Breaking Through to Stable Large-Hole Drilling

Stability problems can be a headache for manufacturers tasked with drilling deep, large-diameter through-holes in hardened materials, but Seco Tools (Troy, Michigan) claims it has a remedy. The new Drill SD609 modular drilling head incorporates a three-contact-point design to overcome challenges with balance, runout, chip evacuation and positioning, especially at the break-through point. Notable features include an adjustable pilot drill, indexable inserts and multiple carbide guide pads shimmed close to the cutting diameter.

While emphasizing that the tool can be applied to any large through-hole, the company says the issues outlined above are particularly common in the machining of fluid ends—large vessels that help release gas during high-pressure hydraulic fracturing (“fracking”) operations. These components are typically machined from solid 4340 and P20 steel billets that range in hardness from 32 to 42 HRc. The Drill SD609 comes into play during the rough-machining stage, part of which involves drilling through-holes as large as 5 inches in diameter and 57 inches deep by penetrating nearly 30 inches of material on either side of the part. Given that these long through-holes involve substantial metal-removal rates and require keeping the tool in the cut for as long as 40 minutes, stability is a must.

Nonetheless, Seco says many fluid end manufacturers struggle to maintain machining balance and achieve 100-percent even cutting forces when breaking through the hardened steel billets. According to the company, the problem with conventional drilling heads is that one portion of the head’s pilot drill breaks through the bottom of the hole before the rest of the tool. This reduces stability and creates the risk of the drill head trending sideways in the cut. In contrast, the Drill SD609’s periphery insert and two guide pads provide three points of contact with the interior of the hole. The pads are positioned below the periphery insert’s cutting diameter to keep the head from deflecting. This design is said to help maintain position when the pilot drill begins breaking through the hole bottom.

Seco also offers a long-reach, fluted holder to complement the Drill SD609. To help maintain stability, the holder’s diameter is close to the size of the finished hole. Constructed of high-tensile tool steel with chrome plating, the holder features a custom flute design that is said to reduce machining time and production costs by effectively removing chips.

Seco recommends applying at least 1,000 psi coolant at 12 gpm to ensure chip control when using the Drill SD609.