This adapter for the Oculus Rift is designed to position prescription eyeglass lenses just above the fresnel lenses of the Rift headset. The prescription lenses that fit this adapter are available by ordering eyeglasses from Zenni optical with frame #550021.
This adapter is the result of a few weeks of design in Autodesk Inventor and tweaking to get it working for my face, then a total redesign using Autodesk Fusion 360. This was my first fully realized 3d design and 3d printing project, so while a lot of people have successfully used this adapter, I make no guarantees that this adapter will work for anyone but me! To make for easier remixes, this design is also available in it's native Fusion 360 format here: http://a360.co/2g4JcHj
Once you have the glasses from Zenni, you need to remove the lenses from the frame, but before you do, make some small orientation marks with a marker on the edge of the lens so you know which way is up and which lens is right and left. You want to maintain the correct orientation when transferring the lenses to the adapter.
With the lenses out of the Zenni frame, you should fit the lenses into the groove in the inner rim of the adapter. Outside of the Rift headset the lenses will fit somewhat loosely in the adapter. Once the adapter is fit onto the headset the tension on the adapter will make the lenses more secure.
There are tabs at the bottom of the adapter that should straddle the plastic rim at the bottom of the facial interface.
The top curved part should be oriented so its sitting flush against the indentation on the facial interface that gives clearance for the cord.
Once the adapter with lenses is fit in the facial interface, re-attach the assembly to the rift by pushing in the flat tab at the top, then gently fit the bottom tabs into place.
Replaced the main file with a new file that is correctly manifold.
Added an in-progress version that is designed for the lenses to snap into place. (I like this version because the lenses are solid even when the adapter is removed. Makes it easier to pull the adapter out to demo the rift. I still like the old version too because it has more clearance around the nose area.). Download the fusion 360 format files here - https://a360.co/2IKZXXe
.2mm works fine. .1 is slightly better