HOLE IN ONE

The name says it all: Hole Specialists, Inc. Company president Larry Robinson is equally succinct: "We take the things people send us and we either put a hole in them or we make their holes better, then we send them back. That's our business."

That humble introduction does not reflect that these holes are in mission-critical parts in Bell helicopters, B-1 bombers, firearms, space shuttles and medical implants. Customers of Hole Specialists (Tomball, TX) represent a diverse group that includes automotive, plastics, chemicals, shipping and food. Located near Houston, the company naturally does considerable work in the oil industry on drilling and extraction tools. Every one of these customers needs holes: deep, round, straight, sized and finished with extremely precise tolerances, or in the case of oil drilling, with the API-specified drift diameter so that a "down hole" tool can descend thousands of feet without getting stuck.

This one-stop drill, bore and hone shop works with major manufacturers such as Halliburton, Schlumberger, Baker, Dresser and many of their suppliers who make parts and tools for them. According to Robinson, "We produce the gamut of things that require a hole: hydraulic blocks, oil rig control blocks and parts so big that a six ft tall man can walk through them. We can do light honing or take inches of stock out, as the need requires."

The shop employs about 40 people and is one of an elite few plants that is capable of drilling holes to depths 200-600+ times the diameter, with diameters ranging from 0.078 in to 5.5 in. "A 0.218 in hole to 135 in depth is well within our capability, while 20 times depth would be considered good in most shops," say Robinson.

In his 35,000 sq ft facility, Robinson may be proudest of one of his custom-built gun-drills or "Larry's" as they are affectionately known. He says it is the world's largest gun-drill, a Texas-size claim he backs up with impressive numbers. This 157,000 lb hogzilla handles 50,000 lb parts and can drill holes for a 79 in bolt circle with diameters up to 4.5 in without moving the part.

What really sets this company apart is its one-stop capability to drill and then precisely size, straighten and finish exceptionally long bores. To do this, it relies on one of its eleven Sunnen honing machines. Its latest acquisition is a second 25 ft GH-210 tube hone equipped with a 25 hp spindle that gives the machine the punch to run double- and triple-length hone heads in diameters up to 18 in. "We have the ability to take a 40 ft part with a one-inch hole and hone it up to 18 in if we need to," explains Robinson. "With a 25 ft stroke on our machines, we'll do lengths up to 50 ft, working from both ends."

Depending on the parts, diameter tolerances may be as small as 0.0002 in. Finishes of 4 µin to 6 µin are typical, which Robinson measures by profilometer. Exact crosshatch angles ensure correct sliding/sealing surfaces between "down hole" parts, such as liner hangers, rotors and stators. "Our tool inventory, which would probably cost $2 million to replace, has some very rare honing heads," he adds. Because of the wide range of honing requirements ? from roughing drill tubes to finishing a surface ? the shop employs all types of abrasives, including aluminum oxide, silicone carbide, superabrasives, and diamond.

Materials include Hastelloy, Inconel, Super 13 Cr, high-nickel alloys, stainless, 4140, plastics, ceramics, hard-chromed parts, 4340 and similar high-alloy steels, because oil-field parts are frequently exposed to corrosive materials, wear, extremes of temperature, pressure, and vibration.

Offshore drilling equipment is a core part of this business ? boring, drilling and honing parts for the drill string, an assembly of drilling or extraction tools running from the surface to the hole bottom. Much of the work involves precise tubes, liners, pup joints, thrust nipples, control blocks, liner hangers, mud pump liners, chamber housings and firing pin liners.

Drill string tools, including rotors, stators, battery-powered telemetry units, and hydraulic tools that drive the drill bit must pass through this series of tubes and liners. "Up hole" mud pumps, with their own critical bores, move drilling mud and broken rock away from the bit toward the surface.

Parts may need to pass freely through one another, or a sliding seal surface may be needed for pump and motor parts. Liner hangers, for example, typically require an 8 µin to 16 µin finish, with a 45 deg to 48 deg crosshatch angle, creating oil retention grooves to facilitate the suction from a piston.

Tolerance is critical when it comes to diameter and straightness to avoid a "stuck tool" thousands of feet down. If a bore bows only 0.005 in, a part moving inside might come to a dead stop. In sub-sea drilling, the problem can also occur because drill pipe from the surface isn't always perfectly vertical. A 43 in long component, for example, may need to pass through a pipe sloping through a 90 deg bend. To avoid problems, API requires pipe and cylindrical tools to be certified for their drift diameter.

The longer the part, the greater the potential for drift error. A 42 ft pipe, for example, with an 8 in OD and wall thickness of 0.7 in requires straightness to 0.003 in on all sides for the entire length. The industry rule of thumb says deviation cannot exceed half the maximum of the difference between the diameter and the drift gage.

Determining straightness can involve both art and science depending on the part being honed. This shop employs ultrasound through the pipe wall to determine internal concentricity, end to end. "We can tell if it's getting off-center, in which case we move or rotate the part on the hone to straighten it out," notes Robinson. To ensure precise diameter the company uses dial bore gages, checking at least six different angles on a 24 in liner, but that approach is not practical on the longest parts. "Unfortunately, no one makes a 50 ft bore gage," quips Robinson. Final inspection for cylindricity and roundness, especially on long tubes, often involves physically sliding a drift gage through the entire length to make sure it clears.

Hole Specialists' versatility is important to its customers, and its reputation for responsiveness in a "rig down" emergency keeps them coming back. Downtime costs for crews, specialized equipment and R&D investment run into hundreds of thousands of dollars per day, and if a spare part isn't readily available, the rig operator may face 16 weeks or more to make a new part. "We're in a service business and sometimes customers come to you in the middle of the night with a '9-1-1' problem," explains Robinson. "So we hustle into the shop to make it happen."

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Bob Davis is the global communications manager for Sunnen Products Company, 7910 Manchester Avenue, St. Louis, MO 63143. For more information, Bob can be reached at 314-781-2100 or bdavis@sunnen.com.