Ejector-Drilling

Ejector drilling uses a double-tube system where coolant flows between the outer and inner tubes and returns through the inner tube by Venturi effect. When problems happen, they are almost always related to coolant flow or nozzle condition. I have worked through enough ejector drilling issues to recognize the patterns fast. The double-tube design gives ejector drilling advantages in portability and setup simplicity, but the troubleshooting demands a different mindset than standard gun drilling or BTA drilling. ...

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. ...

I choose between gun drilling, BTA, and ejector based on hole diameter, production volume, and surface finish requirements. Each process exploits a different chip evacuation mechanism, and that single design decision ripples through every performance metric — penetration rate, surface quality, tooling cost, and machine requirements. Gun drilling uses a V-shaped carbide tip with a single cutting edge and a high-pressure coolant port behind the cutting face. BTA drilling pushes coolant through the annulus between the drill tube and the hole wall; chips travel back through the tube’s hollow center. Ejector drilling splits coolant flow: most goes to the cutting zone, a smaller portion diverts through annular nozzles inside the head to create a Venturi effect that pulls chips back out. ...

How Ejector Coolant Flow Works: Inner and Outer Tube Before you can troubleshoot an ejector system, you have to understand how the coolant actually moves through the tool. I spent my first year working on ejector drills thinking the coolant flow was similar to BTA – and I paid for that assumption with scrapped parts and broken tooling. Ejector drilling uses a dual-tube system. The outer tube carries the drill head, and the inner tube runs concentrically inside it. Coolant enters the system at the outer annulus – the space between the inner and outer tubes. About two-thirds of the coolant flows forward to the drill head, where it exits through the clearance gap between the drill head and the bore wall. This forward flow lubricates the cutting edges and guide pads, and it carries chips back along the flute area into the outer tube annulus. ...