Can't find supplier for ~1 inch Viton stopper

[Nathan McCorkle]

looking to make a vacuum container wire feed-through, thinking I'll
drill a hole into an existing aluminum blocking plate (maybe with a
chamfer/angle to it), shove some piano wire through the stopper, then
shove that into the blocking plate and pump down. Maybe I'd extend the
existing blocking-plate screws and screw down a clamp on the stopper.

But I can't find a supplier for these. The closest I've come is this
list (personally I think I'd pick the sphere out of any of these, as
it seems like it'd seat more like a stopper in the hole):
$5.46
3/4" inch
Viton Fluoroelastomer Sphere, 70A Durometer, Precision Ground Finish,
No Backing, Black, Inch
http://www.amazonsupply.com/dp/B00CCGYHZO?ref_=sr_1_9_txt

$45.62
1 sq ft of 1/8" inch sheeting
http://www.amazonsupply.com/dp/B0075ZN4RE?ref_=sr_1_2_txt

$7.09
Stopper that is questionable as to whether holes come as-purchased:
http://www.amazon.com/Universal-Stopper-Viton-Synthetic-Rubber/dp/B0011Z90P4/ref=sr_1_1?ie=UTF8&qid=1406519692&sr=8-1&keywords=viton+stopper

$24.90
VITON RUBBER SHEET 1/8" THICK 6" X 6" SQUARE ACID CHEMICAL HIGH TEMP
http://www.ebay.com/itm/VITON-RUBBER-SHEET-1-8-THICK-6-X-6-SQUARE-ACID-CHEMICAL-HIGH-TEMP-/200891967372?pt=LH_DefaultDomain_0&hash=item2ec618278c

$6.50
1 Gasket 2in Disc 1/16 Thick Replacement Viton Rubber MadeBy ElisGeneralStoreLLC
http://www.ebay.com/itm/1-Gasket-2in-Disc-1-16-Thick-Replacement-Viton-Rubber-MadeBy-ElisGeneralStoreLLC-/251595451636?pt=LH_DefaultDomain_0&hash=item3a9441ecf4

(I also found some someone on youtube or something claiming to have
made some viton stoppers in a small batch and had some for sale, but I
never
heard back from them)



--
-Nathan

[John Griessen]

On 08/29/2014 03:29 AM, Nathan McCorkle wrote:
> looking to make a vacuum container wire feed-through, thinking I'll
> drill a hole into an existing aluminum blocking plate

How about buying a ready made terminal with plastic around it to silicone into
a hole in a plate, or hole in a rubber stopper?

Or, the spark lighting electrodes from gas grills (like piezo sparkers come from)...
They look like a glass to metal assembly that might be fairly hermetically sealed
just by accident... They're 0.25 inch diameter and would fit in a stopper hole also.
I think there's one of those just down the street at the moment...

[Nathan McCorkle]

On Fri, Aug 29, 2014 at 7:51 AM, Jerry Biehler <jerry....@gmail.com> wrote:
> If you need a vacuum feedthrough use a spark plug.

A sparkplug has been mentioned elsewhere to me, the problem is that it
is quite large compared to the space available. I've only got about an
inch or inch-and-a-half to work with and need at least 3 wires to
begin... tapping holes also sounds harder than jamming a rubber
stopper!

[Nathan McCorkle]

On Fri, Aug 29, 2014 at 5:48 AM, John Griessen <jo...@industromatic.com> wrote:
> On 08/29/2014 03:29 AM, Nathan McCorkle wrote:
>>
>> looking to make a vacuum container wire feed-through, thinking I'll
>> drill a hole into an existing aluminum blocking plate
>
>
> How about buying a ready made terminal with plastic around it to silicone
> into
> a hole in a plate, or hole in a rubber stopper?

All the terminals I've seen that mention anything about vacuum or
hermetically sealed seem to ring-in in the hundreds of dollars.

Also I'd like to try and keep the chemical list down to a minimum, as
certain materials like to off-gas for a very long time and that
behavior can foul the vacuum and imaging system contained therein.

>
> Or, the spark lighting electrodes from gas grills (like piezo sparkers come
> from)...

Hmm, I haven't look at one of those in a while, I've got a box of
gas-leaked-out piezo hand-held lighters but they've just got a
plastic-insulated wire. Do you have a certain brand?

> They look like a glass to metal assembly that might be fairly hermetically
> sealed
> just by accident... They're 0.25 inch diameter and would fit in a stopper
> hole also.
> I think there's one of those just down the street at the moment...

I'd really like to try the Viton stopper approach, NASA seals walk-in
vacuum chambers with doors >15ft wide using Viton o-rings (or used to
at least). The rest of the vacuum system uses Viton, which may not be
required as this doesn't go through temperature swings or harsh
chemical treatment. But I have only really scratched the surface on
o-ring vacuum sealing technology, so I'm not sure which rubber
compound would be second-best (in terms of how flexible, and also in
terms of off-gassing). I know off-gassing can differ between different
kinds of RTV silicone, as I've researched the various types of those
available for potting electronics.

I'll take a look at the grill lighters for sure when I go to the
hardware store to look for stoppers.

Thanks!

[John Griessen]

On 08/29/2014 10:36 AM, Nathan McCorkle wrote:
> I'd like to try and keep the chemical list down to a minimum, as
> certain materials like to off-gas for a very long time and that
> behavior can foul the vacuum and imaging system contained therein.

OK, now I get that you're working on getting real vacuum over time
and are investigating low cost rubber and wire, so that's why the piano wire
idea. Piano wire rusts though...

Probably you could get decent results with a sharp sewing needle threaded with some
stainless wire. A #16 or #18 needle could be just right -- they come with standard sharp
points, rounded points triangle knife points for leather. Standard is going to be good for your
test, and qty ten available on ebay for $4 shipped. Maybe even hone it
some on a fine ceramic whetstone, or piece of alumina like an
old X86 computer chip package...those light purple ceramic computer chip packages.

[Nathan McCorkle]

All good ideas! I'm not sure how much I'd need to worry about rust, as
the inside of the vacuum should be quite dry, and the outside would be
very short... short enough that I could tin the wire with solder.

[Nathan McCorkle]

On Fri, Aug 29, 2014 at 9:06 AM, Jerry Biehler <jerry....@gmail.com> wrote:
> Ahh, I see why viton now. Viton and nitrile are pretty interchangeable for
> vacuum systems. They both have their advantages and disadvantages. Viton is
> more chemical resistant but it also holds water and out gasses longer than
> nitrile. Almost all of the electrometric seals in my system are nitrile and
> I can get down to 10^-8 torr without much problem.

Cool, good to know, I guess I want a nitrile stopper then! That is
something I didn't search for at all... I wonder what NASA has to say
about them (though of course they're probably swinging the temp in
their walk-in space simulator chambers since space is cold).


> How low are you trying to go?

10^-8 is where the instrument hovers I believe.

>
> This is my little system at home: http://flic.kr/p/kaT8XR

Sweet! For imaging?

[Nathan McCorkle]

On Fri, Aug 29, 2014 at 12:48 PM, Jerry Biehler <jerry....@gmail.com> wrote:
> If you are trying to get to 10^-8 right now forget the stopper. It is never going to happen with a seal like that. How many connections do you need? What kind of pump are you using to get that low? What kind of chamber?

Oh, why not? I mean, the seal on the blocking plate is just a Viton o-ring...

The setup is an FEI 200 xP, it's got a roughing pump, a turbo, and a ion trap.

I need at least 3 wires to begin, I might be able to get away with 2
if I use the feed-through metal for the ground.

[Nathan McCorkle]

On Fri, Aug 29, 2014 at 1:05 PM, Jerry Biehler <jerry....@gmail.com> wrote:
> It will leak. I guarantee it. If not you will have a virtual leak. Vacuum
> design is not easy, especially at this level.

Hmm, alright, I have been trying to be careful! Glad I haven't cut
into the blocking-plate yet!

> I have a couple small 3 pin feedthroughs you can have. What kind of voltage
> are you working with? Current?

I think 30V max, not sure of current but the first-application-attempt
is a photodiode in reverse-bias mode, buffered by a MOSFET. These
parts:
BPW34
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1621132_-1
2N7000
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_178669_-1

and the schematic (I'm planning on only having the 'light shield'
section in the vacuum, maybe only the photodiode, 10M, and
2N7000)(don't mind the BPW34 being mislabelled on the image):
http://imgur.com/ozKQkUj

[Nathan McCorkle]

On Fri, Aug 29, 2014 at 1:18 PM, Dawes, Andrew M. <da...@pacificu.edu> wrote:
> The o rings have probably been cleaned and baked, a stopper could have
> enough residual material inside it (like a sponge holding water) that it
> would outgas so much that it looks like a leak -- i.e. virtual leak. You
> could find some vacuum-friendly epoxy (vacseal) and fill a narrow hole in a
> flange but everyone I know who tried to roll their own UHV parts gave up or
> regretted it. It's so picky that there is a reason stuff is expensive.
> Surplus is a great option as long as you can get the parts super clean.
>

Hmm, makes sense. I've seen that epoxy somewhere, though the FIB
operator had a bad experience with epoxy fouling his system (probably
didn't use the 100% solids epoxy, and maybe didn't degas before it
set)... so I'd have to sneak the epoxy in if I wanted (I was thinking
of potting the electronics, if needed).

Thanks for the opinions, they're definitely valuable!

[Jonathan Cline]

I have recently used butyl rubber for sealing, it is very easy to work with & clean up easily (even vs. silicone), stays soft & rubbery indefinitely, stays tacky, and very high stretch.  Form it around the wire and neoprene sheath and tighten down washers on both sides, it will compress to form a gasket-seal (ooze out with mechanical compression).   It is also incredibly inexpensive.  There are different product qualities (purities?) so look into the source.  Cheaper versions are sold for automobile doors, HVAC seals, etc.  It will outgas (maybe forever?).  I think it could work well for you.  You'll need maybe a 3" length of 1/4" strip, to hand form into the shape you need, and the lengths you find to buy (comes in rolls) might be 10' etc (a few bucks a foot?), so you'll have enough to last a lifetime.


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