The Skinny on Microdrilling - Cool Jet Systems - #1

JANUARY 2003 / VOLUME 55 / NUMBER 1 ► BY BILL KENNEDY, CONTRIBUTING EDITOR

The pursuit of productivity when applying microdrills (tools less than 0.125" diame­ter) may be as much creative as it is scientific. The charac­teristics of the drill itself, machining parameters, hole depth, setup integrity and workpiece composition play deli­cately intertwined roles.

"In some cases, all you're doing is guessing," said Mark Megal, market­ing manager, Guhring Inc., Brookfield, Wis.

Fortunately, tool manufacturers have developed microdrill materials and geometries that take application sub­stantially out of the realm of trial and error. Yet the task is not simple, and many factors must be considered and controlled to get the most out of these tiny tools.

As a drill gets longer, relative to its diameter, its tendency to bend in­creases. A low length-to-diameter ratio minimizes the deflecting forces that

break drills and produce crooked or mis-sized holes. Deeper holes mean higher length-to-diameter ratios. In general, hole depths three or more times drill diameter are considered "deep." But microdrills usually far ex­ceed those ratios.

For example, drilling a 1.25"-deep hole represents a length-to-diameter

ratio of 10:1 for a 0.125" drill. Even more extreme, drilling a 1"-deep hole represents a length-to-diameter ratio of 50:1 for a 0.020"-dia. drill.

Deflection becomes more of a prob­lem as drills grow smaller and more fragile, and the degree of fragility re­flects the trade-off between the sub­strate's hardness and toughness.