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Part 96: A 3D Printed Case Mod

September 8, 2015

The PrintrBot
I've wanted to build a custom computer case (case mod) for years, but I'm not very good with tools (too clumsy). I tried years ago with acrylic sheets, but couldn't produce anything I liked. After a few days of fussing around with glue and trying to drill holes in acrylic, I gave up on it.

When I started playing with 3D printing on Shapeways, I realized that a Mini ITX motherboard (170mm by 170mm) would fit within their maximum build volume. Full of excitement, I bought a board (the ASRock H77M-ITX) and built a system. Not long after that, I realized Shapeways was just too expensive to prototype with and build a case.

Last year, I bought a PrintrBot Simple Metal 3D printer. Looking around for a project to do this spring, I decided to print a case for my computer.

Designing for Home 3D Printers

Overhang example

Most home printers are FDM (Fused Deposition Modeling) printers, which draw a layer of lines in hot plastic, then raise the print head (or lower the bed) and draw another layer. This means that each layer has to be supported by the one below. New layers can partially overlap an existing layer, like a staircase, to make an overall slope of up to 45 degrees. This allows limited overhangs.

To print more general structures, the slicer software (which converts the 3D model into a series of 2D layers) will build supports. After the print these are removed.

The slicer I'm using (Cura) doesn't do a great job on supports. The problem is that they are made of the same plastic as the model, and must touch it, so of course they stick. Some supports break away easily, but others are welded into the model so thoroughly that they just can't be removed.

You can also rotate a model to try and find a good angle that minimizes overhangs and the need for supports. My computer case, being mostly cubical, wasn't much of a problem. Most of it printed without any supports. This corner piece has very small supports under the pegs and the elevated portion of the edge, and they removed easily.

Case part with supports

Multi-piece Models

Pieces don't fit
The PrintrBot can create models 150mm by 150mm by 150mm (6" cube), but not really. There's an outside perimeter a few millimeters wide around the piece. Or to reduce warping, you can use a "brim" to increase the area sticking to the bed. I'm using a 10mm brim, so that reduced the build size by 20mm overall. Since my case turned out to be about 250mm across, I have to break it into chunks.

The problem with doing that is the PrintrBot just isn't exact enough to give you a clean fit on the finished chunks. The image shows what I'm dealing with. For scale, that's a standard PC power connector at top-left. The holes are about 20mm.

What's happening here is that the piece curls up (warps) as it cools. Then the later layers on top crush it down. So you get a thinner piece than desired on the result. There are things you can do to prevent this, but they are extra work. This part doesn't show on the outside of the case, so I didn't bother. Think of this as the worst case if you do nothing.

Even in the best case though, there can be gaps of up to 1mm between parts. They just don't fit together cleanly.

Constraints

The system consists of motherboard with graphics card, two hard disks, one DVD drive, a power supply and a fan. I'm using an older non-modular power supply, so there are unused cables to stuff in the case as well.

The first constraint, as you can see from the pictures above, is that many of my ideas just weren't printable due to overhangs or the sloppiness of the printer output.

How about a dodecahedron?

The next constraint is the strength of the plastic. In general, a thick model is fairly strong (can't break it with my hands), but there are screw holes to worry about. If you stick with the standard PC screws, you need to use thin walls around the screw holes, and these won't take a lot of weight. I didn't want to try suspending the power supply from the top, for example.

Next there is cooling. I need some kind of airflow around all the components. This was harder to deal with than I expected, since components in front of the fan block everything behind. I looked at commercial cases on the net to see how they were built.

Another constraint occurred to me only after I started printing parts -- I have to get my big fat hands into the guts of the thing! And there has to be room for a screwdriver to screw in all the parts. That led to a couple of complete redesigns.

The biggest problem was that I just didn't know what I wanted. I never have much confidence in my artistic judgement and kept changing my mind.

The Frame

Since I couldn't make up my mind about the look of the case, I decided to split the task in two. I would build an inside frame that holds all the components, and then a decorative case that slides over the frame like a lampshade. Then I could even have more than one case and switch them out when I got bored! (rationalizations are wonderful, aren't they?)

The inside frame didn't have to be pretty, and since the motherboard is just 6.7" across, I thought a 9 inch cube would hold all the parts. And it does, if you ignore those constraints about airflow and being able to actually install the components!

I had several weird designs with disk drives stuck in odd places, but once I realized I couldn't actually reach the drive screw holes, I started over. Instead of trying to pack everything into a cube, I decided to just arrange the components simply and see how big a box that requires.

A simple design
I also changed two design requirements. Instead of a standard 120mm case fan, I would use a smaller 80mm fan. And instead of putting the DVD drive inside the case, I would build it into a pedestal below the case. I don't use the DVD much any more, and I didn't think it needed much cooling. Most commercial case designs stick it on top, far away from the fans.

With that new set of requirements and a "build up a box" instead of "force inside a cube" attitude, a simple design popped right out. And it was almost as small as what I had been trying for. I really felt like an idiot when I finished this!

The drives are over the power supply, and the motherboard is sideways next to it. Not visible is the case fan, which sits right in front of the hard drives, giving them excellent cooling. The power supply fan pulls air right from the motherboard and graphics card. The graphics card still gets pretty hot, but that's what they do... The DVD drive is on the bottom.

Cut Into Chunks

Chunks with tabs and slots
I split the side panels into four pieces each so that they were small enough to print. Since the printer output is so sloppy, I knew I would not be able to simply glue pieces together along the edges (not smooth enough). Instead, there are tabs and slots on the edges of each piece.

I'm using a "hot glue" gun to glue pieces together. It seems to stick to the PLA plastic well enough, and gives me 15 seconds or more to wiggle pieces together before it sets up.

To my surprise, each of these 120mm by 120mm by 8mm pieces takes nearly an hour to print! To speed that up, and cut down on filament used, I added a bunch of holes in the panels. Even with that, it was a 45 minute print for each of twelve pieces for the complete frame.

Unfortunately, I made some stupid mistakes. I accidentally positioned the motherboard an inch too far in, so that the I/O ports were not flush with the back. I didn't realize this until I had glued the whole thing up, put in the motherboard and tried to plug in all the cables. Time to reprint the whole thing!

Then I discovered that although the graphics card connectors were now in the right place, the hole wasn't wide enough for the monitor cable plugs. I think I printed parts of the frame three times before I got it all right...

Getting this far was a nuisance. The PrintrBot is noisy and prints take hours. There's a slight smell of melted plastic. The printer had also broken down twice requiring me to figure out what was wrong and repair it. At this point, I was completely sick of the project. I ran the computer in the frame for a month or more before I got around to designing the decorative case.

Completed frame

The Decorative Case

My experience designing and building the frame (which had taken far too long) left me wanting to do a very simple decorative case -- something cube shaped! And I didn't feel up to designing anything unique. I thought I'd just grab something from movies/TV, etc.

Many Cubes


Celtic borders

Case borders

A leaf vein pattern
That didn't really solve my problem though. I'd have to break my design into printable pieces, and I'd need to do something about the seams between parts. The only thing I could think of was to break the design on some feature of the artwork, and hide the seam that way. For example, if the face pattern is a curve, cut it in two along the curve, so the seam is part of the design.

That got me looking for vector art with a lot of contrast. Following links on Google Images got me to Celtic knot patterns. I decided to try a border with repeating elements, joined together with pegs and holes. I thought that should hide the joins between pieces.

I designed a simple chain of boxes with the corners cut off, and pegs to join them. The corner of the case is the piece in the "supports" example above. The final box didn't look bad. Up close, I can see where the breaks are, but from a distance, it's not obvious. I decided that would be the border and there would be some kind of panel inserted into each face.

The Inserts

At this point, I thought of just printing some photographs and gluing them inside the border. Then my case would just be a large picture cube! But I couldn't bring myself to quit like that. I wanted a fully 3D printed case, so I needed to come up with a design.

I've been using white filament in my printer, figuring I would paint it if I needed to. But there are a few other colors. In particular, they have a transparent blue. That made me think I could do some kind of greyscale image, by printing it thin for light blue, and thick for dark blue.

I was tempted to do a Simplex noise cube, in tribute to all the stuff I did with that code in my game work. I bought blue filament and printed a test patch, but it didn't work.

The printer really isn't up to making a detailed greyscale pattern from thicknesses of filament. The printer works by printing lines, not pixels. In fact, if you try to do a single dot of filament, it will either fall off or get stuck in the extruder head and smear into the next feature. So I needed a bold pattern.

In contrast to the geometric frame, I wanted something organic, and searched Google Images again for interesting textures. I was looking through enlargements of bacteria, rock patterns, wood grain etc., and hit an enlargement of a leaf vein pattern. That looked like the right thing, with only a few levels of grey and big bold patterns. I inverted this and played with the contrast, then cut it up to make faces of the cube.

But of course a complete face is too large to print, so I broke each face up into quarters, with a central disk. I also printed a join between all the pieces (like grout between tiles) that I thought would let me adjust for the sloppiness of the printer.

Combining insert pieces

Unfortunately, the gaps were too irregular, and the glue blobs were very visible at the joins, since the piece is transparent. After two or three different attempts, I decided to just glue the quarters without the "grout" to a piece of white poster board, and then glue that into the border cube.

From the front, that looked OK. The white of the poster board filled the gaps between the pieces. But from an angle, you could see that they were all separate pieces and not connected. It bothered me enough that after a couple of days, I printed some white pieces to fill the gaps and glued them in as well.

The Final Result

My computer

As usual, I have no confidence in my artistic judgement, so I have no idea how this will look to other people. I find it interesting to look at from across the room. Up close, I can see all the errors made by the printer, the gaps between pieces, and some glue that seeped out around the corners. The OCD part of my personality is itching to fix it all somehow!

Now that I know more about designing for the PrintrBot, perhaps I'll do another decorative case. Or build another complete case for the other systems I have. It will have to wait though, since I really want to get back to Sea Of Memes.

This was all too much work for the result I got, but that wasn't the point of the project for me. I had a lot of health issues this spring, and completely stopped working on my hobby projects (including game development, as I'm sure you noticed.)

The point was to do a small project and see it through despite any setbacks. There were more difficulties than I expected, but it's done now and I'm glad I finished it.

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