Process Deep Dives

Over the years I have been asked the same questions repeatedly by new operators, engineers, and shop managers. Here are the answers, with links to detailed articles for each topic. 1. What qualifies as a deep hole? A hole is considered deep when the depth-to-diameter ratio (L/D) exceeds 10:1. Below that, standard twist drills can handle the job. Above 10:1, you need specialized tooling and coolant systems. Full article: Deep Hole Drilling vs Conventional Drilling ...

Carbide is the standard for gun drilling, but it is not always the best choice. In specific applications — high-silicon aluminum, hardened steels, and abrasive composites — PCD and CBN gun drills can outlast carbide by 10-50x. The catch is that these tools are expensive, brittle, and require a rigid setup. Here is what I have learned about when they work and when they do not. What PCD and CBN Are PCD (polycrystalline diamond) and CBN (cubic boron nitride) are superhard materials. PCD is the second-hardest known material after natural diamond. CBN is the second-hardest after PCD. ...

Hastelloy, Stellite, Monel, and Waspaloy are not as common as Inconel 718, but when a job comes in requiring one of them, the parameters that work for standard steel will not work at all. These materials combine work-hardening, abrasiveness, and low thermal conductivity in ways that punish mistakes. Here is what I have learned about drilling each one. Common Characteristics of Exotic Alloys All four of these materials share properties that make deep hole drilling difficult: ...

I get more questions about drilling small holes in Inconel 718 than almost any other topic. A recent Practical Machinist thread about drilling 3mm holes 160mm deep in Inconel 718 at HRC 40-45 got over 3,500 views. The user was struggling with drill breakage, centerline deviation, and surface finish. The root cause in that thread was the same one I see most often: coolant pressure at 8 bar (116 psi) when the job needs 100 bar or more. Here is what I have learned about getting this application right. ...

The paperwork side of deep hole drilling has grown significantly over the years. Customers who used to accept a simple dimensional report now require material certifications, process validation, and full inspection data for every batch. I have adapted my documentation system to meet these requirements without slowing down production. Here is what I document and how. What Customers Typically Require The level of documentation depends on the industry and application. Here is what I see most often: ...

I used to think chip breaking was entirely about feed rate. If the chips were too long, I increased the feed until they broke. That works up to a point, but the drill’s chip breaker geometry sets the baseline for what feed rate will work. Understanding chip breaker geometry helps you choose the right drill for the material and know whether a regrind is maintaining the correct geometry. What a Chip Breaker Does A chip breaker is a groove or step ground into the rake face of the gun drill tip, just behind the cutting edge. As the chip slides across the rake face, it hits the chip breaker and curls. The curl creates bending stress in the chip, and when that stress exceeds the material’s fracture limit, the chip breaks. ...

A gun drill specification sheet can look intimidating the first time you see one. There are diameters, angles, lengths, and tolerances — and each number affects how the drill performs. I have ordered hundreds of gun drills. Here is how I read a spec sheet. Tip Diameter: The Number That Determines Hole Size The tip diameter is the most important number on the sheet. It determines the finished hole size. But the tip diameter is not exactly the hole size — there is an oversize allowance built in. ...

I have run gun drilling with both oil-based and water-based coolants across hundreds of jobs. The choice between them is not about which is better in general — it is about what matters more for your specific work: tool life and finish, or cost and cleanliness. Here is what I have found. The Core Difference: Lubrication vs Cooling Oil lubricates. Water cools. That simple distinction drives every other difference. A gun drill cutting edge needs lubrication to reduce friction between the tool and the workpiece. Oil does this naturally. Water-based coolants need chemical additives to approach the same level of lubricity. ...

Chip removal systems automatically move chips away from the machine and into a collection bin. Without a chip removal system, the operator spends hours each shift shoveling wet, heavy chips from the coolant tank. An automated chip conveyor is one of the best investments I have made for production efficiency. Auger Systems: Simple and Reliable Auger systems use a helical screw rotating in a steel trough to move chips horizontally or at a slight incline. The auger is simple, reliable, and inexpensive. It has one moving part, which means little can go wrong. ...

A manual lathe can be converted for gun drilling with the right equipment. The conversion costs a fraction of a dedicated machine but comes with real limitations. I’ve done this conversion on a 14-inch Colchester lathe and gotten usable results. The main requirements are a through-coolant toolholder, a high-pressure coolant system, and a guide bushing support. The toolholder mounts on the lathe carriage and holds the gun drill. The coolant system delivers fluid through the tool at the required pressure. The guide bushing supports the drill at the workpiece entry. ...