Chip-Evacuation

The coolant pressure gauge is the most informative instrument on a gun drilling machine. It tells you about chip evacuation, pump condition, filter status, and drill condition — all in real time. But only if you know what to look for. I have spent years learning to read pressure patterns. Here is what I have found. Where to Measure Pressure The pressure at the pump gauge is not the pressure at the tool tip. I install gauges at two locations: ...

BTA drill head jamming is one of the most difficult problems to recover from in deep hole drilling. The head binds in the bore, the spindle stops under overload, and the head cannot be retracted by normal means. I have dealt with this on holes from 20mm to 150mm diameter, and the recovery approach depends heavily on how badly the head is wedged. Problem Description A jam occurs when the drill head becomes mechanically locked inside the bore. The spindle torque spikes to 100% or more of the rated maximum, the machine triggers an overload alarm, and the head refuses to move in either direction. In severe cases, the drill tube twists visibly before the spindle stalls. ...

Chip blockage in BTA drilling happens when chips accumulate inside the drill tube and restrict the coolant flow path. I have seen this on holes as small as 18mm diameter and as large as 200mm, and the damage is always expensive. When the tube blocks, coolant pressure spikes, feed drops, and the tool can fail within seconds if not caught in time. Problem Description The coolant delivery system in BTA drilling serves two purposes: lubricating the cutting zone and transporting chips through the drill tube back to the chip tank. When the tube blocks, both functions stop. The coolant pressure at the pump rises sharply because the flow path is restricted. The cutting zone loses lubrication, and the chips pack tighter. ...

I spent the first three years of my career watching the coolant pressure gauge like a hawk. If it held steady at 1200 psi, I assumed everything was fine. Chips were packing? Must be a feed issue. Drill broke? Wrong parameters. Then a senior engineer walked over to my machine one afternoon, pulled out a bucket and a stopwatch, and showed me that my pump was delivering less than half the flow the drill actually needed. The pressure gauge never flickered. ...

Every time I talk to a shop that wants to start gun drilling, the question comes up: how much coolant pressure do I really need? The manufacturer’s spec sheet usually says 1000-2000 psi. But real-world results vary depending on diameter, depth, and material. Here is what I have found works — and what does not. Pressure vs Flow: What Matters for Chip Evacuation Coolant does two jobs in gun drilling: it lubricates the cutting edge and it pushes chips back along the flute. Lubrication needs pressure. Chip evacuation needs flow. You need both. ...

Through-tool coolant delivers coolant through the center of the drill directly to the cutting edge. Flood coolant sprays coolant over the outside of the drill and relies on flow to reach the cutting zone. In deep hole drilling, the choice between these two methods determines whether the process succeeds or fails. How Through-Tool Coolant Works For gun drilling, through-tool coolant is essential. Coolant enters through a rotating union at the spindle, travels down the center of the gun drill tube, and exits at the cutting edge. The coolant cools the cutting edge and then flushes chips back along the external flute of the drill. ...

Problem Description Foaming robs a high-pressure coolant system of its ability to evacuate chips. The air bubbles in foam take up volume that should be occupied by liquid coolant. I’ve watched a foaming system lose 35% of its chip-carrying capacity — the chips stopped flowing out of the bore and started packing. In deep hole drilling, where chip evacuation depends entirely on coolant flow, foaming is one of the most disruptive problems you can encounter. ...

Why Chip Clogging Is the #1 Problem After dealing with chip clogging on maybe fifty different jobs across gun drilling and BTA, three root causes keep showing up. Chip clogging accounts for roughly 60% of all troubleshooting calls I handle. When chips pack in the flute or bore, coolant flow stops, torque spikes, and the tool breaks within seconds. The mechanism is simple: the drill generates chips faster than the coolant stream pushes them out of the bore. The chips accumulate, jam against the drill body, and block the chip flute entirely. Once the flute is blocked, coolant cannot reach the cutting edge and the drill fails almost instantly. ...

Coolant pressure is the single most critical parameter in gun drilling. I have seen a 15% drop in pressure double the chip packing frequency and cut tool life in half. Getting the pressure right matters more than speed or feed on every job I run. Pressure Requirements by Diameter Small drills need high pressure because the coolant hole area shrinks faster than the drill diameter. A 2 mm drill has less than one-tenth the coolant hole area of a 6 mm drill, so the pressure must be much higher to move the same volume. ...

Problem Description The coolant system is the heart of any deep hole drilling operation. When it works, the process runs smoothly. When it doesn’t, drills break and scrap piles up fast. I’ve traced roughly 70% of my tool breakage incidents back to coolant system issues rather than cutting parameters or material problems. The three most common failures I see are low pressure at the tool tip, clogged filters, and external leaks. Low pressure causes chip packing inside the bore — chips can’t evacuate and the drill jams. Clogged filters slowly strangle flow until the system can’t maintain pressure. Leaks rob pressure and make a mess of the shop floor. ...