https://www.reddit.com/r/typewriters/comments/1caofcz/how_to_get_my_silentsuper_to_not_rotate_to_the/

Because of aging, the rubber feet of many typewriters can harden thereby reducing their friction against the table on which they sit. As a result, this can cause one's typewriter to "walk" across the table as they type for extended periods necessitating their recentering from time to time. To remedy this, one could use custom made typewriter mats with rubber bottoms to prevent this walking as well as to protect the table underneath. Other options which may also work are either wool or felt pads from fabric stores or from Chinese/Japanese calligraphy stationers. In Japanese these mats are called shitajiki.