How can I make accurate holes in sheet metal?

Hi, Gang.
I have a need to make a bunch of 4" holes in 24 or 26ga sheet metal accurate
to + or - 0.0625". My first thought was a electrical knock out punch but the
4" punch is a nominal size (The actual hole is 4.5"). My bandsaw won't cut a
radius that small and snips are not good either. I sure could use some ideas.
Thanks.
Roger in Vegas
Worlds Greatest Impulse Buyer
Reply to
Roger Hull
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Plasma torch on a CNC table. A Laser on a CNC table.
A pick axe and a six pack of beer.
Martin
Reply to
Eastburn
Cut a 4-1/4" hole in a piece of 1/4" masonite and use that as a cutting guide for a plasma cutter.
You can rent small plasma cutters for cheap.
Reply to
Ernie Leimkuhler
4" hole saw should work pretty fast on sheet metal.
Regards Tom.
Reply to
AZOTIC
Short of CNC or a custom sheet metal punch ... I have successfully improvised with a TC burr in a dremel (you can get them for 1/4" routers too) with the router attachment and a circle jig. . should tackle 24 gauge easily ... so if funds are low this might get you by. It's not something I would want to do a lot of holes with though. If you have a lot of holes to do, find a tool maker and get a punch made.
Reply to
Simon
TYhat's the problem. A 4" holesaw would need an extremely low RPM drill motor to be used safely on thin sheet. If it catches at high speed, you can be in a world of hurt.
Reply to
Ernie Leimkuhler
Purchase a Greenlee chassis punch, I think they go up to four inches.
Jim
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Reply to
jim rozen
what about a scroll saw. didn't home shop machinist have an article about clock making where the writer cut fretwork for the clock on a scroll saw.
Reply to
Jran
Roger,
It's not at all clear what you're trying to accomplish.
You say you could do this on your bandsaw if it would cut that small a radius?
Are you trying to cut holes or make round blanks? Since you mention the bandsaw that implies round blanks and not holes.
Tell us more about what you mean by accurate holes. Do you mean accurately round, or clean edge, or what?
Also 24 or 26 ga is pretty thin to be punching without low clearance dies, so forget the idea of an electrical knock out unless you want a ragged edge.
Reply to
DougR
How about a portable saber saw, with a trammel attachment. I've cut light gauge sheet metal with these, using a fine tooth blade. If the pieces aren't too big, set up a platform of plywood or chipboard--a hole to put the pivot pin in, another hole for the blade to clear. Rotate the piece, keeping the saw stationary. You need a support platform to keep the metal from jumping around. Use a high speed, and light feed.
Ken
Reply to
Ken Grunke
The knockout punch you describe makes a pipe size hole.
I'm hure you can can knockout punches in inch sizes.
There are mechanical ones that stand alone, or ones that you attach to a hydraulic operator
Reply to
Jon
They actually go up to 5 and 5/8 inch. However, the 4 inch punch, Greenlee number 741BB, actually makes a 4.044 inch hole. That's within his spec, but doesn't leave a lot of room for error.
Gary
Reply to
Gary Coffman
Ernie, wouldn't it work with a hole saw if you clamped the sheet metal to a board, plywood or particle board and then drilled? The board would also need to be clamped to something so it wouldn't be able to spin. I'd then drill with light pressure.
John
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Reply to
John Flanagan
$450.00 new. You may be able to find them on Ebay or some discount house. Not sure where though.
John
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Reply to
John Flanagan
I may be needing to punch some 3-3/4" holes in .060 aluminum sheet soon. The metal is only 5" wide and maybe 20" long. I was thinking of clamping this to a board or piece of Al plate and first using a hole saw to rough it in and then a boring head to finish it to the correct diameter in my mill/drill. I don't think this would be a problem but I've never tried it before. I would think as long as the sheet metal is clamped strongly to the backing plate it shouldn't grab.
What say ye?
John
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Reply to
John Flanagan
They make holesaws specifically for thin sheet metal. They have only 3 or 4 teeth, and cut slower, but safer.
I still think they are a OK solution for one of two holes, but not for production work. I have a huge set of holesaws, and not the cheap stamped steel ones, but fancy machined ones I got fromn Boeing Salvage's toolroom. I use them rarely now because I accquired a large assortment of greenlee punches from ebay over the last year.
I have both a speed puller and a hydraulic puller for the greenlee chassis punches. I have about 30 of them from 1/2" to 5", as well as a bunch of square sizes.
BTW if you want dimensional sizes of greenlee chassis punches you go for the #730 series. The normal ones they sell are knockout punches for electrical work and are sized by conduit size.
You can buy them up to 8" diamter.
Reply to
Ernie Leimkuhler
Sounds like a perfect application for a chassis punch.
Here is a 3" one
Here is a 3-1/2" one (3" conduit)
Just do a few eBay searches using the terms "greenlee punch -stud" and "chassis punch".
You are bound to find a 3-3/4" punch eventually. I have a massive set now all via eBay.
The hydraulic pullers are really nice for holes larger than 2".
I got mine as a seperate pump and ram.
They make a one-shot puller that is a compact hydraulic puller.
Reply to
Ernie Leimkuhler
Heard of it, never made nor seen one. What is it?
John
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Reply to
John Flanagan
Here's a photo of homemade one (bottom of the page):
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The good trepanning tools are > $200 and cutters maybe $20.
BTW, KBC has a cheapie "General" circle cutter for < US$25. P/N 1-805-55. They say: "With 1/2" diameter round shank for drill press use, adjustable for making 1-3/4" to 7-1/2" holes in steel, brass, aluminum, plastics, wood, hardboards, and other materials. Complete with 1/4" high speed steel cutter bit and 1/4" drill and hex wrench.
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
This is great stuff, Sphero! I *especially* liked the home made multi-meter, including the carefully laced (laced!) wiring harness inside. I myself still have a couple of panel meters that were installed inside cigar boxes, with binding posts. Quite handly really.
Plus the obligatory tap wrench, die stock, and faux-starrett wiggler centerfinder.
Jim
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Reply to
jim rozen

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