As mentioned at the end of the intro post
, after I had figured up a rough parts list I set to work mocking things up in SketchUp.
I want to detail my process of going from idea to finished CAD model that's ready to manufacture so grab your beverage of choice, this will be a long post (actually posts it turns out)!
Designing the case part 1: SketchUp
The whole point of this project is to fit a complete computer within the dimensions of an ATX PSU-sized housing. So my first step was to double-check what those dimensions were. The form factors of standardized things like ATX power supplies, Mini-ITX motherboards, PCIe cards, and so forth are typically defined by long, technical spec sheets. Many of which are available from formfactors.org
Strangely they don't have the newest ATX revision v2.4, but luckily @EdZ
has uploaded a copy
to the Resources section since it's no longer available from Intel's site either. The physical dimensions haven't changed in many years but it's good practice to work with the latest version of a spec.
Few things of note though, while it's good to adhere to the spec as much as possible to maintain compatibility, it's also necessary to be aware of how other manufacturers deviate from it in practice to make sure whatever you're designing will work in the real world.
For example, the ATX spec officially only allows for a housing with a 140mm depth. But anyone who's shopped for ATX power supplies knows that almost all the higher-end units are 160mm deep or more. What's going on is that most enthusiast power supplies are actually using a combination of the ATX and the Entry-Level Power Supply (EPS)
specs. Entry-level in the context of server PSUs BTW, it's actually meant for higher wattages than ATX and because of that it allows for much longer depths, up to 260mm I believe.
The height, width, and mounting holes are the same though so I'll just use the figure 12 from the ATX spec for reference.
Another deviation is the mounting tabs visible at the front edge of the unit in the diagram. I'm not sure if it's an optional part of the spec or not, but either way, nobody ever implements it in consumer units so adding support for them in a consumer case is pointless.
So with that little lesson out of the way, what are the dimensions I have to work with? Well, it's 86mm height x 150mm width x ? depth.
Now that I've used "real" CAD programs, I don't think that SketchUp
is the best program for designing a case. It's really meant to be used as the 3D equivalent of a paper sketch (hence the name) and while people have done really cool things with it, a proper solid modeler
with sheet metal support is much, much better suited for designing a case. That's a topic for another day though.
But for quickly roughing out a layout, it's the perfect tool for the job, so SketchUp is still where I usually start with a case design.
Here I've made a simple wireframe outlining my starting dimensions. The height and width are locked in but the 160mm depth is just a starting point until I get mockups of the parts in there and starting figuring out how much room I'll need.
Next I dropped in a very rough placeholder for the Mini-STX board and a PCIe video card from subtec's excellent precise blank model
, modified to the length of the EVGA GTX 1060.
And duh, a video card that's at least 172mm long won't fit in a case that's only 160mm deep
At this point I was still thinking I could take a dead ATX unit and mod it. The next common size up for ATX units is 180mm so I adjusted the model and continued to add placeholder parts.
After mocking up the two HDPLEX units, it became obvious that 180mm wasn't enough either. 200mm then?
Success! Or is it? It's tempting
to think this will work since the parts fit within the outline but that's an easy mistake to make. Manufacturer dimensions for video cards are notoriously unreliable so it's naive to assume the card conforms to the official dimensions in reality.
Not only that, but the available space will be reduced 1-3mm in each dimension due to the thickness of the panel material. There's also manufacturing limitations like bend radius, minimum flange length, available standoff lengths, etc. that have to be taken into account. I'll go into those issues later.
Plus future you that has to actually assemble this thing will curse past you who designed it if you don't include a bit of wiggle room around components for installation.
The other limitation I ran into is that I did not want to permanent modify either the motherboard or video card. This is just a project I'm doing to see if it's possible and I will probably sell many of the parts eventually to recoup costs so I want to keep them in resellable condition. Problem is, the ASRock H110M-STX does not have an internal power connector, it only has a DC jack on the rear. I want to avoid having a power cord sticking out of the case and then running back inside to connect to the HDPLEX so that meant the rear IO had to be on the inside.
As can be seen in the above pic though, that means there has to be enough space between the HDPLEX AC-DC unit and the board for the power connector to fit. A quick look at the available right-angle 5.5mm x 2.5mm plugs though showed that I'd need about 20-30mm of clearance. This has the advantage of allowing for longer video cards if I want to upgrade and will allow space to tuck cables and work in the case.
Quick aside: It's easy to get lost in the 3D model because you can zoom in until the tiniest detail fills the screen. It's important to keep in mind the physical size of what you're designing so you don't end up in the situation of what looks like a huge gap in the model turns out to be way too small to fit your hands in so you can't easily work in the chassis without lots of cursing, sweating, and possibly gaining a few scars.
For example, it looks like there's lots of wasted space in the above pic when I increase the depth to 230mm. But really that's only 30mm, typical USB plugs wouldn't even fit in the back of the motherboard without seriously bending them!
Anyway, now I had to make a decision. Up until this point I wasn't sure if I would just get a custom case made from scratch or mod a dead ATX PSU for maximum sleeper PC cred. 160mm-180mm units are very common so dead ones are fairly available too.
200mm+ ATX units is typically the realm of high-end 1000W+ power supplies though, so they're much rarer and thus dead ones that I could pick up for a reasonable price are much rarer too. 230mm units are particularly uncommon too and that's the depth it was looking like I'd have to do to have room for everything.
After poking through eBay listings for a day or two I decided to just go for the custom case. I'm lazy so if I could just push pixels on a computer screen and let someone else do the dirty work of cutting and bending metal then that's fine with me
With that decision made, I needed more accurate models of the parts to better figure out the layout so I could start designing the chassis. Here's where SketchUp really shines, I've been using their Match Photo
feature for years and it's awesome for this. Basically you import a picture into SketchUp, tell it where the perspective lines in the image are, and then you can model over top of it. And of particular importance for this kind of work, you can input a dimension for a known feature, and it will scale the whole model to match. Example animation with the P4SM2 here
So I used Match Photo to make models of the motherboard and P4SM2 to continue testing layouts. Here I'm experimenting with putting the AC-DC up high and the DC-ATX in the corner to maybe make room to run short extension cables from the motherboard's rear IO and the case.
It was quickly becoming apparent though that any future decisions for the layout would be dependent on the specifics of the case. So my time with SketchUp has come to and end and in part 2 (and maybe part 3 at this rate) I'll go over some of the details of designing a sheet metal computer case.
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