Bannow was born in Sweden and came to the US at 13, learned the pattern maker's trade, and later became a foreman at the Bridgeport (Conn.) Pattern and Model Works. He bought the company in 1927 and took in Magnus Wahlstrom as a partner two years later. The partnership soon produced a high-speed milling attachment, followed by a version with a quill.
In 1936, while delivering a pattern, Bannow got the idea for a machine built around the head the firm was producing. He sketched the Bridgeport turret milling machine on a paper bag while sitting in his truck. The first Bridgeport mill was shipped in 1938, and more than a quarter million have been built. This versatile machine became the foundation of the "tool and die" business of thousands of small job shops.