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 examine every broken gun drill to figure out what went wrong. A broken drill is not trash — it is evidence. The break pattern, the fracture surface, and the location of the break all tell you something about the cause. I have learned more about deep hole drilling from examining broken tools than from any textbook. Problem Description Gun drills break for many reasons, but the break itself is the end result of a chain of events. The drill does not snap spontaneously. Something causes the load to exceed the strength of the drill body. The break pattern preserves information about what that something was. ...
I select gun drill geometry based on the material I’m cutting. In my experience, the geometry is the single biggest factor determining whether a job runs smoothly or produces scrap. I have seen shops spend thousands on premium carbide drills only to get poor results because the geometry was wrong for the material. The geometry of a gun drill’s cutting tip determines how the drill performs. Different geometries are suited to different materials and applications. ...
Gun drills are precision tools that are surprisingly easy to damage. The long, slender shank and the exposed carbide tip are vulnerable to handling damage. I’ve seen good drills ruined by careless handling. Here’s how to prevent damage and what to inspect for. Common Damage Modes Bent shank. The most common damage. A gun drill that’s dropped or handled roughly has a bent shank. Even a slight bend causes runout. ...
The way you hold a gun drill determines the runout at the cutting tip. Runout affects hole diameter, straightness, surface finish, and tool life. I have used all three holding methods extensively and know the trade-offs. I choose the holding method based on the tolerance requirements and the number of diameter changes in the job. Here is my detailed comparison. Collet Holders Collets provide the most concentric holding of any method. A collet grips the drill shank evenly around its full circumference. Runout at the collet is typically 0.005-0.01mm if the collet is clean and the shank is ground accurately. ...
Regrinding a gun drill requires precision. The angles on the tip determine how the drill cuts, how chips form, and how the tool wears. Getting them wrong means poor hole quality and short tool life. Here is the procedure I use. When to Regrind I regrind a gun drill when any of these conditions are met: Surface finish degrades beyond spec Cutting forces increase noticeably (spindle load rises 20%+) Flank wear exceeds 0.2mm on the primary clearance Corner wear exceeds 0.1mm Chips change from short broken segments to long stringy ribbons For production work, I track holes per regrind and schedule regrinds at a fixed interval. For most steel applications, this is 150-250 holes per regrind depending on diameter and material. ...
I have been diagnosing gun drill breakages for over a decade now, and I can tell you one thing for certain: a broken gun drill is almost never a single-cause failure. It is a chain of events that lines up in the wrong order. But certain root causes show up again and again. Tool breakage is one of the most expensive problems in deep hole drilling. A single broken drill can mean a scrapped part, a stuck tool removal job, and days of downtime. Here are the ten most common causes I have seen, ranked by how often they show up in my shop. ...
How to Use This Card I designed this quick reference card to be posted on every machine in the shop. It covers the six most common gun drilling problems and their solutions. Each entry follows the same format: symptom, most likely cause, first action. Operators who use this card solve most problems without waiting for a setup technician or engineer. I’ve seen operators resolve coolant pressure issues in under two minutes by following the card instead of waiting 20 minutes for a technician to arrive. The card does not cover every possible problem, but it covers the 90% that happen regularly. ...
Hot runner manifolds are one of those jobs where the drilling itself is not the hard part. The hard part is making sure the holes meet where they are supposed to meet, and that the intersections are clean enough for plastic to flow through without hanging up. I have done my share of manifold drilling. If you are new to mold drilling in general, the injection mold components article covers the basics. This one is specifically about manifold channels and the techniques I use for deep hole drilling of hot runner manifolds. ...
Drilling a long shaft — say 1.5 meters of solid steel with a 10mm hole through the center — looks simple on paper. But it’s one of those jobs where the setup matters more than the cutting parameters. If you’re working on cylinder bores instead of solid shafts, I covered BTA drilling for hydraulic cylinders here. This one is about shafts. The shaft wants to whip. The drill wants to wander. Coolant has a long way to travel. Here’s how I deal with each. ...
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. ...