Automatic dilator devices for generating minimally invasive access apertures for surgical procedures or endoscopic surveillance. The automatic dilators comprise a number of spreader tubes nested one inside the other. The devices deploy automatically by means of coupled mechanical mechanisms which insert one spreader after the other distally into the patient's tissue. Each spreader moves distally into the tissue by means of a screwing action, by which rotation is converted into linear motion of the neighboring spreader, immediately external to it, by means of interaction between a helical thread form on a surface of a spreader being engaged by a section of thread, or by one or more protrusions on the opposing face of the next spreader external to the rotating spreader. Such a combination of helical thread and follower enables a rotatory mechanism to be used to deploy one nested spreader tube after the other, by continuous rotary motion.
