Even 12V connections? If that's the case, I'll have to modify the top so it can hold the wire connection as well. Hmm... I wonder if I can make a wire connector integrated into the top...

I was skeptical when I first got interested in 3D printing, but then found things like this:

newest - Thingiverse

Some of these designs are ingenious. There's a surprising amount of useful stuff out there :)

So, I've read through everything I could find on low voltage electrical code. It seems my installation is a class 2 circuit. The power supply is 100W with two 50W outputs, which conforms with class 2, and the wire splices are in a location where they're not subject to inadvertent physical stress.
I can't find any requirements for wire splices for class 2 needing to be inside a box, but I'm certainly not a NEC specialist. Anyone have any more insight?

Still, I like the idea of having the connector integrated in the fixture top. I may get a bunch of Molex or lustre connectors and design the top part so that the connector can be integrated into the fixture top itself :)

That looks awesome. where did you get the 3d printer from?

It's a Printrbot Jr. kit I bought from MCM electronics. I think I got the last one of the version 1 PbJrs, they went out of stock as soon as I ordered mine :P
Printrbot.com sells a few different models, unfortunately all a bit more expensive than the Jr. V1.

I did not realize it was low voltage. That may be alright depending your local code. I like your idea about molex plugs. Sounds like a good compromize for safety.

So, I did some more research into what the code says about recessed fixtures. It seems that, regardless of the type of light used, if you want to put insulation on them, you have to get an IC rated canister on the top side. What makes an enclosure IC rated? Certification by an approved laboratory. Makes me wonder if I can send in one of my homemade fixtures to get them tested and certified, ha!

I just measured with an IR thermometer, and after 48 hours on with insulation on top, the temperature is on the order of 115F directly on the top of the fixture.
However, there don't seem to be any public specs about maximum temperature that a fixture can have to be OK for direct contact. It's really a bummer, because it means that, to be code compliant, I have to enclose the tops of these fixtures. Luckily, what seems to be a compliant way to enclose them is to build a box out of fire rated drywall, taped together with fire tape, and put it over the top. Yes, seriously. Taping a drywall box together and putting it over the top is compliant. Having a fixture that doesn't exceed 120F to begin with is not. I understand the needs for standardization in building codes, but that still left me with an incredulous look on my face.

So, just to be safe, I'll buy a sheet of 1hr fire rated drywall and build a 5" box around each of the fixtures. Does anyone have any more insight into fire codes, is there maybe something I've missed?