CNC Brand Profile

Okamoto and the 1953 Surface Grinder That Became Engineering Heritage

Okamoto has built surface grinders since 1953, and the first one is now on display as a piece of Japanese engineering heritage. Here is how a one-man Tokyo machine shop became a grinding specialist, and what to check on a used Okamoto.

Okamoto at a Glance

A One-Man Shop in Tokyo

Okamoto's own company filing tells the story. In November 1926, Kakuzaburo Okamoto started a one-man business in Tokyo building special-purpose machine tools. It became a corporation, Okamoto Machine Tool Works, in June 1935, and opened a plant in Yokohama in 1942.

In September 1945, U.S. forces requisitioned the head office and the Yokohama plant, and trading in the company's shares stopped. The filing says the requisition was not fully lifted until March 1957. Okamoto built its first surface grinder in the middle of it.

1953: The PSG-6B

Here is the part most machinists never think about: Japan's mechanical engineering society credits a 1953 Okamoto with pioneering the basic layout of the surface grinder in your toolroom.

The Okamoto PSG-6B was the first surface grinder Okamoto built. The Japan Society of Mechanical Engineers lists it as Mechanical Engineering Heritage No. 114. According to the society, it "pioneered the basic structure of today's surface grinding machines," including hydraulic cylinders to drive the table, and its accuracy made precision work on the order of 1/1000 mm possible. The machine is still on display at Okamoto's headquarters in Annaka, by reservation.

A hydraulic table that reverses smoothly, end to end, all day, is still what you are paying for in a surface grinder. Okamoto has been building around that idea for more than seventy years.

Gears, Castings and a Second Business

Okamoto was never only a grinder company. A company profile for its subsidiary Okamoto Koki says a Hiroshima plant began making spur and bevel gears and gear-cutting machines in 1944. The gear business was spun off in 1973 and later folded into Okamoto Koki, and Okamoto still makes gears and castings today.

The bigger second business is semiconductors. Okamoto builds grinding and polishing machines for silicon wafers, and in its filing for the year ended March 2026 that segment brought in about 13.6 billion yen, against about 28.9 billion yen for machine tools. The same skill, taking material off flat surfaces to tight limits, runs through both.

Built in Japan, and Beyond

Okamoto opened its Annaka plant in Gunma in 1982 and moved its head office there in 2012. It also builds outside Japan. Its filing describes the Singapore subsidiary it founded in 1973 as the first company to manufacture machine tools in Singapore, and it added a Thailand subsidiary in 1987 and a machinery operation in Changzhou, China, in 2013.

For a used buyer, that means two machines with the same model name may come from different plants. Read the nameplate.

In 2023 Okamoto bought Daiwa Kiko and took over Nikko's surface grinder business. In June 2024 it entered a capital and business alliance with Mitsui and Co., and its June 2024 results presentation set a goal of becoming the global leader in surface grinders and wafer polishers.

Okamoto in America

Okamoto Corporation, the U.S. sales company, was founded in Chicago in November 1972. Today it is based in Vernon Hills, Illinois, with regional offices in Placentia, California, and Windsor, Connecticut, and its site lists grinding machines, semiconductor machines, gears and castings. A 2020 case study by the Japanese firm Macnica put Okamoto's share of the Japanese surface grinder market at about 40 percent, which is the company's figure for Japan, not for the U.S.

The Lineup in Shop Language

The number in an ACC model name tracks the chuck size. An ACC-1224 is a 12 x 24 inch machine, an ACC8-20 an 8 x 20 and an ACC-2040 a 20 x 40. The letters after it mark the feed and control package, and Okamoto does not publish a decoder for them, so read the spec plate rather than the suffix.

On Our Floor

We have five Okamoto grinders in stock:

2022 Okamoto ACC-2040-SA1 (stock 17046): 20 x 40 in chuck, 1,540 lb table load, Okamoto MDI touch control and AC servo cross and vertical feeds.
2022 Okamoto OGM-12-40-UNC: CNC Cylindrical Grinder.
2015 Okamoto Linear-612B: toolroom surface grinder.
Okamoto ACC-1224ST (stock 16951): 12 x 24 in chuck, 3-axis automatic hydraulic, 12 in wheel.
Okamoto ACC8-20DX (stock 15447): 8 x 20 in chuck, 3-axis automatic, filtration with magnetic separator.

Confirm specs, year and condition on any of them with our team before you buy.

For more grinding at Resell CNC, see our Chevalier Brand Profile, our Meet the Machine on the Studer S33 and our Mitutoyo Brand Profile for measuring what you grind.

What to Check on a Used Okamoto

Listen to the spindle. Run the wheel spindle up, listen for bearing noise, feel for vibration and check how warm it gets.

Watch the table. The hydraulic table should travel and reverse smoothly with no stick-slip or hesitation at either end. Check the hydraulic unit for leaks.

Check the chuck. Indicate the magnetic chuck for flatness and test its holding power. A chuck that has been ground many times may need attention.

Test the downfeed. Run the automatic downfeed through small increments and confirm the wheelhead moves what the dial or screen says.

Look at the ways. Check the table and saddle ways for scoring, and confirm the way lubrication is working.

Grind a test part. Grind a block flat and parallel and measure it. That one test proves the spindle, the table and the downfeed at once.

Seventy Years of Flat

Okamoto started as a one-man shop, lost its Yokohama plant for twelve years and built its first surface grinder in the middle of it. That grinder is now an engineering heritage machine, and the company still builds them. For a used buyer, the brand is a good start. The spindle, the table and a measured test part tell you the rest.

Resell CNC Take

A surface grinder is only as good as its spindle, its table and its chuck, and an Okamoto is no different. Buy on a measured test part, not on the name. The name does tell you that parts and support run through a U.S. company that has been here since 1972.

Frequently Asked Questions