Operating in essentially the same manner as a pipe clamp, this vise is straightforward and inexpensive yet remarkably adaptable. It consists of two main components: a head, which attaches to a length of 3/4" black gas-pipe that you supply, and in place of the usual pipe-clamp tail piece, it has a base fixture that mounts on the underside of a benchtop or other wooden surface. One of the virtues of this design is that you can mount additional bases (available separately) in alternative locations, so a single head and pipe assembly can serve as a front vise, a tail vise or even a jobsite vise mounted on a portable surface. And because the head can rotate to any orientation, it can be used to clamp against a bench stop for horizontal clamping or against the bench skirt for vertical applications.
The head has two through-holes for mounting your own custom-made jaw, which is driven by an Acme-threaded screw with 1" of travel for final tightening. A positive-locking clutch-plate mechanism holds the pipe, and can be disengaged for fast positioning by pushing a front release button or pulling a rear eye bolt that can be linked to a user-made foot pedal for hands-free operation. The release button can be oriented for right- or left-handed use, and is length-adjustable from 3/4" to 2" to suit the thickness of the bench skirt.
Overall clamping capacity is limited only by the length of pipe used. Requires an unobstructed mounting area at least 3" x 6" and 1-1/2" thick. Head and base are largely made from cast iron with some steel parts.