From April 1922 Mill Supplies

Modern Grinder Manufacturing co. was established in Milwaukee in late 1915, and by September 1920 they had recapitalized twice, growing their capital from $10,000 to ten times that. The company made hand-cranked grinders, grinder arbors, and at least one electric bench grinder. They were granted grinder-related patents in 1922-23. By that time they were also making small clamp-on bench vises. In about 1936 the company relocated to Fond du Lac. By 1941 a pair of mergers had occurred, including one with Luther Grinder Manufacturing Co. In 1941 the parent company became American Hydraulics, Inc., with both Modern and Luther remaining as separate divisions. The following year, a group of Sheboygan-based investors acquired American Hydraulics and relocated all the Fond du Lac operations, including both Modern and Luther, to Sheboygan. The trail grows cold in the late 1940s, by which time hand-cranked grinders had become largely obsolete.

Information Sources

• November 1915 Mill Supplies.

  The Modern Grinder Manufacturing Co., Milwaukee, Wis., $10,000, to manufacture portable and stationary grinding machinery. Incorporators: Charles Cohn, Toney Colin and Ely Bockshe.

• September 1920 Mill Supplies.

  Modern Grinder Manufacturing Co., Milwaukee, Wis., has increased its capital stock from $25,000 to $100,000. The company is planning to build a new machine shop and make other improvements.

• A couple of grinder-related patents were assigned to this maker, issued in 1922 and 1923. The company location at that time was Milwaukee.
• A lawsuit citation, Modern Grinder Manufacturing Co. v. Dazey Churn & Manufacturing Co., 22 F.2d 950, 951 (7th Cir. 1927) turned up on a Google search. The judgment will likely have some interesting information but we have not seen it.
• A Google search on "Grinder Mfg" "Fond du Lac" got one match: a mention of "Modern Grinder Mfg Co." of Fond du Lac in "Machinists Monthly Journal, OFFICIAL ORGAN OF THE International Association of Machinists", 1938. A Google search on "Modern Grinder Manufacturing" got a match for the auction of a "vintage hand bench grinder".
• A 1941 issue of Iron Age. "John Henronymous, Sheboygan, Wis., has been elected president of the American Hydraulics, Inc., Fond du Lac, Wis., and its divisions, Master Grinder Mfg. Co., Modern Grinder Mfg. Co., and Luther Grinder & Tool Co. ..."
• 1941 Mergent Moody's industrial Manual. "AMERICAN HYDRAULICS, INC. / History: Incorporated in Wisconsin in 1915 as Modern Grinder Mfg. Co. Present name adopted in March, 1941. / Business: Manufactures hydraulic jacks, files, grinders, planes and vises. ... Officers: John Heronymus, Pres.; H. A. Schauer and C. H. Schmidt, Vice-Pres..."
• The 1947 book The Prewar Industrial Pattern of Wisconsin by Edgar Z. Palmer.

  In 1938 the city of Fond du Lac appropriated $10,000 to a relief organization, and this money was made available to Luther Grinder Co. to pay the expense of moving that company to Fond du Lac. Luther Grinder Co.—which changed its name to the Modern Grinder Co. and later to American Hydraulics, Inc. as the result of two successive mergers — operated in Fond du Lac for five years, employing about 150 people and having an average annual payroll estimaged at $175,000 or more. During this period the city received a total of $8,060 in personal-property taxes from the Luther Grinder Co. and its successors, so that, taking account of the income-tax revenue derived from the company, it appears that the city more than recovered its $10,000 subsidy through tax revenues. In 1942, however, a controlling interest in American Hydraulics, Inc. was purchased by Sheboygan interests, and the company was moved to Sheboygan where it was subsidized by the city to the extent of $19,750.

• An OWWM.org posting first brought this maker to our attention.
• Postings on the OldTools hand-tools email list provide some information about different grinder models from this maker.
• The auction history site WorthPoint has a 2018 eBay sale, with photos, of a Modern No. EP2 bench grinder with a type B universal motor, made in Milwaukee.