Low-cost interchangeable high vacuum feedthrough

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Post Reply
ChristofferBraestrup
Posts: 131
Joined: Sat Apr 11, 2020 9:47 am
Real name: Christoffer Braestrup

Low-cost interchangeable high vacuum feedthrough

Post by ChristofferBraestrup »

This idea came to me from just browsing my box of vacuum clamps and hardware (as one do, on a sunday night).

I wanted a cheap, solderable feedthrough system to allow a muriad of small hermetic seals or 1/8" copper tubing through.

I also wanted to find a use for those KF-to-baseplate or heavy vessel wall clamps, that can't be used for flange-flange interconnections.

Here's my feedthrough. The assembly is laid out in the images.

The sealing surfaces are 1.5mm brass plate (2) against a KF-25 O-ring with one centering ring filed down (3) to allow mating onto a flat surface.

This is held in place with a heavy 10mm aluminium plate (1) bored out to 22 mm (ID of a KF25 tube) and 8mm holes for the half-clamp (4), which is then clamped down on a KF flange, in this case a Tee.

The brass plate holes are 1mm oversized to avoid the plate catching on the threads or bowing outwards due to sloppy tolerances.
Everything is re-tightened under rough vacuum, as is customary.

With the setup as pictured, the setup reaches 10^-6 torr within half an hour, about the same rate as observed before its addition.


The benefits of this system is:

- The soldered/brazed brass plate with whatever feedthroughs can be swapped easily, and is not a vacuum specific part.
- The heavy aluminium backing plate may not be necessary with a thicker sealing plate, but could be replaced with a die-cast Hammond enclosure with the same hole pattern,
feeding the feedthroughs directly into an electronics box or to larger connectors.
- Finally a use for those pesky half-clamps!
- Can be built within half a day

downsides:

-Brass is a rotten material for vacuum, consider sustitution for pure copper.
-Clamping on a smaller area of the KF flange sets higher requirements to the backing plate's rigidity.


Hope you all found this helpful!
vacft1.jpg
vacft2.jpg
vacft3.jpg
vacft4.jpg
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Low-cost interchangeable high vacuum feedthrough

Post by Richard Hull »

Looks good for the man who can do with materials at hand. I see that you, like me, don't throw out good hardware just because the outside surfaces are covered in rust. As one takes things apart from scraping junk, no need to throw out perfectly good hardware. 3 ata-boys for recycling and saving money.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
ChristofferBraestrup
Posts: 131
Joined: Sat Apr 11, 2020 9:47 am
Real name: Christoffer Braestrup

Re: Low-cost interchangeable high vacuum feedthrough

Post by ChristofferBraestrup »

It's much worse than that: I had to borrow those nuts from my shortwave antenna mount. Running out of M8 bolt hardware in a metric country is bizzare, but all shops are closed at the moment.
Post Reply

Return to “Vacuum Technology (& FAQs)”