“KNOCK UP BALLS: To knock up balls is the term used for making balls: it is to cut the pelts to a proper size; to fill them with a proper quantity of wool; to nail them to the ball stocks; to trim them; and to put them into working condition. See Balls.” From A Dictionary of the Art of Printing, by William Savage (1841).
Note: According to A Dictionary of the Art of Printing, “balls” in printing refers to “two pieces of circular leather, pelt, or canvass covered with composition” and stuffed with wool. They were used to “cover the surface of the article to be printed with ink, in order to obtain an impression from it.” See also Ink Balls and Printing from the American Bookbinders Museum.
Old Town Editing 