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When Robert Bergstedt says “tenths,” the lingo really means ten-thousandths of an inch. He manages sheet-metal fabrication for Donal Machine, based in Petaluma.

No customer ever cares so little about precision that metal parts can be cut to within a tenth of an inch. If parts require welding, that’s typically done first so that holes or cuts can be made to within a few ten-thousandths of an inch.

For Donal, sheet metal is rarely thin stuff used for gutters or ducts in heating and ventilation. These sheets are often a quarter of an inch thick. With thinner material, Donal’s work is extremely precise.

The Petaluma manufacturer, founded by Bergstedt’s father Don Bergstedt in 1969, is co-owned by his sister Donna Bergstedt, CEO, and his brother Chris Bergstedt, president. Bob Bergstedt is vice president. Total revenue is nearly $7 million a year with about 35 employees.

In recent years the company relied more on computer-numerical control to handle sequences of cuts on metal parts.

“It’s for everything,” Bergstedt said.

Some computerized machinery is connected to a flexible-manufacturing system that allows the machine to react to changes, even unpredictable ones. The machine can adapt to new products, change its order of operations on a part or use different tools to make the same operation as material-handling components optimize work flow. One machine might have 200 different tools available. “It’s running a program,” he said, with a sequence of tools. “The machine knows the lengths, the diameters. It’s all in there if you need to run it again.”

Several of Donal’s automated milling machines cost more than $400,000. A laser cutter is even more.

“You can machine multiple surfaces,” including edges of a part, Bergstedt said. Metal chips or filings are automatically evacuated as recyclable waste.

“This is a little bit of robotics,” he said. “It’s on a track, like a little forklift. Then it rotates.”

Except for welding, most of the shop’s work is subtractive — drilling, cutting or carving holes in metal parts. “One aluminum part starts at 11 pounds and finishes at 1.2,” he said. Nearly 90 percent of the metal ends up as scrap. It was still cheaper to machine the part, formerly a casting, out of solid aluminum.

Additive technology, such as 3-D printing, builds parts out of layers of material.

With sophisticated components used in aircraft or trash-pickup lifts, a part might take hours to finish. Automated machinery changes its own drill bits and cutters, and repositions parts as needed to continue manufacturing.

On occasional jobs, especially for a single part, workers use lathes to make cuts.

“Geometry has an effect. Something simple, it’s easy to make it manually,” he said. “Quantity plays a big role.”

Donal made more than 22,000 battery-box bottoms for Tesla’s Model S electric car out of quarter-inch aluminum sheets. “They call it armor. It’s pretty stout,” Bergstedt said, to protect lithium-ion batteries from being penetrated by road debris flying up. The job lasted about a year starting in October 2012, at one point cranking out 600 battery-box bottoms a week. “Eventually they outsourced it to somebody else. It almost tied up my whole shop,” he said.

Tesla supplied the material. Each piece brought about $40 of revenue initially, dropping to roughly $30 as quantities rose. The whole job brought nearly $800,000. “It was a good job.”

Donal makes cargo-handling equipment indirectly for Boeing through an intermediary called UTC Aerospace Systems, a company with worldwide sales of nearly $14 billion. “The actuators have urethane wheels and a motor. The containers power themselves,” he said, allowing an operator to place cargo efficiently to balance the plane. That business accounts for nearly half of Donal’s revenue.

Another regular customer needs components for garbage collection devices. Some are machined with vertical or horizontal milling machines.

“This thing is a canister, but has a side-loader built into the canister,” Bergstedt said. “The system uses their regular trucks. You can see what is dumping into the can. It’s right in front of you.” Donal started making the trash-loader parts out of steel that ranges in thickness from a quarter to half inch in 2009, using a laser cutting machine and metal-inert-gas welding, where a solid wire electrode feeds through the welding gun. “Wire is coming out fast,” Bergstedt said.

Another client has Donal cut aluminum tabletops with precise decorative designs using a laser. The sheets are three-eighths of an inch thick.

Donal owns its facility with nearly 30,000 square feet and has plenty of production capacity to grow.

James Dunn covers technology, biotech, law, the food industry, and banking and finance. Reach him at: james.dunn@busjrnl.com or 707-521-4257