Marine transmissions demand truly seaworthy machining.



Twin Disc, a family-owned manufacturer of marine propulsion systems, has been in business for 75-plus years, making more than 30 different marine transmissions in a variety of configurations ranging from 25rpm to 3600rpm. The transmissions can be found in crafts from luxurious pleasure craft to stealthy military vessels to hard-working tugs, pushboats, heavy-duty fishing boats, ocean-going shrimp boats, and crew boats. The Racine, WI, company even has ties to turning points in American history. Allied forces depended on Twin Disc marine transmissions to drive some 40,000 landing craft loaded with troops and supplies onto beaches during the Normandy invasion and throughout the South Pacific during World War II.

Today, Twin Disc marine products can be found propelling all kinds of vessels, on all kinds of water, all around the world.

But that's not all. Twin Disc also makes transmissions for over-the-road heavy duty trucks (Freightliner, for example), trucks for the mining industry (think Volvo and Terex), and for the Bradley fighting vehicle, and tank-retrieval vehicles like the one that pulled down the statue of Saddam Hussein in Iraq all of which suggests these transmissions are remarkably rugged and up to any challenge, on or off the water.

Shafts are key

Gary Pope, plant manager, says there are actually two plants in Racine, the 21st Street plant and the 14th Street plant, with a combined 551,271sq ft of manufacturing space. Corporate headquarters is on 14th Street, and the three facilities employ some 400 between them.

"The company operates in cells," Pope says, "manufacturing cells and non-manufacturing cells (assembly, stator and motor drive, process completion and so forth). There are 21 cells in all, 14 of which are manufacturing cells--milling, turning, grinding, drilling, finishing, et cetera. Raw stock comes in one end of the plant and the finished product goes out the other end. The only thing we don't do is heat treating. That's sent out."

Critical to the operation of the Twin Disc transmissions are the drive shafts. "We do shafts up to 10 different diameters with a number of different tapers. These weigh from lib to 350lbs, and there are probably some 1,200 different shafts," Pope says. "They're from 8" to 48" long and from 0.500" to 10" in diameter. We hold tolerances from 0.0002" to 0.001", with surface finishes from 10Ra to 40Ra. The materials run from 1144, Cl144, 4145, 4140, 8620 and some stainless. Order quantities range from a single shaft to 500 pieces."

Changing methods

Terry Andersen, team leader, programmer, and machine operator in the grinding area, says the company has been looking for a process change in the production of the transmission shafts.

"We used to have two Okuma grinders," he says, "which would grind the straight ODs and an old Cincinnati that would do the tapers. But that was...

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