Epoxy to attach KF flanges to baseplate

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Arun Luthra
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Epoxy to attach KF flanges to baseplate

Post by Arun Luthra »

I have a 1/4" thick steel baseplate for a vacuum bell jar. I'd like to attach these KF-16 and KF-25 flanges (half nipples) to it with vacuum epoxy. Is it possible, or do I need to get them welded? There will be a cathode and anode elevated above the baseplate, not more than 1kV. The baseplate is connected to the cathode/ground but I will try to keep plasma away from the baseplate.
kf.jpg
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Joe Gayo
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Re: Epoxy to attach KF flanges to baseplate

Post by Joe Gayo »

Whenever I want to avoid welding and the max temperature is low, I use orings. Orings are your friend. For a baseplate use something like a baseplate KF port -- https://www.ebay.com/itm/164791120703 (https://www.idealvac.com/Feedthrough-Ba ... pp/P101602)
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Mark Rowley
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Re: Epoxy to attach KF flanges to baseplate

Post by Mark Rowley »

I’ve used JB Weld for a similar purpose. However (IMPORTANT), a very special seat was machined in place for the fitting to lock into. Even though it worked and maintained an excellent vacuum, I strongly advise to go with what Joe said. Purchase or machine your own flange using o-rings. It’s the best option.

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Jim Kovalchick
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Re: Epoxy to attach KF flanges to baseplate

Post by Jim Kovalchick »

My son used JB weld to fix a similar KF fitting to an aluminum plate. He made lots of neutrons without the fitting failing, and his chamber was at 10-7 torr level at its best.
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Re: Epoxy to attach KF flanges to baseplate

Post by Jim Kovalchick »

Depending on how big your plate is, a flat 1/4" aluminum plate may flex under vacuum.
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Re: Epoxy to attach KF flanges to baseplate

Post by Arun Luthra »

Joe Gayo wrote: Wed Apr 28, 2021 6:32 pm Whenever I want to avoid welding and the max temperature is low, I use orings. Orings are your friend. For a baseplate use something like a baseplate KF port -- https://www.ebay.com/itm/164791120703 (https://www.idealvac.com/Feedthrough-Ba ... pp/P101602)
I'm leaning toward using the baseplate o-ring feedthroughs. Probably going to set aside / abandon the 1/4" steel plate that I already drilled and use a 3/8" aluminum disk which will be easier to drill.
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Rich Feldman
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Re: Epoxy to attach KF flanges to baseplate

Post by Rich Feldman »

Two-piece KF bulkhead clamps served me well years ago.
Flat plate needs a not-too-precise round hole matching the nominal KF size.
https://www.ldsvacuumshopper.com/qfbulclam1.html
nw25-bulkhead-clamp-16.jpg

1/4" thick steel is plenty stiff for base of a 8 inch bell jar, probably bigger.
I got away with a 3/8" _plastic_ baseplate for what I think was 8 inch jar.

A good source for aluminum disks is S and S Machine company.
http://www.sandsmachine.com/alumweb.htm
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Arun Luthra
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Re: Epoxy to attach KF flanges to baseplate

Post by Arun Luthra »

Rich,

I'm trying to understand the geometry of the bulkhead clamp. Does it install flush with the bulkhead? Then, there would be no way to attach the outer KF clamp.
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Richard Hull
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Re: Epoxy to attach KF flanges to baseplate

Post by Richard Hull »

The lip on the split clamp catches the KF and mashes it into the normal required centering and sealing viton ring. The mating hole in the plate must be big enough to fit the normal KF centering and sealing ring so the viton can seal against the plate or bulkhead. Note: Ideally the bulk head might not want to be tapped all the way through for the screws to avoid vacuum sealing issues with the screws. This means either a thick bulk head or using a flat ended, plug tap in threading short tapped holes in a thinner bulkhead so as not to pierce the bulkhead. Trimming the screw lengths may be demanded. You have to figure all of this out on your own. In the end, this is the absolutely perfect solution as Rich noted.

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Re: Epoxy to attach KF flanges to baseplate

Post by Arun Luthra »

Thanks Richard, I understand now. Far cheaper than the other kind, but requires making threaded holes.
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Rich Feldman
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Re: Epoxy to attach KF flanges to baseplate

Post by Rich Feldman »

Arun, it's a good opportunity to learn how to use threading taps. They are a little bit more complicated and expensive than drills, and you can read all about them on the Internet.

When I used bulkhead clamps on a 3/8 inch plastic baseplate, it was no big deal to tap the blind holes as Richard mentioned. 10-32 regular tapered tap followed by 10-32 bottoming tap.

For a 1/4 inch thick plate I would drill and tap holes all the way through, then plug them on vacuum side.
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Joe Gayo
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Re: Epoxy to attach KF flanges to baseplate

Post by Joe Gayo »

Bulkhead split ring clamps are great and I use them frequently, but my opinion is use the simple baseplate port I originally posted and move on to other challenges.
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Re: Epoxy to attach KF flanges to baseplate

Post by Arun Luthra »

Rich Feldman wrote: Fri Apr 30, 2021 11:24 am Arun, it's a good opportunity to learn how to use threading taps. They are a little bit more complicated and expensive than drills, and you can read all about them on the Internet.

When I used bulkhead clamps on a 3/8 inch plastic baseplate, it was no big deal to tap the blind holes as Richard mentioned. 10-32 regular tapered tap followed by 10-32 bottoming tap.

For a 1/4 inch thick plate I would drill and tap holes all the way through, then plug them on vacuum side.
How are they plugged?
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Rich Feldman
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Re: Epoxy to attach KF flanges to baseplate

Post by Rich Feldman »

Depends on baseplate material, operating temperature, and whether vacuum side needs to be flat in the area.
Practice on a piece of stock which is not your real baseplate.

You could cover the holes with small flat disks or squares on vacuum side; tin can metal is thick enough for that.
Or plug holes with screws that engage the first couple of threads, and could be cut off flush.
Secured and sealed with solder, epoxy, etc.
The stresses are negligible compared to those on a KF-to-baseplate adhesive bond, which worked for Jim K's son.

Joe's suggestion is less trouble, though I expect it encroaches more on the vacuum space.

By the way, I used a hole saw to make the big hole in my baseplate. On another job I had no trouble going through 3/4 inches of mild steel with a hole saw, employing drill press with very slow spindle speed and plenty of cutting oil.
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Chuck Sherwood
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Re: Epoxy to attach KF flanges to baseplate

Post by Chuck Sherwood »

I placed an online order for several "bulkhead flanges" from LDS link in this thread. The online order says shipping was free for orders over 75 dollars.
I received multiple invoices showing zero shipping charges.

Several days later I got an updated invoice with a $28 dollar shipping charge because it was a residential deliver. That is outrageous for a couple pound package.

I'm very disappointed because I thought I had finally found a decent company to work with. Duniway has gouged me for shipping on a few occasions.

BTW, someone was looking for custom made flanges. LDS states they will make custom fittings and there is a link on their website to get a quote.
Based on this experience, I wouldn't count on an affordable price.

chuck
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Re: Epoxy to attach KF flanges to baseplate

Post by Mark Rowley »

Best to find a friend with a lathe. Specially made parts from mainstream suppliers could easily exceed the cost of an operational fusor.

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Richard Hull
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Re: Epoxy to attach KF flanges to baseplate

Post by Richard Hull »

LDS is a business and you must read all the shipping caveats! there is a premium attached to home delivery by all shippers like UPS and FedEx. Shippers rather not wander around neighborhoods looking for a single package delivery... They like going to a familiar business each day and dropping off 10 to 50 packages.

Since shipping will always be charged you need to order over $100 worth of stuff to even come close to netting some sort of value in mail order. With inflation and skyrocketing gas prices expect big shipping increases. Buying brand new vacuum components is expensive, but you know what you are getting as opposed to e-bay.
Like Mark said.....find a friend who is a machinist. I will add....or learn to machine and weld yourself. You ain't seen money disappear at the rates charged by professional, small job machining and welding shops.
Even then, most shops do not know the specifics of vacuum system welding.

Richard Hull
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Re: Epoxy to attach KF flanges to baseplate

Post by RobertMendelsohn »

+1 to what is said so far here.

I have used epoxy to connect various metal parts before for vacuum use, rather than weld, and have found great success with Hysol EA1C. JB Weld may be the 'duct tape' of the vacuum world, but I think Hysol is a lot better; it can be used below 10^-9 mbar and is really easy to work with. I've used a blowtorch to weaken and remove the epoxy easily when parts need to be disconnected. Overall I've been able to create really high quality DIY components using it, and have never had a leak while using Hysol EA1C. One application specifically mentioned by the manufacturer is as a 'vacuum feedthrough sealant', and it is a great electrical insulator. Hope this helps.
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Jim Kovalchick
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Re: Epoxy to attach KF flanges to baseplate

Post by Jim Kovalchick »

I like Hysol, but it does not hold up well when exposed to plasma.
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Re: Epoxy to attach KF flanges to baseplate

Post by Mark Rowley »

Same experience here as Jim. Hysol is also brittle. After using it exclusively for more than a decade (2001- 2012), I'm no longer confident in it's ability to withstand mechanical stressors or provide equal adhesion on par with JB Weld. Not saying its bad stuff, I've just found JB to be stronger and considerably easier and cheaper to obtain.

I'm curious how Hysol perform against JB Weld in a similar round of tests like this:

https://www.youtube.com/watch?v=R3r0UZ7txzs

Mark Rowley
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