ASK THE EXPERT: High-speed steel is definitely not speedy

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HSS end mills typically have Weldon shanks, leading to tool-life-killing, chatter-inducing imbalance. Solid carbide tools (as shown here) don't have that problem and also offer greater choice. PHOTO courtesy Kennametal.

What if someone told you that 400% productivity increases are possible with a 37% increase in tool cost? Would that perk your interest?

I’ve written several hundred magazine articles about cutting tools over the past 14 years or so, but with the exception of the drills, taps, and hole saws purchased for home repair, it’s been a while since I last bought one. So I looked up the price of a 1/2” four-flute, square-end, high-speed steel (HSS) end mill on a well-known tooling supplier’s website. The price? $26.26 each (USD). Its solid carbide counterpart from the same manufacturer was a bit higher at $35.98. 

Spend a few bucks more for one with AlTiN, TiN, or competing high-performance coating and you can expect the four-fold increases mentioned a moment ago to jump substantially, never mind the better tool life, improved process security, and reduced downtime. 

Here are a few other considerations in the ongoing HSS vs. carbide battle. HSS end mills typically have Weldon shanks (dare I say always), leading to tool-life-killing, chatter-inducing imbalance. As Emuge-Franken milling product manager Dan Doiron noted in a 2023 article, side-lock shanks might rock at clamping force, but basically suck at everything else. Not so with solid carbide, although you will need to invest in far more expensive toolholders to grip them properly. 

Carbide also offers greater choice. That particular cutting tool manufacturer lists 18 such HSS end mills, compared to 48 in solid carbide. Remove the brand filter and it’s HSS at 128 options vs. 929 for carbide. See where the market is headed?

Much of this disparity is due to giants like Kennametal, Iscar, and Sandvik Coromant no longer carrying HSS tooling of any kind. The sole exception are taps, which for a variety of reasons perform better when made of HSS or powdered metal. Spend a few minutes catalog cruising and prove me wrong. 

I know. Machinists who spend their days in front of a knee mill or engine lathe will argue that carbide is more prone to chipping. It can also be difficult to achieve carbide’s higher cutting speeds on manual machinery. And with larger tools, say one-inch and above, carbide’s higher cost can be prohibitive for all but long-running jobs, especially for hobbyists and startup shops. 

And yet, how many CNC lathe turrets and machining center carousels are still sporting cutting tools that were sliding into obsolescence when I first set foot in the machine shop more than 45 years ago? Judging by the countless discussions I’ve had with sales and applications people from the companies listed on the website described earlier, my guess is that it’s still far too many.

You might not see it yet, but the manufacturing world is changing. Between ongoing reshoring efforts and chronic skilled labor shortages, the industry overall is embracing automation like never before. Doing so not only increases throughput, but opens the door to lights-out manufacturing, and for that, stable, predictable processes are crucial. 

So with a few notable exceptions, forget HSS. It has no place in today’s CNC machine shop, and those of us still concerned over carbide’s higher tooling costs will eventually find they don’t need to buy any cutting tools at all.

Kip Hanson

TECHNICAL EDITOR KIP HANSON has more than 40 years experience in the manufacturing industry. He is the author of Machining for Dummies and Fabricating for Dummies and has written over 1500 articles on a diverse range of metal manufacturing topics.

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