Well the "O" ring retention does work...ie to hold the lens in place, but I have a tiny bit of slop between the lens and the "O" ring so what happens is that the lens starts to vibrate a bit when air assist pressure is applied. The error was in the machining and not in the concept......well thats my story and I'm sticking to it
What I did then was to machine a sleeve to hold down the "O" ring in place and then hold the ring with 3x 4-40 grub screws. This really does hold the lens in place with the ring providing a slight buffer between the lens and the sleeve. The lens sits flush inside a machined pocket. Its a bit of a patch, but at least I didn't have to machine a whole new focusing lens ass'y.
The final two pictures show the last mirror ass'y.
Everything that is shown here was scatch built except for the mirror ass'y which was from a surplus laser medical equipment.
Time to start cleaning up the area around the machine and hopefully start applying some power to the system this week.