Difficult-Materials

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: ...

Inconel 718 is a nickel-based superalloy used in aerospace and power generation components. It retains its strength at high temperatures but is extremely difficult to machine. The material work-hardens rapidly and retains heat at the cutting edge. I have drilled hundreds of holes in Inconel 718 across multiple jobs. Every one was a battle against heat, work-hardening, and tool wear. Here is what works for me. Cutting Parameters for Inconel 718 The cutting speed is the single most critical parameter. Above 25 m/min, the edge degrades rapidly from heat. Below 15 m/min, the tool rubs instead of cutting and work-hardens the surface. I start at 20 m/min and adjust based on tool life. ...

Titanium is the material that separates experienced deep hole drilling shops from the rest. I have drilled more titanium holes than I can count — here is what I have learned about making them consistently. Every titanium alloy behaves differently. Get the parameters wrong on one alloy and you lose the tool, the part, or both. Get them right across the board and titanium becomes predictable. I cover the broader aerospace deep hole drilling landscape in another article. This one is specifically about titanium parameters, tool life, and coolant — the three things that matter most when the material is titanium. ...

I started drilling additively manufactured metal parts expecting them to be harder than wrought. The porous, layered structure looked like it would eat tools. The data surprised me. AM metals — specifically laser powder bed fusion Inconel 718 — machine differently than wrought. Tool wear is lower, cutting forces are lower, and the wear mechanism shifts from adhesive to abrasive. Understanding these differences changes how you set up parameters and select tooling. ...

I use the slowest speeds and highest coolant pressures for cobalt chrome drilling — and I still expect to change tools frequently. Cobalt chrome and other superalloys are among the most difficult materials to deep hole drill. They are hard, abrasive, and retain heat at the cutting edge because their thermal conductivity is a fraction of steel’s. I have broken more gun drills in cobalt chrome than in everything else combined, and every break taught me something about what this material demands. ...

Difficult materials need different parameters than standard steel. I have drilled all three of these materials extensively. Each one presents unique problems that require specific solutions. The common thread across all difficult materials is heat management and work-hardening. Here is my detailed approach for stainless steel, titanium, and Inconel. Material Difficulty Rating Before I get into the specifics, I want to lay out a difficulty framework. Not all difficult materials are equally hard to drill, and the ranking matters for quoting and tooling decisions. I rate materials on a 1-10 scale based on tool wear rate, achievable penetration rate, and coolant pressure requirements. ...

Deep Hole Drilling Hardened Steels (HRC 40+): Parameters and Tooling That Work Hardened steels are a different animal. I learned this the hard way — watching a brand-new carbide gun drill snap on the third hole because I treated the material like it was standard 4140. After a lot of scrap parts, broken tools, and late-night spindle-side debugging, I landed on a set of parameters and tooling choices that turn hardened steel deep-hole drilling from a gamble into a repeatable process. Here is what actually works on the floor. ...

Why Stainless Steel Is Different Stainless steel is the material that causes the most tool breakage in my experience — not because it’s the hardest, but because it work-hardens and grabs the tool if you hesitate. I’ve watched operators who can drill aluminum all day snap a carbide gun drill inside the first inch of 304. It’s not a material you muscle through. Over the years I’ve drilled thousands of holes in three stainless grades: 304, 316, and 17-4 PH. They look similar on paper but behave completely differently under the cutting edge. This article is what I wish someone had told me before I broke my first $400 tool. ...