As the smartphone spectrometer is going into production, we're also posting the most recent 3d printable version for sale on Shapeways:
This is the design by Brad Dudenhoffer, which remains the best for 3d printing, although it was redesigned by Mathew Lippincott for injection molding.
I also posted it on Thingiverse, although if Brad would like to do so, i'll switch to the version he posts.
Update: 3d printing tests
I had a chance to use the 3d printer at MISiS in Moscow, i forget what kind it was but will ask; it was large (2.5 feet cubed) and made of lasercut clear plastic. Someone said 3DSystems bought the company... anyways here are the prints. It was not super well calibrated, but we had trouble printing them well enough for the bosses to fit in the holes: