fura-2 wrote:

Greetings all: I'd like to generate a bunch of 3 to 4" disks of sheet
metal (pretty thin, 20-ish and thinner gauge), and am looking at
punches to do the job. Would a Greenlee-type punch preserve the
structure of the punch-out (I realize its main purpose is to make the
hole, but I'm actually interested in what will be punched out)? Is
there some other method that I'm not thinking of (I figure a hole saw
is too aggressive and will leave a pretty rough product on both the
hole edge and what falls out). Any advice would be appreciated.

You need a die blanking punch set and a press big enough to do the job.
You're barking up the wrong tree with any manual electrician's type punch like
Greenlee because they use central holes for a bolt.

When you want the hole sized right, the punch is the right size and the die has
clearance. When you want the blank sized right, the die is the right size and
the punch has clearance.

Another way is to use a trepanning cutter on a mill or lathe.

GWE