Wear or When: Drilling Performance

END USER: Windings Inc., (800) 795-8533, www.windings.com
SOLUTION PROVIDER: West Ohio Tool Co., (937) 842-6688, www.westohiotool.com
CHALLENGE: Extend tool life when drilling a high-silica part.
SOLUTION: A solid, cross-center PCD-tipped drill.

Windings Inc., New Ulm, Minn., specializes in manufacturing motors and stators—the stationary parts of electric motors—but ran into a challenge after it was contracted to build some custom stators for a transportation application.

Each stator was part of a linear motor to be used for propulsion and measured 3′ (914.4mm) long, 2′ (609.6mm) in diameter and about 4″ (101.6mm) thick. They contained copper coil protected by a thick layer of epoxy resin with a high silica content. Eight holes, roughly 0.6″ (15mm) in diameter, were drilled through the resin, into the stator. And here, according to Director of Operations Seth Visser, was where the challenge came in.

A solid, cross-center PCD-tipped drill, on which both cutting edges and the drill tip are made from a single piece of PCD. Image courtesy West Ohio Tool.

Windings successfully drilled holes into the high-silica resin that covered each stator. Image courtesy Windings.

The high silica content in the resin made it extraordinarily abrasive, Visser said. “So abrasive that the first drills we tried, solid HSS, burnt up in the first quarter-inch of drilling.” Windings then tried solid-carbide drills—first without and then with a PCD coating. An uncoated carbide drill would be able to make two or three holes before losing its edges and needing to be reground. The diamond-coated drills didn’t fare much better against the resin, lasting only a few holes before losing their cutting edges.

The expense of PCD-coated drills, machining costs and time lost to frequently retool made for a prohibitively high cost per hole. Visser needed a tool that—at a minimum—could last eight holes.