, and days of troubleshooting. ...

Deep hole drilling machines are not the most energy-intensive machines in a shop, but they use significant power. The main energy consumer is the coolant pump, which runs continuously during the drilling cycle. I’ve found several ways to reduce energy consumption without affecting cycle time or hole quality. I cut my own shop’s energy bill by 18% over two years by implementing the measures described below. Where the Energy Goes On a typical deep hole drilling machine, the energy breakdown looks like this: ...