High Voltage Feedthrough Experiment on Flickr.
So it turns out that spark plugs make terrible high vacuum devices, and this became quite apparent before even introducing one into the chamber. While attempting to “alter” one on the lathe, the metal sheath became very loose and it was evident that there was neither an o-ring nor any sort of sealant nor braze connecting the ceramic core to the metal jacket which contains the threads.
A couple of lathe-hours later…
"Yo dawg, I heard you liked holding work-pieces so I put a chuck in your chuck so you could use inner jaws while you use outer jaws"
Upon discovering this I simply removed the entire jacket and turned the profile of the Al2O3 core into a custom KF-25 flange. The fit was so snug it required a special jig just to remove once I had “test fit” the part.
Add in some hysol 0151 low out-gassing epoxy and viola! A high voltage feedthrough :)