Deep Hole Drilling Tech Blog

I keep gun drills that are past their prime for finished holes and use them for roughing work. When a gun drill has been reground a few times or has minor edge wear, it still has life left for less demanding jobs. I have been doing this for years and it saves my shop thousands of dollars annually. The system is simple but it requires discipline to maintain. I check the tool rack at the end of every shift to make sure drills are returned to the correct section. A misplaced drill defeats the purpose of the system. ...

A batch of hydraulic cylinders came out with a strange discoloration on the bore surface. The dimensions were fine. The surface finish was fine. But the parts looked wrong. The customer rejected the whole batch. I checked the coolant and found the pH had dropped to 7.5. The coolant had gone acidic, which caused it to etch the steel surface. The discoloration was light surface corrosion. The fix was simple. I changed the coolant and added biocide to prevent bacterial growth. The pH returned to 9.5 and the next batch was fine. But the rejected batch was a total loss. The cost of those cylinders was several thousand dollars. ...

I volunteered for the night shift about five years ago and never looked back. Most guys hate it – the weird sleep schedule, the social isolation, not seeing your family for dinner. But for running a deep hole drilling machine, night shift is the best time to work, and I will die on that hill. The day shift at our shop starts at 6 AM and by 7:30 the place is a zoo. The material handling guy is dropping off pallets of blanks. The quality engineer is walking around with a stack of inspection reports, asking questions about every job. The production manager is running around putting out fires. There are safety meetings, toolbox talks, lunch orders, visitors from the front office walking through with hard hats. ...

I’ve run both 3-axis and 5-axis deep hole drilling machines. The 5-axis machines cost more — sometimes significantly more — and they’re more complex to program and maintain. But for certain types of work, they’re the only practical option. Here’s how I think about the decision. What the Extra Axes Give You A standard 3-axis deep hole drilling machine (X, Y, Z) can position the drill at any point in a plane and drill straight down. The drill axis is fixed vertically or horizontally. ...

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. ...

Automation in deep hole drilling ranges from simple part loaders to fully integrated production cells. The level of automation you need depends on your production volume, part variety, and labor availability. I’ve worked with manual machines, semi-automated cells, and fully automated lines. Each has its place. Levels of Automation Level Description Typical Volume Labor Manual Operator loads, starts, unloads Up to 500 parts/year 1 operator per machine Semi-automated Operator loads, machine cycles automatically 500-5000 parts/year 1 operator per 2 machines Automated cell Robot loads and unloads, machine cycles automatically 5000-20,000 parts/year 1 operator per 4-6 machines Integrated line Full automation with conveyor, gantry, or robot 20,000+ parts/year 1 operator per line The jump from manual to semi-automated is usually the easiest and has the fastest payback. ...

I select BTA drill heads based on the material and tolerance requirements. After running BTA drills on thousands of parts across carbon steel, stainless, and superalloys, I have settled on a selection system that covers 90% of what comes through the shop. BTA drill heads come in four main types, each with specific diameter ranges and applications. Pick the wrong head and you will fight chip evacuation, poor surface finish, and short tool life. Pick the right one and the hole drills itself. ...

I use BTA drilling for holes over about 20mm that need fast cycle times. When I need to remove a lot of material quickly and the diameter is large enough to support the tool, BTA drilling is my go-to process. It is also called single tube system drilling because the coolant flows around a single drill tube rather than through a double-tube arrangement like ejector drilling. BTA drilling — named after the Boring and Trepanning Association — is a deep hole drilling process for larger diameters. It’s the method I use when the hole is over about 20mm diameter and needs to be cost-effective. The process was developed in Germany in the 1930s and has been refined continuously since then. Modern BTA drilling machines can produce holes up to 300mm diameter and 20 meters deep. ...

Problem Description BTA drilling machines face unique wear challenges that standard gun drilling machines don’t. The coolant and chips flow through the center of the drill tube, so internal abrasion is constant. I’ve cut open BTA drill tubes that had worn through 2 mm of wall thickness over 2,000 hours of operation — hidden damage that would eventually cause a catastrophic tube failure. The support pads on BTA cutting heads also wear in ways that affect bore quality. Worn pads allow the head to chatter, producing a bore with spiral marks that fail surface finish requirements. ...