In-depth reliability: Drilling Performance

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END USER: Machine Tech CNC, (780) 461-0890. CHALLENGE: Accurately bore 14 diameters deep and deeper. SOLUTION: Carbide-reinforced boring bars with built-in vibration damping. SOLUTION PROVER: Sandvik Coromant Co., (800) SANDVIK, www.sandvik.coromant.com/us

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Machine Tech CNC, Edmonton, Alberta, machines downhole-well-equipment parts for the oil and gas industry. They include components for multistage hydraulic fracturing equipment, directional drilling motors and hydro- mechanical jar assemblies to free jammed drill strings. Workpiece materials range from chromium-molybdenum steels to 13 chrome stainless and high-strength 4330-V steels. Production volumes extend from single parts to more than 500 pieces, and lead times vary from 1 to 2 days to 2 months.

Many of the components are long cylinders with bored IDs. According to Machine Tech President Bob Johnston, bores can be as long as 48 ” with diameters typically from 3 ” to 5 “.

The large length-to-diameter ratios are challenging to machine. The shop employed a 4 “-dia. bar with damping features but it was reliable only to a 10:1 ratio. “With a 4 “-dia. bar, you could only bore about 38 ” deep and then try and back bore from the other side,” Johnston said. “You have to maintain the tolerances on length, and it becomes very critical.” And for bores smaller than 4¼ ” in diameter, the company couldn’t do many of them. “There was no room for the bar to fit,” he said.

To improve boring, the shop sought assistance from Jim Cordoviz, Alberta team leader for Sandvik Coromant Co. He suggested applying the Fair Lawn, N.J., company’s 80mm-dia. (3.149 “) Silent Tools carbide-reinforced boring bars tooled with CoroTurn SL quick-change cutting heads. A Silent Tools boring bar contains a heavy tuning body suspended between two rubber bushes; inertia of the body absorbs vibration generated in the cutting process. The damping is factory-set and requires no adjustment. “There are no tuning screws,” Cordoviz said. “I call it a plug-and-play tool.”

The bar’s carbide reinforcement reportedly makes a smaller-diameter bar more rigid than a larger-diameter tool. Johnston noted that, in most cases, the bar eliminates the need to machine a long bore from both ends. “While a 4 “-dia., 10:1 bar extends 40 “, a 14:1 Silent Tools 80mm-dia. bar extends 42 “,” he said.

The extra length enables most bores to be a machined from one end. “It makes a huge difference,” Johnston said. “We actually exceed the guaranteed capacity of the bar, run them out to 48 “, and they don’t vibrate.”