This article is in response to the drifting topic "A few Technical PSU Questions", which turned towards sheet metal. I think a new, more visible thread is in order for this topic. So here's a starting contribution...
Tin Snips for Cutting Metal, and Making Holes In Things
...including computers. So you want better airflow, real fan grilles, ducts, etc., maybe even a window. It's time to get cutting. This article is a detailed introduction to basic sheet metal cutting, in aid to fixing all those details that make our computers quiet. I wrote this article because a whole lot of people who want quiet computers aren't big-time case modders, and never really wanted to be. But we end up fixing and tweaking out of necessity. If we're lucky it even get's fun.
You might look into this mess and think "I'm only gonna do this once and I will never use the tools again." But you have a really neato idea and it just has to get tried. Find a friend with tools, or hire someone. If it's to hire, look for smaller heating companies or sheet metal shops. Find a place where you can work it out with someone in the shop. Most little things, like cutting holes or making simple brackets, are so easy that a cool metalworker will do them in a flash, and you can avoid nasties like 1 hour minimum shop charges. They might not even charge for metal if it's in their scrap pile, and there's always lots of good scrap. Best is to find someone who wants to do the job because it's interesting. They will be cheaper and do better work.
If you decide you want to dive in then... below you will find way too many
gory details, and full blow-by-blow how-to's and why-for's. After that, a gentle nudge into the world of basic sheet metal work and what it can do for you. If you think any of that will help you on your way, then steel yourself and read on...
Dremels, the ever present. I admire and appreciate the one-tool versatility of dremel cutting, and have no argument with the many excellent results. Dremels have good strengths for modding: they can cut a line across/through an existing corner, drill-grind-polish, and do touchups. And they work in almost any material. I do however dread the notion of using them much for most sheet metal cutting. They are just slow
I recently spent two years working in a sheet metal shop. There are lots of fancy big special tools (makes you drool), but the most basic hand tools still do most of the work. My favorite way to cut metal is with Red+Green tin snips (yes you need both). With a little practice you can work honest miracles in mere minutes. Oddly, computer people just never seem to use tin snips, as though they don't exist. I don't get it, since they are my first choice.
Tin snips cut anything from aluminium to stainless steel, from tinfoil to 32 guage (very thin like PSU's) up to 16 guage (thick like a credit card). Thinner is generally easier. Way too thin (tinfoil), very hard (stainless) and very thick (20-16 guage), can all get more challenging, but can still be done very well. Everything in between those extremes is just plain spiffy
I have seen 'nibbler' or 'nibble notcher' tools, and they do some neat things. Some modders even seem to have heard of them! A nibbler is: maybe cheaper than 2 pairs of tin snips (but for a quality one?); definitely slower; and probably more versatile concerning very small square holes (depending on your skill). They probably compliment more than replace tin snips. Nibblers are popular, but I haven't used a pair yet. Many of my tips below would apply well to them too. Especially: buy a good one if you intend to actually use it, and keep it sharp.General Tips for Cutting Sheet Metal
0. Sheet metal is damn sharp, fresh cut edges are bloody sharper!
Be aware and move slowly
to avoid getting cut. Rushing around sheet metal always gives you cuts. They are seldom fatal but always messy.
1. You want (need?) high quality tin snips.
They are the most important sheet metal tool. They must be sharp
. NEVER CUT STEEL WIRES WITH THEM! Avoid cheap combo sets if at all possible
is the brand for any sheet metal pro I've ever met. You only need Red
/right and Green
/left snips, the Yellow/middle is almost never used (didn't even buy 'em in our shop). I suspect the combo sets are an industry subsidized conspiracy: has all the fancy colors, con's you into thinking you own the tool, then discourages you 'till you hire a pro
Live with the cheap ones if you must, but treat them really extra nice.
2. You need a sharp scribe / awl.
A nail or screw seldom cuts the mustard, they are too soft. The scribe / awl is a very handy tool for it's own sake anyways. Lee Valley Scratch Awl
is the best I've seen. Quality - hard steel -
is a must for an awl to outlast it's cost.
3. Measure twice, cut once! Measure twice, cut once!
3b. 2/3 of the job is in the measuring and layout.
I measure on 1/16" rules, but my marks are within about 1/64" or less by eye. Have fun with metric. Accurate layout is the hardest but most important part of the job.
4. Use a metal ruler and scribe to mark out your cut lines.
Use a compass with a point for round shapes. You can cut within less than 1/64", if
you mark that accurately. A scribe line is shiny and very precise, and it actually guides the blades a wee bit, allowing shockingly accurate and neat work. If you can support the metal on a hard surface, use the awl to 'punch' the corner points first. You don't need to go right through the metal, but do put a good little dent there. These punchmarks help placing the ruler when marking lines, and stop the snips cutting when you get to a corner. If you want more visible lines then colour beside
your scribed lines with a Sharpie felt pen. Always scribe your cut lines unless you're freehanding. Always.
5. Cut square to the metal.
If you don't hold the snips straight up and down, you won't get a square edge. Take your time, be precise. It's still the fastest way you can do this job by hand.
6. Red vs. Green:
when the metal you are keeping is to the Right
side of the line. Use Green
when the keep is on the Left
of the line. The kept metal stays flat. The cuttings curl upwards and away from the line. Right handers use the Red by default, left handers use the green, it's easier that way to see the line you're cutting. But you switch back and forth freely as needed or desired. Tight spots will often make the choice for you too, that's one of the reasons you need both sides.
6. File your work lightly.
Use a fine mill-file: good ones ($) are harder and sharper. Stroke it mostly along
the cut edge, not across. You can get nearly machine precision touch-ups with a little patience and a sharp file (not that rusty/shiny toothed thing from the lawnmower shed
). Because you have a good file you don't have to push hard. Or use a Dremel tool ...now how about those holes...
So much for the basics. Now on to the job. A new fan hole. A new window hole. Maybe as an air port for a duct or muffler box you're adding on (build that too!). Tin snips will cut holes down to about 3/4" in lighter metal, maybe 1 1/2" in heavy stuff. The problem is this: flat metal; no hole; need hole x by x, or x around. Easy strategy:
1. Measure Measure and mark and measure your hole and measure.
2. Punch a hole near the center.
This is where you will start your cut from. You might need to support the workpeice on a damageable wood backing to prevent it from bending, like for a thin PSU cover or a flat side cover panel. I use my Lee Valley awl, just drive it right through. You could use a hammer and nail, drill a hole, shoot it with a gun.... If it's a small hole (nail, awl) you need to warp the metal a bit so that one side of the hole is bent up and one side is bent down. This gives you a raised lip to start cutting from. I do this with the awl by just pushing it over sideways before I pull it out of the metal. A bigger hole, say 3/8" drilled, is big enough to start your cut from flat.
3a. Fun: Cut outwards in a spiral.
Freehand. This step is what lets you cut a hole without
bending the the metal left outside the finished hole. You'll be amazed. You can start from even a wee hole, and spiral outwards with your cut. The metal will get a bit bent near the cut at first, that's ok, by the outside of the spiral you can get your flat cut easily. By cutting a spiral, you let the waste metal from hole spiral up and away from the snip's blades, as it needs to do. You can stop any time and cut off the emerging waste spiral to get it out of your way, at your convenience.
3b. Strategy: Spiral out in 2 or 3 or more rings, leaving the last 1/4".
By spiralling outwards in say 1" to 2" swaths you can now cut up to the last 1/4" from the finished hole. The width of your swath is actually limited by the guage. The waste swath needs to keep curling up and out, without a big struggle. Cut too wide for the guage and it gets hard to curl away, so cut a narrower swath. On square holes just leave the corners rounded for now, they get squared out later. But leave that last 1/8" to 1/4" in for now
. You are not trying to finish the hole here, just get it opened up to make the final cut really easy.
4. Now cut the finished hole very carefully.
The last 1/4" strip always spirals out of the way very easily, so it's easy to stay right bang-on line. On straight lines you can feel the line, and ride it with the blades.
4a. For square holes
you angle in very gently and sidel up to each line, then follow it to the far corner. That cuts out most of each side, right up to its far corner. To cut the other end of each side, and finish the corners, you change snips from Red to Green or vice versa. Start cutting up against each side where it's already cut straight, easing into the remainder. Cut back along the side to the corners that are still left. When you hit each end the corner bit will fall out and you are done, with a nice clean flat hole every time.
4b. For round holes
just cut the last ring out very carefully. Ease into the edge at a very gentle angle. That last little strip peels out in a nice spiral.
4c. For small holes.
You probably want to cut these as the last, careful, step of your spiral, because there just isn't always enough metal to leave that last 1/4" strip. Still, you might try for a last 1/16". The metal outside the finished hole will often get a bit bent, but you can flatten it afterwards. For smallish holes in thick metal, the whole spiral thing might just not work well. You probably need to drill the starting hole, and warp it. From there I usually just make a ratchety mess (chop hack chop), leaving the last 1/32" to 1/64" inside the line. That way you can hammer the work flat, and file out out the hole cleanly up to the line using a round file. Small holes can be done, and they go quickly enough, even if they are fiddely. Of course a hole-punch set would be lovely.
5. File and flatten as needed.
Well it should have been perfect, but a bit of filing and a few hammer taps will fix almost any remaining flaws. The trick to flattening sheet metal is to put a heavy flat
peice of metal behind it, and tap it gently with a hammer. We used a 2" round by 4" long chunk of steel, very nice. You just work around your cuts, giving gentle taps till it's all flat. With care the results look almost like they came out of a machine.
Well, after all those details I'm sure it's clear as mud. Try it out, play with some scraps from a sheet metal shop. Sheet metal is easy stuff to work with a little practice.
Afterward: fun in the metal shop:
I had lots of fun at my sheet metal job, and I found out how great sheet metal is. I've done lots of wood, steel, plastic and composites, and fabric, but sheet metal is still my favorite material. It's so clean, quick, strong, formable, and versatile: it's almost as useful as duct tape. Once you get used to it, you find that you just whip up all kinds of little holders, brackets, covers, connectors, braces, boxes... it's just amazing. It quickly replaces lot's of other quick-fix or home-brew solutions with something easier and better, and often 'right' instead of 'improvised'.
You don't need much to use sheet metal at home. The tools mentioned above are almost all you need to make practically anything. A few other handy tools are some pliers, a drill, a pop-rivet tool, and maybe a vice for doing small easy bending jobs. There are cool little $20 bender jaws
that fit in a vice too, and do a better job than a naked vice. So, that's what you need to make most all of the little things you could want to make from sheet metal.
There is only one last thing that opens up all the possibilities, and it's the hardest thing: long bends or folds can't be done well by hand, not even over a good edge. If you can live with just bending a narrow edge on not-too-heavy sheet, ask a sheet metal shop to make you a folding bar: up to 2' long, double sided for two widths, maybe 1/4" and 1/2", or anything up to 1". They would probably want $50 to $75 for one, but it will do an awful lot and not take up any space. Better would be a small break (or bender), and I have seen them > 24" for $150'ish, but that's for a cheapy. Still, you could probably even make good custom cases with care and cleverness, and that's something most people wouldn't even dream of for a mere $250 total worth of tools. The best thing is a real box break, but that's big, heavy, and >$500 or way more: you would have to have some serious ambitions in mind, and you should just go hang out at a real sheet metal shop.
At the metal shop we put in furnaces, made up all the ducts, and did just about every odd thingy a sheet metal shop does. Having all the big tools to play with off hours was really fun. I made up some custom Hi-Rise covers for a trio of very slim MSI desktop book-PC's, so we could add extra HD's and normal CDRW's. They were regular, inverted-U type desktop covers, but with extra panels hanging down in front and back to cover the new hight. They were done in heavy 18 guage, which made them fairly difficult to cut but very strong. The light 30 guage internal drive cages and brackets were much easier, if a tad flimsy. Fun projects, lots of possibilities.
I hope you have got something out of all this, or
maybe even enjoyed yourself.
Happy computing, Crisspy.