Cutting Tool Engineering
August 2012 / Volume 64 / Issue 8

Multi Grind

By Robin Yale Bergstrom, RYB Communications

Minnesota shop succeeds by being good at many different part-grinding methods.

Minnesota Grinding has grown a lot in its 53 years in business.

It was founded by two partners in 1959 as a small tool grinding shop in a garage behind a White Castle restaurant in Minneapolis. In 1961, the partners built a 6,000-sq.-ft. facility in Minneapolis and began to add employees. That facility was expanded several times until it became landlocked at 23,000 sq. ft.

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All images courtesy Minnesota Grinding

John Glatczak of Minnesota Grinding programs one of the shop’s Studer S40 grinding machines.

In 2005, Minnesota Grinding moved into its current 43,000-sq.-ft. facility with high bays, overhead cranes for handling large pieces and 35 employees working three shifts, 5 days a week. As you might expect, business is very good—but it took some work to get there.

“We gradually expanded into centerless, cylindrical and thread grinding,” said David Schranck, human resources manager and information technology manager (and manager of “the intangibles”) at Minnesota Grinding.

“In the 1980s and early 1990s we added horizontal machining capabilities, but being a job shop we found it difficult to compete with high-volume, production-type operations,” Schranck said. “We realized our greatest strengths were in precision grinding and advising customers on how they could modify parts or manufacturing processes to achieve a better end product, often at a lower cost. Eventually, we added machines for flat grinding, honing and lapping.”

In 1995, the company began focusing on precision grinding. It eliminated much of its machining capacity and continued to add grinders—mostly CNC machines. By 2005, Minnesota Grinding had outgrown its building and moved into its current Crystal, Minn., plant.

The company offers centerless, cylindrical and thread grinding, lapping, honing, double-disc grinding, Blanchard and surface grinding, and some CNC turning and Swiss-style machining. Industries served include medical, automotive, aerospace, food processing and roofing.

“We could be centerless grinding bar stock, and a few hours later the same machine could be grinding pins for hard drives,” Schranck said. “We may be repairing a large roller for a roofing customer in one department, while thread grinding titanium bone screws in another. We like to be challenged. We pride ourselves on doing work right the first time, on time and with impeccable quality.”

Workhorse Grinders

The grinder brand of choice is Studer from United Grinding Technologies Inc., Miamisburg, Ohio, said Harlen Gibbs, operations manager at Minnesota Grinding. “They’re real workhorses,” Gibbs said. The company has four Studers: an S20, two S40s and a new S33. The company’s first Studer, the S20, was purchased in 1988.

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Operations Manager Harlen Gibbs with Minnesota Grinding’s new Studer S33 grinder.

“We found the rigidity of the Studers is key to our precision and repeatability requirements, and the service we’ve received from UGT, the technical support—whether it’s helping with a programming issue or just fixing or adjusting the machine—has been remarkable,” Gibbs said. The shop’s S20 has been running every work day for 24 years.

Minnesota Grinding’s Studer grinders achieve tolerances of ±0.0001 " to ±0.0004 " and impart surface finishes from 8µin. Ra to 16µin. Ra. Gibbs said the machines can tackle just about any workpiece material, including aluminum, titanium, Hastelloy, stainless steel, Inconel, carbide and plastic.

“We just had a job that was made of rhenium, an exotic, expensive material,” Gibbs said. “Not the kind of stuff that leaps out at you from the periodic table.” The part was an aerospace coupler that required ID, OD and thread grinding.

Before the shop decided to buy the S33, Minnesota Grinding looked at other, less-expensive grinders, but they were less rigid and lacked the service and support track record UGT provides, according to Schranck.

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The S33 grinds a 16 "-long shaft that requires nine different diameters.

The S33 has the latest generation of high-frequency, internal grinding spindles that have maximum speeds of 120,000 rpm, allowing the grinding of very small bores, according to UGT.

The basic wheelhead on the S33 can be indexed at 0° or 30° for straight and angular plunge grinding. A universal turret wheelhead swivels manually or automatically, permitting OD, ID and face grinding in a single setup. The machine features a Hirth coupling B-axis with a 1° indexing that repeats within 0.08 arc-seconds. This permits extremely accurate ID-to-OD runout and concentricity.

Also, the S33 has a shoulder probe and a B-axis that automatically rotates the wheelhead to do different kinds of features, such as ID grinding.

“In the past, we probably quoted jobs based on running a part on multiple machines,” Gibbs said. “The new Studer, with its Fanuc 0i-TD control, allows us to do a job with multiple diameters and multiple faces and shoulders in one setup in a single machine versus using multiple manual machines. This makes us more productive, more competitive and more cost effective. Also, the S33 will open up other market opportunities because the machine is much more precise, faster and more flexible than any other cylindrical CNC grinder.”

Flexibility and Growth

Joel Schoening, grinding technician and lead man at Minnesota Grinding, runs through a common part-grinding scenario: “The part, with nine diameters, is a 16 "-long shaft, and we grind the entire shaft in two operations. I chuck on one end and grind six diameters from the shoulder to the end. Then I flip the shaft and grind the other shoulder and the three remaining diameters.”

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Joel Schoening, grinding technician and lead man, checks the shoulder probe on the new Studer S33.

The diameters are from 1.5 " to 0.750 " and gradually step down. There are bearing journals on each side that are about 1 " in diameter. There is a keyway on one end.

“These parts have a print tolerance of 0.0005 " runout,” Schoening said. “We’ve run these same shafts on other machines and achieved 0.0003 " from diameter to diameter, giving us a Cpk of 1.394. On our new S33 we are holding 0.000050 " from diameter to diameter, giving us a Cpk of 3.0134.”

When Schoening initially ran this part on the S33 and checked it with his tenths indicator, the needle didn’t even move. “I had another operator check the part and he said my indicator must be broken. Then we checked it with a 20 millionths indicator, turning the part slowly, and found it to have 0.000050 " runout.”

According to Schranck, there are about 12 grinding shops in the immediate vicinity, but Minnesota Grinding offers the most flexibility. “The majority of these shops offer only a few types of grinding services,” he said. “Because we do so many different types of grinding we have far more flexibility when it comes to accepting a wide variety of different jobs.”

Gibbs said, “If it uses grit and takes off material, we’re probably in it.”

Tough Times

During the Great Recession, hours were cut at the company, but there weren’t any layoffs. “We all took it on the chin,” Schranck said. “We went from the low point in the economic cycle, where we were running our shop just 32 hours a week, to where we were back running 40 or more hours a week. We then expanded our second shift, and in 2011we added a third shift.”

Most recently, the company added several grinding and honing machines and retrofit several other machines. There are also plans to purchase another Studer this year in response to growing demand.

With such growth comes a need for more skilled workers. Gibbs said it’s best to hire a machinist who doesn’t know grinding. As long as the machinist has basic metalworking skills and inspection skills, grinding can be taught.

Schranck said the company has its own custom-designed skills test. “We’ve used this assessment for the last 15 years on everyone who comes through the door looking for a job,” he said. “It’s not difficult, but covers a variety of topics, including reading the most rudimentary drawing, questions about gaging, a few math problems and some things that reveal their attention to detail. You find out very quickly who the detail-oriented, technical people are.”

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Matt Wilkie adjusts the shop’s Studer S20 grinder. Purchased in 1988 to run one shift, it now runs three shifts a day, 5 days a week. The machine still holds tolerances as tight as 0.0001 ".

The test is part of the screening process. Schranck said: “If they tell me they have experience, I give them an application and the assessment, put them in a room and close the door. Nine times out of 10 they’ll go through the application and assessment, but the 10th person just walks out the door, leaving the pencil and papers behind. This separates the talkers from the doers.”

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The Studer S40 grinding area (top). Note the flow of coolant and the angle of the wheel (above).

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The nine diameters on this shaft are from 1.5" to 0.750". The diameters gradually step down.

If an applicant does well on the assessment, an interview follows. It includes a verbal introduction to the company’s technology and operations. “Very few applicants walk in with a skill set that fits what we do,” Schranck said. “So we explore their experience in depth to determine what skills would be applicable in our shop.”

Because of the proprietary work the company handles, prospective employees aren’t allowed to see much of what goes on at the shop. “In fact, many of our customers would like to tour our shop, but we have a closed-door policy because we have so many confidentiality agreements,” Schranck said.

Gibbs noted many prospective customers will e-mail a part drawing and want to start discussing the best ways to make the part—but that’s not quite how Minnesota Grinding works. “Our philosophy, which differs from a lot of shops, is not to just take a print and make the part to the print,” Gibbs said. “We really discuss what the customer needs and wants out of that part. We look thoroughly at design and process, and we make suggestions about other possible ways for us to grind the part, offering the customer options other than what they may have been thinking about.

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Harlen Gibbs and part of the Minnesota Grinding staff.

“In some cases we go back to them and say, ‘If you did this differently, we could make you a better part and at lower cost,’ ” he continued. “We just don’t make things to print.” CTE

About the Author: Robin Yale Bergstrom is principal and editorial director at RYB Communications, Hebron, Ky. He can be reached at (859) 689-9551 or www.rybcom.com. For more information about United Grinding Technologies Inc., call (937) 847-1253 or visit www.grinding.com.

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