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.
Unless you use an external press there will be a hole in the middle from the draw stud. The punch is also angled which tends to bend the piece that comes out. I guess you could flatten a twenty gauge disk fairly easily. You would want the old style punches, not the slug busters. What are you going to do with the discs?
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.
Greenlee punches require a drilled hole (maybe something like 1/2" for that size, I don't recall) and they cut with a curved edge, so the result is a rather curved slug with a fairly large hole in the middle, probably not what you want.
If a hole in the middle is acceptable, maybe you could stack blanks and turn them on a lathe.
I now it takes all the fun out of it but you can buy these from a trophy/awards supply outfit like Freeman. They come in brass and aluminum with protective paper. They are perfect circles and the edges are smooth. Lots of sizes and finishes. Natural, shiny, blue, red, green, white, black. I have printed thousands of these over the years. Google for trophy supplies. If you want to make them I would suggest a router or you could buy this nice rotary tale I have here and bolt it to your milling machine. Good luck Dan
You're absolutely right. There will be a hole, and I forgot to take this into account in my post. I guess in the worst-case scenario I could configure things so that I could fill the hole with weld (if I'm good enough).
Thanks very much for the links. The punch is indeed what I was inquiring about, but as has been pointed out by others I guess I don't necessarily want the hole in the middle. The detail of the bobeche shown in your link it quite a bit greater than I really had in mind, as I'd be happy with simply steel in various shapes.
Assuming I could weld the hole closed I don't think the hole is too great a problem (and could even come in handy at times). I just tinkering with metal candle holder ideas, just for projects at home. Thanks.
I hear what you're saying, but maybe I could just bang 'em back to near-flat or cupped, depending on what looks best. I've got an arbor press -- you think that would give me enough force, esp. if I used a pipe extension on the handle?
Frankly, I doubt it. (Aside from the problem of maintaining proper alignment.) What tonnage rating of arbor press? I would not try a 1" or larger punch with my 3-ton arbor press -- pipe extension or no.
I remember the effort I had to put onto a 1/2" drive ratchet when punching steel relay rack bottoms with a ball-bearing screw and grease on the threads.
And I remember breaking the drive screw on one of the 1/2" punches. And that is one *tough* screw.
Greenlee sells a hydraulic drive for the bigger punches.
And the amount of force needed on the handles of a Weldon hand punch with 1/4" punch and die installed -- if you are working on steel makes me think that you would need more force for a larger punch than an arbor press is capable of providing.
Although -- if your metal is thin enough and/or soft enough, and the holes are small enough, *maybe* you can get away with it. Make sure that the die is firmly mounted on the anvil, and that the punch does not wiggle far enough to the sides to contact the edges of the die.
Maybe make a fixture to hold the two parts with guide rods and springs to pull the punch back out of the die and the sheet of metal stock which you are using. (But this is pretty close to what you need for a punch and die which will give you flat workpieces.)