During these years, he began taking an interest in contemporary music under the influence of another lecturer at the Hochschule, the cellist Maurits Frank.
[2] By the beginning of the 1960s Caskel had become known internationally as a performer of chamber music and solo works by contemporary composers, taking part in the premieres of important works such as Karlheinz Stockhausen's Zyklus (1959) and Kontakte (1960), Helmut Lachenmann’s Intérieur (1966), and Mauricio Kagel’s Transición II (1958–59), all of which he also recorded.
[2] He has also taken an interest in historical percussion instruments, serving as timpanist in the early music orchestra Capella Coloniensis.
[2] In 1963 he was appointed to the faculty of the Rheinische Musikschule [de] in Cologne, and in the same year formed a duo with the harpsichordist Franzpeter Goebels.
[3] In 1963 he received the Förderpreis des Landes Nordrhein-Westfalen für junge Künstlerinnen und Künstler [de].