VMC brings gear machining in-house

For Southern Technology & Services Inc. in Houma, La., jack-up systems for offshore oil rigs are a mainstay, making up about half of the company's workload. Jack-up systems, or jacking rigs, lift a drilling platform out of the water once it has been f

For Southern Technology & Services Inc. in Houma, La., jack-up systems for offshore oil rigs are a mainstay, making up about half of the company's workload. Jack-up systems, or jacking rigs, lift a drilling platform out of the water once it has been floated into position. These devices work much like the lift rack at an auto-repair shop. However, producing the gears for these rigs was a problem for Southern, which was sending gears as far away as Seattle to be machined.

"One of the gears we make has a 2 /3 diametrical pitch on the tooth," says Bryan Bunn, one of the owner's four sons. "There are only two hobbing machines in North America that have the cutters to cut the tooth, one in Seattle and one in Canada."

After some research, Southern found it could profile the gear on a CNC vertical machining center, rather than having it hobbed. The potential cost savings was tremendous, and producing the gear in-house also promised to speed turnaround times.

Southern worked closely with the local Haas Factory Outlet (HFO) in Lafayette to select the right machine and prove out the process. "We basically did a turnkey for them, with all the testing, to make sure we could do what they wanted to do," says Pat Kane, president of the HFO. "We ran several prototype gears in our showroom and basically had the programs ready to go for them." Southern manufactures five different gears for its jacking systems, ranging from a 76-tooth to an 8-tooth gear. The 8-tooth gear is what led to buying a Haas VF-9 50-taper VMC.

Raw material for the gears, 4340 alloy steel, comes in two forms. One is solid barstock in an annealed state, and the other is rough-cut forgings up to 1-in. oversize. Southern first roughs O.D.s, leaving 0.001 in. of stock for heat treating. Next, it turns the gear diameter to size, fixtures the blank between the VMC's HRT 450 rotary table and a tailstock, and machines the gear in a single operation. "We go down with an end mill first," explains Dustin The-riot, Southern's CNC administrator, "and start roughing it out. Then we use a ball mill and profile the tooth shape specified for that gear. With a finish mill,

we cut the gear to size and have it heat treated. After which, we turn the O.D.s to size on a lathe and cut a keyway using the mill."

By optimizing tooling and feedrates, Southern cut cycle times on the 8-tooth gear from 18 to 8 hr. "We've tripled our production," Theriot says, "and are looking to increase it more. We'd like to get it down in the 5-to-6-hr range."

Haas Automation Inc.
Oxnard, Calif.
www.haascnc.com

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