In 1938 Julius Keilwerth bought the villa of Anton Richard Breinl, Lipova Ceste 17.

In 1937 despite the crisis he extended the factory. In 1930 he built a factory with a house at the Silberbacherstrasse 1348 (now Havlíčkova). Soon 100 employees worked in the Keilwerth factory, and an additional 50 were homeworkers. But he saw the possibilities for scaling up, hired a number of people, grew and bought a modern company building equipped with modern machines and a production of 85 saxophones per week and sold them to 30 countries around the world. First Keilwerth delivered his saxophones piece by piece to Markneukirchen. Once these two saxophone types were extremely successful, he began making sopranos, baritones and, upon special order, bass saxes. The Julius Keilwerth company was founded in Graslitz in 1925, when Julius started making alto and tenor saxophones. They primarily manufactured saxophones for Adler and F.X. Then Julius Keilwerth and his brother, Max, established a workshop in their home around 1920. He then went back to work as an instrument maker, his injuries hindering him. After the end of the First World War, he found no work and started working on his father-in-law's farm and later coal mining in Falkenau. After his apprenticeship, he worked abroad for quite some time, including Switzerland and Germany. He first apprenticed for the Kohlert company in Graslitz, Czechoslovakia.

Julius Keilwerth ( – ) was trained as an instrument maker.

Amati saxophone serial numbers