Experience

Reading chips is one of those skills that separates real deep hole drillers from everyone else. The chips tell you everything — coolant pressure, feed rate, tool condition, material consistency, heat generation. They’re like a conversation the machine is having with you in real time. The problem is, sometimes you don’t want to hear what they’re saying. You’re on a deadline, you’re tired, you’ve got pressure from above to keep the parts coming, and it’s easier to tell yourself the chips look “close enough.” ...

I was running a job in 304 stainless steel, which is not my favorite material to begin with. It work- hardens, it galls, and it has a habit of making you think everything is fine right up until the moment it is not. The part was a flanged fitting, about 300mm long, needing a 16mm through-hole with an Ra 0.4 finish. The feed rate on the setup sheet said 0.08 mm/rev, which seemed aggressive to me for stainless. ...

I was sitting in on interviews for a deep hole drilling position at our shop. We needed someone who could run our BTA machines — not just push the green button, but understand the process well enough to handle the tough jobs, the ones where the parameters aren’t in the manual and you have to figure it out as you go. The pay was good — twenty-eight an hour plus benefits for the right candidate — so we got a lot of applicants. The stack of resumes on the HR manager’s desk was three inches thick. ...

It was 1:47 AM on a Wednesday in March, and I was already in trouble before I touched the control panel. The day shift guy, Danny, had flagged the handover log as urgent. “Drill acting weird near the end of the shift,” he wrote. “Reduced feed rate to try to finish the last part. Might need looking at.” The log was sitting on the desk in the break room where he’d left it, next to an empty coffee cup and a half-eaten granola bar. I read it, nodded to myself, and walked straight past the machine to clock in. That decision cost us almost two thousand dollars. ...

His name was Frank, and he had been running deep hole drilling machines since before I was born. Frank retired in 2018 after forty-two years in the trade. He had started on manual machines in the 70s, drilling oil field components, and had seen the transition to CNC, to BTA systems, to everything we use today. When he walked away from the trade, he took forty-two years of knowledge with him. ...

A customer sent me a print for what looked like the simplest job I had seen in months. It was a 4140 steel shaft, 600mm long, with a 20mm through-hole drilled axially from end to end. The print had no tight tolerances. The bore diameter was 20mm plus 0.5mm minus zero. The position tolerance was 0.5mm. The surface finish was 3.2 micrometers Ra. I had drilled hundreds of similar holes in 4140 over the previous five years. I quoted it as a standard gun drilling job at $85 per part for a batch of thirty-six pieces. ...

The Routine Job That Wasn’t I was working with an older machinist named Carl who had been running deep hole drills since before I was born. He had started his career in the 1970s working on oilfield gun drilling machines, then moved into aerospace in the 1990s. By the time I met him, he had over thirty years of experience and could tell you the chip load for any material combination from memory. A job came in drilling a 25mm hole through 3 meters of barrel. The print called for 4140 steel heat treated to 28-32 HRC. For Carl, this was a routine job. He had drilled hundreds of similar barrels. ...

A customer sent a print for a hydraulic cylinder barrel. The print called for a 100mm bore through 3 meters of barrel with a surface finish of Ra 0.2um as-drilled, with no honing allowed. I looked at that print for a solid five minutes before I picked up the phone. I checked it twice to make sure I was reading it correctly. The no-honing note was circled in red with an exclamation mark. Someone at the customer had already flagged this as a critical requirement. ...

The First Setup: Misalignment I had a job drilling a 20mm bore through a 300mm stainless steel block. The material was 316L, which is notoriously gummy and work-hardens at the cut zone if the tool rubs instead of shearing. The customer spec called for a positional tolerance of 0.1mm at the exit, a diameter tolerance of H8, and a surface finish of Ra 0.8 microns. Simple, right? I had drilled hundreds of holes through stainless steel. I set up the machine, aligned the guide bushing with the tailstock center, and started cutting. ...

Early in my career, a senior engineer watched me setting up a gun drilling job. I was fussing with the cutting parameters. Should the feed be 0.04 or 0.05 mm/rev? Should the speed be 3000 or 3500 RPM? He watched for a minute and said: “You are worrying about the wrong things. Check the coolant pressure first. If the pressure is not right, nothing else matters.” He was right. I have seen more deep hole drilling problems caused by coolant pressure than by any other single factor. Worn tools, misalignment, and wrong parameters are easier to fix than chip packing from low coolant pressure. ...