The main difference between the Shopsmith 505 and 510 is their production years and some minor feature variations. The 505 model was produced from 1986 to 1996, while the 510 model was introduced in 1996 and remains part of the current lineup as of now. One noticeable difference is that the airflow control lever on the back of the headstock was redesigned on the 510 model for smoother operation compared to its predecessor. Some other slight improvements were also made over time regarding certain knobs or handles for better ergonomics or ease of use. However, both models generally offer similar functionality and retain the core features that make Shopsmith an efficient woodworking system.