His first job, after graduation, was shovelling coal into the firebox of a locomotive on the Cologne-Minden Railway. It was an odd start for a Karlsruhe-trained engineer, but it was how the railway business inducted graduates in the 1860s - feel the heat first, design the machines later. He moved up quickly. By 1872 he had co-founded Lämmerhirt, Brandenburg & Co, a mining machinery factory that would eventually evolve into Westfalia Dinnendahl Gröppel, a name still familiar in German industrial history. The firm faltered on liquidity in 1874 and was sold off. Lämmerhirt was not yet thirty-five and had already built and lost a company.

He took the next decade abroad. In 1876 the family moved to Winterthur, Switzerland, where he became general director of the Winterthur Casting Factory, part of the Sulzer Brothers concern. A short detour to Berlin and back, and then between 1879 and 1883 he served as lead engineer at the Bureau Fritz Marti in Winterthur - which was, at that moment, involved in building the Gotthard Tunnel. The Gotthard, when it opened in 1882, was the longest railway tunnel in the world: 15 kilometres bored through the heart of the Alps, a feat that killed close to two hundred workers and rewrote European geography. Lämmerhirt's exact role is not detailed in the surviving records, but it was the work he was proudest of.

In 1883 he relocated to Warstein in Westphalia to direct the local mines and smelting association, the position he would hold until his death sixteen years later. He had married Emilie Louise Schmiedt in 1869 and they raised eight children, six of whom reached adulthood. His daughter Luise married into the Siepmann family of Warstein, founders of the local drop-forge works; the Lämmerhirt and Siepmann names would soon become inseparable in the small industrial geography of the Sauerland region. His son Rudolph would rise to vice-president at Krupp in Dortmund. The family fanned out into the upper layers of German industry - Krupp, the Prussian Army officer corps, the brewing trades - in the years when those layers were forming.

Lämmerhirt died on 10 July 1899 in Frankfurt am Main, sixty years old, from cancer of the chest. The Warstein iron foundry kept running after him, the Siepmann marriage produced grandchildren who would inherit it, and the German industrial expansion he had helped power continued for another fifteen years before the catastrophe of 1914. His name is not famous. The Westfalia Dinnendahl Gröppel he co-founded still exists. The Gotthard Tunnel is still in service, although a longer base tunnel now runs beneath it. The lives Lämmerhirt's career touched - workers shovelling coal in Cologne, miners in Sauerland, the daughter who married into Warstein steel - kept turning long after he was buried.