OT : Chassis punches

On 12/16/2014 12:49 PM, tony duell wrote: Do investigate Pexto hand and arbor punches. These do not require a pilot hole and, in, at least in the case of aluminum, have an interesting property. I was chatting with the guy who ran our model shop, when one of the mechanical engineers came in holding a chassis plate that was already pre-punched. Don asked what he needed and Mario said "I need this hole to be smaller by about 125 thousandths." So how does one make a negative hole? I was really interested. Don went over to the Pexto arbor punch and select a die that corresponded to the size of the existing hole. He grabbed a sheet of scrap, punched the hole out, then took the resulting slug, inserted it into the appropriate place in the chassis plate and pressed it into place on an arbor press. He then took it over to the drill press, marked and drilled a new hole right in the center of the slug. Since the screws being used were coarse thread sheet metal screws, I wondered if that could possibly hold a screw. He stated that it would hold at least as well as the rest of the holes in the plate. It did. The trick was apparently that the slugs that come out of the arbor punch come out a bit concave. Pressing them into place causes the diameter of the slug to expand slightly, locking it in place. --Chuck