Ran up a very rough proof of concept for the Juki quick change nozzle holder.

Material is phosphor bronze (from scrap bin - valve guide stock), wee magnets from the fridge and a dummy juki nozzle roughly turned from steel.

The magnets hold and grab the "nozzle" gently but firmly, but removal force is just a few grams. Most importantly with the magnets installed the right way round, the tip is not noticeably magnetized. 

Positioning of the magnets is critical - looke like they should be a little above the bulge in the nozzle shank. There is a strong centering force right there, so we'd want to use that to pull up and make the nozzle face pull against the face of the part. 

Presumably when a component is being held the vaccum will strengthen the bond, but we don't want the thing to re-center and drop when vacuum is released.

So hole depth is critical, as is magnet placement, as is nozzle seat diameter. I see some jigs and a reamer in my future.

Thinking black Delrin for the material for the real thing.

Credit where credit is due, this idea came from "alex" https://groups.google.com/d/msg/openpnp/IG9cEUypjtM/bqkRM8PEHwAJ

with the lightbulb moment at:

https://groups.google.com/d/msg/openpnp/IG9cEUypjtM/1sfj1XyzKAAJ