Easiest way to enlarge an electrical knockout?

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I just bought a new heater for my garage, but all the electrical knockouts are sized for 1/2" conduit. I need a hole for 3/4" conduit to accomodate the size of my power cable.
My first thought was to use a knockout punch, but good golly those things are expensive. I don't want to spend $60 for a one time task like this. I'm also curious if a punch would work for enlarging an existing hole?
Another option is a step-drill, but those are almost as expensive at the home centers. I'm also a little worried about metal shavings falling inside the heater, or overshooting the size I need and making the hole too big.
I haven't had time to check, but I wonder if anyone rents the knockout punches?
Thanks,
Anthony
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On 2/21/14 7:46 PM, HerHusband wrote:

You might find a set of used KO punches on Ebay for a decent price. I knew a guy years ago who used a hole saw. Metal shavings weren't a problem for his work. It wasn't a super neat job either. The saw would wander a bit if I recall correctly.
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On 2/21/2014 7:46 PM, HerHusband wrote:

1/2" KO. If you have an automatic center punch, use it to pop little pits around the hole a bit more than 1/8" apart. Use your drill with a 1/8" bit and drill through wherever you have the small pits which keep the drill bit from sliding away from where you want to drill through. You can do it without an automatic center punch if you put moderate pressure on the drill and start very slowly until you're sure the bit won't slide. After you've drilled all your closely spaced holes, you can go up another bit size to remove more metal. You can use diagonal wire cutters and pliers to cut out and break off the little tags of metal left around the circumference. You can finish up with a round or half round file if you want to make it prettier. An automatic center punch and half round file can be purchased from Harbor Freight for very little money. It may cost more at Lowe's Depot but you will be surprised at all the uses you will find for an automatic center punch. ^_^
http://www.harborfreight.com/catalogsearch/result?q=automatic+center+punch
http://preview.tinyurl.com/qc64pap
http://www.harborfreight.com/8-inch-half-round-file-96629.html
http://preview.tinyurl.com/ornsdm3
http://www.harborfreight.com/8-inch-round-file-96628.html
http://preview.tinyurl.com/njeasyd
Harbor Freight also sells step drill bits.
http://www.harborfreight.com/2-piece-titanium-nitride-coated-high-speed-steel-step-drill-bits-69088.html
http://preview.tinyurl.com/q5spon9
TDD
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On Fri, 21 Feb 2014 21:00:32 -0600, The Daring Dufas

buy him a beer.
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Oren,

I have a Fahrenheat FUH54 space heater, not a water heater. I have full access to both sides of the opening.
I just wonder how well a punch will work only having an extra 1/8" on each side of the existing opening.
Anthony
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On 2/22/2014 1:10 AM, HerHusband wrote:

If you have a good rental place it should have KO punches.
Change the wiring method to something with a 1/2" connector?
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any I've worked on.. And I was not under the impression this was a water heater, but I may have missed it.
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On 2/21/2014 7:46 PM, HerHusband wrote:

If you are near a big city I think it is real likely you can rent them.
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will the box be overfilled? might be easier and more code compliant to just replace the box
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On 02/22/2014 08:15 AM, bob haller wrote:

YEP, this is exactly what to do.
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On Saturday, February 22, 2014 11:03:51 AM UTC-5, philo  wrote:

Except that from what is described, there is no box to replace. The NO is on a *heater* he's trying to connect. I suspect he has a *cord* that's too big. An option might be to install a box and transition from the cord to 1/2" liquidtight, etc that will fit.
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On 02/22/2014 10:32 AM, snipped-for-privacy@optonline.net wrote:

Good point and now that I think of it the answer by "Caulking-Gunn" might actually be the best...to simply use a transitional fitting.
Half inch hole, 3/4" conduit such things exist and would make it a "no-mod" job.
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On 02/21/2014 08:46 PM, HerHusband wrote:

Yes, the easiest way is a knockout punch. You, however, seem to be looking for the cheapest way. That would be a round file.
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*I seem to recall a tip from one of the trade magazines. Try clamping a piece of wood behind the hole and use an 1 1/8" hole saw to enlarge it. I haven't tried this. Please post the results if you do.
You might find a rental place that has knockout punches.
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John,

After considering multiple options, I remembered I had a metal nibbler in my tool chest. I wasn't sure if it would handle the sheet metal on the heater, but it worked fine.
You can see the full process with pictures at:
http://www.watsondiy.com/heater.htm
Thanks everyone!
Anthony Watson Mountain Software www.mountainsoftware.com www.watsondiy.com
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One thing obvious from a couple of your pictures:
You have too many clamps.
Wait...that's not possible! ;-)
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I only have 8 pipe clamps (four feet long), 12 Jet parallel bar clamps (two feet long), and 12 small bar clamps (one foot long).
It sounds like a lot, but I frequently run out of clamps when gluing up panels, cabinet doors, or similar projects. I usually have to do my glueups in stages over two or three days.
I started out with the pipe clamps, and still use them for larger projects. They also came in handy for construction projects when I needed to pull walls into alignment or something.
These days I prefer to use the Jet clamps when I can.
I don't use the small bar clamps as often, but when I need them they're great to have. They have been most useful when gluing up curved objects like bent wood laminations.
I would love to have more clamps, but I don't know where I would keep them. :)
Ironically, I still don't have a band clamp. I need to get one of those.
Anthony Watson www.mountainsoftware.com www.watsondiy.com
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HerHusband wrote:

Get some pipe connectors (they are about a buck a piece) and you can have even longer pipe clamps. Great for decks, workbenches, ...

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Bill,

I bought a couple of pipe connectors, but so far haven't used them.
The last time I needed to do a long clamp, I just ganged up three pipe clamps so they pulled on each other in series. It was quick and easy, so that's the approach I took. :)
Anthony Watson www.mountainsoftware.com www.watsondiy.com
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On 2/23/2014 8:17 PM, HerHusband wrote:

nibbler too and I often use it to turn round holes into square ones. ^_^
TDD
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