A Salute to Three-Flute

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Kip Hanson

For the right job, the latest generation of solid carbide three-flute drills are unbeatable

Due to their smaller flutes and limited chip space, three-flute drills might be considered niche cutting tools, good for nothing more than coring out cast or pre-drilled holes in soft, short-chipping materials like gray cast iron. And while some of this statement has merit, the fact remains that, for the right job, these specialty tools can punch holes like there’s no tomorrow.  

World class
“These things really fly,” says Paul Larson, product manager for drills and thread mills at Guhring Inc. in Brookfield, Wisc. “When drilling a 12 mm (0.50 in.) diameter hole in a wrought aluminum alloy, for example, you’re looking at cutting speeds of 450 to 600 SFM and a feedrate of 0.3 mm/rev (0.012 ipr) or greater. You can also expect a hole that’s nice and straight, with a reamer-class finish besides.”

This close-up of Guhring’s GS200 solid carbide three-flute drill point illustrates its robust design.   Image: GuhringLarson is quick to point out that the company’s GS200 series three-flute carbide drills machine much more than aluminum. They’re also quite effective in low carbon and alloy steels, as well as the cast iron mentioned earlier. This makes them a favourite of automakers, heavy equipment manufacturers, and producers of heat exchangers or hydraulic manifolds, where the tool’s ability to resist deflection when encountering cross-holes and angled surfaces means greater hole accuracy, improved tool life, and up to 50 per cent higher throughput. 

“The drill’s three margins help to keep it centred and eliminate the wandering you might get with a two-flute,” says Larson. “That said, they do require slightly more Z-axis thrust, and it’s especially important to run them at the correct speeds and feeds if you’re to generate the correct chip form and ensure good evacuation.” 

Material condition, setup rigidity, tool runout, and machine maintenance all play a huge factor when drilling holes. Image: IngersollDouble the tool life
Tim McKnight seconds those views. A product manager at Ingersoll Cutting Tools in Rockford, Ill., part of the IMC Group, McKnight says Ingersoll’s SolidDrill3 delivered double the tool life and productivity when drilling GG25/40 cast iron cylinder blocks at an automotive customer. 

In this particular application, the manufacturer applied MQL (minimum quantity lubrication), although McKnight suggests that high-pressure coolant might have improved these results even further. “Coolant pressure is a huge factor in drill life and performance,” he says. 

Here again, this was a short chipping material, which McKnight agrees is where three-flute drills work best. He also notes that the manufacturer paid special attention to holding the drill—as he points out on Ingersoll’s Machining App calculator, a three-flute drill’s power and torque requirements are roughly half again that of their two-flute cousins. “We haven’t heard any complaints of the drill spinning or pulling out of the holder, but in the application just mentioned, we used a thermal shrink chuck to eliminate that possibility.”

Though dubbed the AlumaDrill, Fullerton’s three-flute tool can be used in a variety of materials, including titanium. Image: Fullerton ToolFast and nimble
Steven Oszust Jr., the product development manager and lead tool design engineer at Saginaw, Mich.-based Fullerton Tool Co., is a big fan of three-fluted drills and disagrees with the “core drill only” reputation they’ve earned over the years. “Speaking for our AlumaDrill, at least, they’re the exact opposite,” he says. “Where I consider a traditional core drill as more of a workhorse that powers through at relatively low speeds and is used to prepare the hole for a subsequent operation, the 1565 AlumaDrill is almost nimble, with a lighter construction, deeper gullets, and lots of room for chip flow.”

Oszust also disagrees with the “short chipping” limitation of some three-flute drills. As its name implies, the AlumaDrill’s original intent was for holemaking in aluminum components. Yet Fullerton also recommends the tool for plastic, composites, yellow metals such as brass and copper, and even titanium, the last of which is notorious for its toughness and long, stringy chips.

“We offer many iterations of the drill, including stock standards, engineered specials, multi-step combinations, and coolant-thru tools, so the name AlumaDrill is a bit of a misnomer,” says Oszust. “For instance, we apply a special coating for titanium applications, but it’s essentially the same tool. We’ve also found it quite effective in mild steel. The tool is designed for relatively light chip loads and higher cutting speeds, which together with the drill point’s double chisel angle and high rake, tends to generate a light, whispy chip that evacuates easily.”

Like his counterparts at Guhring, Ingersoll, and other cutting tool manufacturers, Oszust says three-flute drills produce smoother, rounder, and straighter holes than do two-flute drills. He also reinforces what was said earlier about using the supplier’s feed and speed recommendations, advice that customers should follow for any machining operation. Says Oszust, “About the only materials we steer clear of with these drills are hardened steels and some of the newer metals you’re seeing used in the automotive industry, like CGI (compacted graphite iron). Three-flute drills have their place, but it’s important to remember that there are many other very effective holemaking solutions out there.” SMT

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