Back in the mid-1980s, tired of fighting with the guys in my tooling department over the shop’s meager supply of boring heads, I decided to buy my own. The head came from China, and the salesman assured me it was every bit as good as his U.S. brand, at half the price.

Difficult-to-machine workpieces usually represent “an inconvenient truth.” As material developers improve a metal’s strength and resistance to heat and wear, while often reducing its weight, its machinability declines. Enhancements to alloys such as austenitic stainless steel, titanium and high-temperature superalloys generate an ever-increasing laundry list of machining problems, including built-up edge, chatter, workhardening and excessive tool wear. They make it difficult to impart acceptable surface finishes when micro-endmilling.

Three critical factors must be controlled when holding cutting tools in the spindle for micromachining: runout, runout and runout.

“For very small tools, the amount of runout dramatically affects tool life,” said Alan Miller, engineering manager for BIG Kaiser Precision Tooling Inc. “As tools get smaller, the acceptable amount of runout goes down with them.”

While they are specialty tools, dovetail-style cutters have a broad range of applications. Dovetails are typically used to cut O-ring grooves in fluid and pressure devices, industrial slides and detailed undercutting work. Dovetail cutters have a trapezoidal shape—like the shape of a dove’s tail. General purpose dovetails are used to undercut or deburr features in a workpiece. O-ring dovetail cutters are held to specific standards to cut a groove that is wider at the bottom than the top. This trapezoidal groove shape is designed to hold the O-ring and keep it from being displaced.