You'll want to get a hole saw. It goes into a power drill or drill press and will cut out a hole. They look like this:

4.5" would work for a 120 mm fan.

 

Hole saw for one, but at the size you want expect minimum $30 and I've seen up to $45+ (price circa... holy crap like a year ago).
I'd use a dremel or a jigsaw myself, but I have a funny habit of accumulating tools. edit- so you may or may not have access to certain power tools /edit

quick and dirty method would be to get a power drill with as big a bit as you have handy, a pair of $5-10 tin snips (metal shears), and go at it til your hand and arm are sore (sex joke not intended).

cleaner, but more expensive method would be to use a dremel, jigsaw, or that hole saw

best, in my opinion, would be to get a drill press, a clamped on drill guide (block of wood with desired hole already cut), and the hole saw.

If you're going metal-to-metal contact, remember some lube. even if it's just some WD-40, your tools will thank you.

but if the structural integrity and/or aesthetics don't matter, there's always the sharp object (i.e. chisel, ice pick, screwdriver) + heavy object (i.e. hammer, rock, whatever) way of bashing a new hole into metal.

 

I wouldn't use a holesaw unless you have a drill press, secure side panel between 2 pieces of plywood, secure that in drill press and then use holesaw.

Commercial electricians use knockout punches for making holes in electrical boxes,
http://www.amazon.com/Greenlee-730BB-120-0-Standard-Round-Knockout/dp/B00125D9DW

120mm is big, but call around and you might get lucky.

If that doesn't work, a jigsaw is probably best option. Use very fine blade. Use masking tape to cover both sides so they don't get scratched. Draw your circle where you want it. Drill a hole big enough for jigsaw blade to go through and start sawing. I suggest drawing a 100mm circle and a 115mm circle. Start sawing the 100mm circle to get the feel of staying on your cut line then move to the 120mm circle.

 

Thanks. Should I get a 120mm hole saw or slightly smaller?

 

115mm or 4 1/2" would be better. Most 120mm fans are 115mm id. 120mm x 120mm is outside measurement.

 

An electrician with 4 1/2" hole punch will probably cost less then half what a hole saw will cost... and do a much cleaner job.

 

No, get a nibbler. Look at their pictures. Pretty clear. I tried other ways. Wish I'd known about a nibbler then.

 

Quote:

Originally Posted by ehume

No, get a nibbler. Look at their pictures. Pretty clear. I tried other ways. Wish I'd known about a nibbler then.

Which nibbler is best?
http://www.mcmelectronics.com/product/TL00873&scode=GS401&CAWELAID=220963660

http://www.sears.com/shc/s/p_10153_12605_SPM2466477301P?sid=IDx20070921x00003a&ci_src=14110944&ci_sku=SPM2466477301

http://www.google.com/products/catalog?q=hand+nibbler&hl=en&client=firefox-a&hs=8OZ&rls=org.mozilla:en-USfficial&prmd=imvns&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1076&bih=659&um=1&ie=UTF-8&tbm=shop&cid=2114798219975681118&sa=X&ei=kwvUT5mzJ4SV8QOz7aWMBQ&ved=0CHQQ8wIwAw

http://www.northwares.com/hand-nibbler-sheet-metal-cutting-tool-cut-pc-case-window/

http://compare.ebay.com/like/120821727413?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y

I'm in United Kingdom so have limited availability.

 

Quote:

Originally Posted by doyll

Quote:

Originally Posted by ehume

No, get a nibbler. Look at their pictures. Pretty clear. I tried other ways. Wish I'd known about a nibbler then.

Which nibbler is best?
http://www.mcmelectronics.com/product/TL00873&scode=GS401&CAWELAID=220963660

http://www.sears.com/shc/s/p_10153_12605_SPM2466477301P?sid=IDx20070921x00003a&ci_src=14110944&ci_sku=SPM2466477301

http://www.google.com/products/catalog?q=hand+nibbler&hl=en&client=firefox-a&hs=8OZ&rls=org.mozilla:en-USfficial&prmd=imvns&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1076&bih=659&um=1&ie=UTF-8&tbm=shop&cid=2114798219975681118&sa=X&ei=kwvUT5mzJ4SV8QOz7aWMBQ&ved=0CHQQ8wIwAw

http://www.northwares.com/hand-nibbler-sheet-metal-cutting-tool-cut-pc-case-window/

http://compare.ebay.com/like/120821727413?var=lv<yp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y

I'm in United Kingdom so have limited availability.

The MCM it not a right-angle nibbler, so it's right out.

The Sears unit is a Klein nibbler -- that's the one I linked to at a different vendor. Kudos to you for finding it.

The Malco is not a right angle nibbler. God knows what it is for..

The Northwares unit has been used by others. It works OK, but it has slim handles and hurts your hand when you squeeze it.

The Sealey is not right angled.

 

Do nibbler cut round holes? Looking at the description, it seems that nibblers need someone with a steady hand, which I don't have

 

Yeah you use a dremel and get a stencil online so you cut the right size and have the screw holes in the right spots , the dremel is a good investment your going to use it for mods in the future !

http://www.mnpctech.3dpixelnet.com/picture_library/mnpctech.com_80_92_120_140_fan_grill_templates_rv2.pdf

 

my advice
get this kit, not sure if you guys have homedepot or a lowes but im sure you have something like the two. they carry these kits
http://www.dremel.com/en-us/Tools/Pages/ToolDetail.aspx?pid=4000-2%2f30

if you look at the picture where there is a silver arm with a black round thing attached, you can use that. drill the center of the hole you want to make. do your measurements, and just whip the thing around. presto hole made

having that kit comes in very handy as there are an almost unlimited amount of things you can do with it.
i own 2 of those kits

 

And for $100US less you can buy a nibbler. Yes, it will require scribing a circle then drilling a center hole and the a hole at the circumference. Yes, it will take time. But the fact that it nibbles, one small bite at a time, means that following the circle is easy, and you won't need a very steady hand. You just need to take your time.

And unlike a Dremel or other power tools, the nibbler does not lead you to sudden catastrophic slips or mistakes. If you're going off course you will see it as soon as it starts, and reorient your work.

 

So is the nibbler akin to a can opener? I know how to work those, lol

 

Quote:

Originally Posted by ehume

And for $100US less you can buy a nibbler. Yes, it will require scribing a circle then drilling a center hole and the a hole at the circumference. Yes, it will take time. But the fact that it nibbles, one small bite at a time, means that following the circle is easy, and you won't need a very steady hand. You just need to take your time.

And unlike a Dremel or other power tools, the nibbler does not lead you to sudden catastrophic slips or mistakes. If you're going off course you will see it as soon as it starts, and reorient your work.

see below VV
Quote:

Originally Posted by daydream99

Do nibbler cut round holes? Looking at the description, it seems that nibblers need someone with a steady hand, which I don't have

also the dremel as i stated has the bar in that kit where you first drill a hole, pop the bars center into said hole, then zip around. perfect hole every time and lighting fast.
the kit is only $90 but the amount of things you can do with it far beat buying a single tool like a hole saw at $30-40 range that only has a single function.

 

I used a dremel...
Also used a cd as a template, perfect match for the standard round fan grills.

 

Quote:

Originally Posted by daydream99

So is the nibbler akin to a can opener? I know how to work those, lol

1. Drill a 7/16" hole in work material.

2. Insert tool up thru hole until work material rests on platform directly below cutting blade.

3. Squeezing handles, guide tool along, nibbling to size and shape desired.

from MyToolStore.

Insanely easy, with visible chips falling -- no dust.

But it's no can opener. You have to drill that hole first. Or start at an edge:



And then you can use the nibbler for other things, like removing your rear grill, and removing your slot pillars. And no metal dust.

 

Thank you ehume for your reply.

You advise a right angle nibbler.
Assume Klein is one of best. What are others you recommend?

Thanks

 

Can I use a regular pistol drill to make that 7/16 inch hole?

 

Quote:

Originally Posted by daydream99

Can I use a regular pistol drill to make that 7/16 inch hole?

yes, just before you drill into it, place a large piece of wood under the metal. no support should be on the casing to avoid bending the metal. same goes for if you have a press also.

 

Does it matter if that case material is made of steel? Does the pistol drill have enough power?

 

yes, it has enough power. You might need to drill a pilot hole with a smaller bit first.

 

What size hole do you guys recommend for the screws?

 

Quote:

Originally Posted by daydream99

What size hole do you guys recommend for the screws?

To paraphrase "Back to the Future,"

"Screws? Where we're going we don't need screws."

Check out the link in my sig and Velcro that fan.

 

Another way to is using left and right metal master snips.
Must be left and rights for smooth as butter cuts and of very good quality.
If the gauge of the cabinet is not "boiler plate"
Trace the fan size and hole locations for fastening they can be drilled after
Drill a couple small holes then enlarge enough to start the snips