After many trials and tribulations I have finally managed to assemble a vacuum tight acrylic version of the v2.2 attenuator enclosure. The two advances tested with this prototype are the 9 mm acrylic end plates and the vacuum preparation of the Torr Seal epoxy cable through to remove air pockets.

Increasing the thickness of the acrylic end plate from 5.6 mm to 9 mm has made the end plate a great deal more rigid. This improves the compression of the o-ring and eliminates leaks at the o-ring between the corner fasteners.

For sure using a vacuum to degas the Torr Seal epoxy in the cable feed through opening in the acrylic was a big improvement. Looking through the acrylic end plate you can see that the epoxy now fills the entire cable feed through opening. There are no more air pockets in the epoxy that might lead to a leak. There may be tiny air bubbles in the epoxy but the air pockets that could join to make a leak are gone. The only thing I don’t like about the vacuum prepared epoxy feed through is that the epoxy actually expands during the preparation and now overflows the opening in the acrylic end plate. The overflow probably just improves the seal but I hate the look of it. I need some more finesse in this part of the design/assembly process.

Both improvements look very promising and the vacuum has been maintained for 24 hours. I will keep watching this for a week or more as I work on other things. Next up I will finish repairing the v2.2 aluminum/glass version by making a new rear end plate and use the vacuum prepared Torr Seal technique. I will also order parts to make a complete acrylic version.

Acrylic version of v2.2 holding a vacuum.