Elliptical (or eccentric) lathes used to carve finished circular and oval picture frames. The variable elliptical rotation is controlled by a combination of the rear drive mechanism and the large faceplates you see here. To learn how these work, see the link below.
Old Schwamb Mill, Arlington, Massachusetts. See flic.kr/p/rC5Y15 for a description of the site. The overall process of producing a frame and the operation of the lathes are explained here www.oldschwambmill.org/theframes/theframes.html.
