Punching in the sheet material of large diameter or curved forms used by drilling on the contour. However, the punching of the centers of the “contour” hole requires accuracy and is time consuming. Much faster the work will go if the core is to equip a retractable pointed foot with locking screw. Sticking with it the necessary distance between the edges, you can start punching without a preliminary marking: it is enough to set foot into the previous hole.
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