Machinist Mike Conlon at Brooklyn, N.Y.’s Caliper Studio put three bits through an inch-thick bar of 304 stainless steel and into a polyurethane bowling ball. The bit with the fastest average time won.
Bosch: Bosch bits came through the back side of the bar in 1 minute, 11 seconds on average. The fastest trial was just 32.8 seconds. Burrowing the length of the bit into the ball took 3 seconds.
Irwin: Conlon averaged 1:44 boring through the steel. The ball holes took 4.5 seconds.
Milwaukee: The stainless bar lasted 1:24. Four seconds did the ball in.
Conlon sank each bit into the 304 steel repeatedly until the bit broke. He cleared the flutes between holes and lubricated the work with Tap Magic cutting fluid. The winner was the brand that drilled the most holes.
Bosch: Conlon broke one Bosch on its 12th hole—the record high. Other Bosch bits lasted into their third and fourth attempts.
Irwin: Irwin’s bits usually snapped on the second or third holes. One of them bit the dust, so to speak, on the first hole.
Milwaukee: Conlon pushed one Milwaukee into its eighth hole, but killed two on their second holes and a third on its third hole.
The Bottom Line:
Each bit devoured the resin ball. But against the stainless, the Bosch proved the quickest and most durable: One bore set the test’s record time, and a single bit punched a dozen holes. (We all own worn bits—save them for crude drywall or MDF cuts.)
How Bits Fail
Bent shafts, worn flutes and deformed tips signal dull bits, but the machinists at Caliper Studio seek more subtle clues of failure.
Shaving: “You want little fingernail shavings, not long curlicues,” machinist Josh Sledge says. To extend a bit’s life, back it out of the hole to let the flutes eject the cut material, aka swarf.
Shoving: Dull cutting flutes require more pressure to work.
Screaming: Bits change pitch as they dull. Shrieking, chattering or grinding signals a worn edge.
Smoking: The dullest bits emit a plume of smoke—a sign the front cutting spurs are ground to a nub.