Another ingenious example of the use of slip forming to speed up the casting of concrete on the job site is a cattle feed trough forming machine developed by a Colorado contractor. The machine creates a dense concrete which is especially effective in resisting attack by the acids which are almost always present in the feeds used for cattle. The machine is self propelled by means of a 5-hp gasoline engine which winds a seven-sixteenths an inch cable on a winch drum. The cable is anchored to either a dead man or a tractor. In addition to a concrete feed hopper and a steel mold conforming to the cross section of the bunker, the assembly also includes a small generator which produces electrical power to operate the internal vibrators which fill the form and consolidate the concrete. The machine automatically trowels all but the top edges of the walls. According to the inventor, the device makes it possible for a 4 man crew to cast 200 feet of feed trough and apron in a normal work day. Using ready mixed concrete to supply the machine hopper, the full 200 feet of trough can be cast in about 2 and one-half hours.