Drill, Ream or Bore: High-Speed Steel vs. Carbide Tooling

As your shop expands into high-precision machining, it might be time to swap out your HSS cutting tools for solid carbide drills, reamers and boring bars. Here’s why.

There is a place in the machine shop for high-speed steel jobber length drills and chucking reamers, but it’s probably not on any late-model CNC lathes and machining centers.

These cutting tools remain popular for their durability and low cost. Anyone interested in maximizing throughput, however, would be better served with tooling designed for modern machine cutting tools, not for screw machines, knee mills and chucker-style lathes invented before 1950, says Aaron Schade, program manager for Kennametal Inc.’s Knowledge Center Americas. 

That’s because HSS jobber drills wander. They have no coolant-through capabilities, which means loads of pecking and shortened tool life. They’re also at least four times slower than carbide drills.

HSS tools work well for hand-held applications, for prototype and repair work, and where hole quality is not critical. But using them on a relatively new CNC is akin to mounting cheap whitewall tires on a sports car.

The same goes for HSS reamers. Granted, you can feed the heck out of them, but they provide surface finishes and production rates far lower than their carbide counterparts.

Why a Move to Carbide Drills and Reamers Makes Sense

Why, then, aren’t more shops adopting carbide jobber length drills and reamers? The main reason, Schade says, is simple: Manufacturers all too often adopt a “This is the way we’ve always done it” mentality.

If something works, often there’s no impetus to make a change, even if one might make sense for both speed and product quality, he says.

“A job comes in, the people on the shop floor figure out how to produce it, and then they tend to leave it that way because, ‘Okay, we made it work. Time to move on to the next job,’ ” Schade says. “It’s easy to fall into this rut, which is why Kennametal spends so much time trying to get the word out on advances in tooling technology.”

Among these advances are solid carbide drills. At Kennametal, these include general-purpose GOdrill microdrill bits and high-performance SGL bits.

Both these series of cutting tools have diameters up to 20 millimeters (0.787 inches), coolant through the tools and other advances not found in HSS drills.

Depending on the workpiece material, toolholding method, rigidity of the equipment and so on, solid carbide drills might be expected to hold tolerances within a few thousandths of an inch, and surface finishes that eliminate the need for reaming or boring.

“It’s difficult to quantify accuracy expectations because every application is different,” says Joe Slusarcyk, a senior engineer with Kennametal’s Global Machining Technology group. “But given a good setup and minimal tool runout, hole quality of IT8 is certainly achievable with a solid carbide drill. So rather than say ‘it depends’ when asked what tolerance we can achieve, my suggestion is always to give it a try because you’ll probably be delighted with the results.”

Beyond this size range are modular, replaceable tip drills such as Kennametal’s KenTIP FS bits, available in diameters from 6 to 26 millimeters (0.236 to 1.023 inches) and depths up to 12xD. Although hole accuracy with modular drills might be less than that possible with solid carbide tools, it’s still superior to what can be crafted using an HSS drill, at a price point that most shops can handle.

Perhaps more important, the higher performance of these tools and the ability to quickly swap heads make a strong argument for shelving HSS jobbers, silver and deming, and taper-shank drills.
 

What Carbide Delivers for Reaming and Boring

So where does that leave reaming? And what about the other verb in this article’s title: boring? If a job requires a higher hole quality than a carbide drill can produce, a solid carbide reamer might be the next logical step.

“For the most part, people making holes are concerned with diameter followed by surface finish, and reamers do a great job in both respects,” Schade says. “If you’re looking for a higher level of cylindricity, straightness and positioning, boring is a better option, but at the expense of longer cycle times.”

Keith Hoover, a lead applications engineer at Kennametal, agrees. “A reamer is a multi-flute hole-finishing tool, which typically means a productivity improvement four to 10 times that of boring, depending on the number of flutes,” he says. “The flip side to this argument is that a boring tool provides greater flexibility in size control and can cut multiple diameters. Reamers can do this as well, but it requires a custom, multistep tool.”

Carbide tools rule here as well. Kennametal and other tooling makers offer all manner of solid carbide reamer geometries—many with coolant through—so there’s simply no reason to sacrifice cycle time to save a few dollars.

For larger diameters, a range of modular options are also available, including Kennametal’s RHR disc-style reamers.

In those instances where boring is needed, all three experts suggest that shops look at one of the company’s DeVibrator tunable boring bars. The line boasts replaceable boring heads, coolant through and the ability to dampen vibration at lift-to-drag ratios of up to 14xD.

Don’t let the chips fly where they may. Instead, read our “8 Vital Tips to Improve Chip Control When Drilling.”

Critical Role of Toolholders in Drilling, Reaming and Boring

Despite the many advantages of modern drills, reamers and boring tools, Hoover cautions that they might not be for everyone.

“If you’re running one of our drills in an ER collet or Weldon shank toolholder, you’re less likely to see the tool life or hole quality that you would with a hydraulic chuck,” he says. “A similar situation exists with reaming tools, which is why a floating holder or steerable hydraulic chuck might be needed to reduce runout as much as possible.”

The machine setup, the toolholders and the adapters must be of equal caliber to the extremely high-performance carbide drilling and reaming products that manufacturers are producing today, Slusarcyk says.

“If those tools aren’t being put into high-performance adapters, the machine is worn out or the setup less than rigid, then they’re never going to achieve the benefits that they otherwise would,” he says. “That said, even a general-purpose carbide will outperform HSS in virtually all CNC applications, regardless of the holder.”