I wanted to use my old Nikon D40 kit camera's lens with my new Sony NEX-5R so I could have totally mechanical focus, zoom, and aperture control. After a few iterations, this is what I've come up with as an adapter. No clean up or supports required! Print it in PLA and plug the bits together. To attach the Nikon lens, line up the little white dot on the lens with the L shaped indent on this adaptor ring, then screw it in anticlockwise.

My D40's kit lens depends on the camera to set it's aperture via a little prong on the lens mount - so this adapter includes a little poker thingy, so when the lens is totally screwed in, the aperture is fully open. To close the aperture, unscrew the lens slightly - you'll see two little indents on the adaptor indicating the range of aperture settings. Line up the white dot on the F-Mount lens within this range and you'll be sorted. Of course, you'll have to eye it - none of this stuff is calibrated or measured at all!

Version 1.0 of this adaptor was largely guess work and experiments. Version 1.1 is based off real measurements of camera bodies and lenses, and built with precision, lining up the focal plane of the Sony camera accurately. Thanks go to GEsteve for pointing me in the right direction there.

I used nameless911's EOS to Nikon F-Mount adapter as a reference when designing this one, but their actual mesh was not reused.
Todo: design a mechanism to lock the nikon lens in place, so it cannot accidentally come loose