This is an HMD i designed based on the Google Cardboard specifications. The lens fittings are for 37mm lenses (which I had scavenged from a Oculus DK1).
The holder for the smartphone is for a Samsung Galaxy S4, roughly 137mm by 70mm. Distance between lens and screen is 45mm, between lenses 54mm. You can find the qr code for the settings among the images
Images are of a prototype which sadly fell to the floor and broke.
It's designed to be printable entirely without support, although the nose part might benefit from it.
After printing you need to glue the three parts together. User super-glue for that and a softer glue for the lenses (in case you want to use them again some time).
To make the straps you should have about a meter of 30mm elastic band (cut to your satisfaction).
You'll need 3 pieces of the small plastic part (in hmd_strap1.stl) to secure the strap on each side and the large one on the back of the head to join the strap going over the head with the horizontal strap.
You will probably benefit from some kind of foam around the lining next to the face (untested).
Configure the device with the QR-code from the images.