He continued on to Harvard to pursue a Ph.D. but left in 1934, when he was called back to California during the Great Depression to manage the Pomona Pump Company, a family business in the Pomona Valley that made submersible pumps and marine engine parts. His brother Philip McKenna founded McKenna Metals Company in 1940, renamed Kennametal Inc. in 1943, a major steel cutting and mining manufacturer and distributor based in Latrobe, Pennsylvania. Donald was an original partner of what became Kennametal and member of its board of directors. He became chairman of the board in 1969 and retired in 1978.