How can I make accurate holes in sheet metal?

Plasma torch on a CNC table. A Laser on a CNC table.

A pick axe and a six pack of beer.

Martin

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.

4" hole saw should work pretty fast on sheet metal.

Regards Tom.

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.

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.

Purchase a Greenlee chassis punch, I think they go up to four inches.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

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.

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.

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

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

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

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

Please note that my return address is wrong due to the amount of junk email I get. So please respond to this message through the newsgroup.

$450.00 new. You may be able to find them on Ebay or some discount house. Not sure where though.

John

Please note that my return address is wrong due to the amount of junk email I get. So please respond to this message through the newsgroup.

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

Please note that my return address is wrong due to the amount of junk email I get. So please respond to this message through the newsgroup.

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.

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.

Heard of it, never made nor seen one. What is it?

John

Please note that my return address is wrong due to the amount of junk email I get. So please respond to this message through the newsgroup.

Here's a photo of homemade one (bottom of the page):

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

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

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================