When turning 2mm-dia. and smaller parts on a Swiss-style machine, it only makes sense that the radius on the tool should be equally tiny. After all, you can’t cut a 0.5mm bone screw with a TNMG-431 insert—the tool’s nose radius is nearly as big as the part.
In addition, said Jim Gosselin, owner of Genevieve Swiss Industries Inc., Westfield, Mass., “some parts, such as in the RF (radio frequency)-connector industry, can’t have any radius at all. It messes up the component’s electrical properties.”
Without a radius, you’re probably thinking the tool will chip on the first workpiece. Think again. Microscale indexable-insert tools are designed to handle this sort of work. Gosselin explained: “We’ve gone to submicron-grade carbide on all our tools. That means the grain size is very small, so the tools are very tough—even with a dead-sharp radius. And the edges have to be very sharp, so everything is ground to size, and then we use a special process to remove the grinding burr, followed by a PVD coating for good wear resistance.”
Perhaps the most important geometry on a microtool is the wiper that’s ground on the tool tip. This wiper is a flat—perhaps 0.05 ” wide—on the trailing edge, with a clearance angle of 1° or less. “Depending on the material and part diameter, you can actually feed one of these tools at a couple thousandths of an inch per revolution, even with a zero radius,” Gosselin said. Great, the tool might last, but won’t the part have a surface finish no better than a corncob? No. “The trailing edge does more than support the tool tip. It also wipes off the mountaintops, providing a smooth finish,” he added.