The document discusses capstan and turret lathes. It begins by explaining that these lathes evolved from engine lathes to allow for mass production of identical parts. The key features are that the tailstock is replaced by a hexagonal turret tool head that can hold multiple tools, eliminating the need to change tools between operations. The construction of capstan and turret lathes is then described, including the bed, headstock, turret head/saddle, cross slide, and tooling arrangements. The working principle involves automatically indexing the turret head to bring the required tool into position for each operation in sequence. These lathes can perform a variety of turning, drilling, boring, threading and other operations with high efficiency