Cutting rectangular openings in project boxes?

[BurningTantalum]

A really low-tech technique, especially useful as these jobs tend to be one-offs, is the tension file that fits in a standard hacksaw frame. I have used these for years, and they give very good results on complex shaped holes. The best brand is 'Abrafile' although I'm not sure if they are still available. RS used to stock them. I have had mine for 40 years and have never worn one out or snapped one. I have even used them on stainless sheet. Their USP is that the 'pitch' of the abrasive gradates from fine to coarse down the length so starting each stroke is easier.
Only a small hole need be drilled in the panel to insert the file (3.5mm?)
BT

[Fludo]

For metal control panels I'd start with 3/8" or 1/2" clearance hole for a jigsaw blade in one corner of the square.  After that cut the straight lines to the other corners with the jigsaw and clean the edges up with a file.  If you're using plastic or wood, a coping saw would be able to do it using the same technique.  The trick is to not bend the cut to much or the blade will bind/snap. The jigsaw will work as a router by moving the blade side to side as well.  A jigsaw can be bought for under $50 and will produce a clean hole with some practice.  They also come in handy for cutting fan holes as well.

Depending on the component mounting, there's normally a lip around the outside to cover any imperfections.

[cdev]

Do you mean a small table style jigsaw ? 

Ive seen those and wondered how well they worked with metal, specifically aluminum.

I need to read up on and understand more about the various power tools.

For metal control panels I'd start with 3/8" or 1/2" clearance hole for a jigsaw blade in one corner of the square.  After that cut the straight lines to the other corners with the jigsaw and clean the edges up with a file.  If you're using plastic or wood, a coping saw would be able to do it using the same technique.  The trick is to not bend the cut to much or the blade will bind/snap. The jigsaw will work as a router by moving the blade side to side as well.  A jigsaw can be bought for under $50 and will produce a clean hole with some practice.  They also come in handy for cutting fan holes as well.

Depending on the component mounting, there's normally a lip around the outside to cover any imperfections.

[Fludo]

The handheld ones with a vise or clamp work great on steel and aluminum.  It's important make sure the blade TPI is matched for the material.

[MarkL]

These corner punches can be used to finish the corner on plastics and would probably work ok on thin aluminum:

  http://www.micromark.com/search?keywords=corner%20punch

[cdev]

The handheld jigsaws? How smooth are the cuts they cut? (with a linear metal ruler used as a guide)

 I think the very largest hole that I might want to make would be at the most 75-100 cm on its largest side.
That would actually be an unusually large example, I think  The typical application I need a rectangular hole ability for is likely a display or hole for some kind of interconnect.

The circular holes for switches I can do with my drill.

The handheld ones with a vise or clamp work great on steel and aluminum.  It's important make sure the blade TPI is matched for the material.

[Fludo]

With a good layout and careful work, the cut will be acceptable. It will take a bit of file work to get panel meters and displays to fit correctly.  Not CNC machine quality but will need some deburring.

For a display hole you could edge the bare metal with the split rubber gasket material and epoxy or silicone it into place.  The edge will cover any mistakes made while cutting too.
https://www.grainger.com/category/rubber-edge-trim-seals/rubber/raw-materials/ecatalog/N-iqu

[CatalinaWOW]

Unless you are very good a hand sawn hole will not match a CNC hole.  But after hand filling it can be better than all but the very best.

[IanB]

I think it needs shop skills. You saw inside the line and then file to the line. Chris from Clickspring shows how it's done.

Also, why does everyone assume CNC is needed for precision? You can manually control a milling machine and get perfectly good cuts, even better if you have a DRO.

CNC is good for production where you need to make many identical parts. But for a single job you can have it finished before you have even got half way through setting up a CNC program.

[Gregg]

The handheld jigsaws? How smooth are the cuts they cut? (with a linear metal ruler used as a guide)

I have a Bosch hand held jigsaw that I hold upside down in a vise to cut small things.  Holding the saw by hand causes the blade to catch on thin work and not make a nice cut.  Most of the blades cut toward the saw and make a burr along the cut that somewhat obscures the line; upside down, it leaves the line visible.  My Bosch is variable speed and has settings for the orbital action (aggressiveness of the cut) both features that make it a good candidate for thin plastic and sheetmetal.  Holding the work with two hands is much better than holding the saw and trying to clamp thin parts solidly.
For aluminum or steel, lube the blade with stick wax (available at machine shop suppliers) to keep the aluminum from sticking and to lube the blade for much faster and better results.  Cutting a little short of the line and finishing with a file is always a good idea for the really neat stuff. 

[Habropoda]

It seems like a jewelers hand saw would work well for this.  I haven't tried one but they are made to cut intricate holes and you can get many different blades for them.  I've seen one used for cutting the fancy sound holes for a lute.

[phil from seattle]

Thanks for all the suggestions. In my situation, it sounds as though the best solution would be to use a small end mill to cut openings, and optionally finish off the corners with a hand file. I've got a 3D printer on order, so using it to fabricate either bezels or entire front panels may be an option too.

You'll love the 3D printer. Gone are the days of scrounging for the right box and hacking it up to get your project to fit. I've printed a number of boxes at this point.  I do like the look of metal or molded plastic better though. Learn to use ABS as that can be smoothed to get rid of the most of the extruder ridges.

[ez24]

I have a Bosch hand held jigsaw that I hold upside down in a vise to cut small things. 

Thanks  I now need to look for my Bosch and get a vise 

[joeqsmith]

For thin aluminum or plastic I use a nibbler. 

[joeqsmith]

Just in case some of you have not heard of or seen a nibbling tool. 

https://www.amazon.com/Premium-Life-360-022-Nickel-Nibbling/dp/B0002KRACO/ref=sr_1_4/146-4349405-5311219?ie=UTF8&qid=1516063461&sr=8-4&keywords=nibbler

[ez24]

Just in case some of you have not heard of or seen a nibbling tool. 

https://www.amazon.com/Premium-Life-360-022-Nickel-Nibbling/dp/B0002KRACO/ref=sr_1_4/146-4349405-5311219?ie=UTF8&qid=1516063461&sr=8-4&keywords=nibbler

Thank you very much for including a link - I put one in my Cart.   I thought they were very expensive. 

[Bratster]

Just in case some of you have not heard of or seen a nibbling tool. 

https://www.amazon.com/Premium-Life-360-022-Nickel-Nibbling/dp/B0002KRACO/ref=sr_1_4/146-4349405-5311219?ie=UTF8&qid=1516063461&sr=8-4&keywords=nibbler

Thank you very much for including a link - I put one in my Cart.   I thought they were very expensive. 

I've got that same one and it works great,
... as long as you don't use it on 1/16" steel... But it's nice and cheap.

Another good nibbler tool is this: https://www.amazon.com/dp/B00MPHC4TQ/ref=cm_sw_r_cp_apa_Y1vxAbYYTZ5D4

Not as good for precision, but faster due to being drill powered.

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[neo]

My personal favorite way can be done with just a hacksaw blade, some tape and a metal file.

Wrap some tape around one end of the saw blade, enough to hold, as well as some on whatever you are cutting, lay the tape in the outline and then using a ruler for a straight edge mark the exact lines. Remember you can always take a little more away so aim a little bit shy.
Once you get the lines slowly cut the two sides and then angle across the middle. You can then saw out the remainders and file any imperfections out.
REMEMBER, very important, go slow and do not rush. Take your time and be sure. Yes you will cut yourself, but a bit less with practice, yes you will err, but again a bit less with practice.

Masking tape works best.

Also if the hole needs to in the middle and not edge, a couple well placed hole drilled into it and a smaller metal file will help

[nes999]

I good bezel can hide a hideous hole.

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