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.
I reduce feed through cross holes to protect the drill from shock loading. When a gun drill passes through a cross hole, the cutting edge loses contact with the material momentarily and then re-enters on the far side. The impact of re-entry chips the cutting edge if the feed is too high. I learned this the hard way on a batch of hydraulic manifold blocks where I chipped three drills in a row before I figured out the feed reduction. ...
I spot face the entry before drilling eccentric holes. Eccentric holes are holes that are not centered on the part axis. The drill enters the material at an angle relative to the surface, which causes the tip to deflect if the entry is not prepared properly. A bad setup here almost always produces a scrapped part. Preparing the Entry Surface The first thing I do is create a flat entry surface with a spot face cutter. The spot face must be perpendicular to the drill axis, not to the part surface. Without the spot face, the drill hits the curved surface at an angle and slides down it, shifting the hole position by as much as 0.5mm on a 50mm diameter shaft. ...
Ejector drilling parameters are different from gun drilling or BTA drilling. The speeds, feeds, and coolant settings all shift because ejector drilling uses a double-tube system with a venturi effect for chip evacuation. Here are the ranges I use after running ejector drilling on dozens of production jobs. Cutting Speed by Material Ejector drilling operates at cutting speeds similar to BTA drilling but on the lower end of the range. The double-tube design restricts coolant flow slightly, so I run 10-15% slower than BTA speeds in the same material. ...
I set up ejector drilling tooling differently from gun drilling. The double-tube assembly changes everything — how coolant flows, how chips exit, and how I approach alignment. Ejector drilling uses a double-tube tool assembly where coolant travels down the annulus between two concentric tubes and returns through the inner tube. The setup is different from both gun drilling and BTA drilling. Get it wrong, and you will scrap parts. I have scrapped enough to know where the pitfalls are. ...
I use ejector drilling when high-pressure coolant is not available. It is the method I reach for when a customer brings in a part that needs a deep hole but the only available machine is a standard CNC mill with a through-coolant spindle. Ejector drilling is a deep hole drilling method that uses a double-tube system. It is less common than gun drilling or BTA drilling but has specific advantages that make it the right choice in certain situations. Understanding when to pick it over the alternatives saves money and time. ...
Deep hole drilling machines have specific safety requirements beyond standard machine tools. The high-pressure coolant, fine chip mist, and continuous operation create hazards that need specific safety systems. I’ve dealt with a few safety incidents over the years, and I’ve developed a set of practices that keep machines and operators safe. Emergency Stop Systems Every deep hole drilling machine needs emergency stop buttons at multiple locations. The requirements are more extensive than a standard machine tool because of the coolant system and the continuous operation mode. ...
Deep hole drilling machines are not the most energy-intensive machines in a shop, but they use significant power. The main energy consumer is the coolant pump, which runs continuously during the drilling cycle. I’ve found several ways to reduce energy consumption without affecting cycle time or hole quality. I cut my own shop’s energy bill by 18% over two years by implementing the measures described below. Where the Energy Goes On a typical deep hole drilling machine, the energy breakdown looks like this: ...
Deep hole drilling machines are specialized equipment. When a part fails, you can’t always get a replacement quickly. Having the right spares on hand can mean the difference between hours of downtime and days. Here’s what I’ve learned about stocking spares. Critical Spares These are parts that fail without warning and cause immediate downtime: Part Why It Fails Cost Lead Time Rotating union seal Wear, normal $50-$200 2-5 days Coolant hose Burst from pressure cycling $100-$500 1-3 days Guide bushing Wear, normal $50-$200 1-5 days Spindle drive belt Fatigue $100-$300 2-5 days Door interlock switch Coolant contamination $50-$150 2-5 days I keep at least one of each of these on hand for every machine. ...
Why Feed Rate Controls Chip Shape In deep hole drilling, chip breaking is not optional. Long stringy chips pack in the bore, block coolant flow, and cause tool breakage. The feed rate is the primary lever I use to control chip formation. The cutting action of a gun drill produces chips that curl as they travel along the flute. At the right feed rate, the chips curl tight enough to break under their own weight. At the wrong feed, they either form long ribbons or break into dust. ...
The guide bushing is one of those parts that nobody thinks about until the holes start coming out wrong. It’s a simple component — a precision-ground tube that supports the gun drill at the entry point. But when it’s worn or incorrectly sized, it causes more problems than any other single component I’ve dealt with. What a Guide Bushing Does The guide bushing supports the gun drill right where it enters the workpiece. The drill passes through the bushing before contacting the material. The bushing prevents the drill from whipping or wandering during the first few millimeters of engagement. ...