Real problems, real solutions, no fluff. I have spent years working across multiple shops running gun drilling, BTA drilling, and ejector drilling machines — setting up jobs, troubleshooting coolant pressure and chip evacuation issues, drilling deep holes in everything from hydraulic cylinders to aerospace titanium. This site is where I share what I have learned.
A manual lathe can be converted for gun drilling with the right equipment. The conversion costs a fraction of a dedicated machine but comes with real limitations. I’ve done this conversion on a 14-inch Colchester lathe and gotten usable results. The main requirements are a through-coolant toolholder, a high-pressure coolant system, and a guide bushing support. The toolholder mounts on the lathe carriage and holds the gun drill. The coolant system delivers fluid through the tool at the required pressure. The guide bushing supports the drill at the workpiece entry. ...
Biocide prevents bacterial growth in emulsion coolants. Bacteria consume the coolant additives and produce hydrogen sulfide gas — the classic rotten egg smell. Left untreated, the coolant turns rancid, separates into oil and water, and needs to be drained and replaced. I have dumped thousands of gallons of rancid coolant over the years, and most of those dumps could have been prevented with proper biocide management. Biocide Types for Different Situations I use two primary types of biocide depending on the situation, but there are actually four main categories worth understanding. Each targets different organisms and works best under specific coolant conditions. ...
Coolant filter selection directly affects tool life and hole quality in deep hole drilling. I have seen machines that run perfectly with clean coolant and fail repeatedly with dirty coolant—the only variable was the filter. Getting the filtration right is one of the simplest ways to improve drilling consistency. Problem Description Coolant in deep hole drilling carries chips and fines from the cutting zone. If the filter does not remove these particles, they recirculate through the coolant system and pass between the drill guide pads and the bore wall. The particles act as lapping compound and wear the pads, the drill edge, and the bore surface. ...
The coolant filtration system is the first thing I check when a deep hole drilling operation starts producing inconsistent results. Dirty coolant causes more tool failures, surface finish problems, and bore diameter drift than almost any other single factor. I have seen a shop cut tool life in half simply by letting their filtration maintenance slip by two weeks. Why Filtration Matters More in Deep Hole Drilling Deep hole drilling generates fine chips that stay suspended in the coolant much longer than the chips from turning or milling. A gun drilling operation produces chips that are typically 0.01 to 0.05 mm thick and 1 to 5 mm long. These chips pass through the drill head coolant holes at high velocity. If chips recirculate through the system, they erode seals, clog coolant passages, and scratch bore surfaces. ...
Coolant filtration is essential for deep hole drilling. Chips that recirculate through the coolant will damage the drill edge and score the bore surface. I have designed and modified filtration systems for dozens of machines, and the system design has a direct impact on tool life, surface finish, and machine reliability. A well-designed filtration system delivers clean coolant consistently and requires minimal operator attention. Filter Type Comparison There are several filtration technologies available, and choosing the right one depends on your material, chip volume, and coolant pressure requirements. Here is how the main types compare based on my experience. ...
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. ...
The coolant manifold distributes high-pressure coolant from the pump to the drill through the rotating union. The manifold includes the supply lines, valves, pressure gauge, and filter. I have designed and rebuilt manifolds on a dozen deep hole drilling machines over the years, and the layout decisions have a direct impact on drilling performance and maintenance downtime. Manifold Location and Pressure Loss The manifold should be located as close to the rotating union as possible. Every meter of hose between the manifold and the union causes a pressure loss of about 50-100 psi at gun drilling pressures. I keep the distance under 2 meters. On one machine I worked on, the original builder placed the manifold 5 meters from the rotating union, and we were losing nearly 400 psi in the hose alone. Relocating the manifold to within 1 meter recovered that pressure and improved chip evacuation noticeably. ...
Coolant pressure trending tracks the coolant pressure over time to predict when maintenance is needed. A gradual pressure decrease indicates a developing problem. A sudden pressure drop indicates a failure. I started doing this after a surprise pump failure cost me 16 hours of unplanned downtime in the middle of a rush job a few years ago. Since implementing the system, I have caught every developing problem before it became a breakdown. ...
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. ...