It’s a simple fact: if you’re a machinist, you make holes. Lots of them. Unfortunately, drilling is also one of the operations most likely to turn machinists prematurely grey. Poor chip evacuation, heat buildup and drill runout are just a few of the problems common to would-be holemakers.
Drilling gets even more challenging when venturing into hole sizes smaller than 3 mm. Toolmakers classify drills in this region as microdrills, tools capable of punching holes the size of a fat pencil lead, to ones smaller than the period at the end of this sentence. “With some of these drills, you only have to look at them wrong and they’ll break,” says Nika Alex, drilling product specialist at Mitsubishi Materials U.S.A. “Microdrills are very, very sensitive.”
Alex knows drills. The California-based toolmaker offers some of the smallest microdrills around, with solid carbide drills down to 0.1 mm, and coolant-fed versions to 0.5 mm. He recommends 1000 psi coolant pressure or higher for tools this small, using a very low viscosity coolant. “At these diameters, the right cutting fluid is critical. If it’s not possible to run water-based coolant, some of the newer synthetic oils are so light they’re almost like water. Those work fine with our drills.”
In the microdrill world, shanks measure either 3 mm or 1/8 in., depending on which side of the US/Canada border you live. This makes toolholding a relatively straightforward affair. It’s a good thing, too—it’s tough enough drilling a hole the size of a human hair, let alone gripping a shank that small. That doesn’t mean, however, that any old drill chuck will do.
“Runout is everything at this scale,” explains Alex. “Smart shops go with hydraulic holders, or even shrink fit. You have to aim for zero runout.” Mike Hafke, vice president of sales for Guhring Inc., agrees. “It’s an important consideration, to be sure. Optimum results come from toolholders specifically designed for these high performance micro drills.”