Cartoonists and Illustrators School instructor Tom Gill asked Sinnott to be his assistant on Gill's freelance comics work. With classmate Norman Steinberg, Sinnott spent nine months drawing backgrounds and incidentals on, initially, Gill's Western-movie tie-in comics for Dell Comics. Sinnott recalled in 1992 "taking the Long Island Rail Road every weekend and working all day Saturday and Sunday." He said in 2003, "Tom was paying us very well. I was still attending school and worked for Tom at nights and weekends," with night work added after he tired of commuting to Long Island and "began working my room on 75th Street for $7 a week."