Once you find a tool you trust, you’re may be tempted to use it for the next job, … and the next and the next, … just because it’s handy and you know what it can do. It’s like comfort food – warm in the tummy but not necessarily healthy. But, like watching your diet, it’s smarter to take a fresh look at each new job and find a new best practice.

Zack Hilton took that approach when it came time to mill a deep slot in a hardened part at River City Manufacturing and Machine Company (RCMM), in Winona, Minn. He’d had great success on a variety of milling jobs with an Ingersoll Hi-PosQuad indexable end mill, and pretty much made it his ‘go-to’ milling cutter in the busy, 20-man job shop that runs 20/5. Most of River City’s jobs are repeat orders in small lots for tools, molds, and various engine and machine parts.

When he tried out his mainstay cutter on the slot, Zack immediately recognized that there had to be a better way. The principle problem was early, unpredictable edge rupture, which he knew would cause a bottleneck in production for a part with good re-order potential. He could foresee having to stop and change inserts midway through the cut, leaving track marks on a surface with a very tight finish requirement. “Better to solve it at the outset and look beyond the familiar than settle for so-so efficiency,” he reasoned.

The specific job under consideration involved finish-milling a long, very deep slot in S-7 tool steel hardened to Rc 54-56. The purpose is to correct for any heat-treat distortion. It involves removing 0.020 inches from both sides, to +0.002/-0.000 inch, with a mirror finish. The finished part goes into a slide mechanism of a machine that fabricates chains. The 12-inch slot is nearly twice as deep as wide: 4.322 inches deep and 2.724 inches wide.

Fortunately, the Hi-PosQuad was part of an Ingersoll “Top-On” modular tool family, so changing tools was simply a matter of screwing a different tip onto the existing five-inch threaded solid carbide shank. Then, the question became which of more than 50 tip styles available would be the best answer for this job.

Zack consulted immediately with Ondrej Lubinski, the Ingersoll field rep who walks the River City floor almost weekly. Their analysis: long-reach finish-milling job in hardened stock, to extremely close tolerances on both sides and the bottom. Because of the long reach, there’s always the risk that lateral cutting forces on the end of a long extension may cause chatter and excessive impact loads, leading to fracture on the brittle insert – or the shank itself.