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
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.
Use a Sharpie marker to mark the diameter of your 3/4" hole around your
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. ^_^
Harbor Freight also sells step drill bits.
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.
On Saturday, February 22, 2014 11:03:51 AM UTC-5, philo wrote:
just replace the box
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.
On 02/22/2014 10:32 AM, email@example.com 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
*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.
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:
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.
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. :)
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