The knife, which I did, the commercially available and opens cans faster. Its basis was a steel tube and rod, a part of her. The end of the rod is bent, it is inserted, and then open curved steel pin. On one end of the tube brazed to the tool holder, mounted on the other handle of ebonite or wood. The holder has a top threaded hole for the locking screw to the extendable rod, the bottom — slot cutter (knife), fixed by screws on the side. To use a knife like this. First pin breaks the Central hole, and then regulates the position of the cutter so that it was closer to the rim of the lid, and tightened the locking screw. The Mac knife is shown in the figure. It remains to make a circular motion with the handle — opened.