Coolant-Pressure

I get more questions about drilling small holes in Inconel 718 than almost any other topic. A recent Practical Machinist thread about drilling 3mm holes 160mm deep in Inconel 718 at HRC 40-45 got over 3,500 views. The user was struggling with drill breakage, centerline deviation, and surface finish. The root cause in that thread was the same one I see most often: coolant pressure at 8 bar (116 psi) when the job needs 100 bar or more. Here is what I have learned about getting this application right. ...

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: ...

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. ...

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. ...

Titanium is the material that separates experienced deep hole drilling shops from the rest. I have drilled more titanium holes than I can count — here is what I have learned about making them consistently. Every titanium alloy behaves differently. Get the parameters wrong on one alloy and you lose the tool, the part, or both. Get them right across the board and titanium becomes predictable. I cover the broader aerospace deep hole drilling landscape in another article. This one is specifically about titanium parameters, tool life, and coolant — the three things that matter most when the material is titanium. ...

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. ...

I use a fixed setup checklist for every deep hole drilling job. It takes five minutes to run through and has prevented more scrapped parts than any other process control I have implemented. A cold machine, a dirty bushing, or a clogged coolant line will ruin a part faster than any programming mistake. Step 1: Machine Warm-Up I run the spindle at operating speed with coolant circulating for at least 30 minutes before starting a job. A cold machine does not drill straight holes because the spindle, headstock, and bed expand as they warm up. ...

The Five-Step Troubleshooting Sequence When something goes wrong during a deep hole drilling job, I teach operators a five-step sequence. This sequence solves about 80% of all problems without needing engineering support. I post this sequence on every machine in the shop. The sequence follows the most likely cause first. Starting with the most common problem saves time. Do not skip steps and do not jump to conclusions. Step 1: Check Coolant Pressure Low coolant pressure is the root cause of more problems than anything else in deep hole drilling. It causes chip packing, tool breakage, poor surface finish, and oversized bores. ...

When a CNC Lathe Makes Sense for Gun Drilling A dedicated gun drilling machine is the right tool for production deep hole work. But I have run plenty of successful gun drilling jobs on standard CNC lathes when the volume did not justify a dedicated machine. The key is knowing the limits. In my experience, a lathe with live tooling and through-coolant capability can handle L/D ratios up to about 10:1 reliably. Beyond that ratio, the alignment challenges and coolant pressure limitations make a dedicated machine necessary. ...