Grab the 3D printed top part and the 2.2" PiTFT. We need to test the tolerenaces to ensure everything is going to fit right.
Test Mounting Pegs
Line up the buttons cutouts with the ones on the display and place the top part over the display. Press down on the corners to get the pegs to insert into the mounting holes on the PiTFT PCB.
The two 3D printed spacers have holes on boths sides. They should fit into the pegs on the top and bottom parts. These spacers keep the two PCB's from bending and closing in on each other.
The ports should line up with the cutouts on the case. At this point you should check the spacers are still in the right spot. Make sure the holes are lined up.
Yay it's done! If everything snap fits together nicely, you should be good to install an SD card and power up your tiny Raspberry Pi project.
Install SD card
The cutout on the bottom part of the enclosure should let you insert a microSD card.
If you find the pegs from the 3D printed parts don't fit into the mounting holes, you may need to level your printers bed and ensure its not too tight. Alternatively you can resize the diameter of the pegs in CAD or carefully sand them.
They pegs should be pretty ridged and withstand several installations. If you find they easily break off, you may want to turn off your retraction in your slicing software. I’ve personally found Makerware has this problem. Try CURA or Slic3r instead.
If the corners don't quite snap into the case, the spacers are most likely not aligned properly, causing the pegs to only insert half way through. Use a thin pointy tool to poke the spacers and align them into place.