Hole in a metal box

November 27, 2011 10:56 PM

I need to make a hole in a piece of metal. How do I do that?

I have a transformer surrounded by a metal box which I need to drill a hole into so that an electricity cable can enter. It's the top part of a light.

I tried using a hammer-drill with a concrete drill bit but obviously this didn't have the desired effect. To make things complicated the edges of the metal box aren't connected, and so the box has no structural integrity.

What should I do to make a hole? I was thinking a saw would be too messy and make the metal bend. A file seems like a good idea, but would take a long time (is there a file on a drill bit I could use?)

How can I do this? Pic.

posted by devnull to Grab Bag (17 answers total)

Best answer: Just a normal twist drill will do this (like one you would use in wood, not a paddle bit). Use a small diameter first, then a medium one, then the size you want. Drilling holes in metal is a super common thing, literally, just use a normal drill bit.

If you need to brace it, put (or even better, clamp) a piece of wood behind it to keep it from caving back like that...

Easy peasy.
posted by milqman at 11:00 PM on November 27, 2011 [2 favorites]

Also, side note, after the hole get through, use a grommet to keep the edge of the metal from wearing on the wire and eventually shorting it.
posted by milqman at 11:02 PM on November 27, 2011

You'll find a Dremel good for this, and a hundred other uses.
posted by artdrectr at 11:03 PM on November 27, 2011

There are punches designed for exactly this purpose, but they're usually kind of expensive for a single use. Cheaper but less neat would be to drill a small hole then enlarge it with a step drill. (Wikipedia says that what I call a step drill is actually called a unibit.) Check out this Greenlee hole-making guide (8MB PDF).
posted by hattifattener at 11:04 PM on November 27, 2011 [2 favorites]

There are many youtube videos about this sort of basic DIY stuff.
posted by jeffburdges at 11:04 PM on November 27, 2011

Response by poster: Thanks for all the quick answers! I'll try drilling from the other side with a smaller drill bit, braced against some wood.
posted by devnull at 11:17 PM on November 27, 2011

Best answer: I would not use a twist drill so close to the edge of such thin material, as it is liable to grab and tear. A hole saw would've be a pretty good choice if you were to back up the cut with a piece of wood.
posted by jon1270 at 12:12 AM on November 28, 2011 [1 favorite]

Best answer: I'd use a nail to dimple the metal first, so the drillbit doesn't go wandering. Then I'd drill, but would add a little drop of machine oil- keeps things cooler.
posted by jenkinsEar at 2:27 AM on November 28, 2011 [1 favorite]

The reason the concrete bit didn't work is because those bits grind, as opposed to cutting. So, there you go.
posted by InsanePenguin at 3:04 AM on November 28, 2011

The other reason is because when used with a hammer drill those bits bash and chip as opposed to cutting, and metal responds to that by bending and stretching rather than shattering.
posted by flabdablet at 3:09 AM on November 28, 2011

Once you've got your hole drilled, punched, nibbled or otherwise made, you will want to fit it with a grommet. Having a cut metal edge slice through the insulation on a mains cable is not something you really want.
posted by flabdablet at 3:13 AM on November 28, 2011

Yup, twist drill as others have said. Note that if it skates around too much on you use a nail to punch a small dimple in the metal, this will hold the tip of the drill in place as it starts.
posted by Pink Fuzzy Bunny at 8:21 AM on November 28, 2011

You may find it beneficial to spray water on the bit/hole as you drill to keep things cool.
posted by allelopath at 8:49 AM on November 28, 2011

I've used WD-40 and a silicon based lubricant to keep things cool (whatever was handy, I prefer using a lubricant to help things cut properly). Go to the hardware store and get some drill bits for metal (there are multi-purpose metal-wood-plastic bits which will work fine for this). Turn off the hammer function, it's no good with metal.
posted by defcom1 at 9:12 AM on November 28, 2011

Definitely put a rubber grommet in that hole otherwise the edges of the metal are going to go right through your wire insulation, particularly with the burr left from drilling.

Cooling shouldn't be a problem with somomething this thin if you have a sharp drill bit. If you don't have a sharp drill bit cooling might help you not ruin the temper on the bit, but if you don't have a jig to sharpen a bit, you might as well replace it anyway.

Otherwise, what has been said about backing up the workpiece with a block of wood and moving in from the edge a bit.
posted by Kid Charlemagne at 9:22 AM on November 28, 2011

My husband says: You can use a step drill, or, if that doesn't work, try a better step drill. He's a metals guy.
posted by hollyanderbody at 10:03 AM on November 28, 2011

FWIW, rather than a rubber grommet, you should really use a cable clamp (any hardware store will have a binful of them next to the other wiring stuff). A rubber grommet will wear through if there's vibration, and won't keep the cable from being pulled out of the box.
posted by hattifattener at 9:51 PM on November 28, 2011