Hey folks, this list sure has been quiet lately.

I'm restoring an Amray 1200 bench-top SEM, and my attention has turned to the vacuum system. The instrument has been down to air and stored in a garage for 20+ years.

I have some experience with vacuum, but not much.

With all of the valves closed, pumping with a rotary pump against about half a meter of the internal plumbing, I can get down to about 20 millitorr repeatably, if the TC gauge is to be believed. It took about a day to reach that point, but now I can get there from atmospheric pressure in a minute or so. I presume that was adsorbed water.

Now I'm opening the roughing valve and trying to pump down the column and chamber. This significantly increases the volume of the system that's being pumped, so I'm expecting days of getting rid of the water. But, leaving it running overnight last night, it didn't budge from ~220 millitorr. I assume there's a leak.

Hunting around with my cheap-but-functional ultrasonic leak detector, I've found that there's a big ugly wax seal at the top of the column where the filament and HV leads enter the electron gun assembly. See attached photo. (if this mailing list is set up to allow such attachments) There's a significant leak right there, which changes as I massage that gloopy waxy stuff around.

I think that wax may have deteriorated with age. It's pliable, but it doesn't seem to adhere very well to anything, including the wires it's supposed to create a seal around.

Does anyone know what this stuff is, where I can get more (that I can afford), or in general have any other thoughts or advice about this?

This is a stately instrument that's in really good shape, all things considered, and I'd love to get it running again.

Thanks,
-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

开云体育

Howdy,

Good to hear you're still at it! I get nostalgic looking back at the vacuum and lasers lists, I guess they're just not things that folks play with as much these days. BTW is the archive of the lasers list still on your site? I tried the link in one of the old emails but it didn't work.

That whitish goop looks more like just a sort of strain relief or insulation for the cables than an actual seal. Even if it did seal to the outside of the cables, air could still leak down between the strands on the inside, so I'm guessing that there will be some sort of feedthrough or connector beneath the white stuff. If it is indeed causing the leak, then you'll have to remove it anyway, and see what's underneath.

If you did indeed have to replace the goop with a sealant, your best bet is probably a vacuum epoxy. Torr Seal () and Loctite Hysol 1C are two I've read about, although Torr Seal is bloody expensive, and Hysol 1C seems impossible to find! Other option is one of the softer Apiezon waxes - . I recently bought a load of the W wax sticks (the hardest) because I wanted to see just what the stuff was like, not that I've got any time to mess with vacuum stuff now, and it really is quite impressive stuff. Very sticky, to metals and glass, easy to clean/dissolve in solvent. A hot-air pencil is pretty invaluable for applying it.

Hope you have some success, and do post how you get on with it!

Cheers,

Lindsay

? Hey folks, this list sure has been quiet lately.

? I'm restoring an Amray 1200 bench-top SEM, and my attention has turned to the vacuum system.? The instrument has been down to air and stored in a garage for 20+ years.

? I have some experience with vacuum, but not much.

? With all of the valves closed, pumping with a rotary pump against about half a meter of the internal plumbing, I can get down to about 20 millitorr repeatably, if the TC gauge is to be believed.? It took about a day to reach that point, but now I can get there from atmospheric pressure in a minute or so.? I presume that was adsorbed water.

? Now I'm opening the roughing valve and trying to pump down the column and chamber.? This significantly increases the volume of the system that's being pumped, so I'm expecting days of getting rid of the water. But, leaving it running overnight last night, it didn't budge from ~220 millitorr.? I assume there's a leak.

? Hunting around with my cheap-but-functional ultrasonic leak detector, I've found that there's a big ugly wax seal at the top of the column where the filament and HV leads enter the electron gun assembly.? See attached photo. (if this mailing list is set up to allow such attachments)? There's a significant leak right there, which changes as I massage that gloopy waxy stuff around.

? I think that wax may have deteriorated with age.? It's pliable, but it doesn't seem to adhere very well to anything, including the wires it's supposed to create a seal around.

? Does anyone know what this stuff is, where I can get more (that I can afford), or in general have any other thoughts or advice about this?

? This is a stately instrument that's in really good shape, all things considered, and I'd love to get it running again.

??????????? Thanks,
??????????? -Dave

On 4/3/22 19:13, eosraptor1 wrote:

I got nothing on the wax Dave, but it is good to hear chatter on the list.? My guess is that the water was in the oil of the vacuum pump. Vacuum oil is cheap so change it out often.? I am cheap too so I let my old oil sit in a plastic?container for a year or two and then pour off the clean stuff that is floating above the sludge.? the oil itself never really wears out.

It's great to hear from you Drew, I hope you've been well!

I don't think it was the pump oil, because the valve configuration had the diffusion pump cut off during these tests, and the roughing pump had seen use before, fairly recently.

I would be amazed if that wax was really the seal for a vacuum system. have you removed it and looked to see if them wires actually?attach to something that has a gasket.? copper gaskets never age out but people use buna or viton sometimes and that does have a shelf life.? Look for stuff like that.? The wax may just be some high voltage silicone putty sitting over the high vacuum electrical passthru pins.

Lindsay said this too. Thinking about it a bit more, I agree.

The wires go down into the gun assembly, which is a large rather phallic-looking ceramic insulator. I have suspected since I first looked at the instrument that it may be cracked; it has a slight wobble to it which really shouldn't happen. Electron gun alignment is a critical part of SEM adjustment, so I really think it shouldn't wobble.

The gun sticks down a few inches into a chamber near the top of the column. It's a loose fit with an O-ring, and when open to air there's nothing holding it in place, you can just lift it off...or it can slide from side to side.

I suspect what may have happened is, perhaps during transport, that the gun assembly slid sideways until the protruding ceramic insulator hit the inside wall, with sufficient force to crack the ceramic. There are also some small shards of ceramic in the chamber below where the gun sits, and that's the only place they could've come from.

I further (now) suspect that the ceramic is what forms the vacuum seal, and that waxy gloop is just there to immobilize the wires, as vibration up there is also a very bad thing in an SEM when it's running.

I'll take a pic of that assembly soon.

Dont SEM's have scintillation crystals or something that die if they sit in air for too long.? I not up on SEM's but interested in your rebuild.

They do; they're hygroscopic. But I have spares, and they're still available on the market, not too pricey.

Oh,? I have a 68" dia x 68" deep vacuum chamber free to a good home for a tax write off letter if anybody knows a school looking for a great Mars simulation chamber.? contact me directly if you think this is your next great adventure.

I have about all the adventures going on that I can handle right now, but man that's tempting. Why would you get rid of that? Isn't that the gorgeous gigantic chamber that I saw when Autumn and I visited you a decade or so ago?

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 4/3/22 20:01, lrwweb wrote:

Good to hear you're still at it! I get nostalgic looking back at the vacuum and lasers lists, I guess they're just not things that folks play with as much these days. BTW is the archive of the lasers list still on your site? I tried the link in one of the old emails but it didn't work.

Hey Lindsay, it's great to see your name in my inbox!

Yes, the lasers list archives are still up, and the list itself is too, but it sees essentially no traffic lately. I separated the list handling onto its own machine a couple of years ago though (for other lists on there that have more traffic ;)), so the list URLs have changed. For those archives, look here:

That whitish goop looks more like just a sort of strain relief or insulation for the cables than an actual seal. Even if it did seal to the outside of the cables, air could still leak down between the strands on the inside, so I'm guessing that there will be some sort of feedthrough or connector beneath the white stuff. If it is indeed causing the leak, then you'll have to remove it anyway, and see what's underneath.

I agree; see my reply to Drew on this.

If you did indeed have to replace the goop with a sealant, your best bet is probably a vacuum epoxy. Torr Seal () and Loctite Hysol 1C are two I've read about, although Torr Seal is bloody expensive, and Hysol 1C seems impossible to find! Other option is one of the softer Apiezon waxes - . I recently bought a load of the W wax sticks (the hardest) because I wanted to see just what the stuff was like, not that I've got any time to mess with vacuum stuff now, and it really is quite impressive stuff. Very sticky, to metals and glass, easy to clean/dissolve in solvent. A hot-air pencil is pretty invaluable for applying it.

You know, I used to have a handful of those wax sticks, I got them for some repairs on my first SEM many years ago. They were in the toolbox that was stolen when some scumbags broke into the house I was moving out of in Florida, between truck trips #3 and #4. I bet the scumbags had no clue of what they were so they probably hit the trash.

I couldn't talk you out of one or two of those sticks, could I? I can only find places here that sell them in bundles of 20, for like $250. That is, honestly, a lot of money to me these days.

Referring to my description of the ceramic insulator in my reply to Drew, I'm thinking I could repair that crack using some Apiezon W. I will disassemble it further soon to figure out what's going on in there. It's a tough few days here so that may take me some time.

Hope you have some success, and do post how you get on with it!

Thanks, will do!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

THE STAT ARE VEERY LOOOOW

CAN I BE A MENBER OF LASER GROUPE AND LOOK AT ARCHIVE

JACK 47 71

On 4/3/22 20:01, lrwweb wrote:

Good to hear you're still at it! I get nostalgic looking back at the
vacuum and lasers lists, I guess they're just not things that folks
play with as much these days. BTW is the archive of the lasers list
still on your site? I tried the link in one of the old emails but it

didn't work.

Hey Lindsay, it's great to see your name in my inbox!

Yes, the lasers list archives are still up, and the list itself is too,
but it sees essentially no traffic lately. I separated the list handling
onto its own machine a couple of years ago though (for other lists on there
that have more traffic ;)), so the list URLs have changed. For those
archives, look here:


.
com/

That whitish goop looks more like just a sort of strain relief or
insulation for the cables than an actual seal. Even if it did seal to
the outside of the cables, air could still leak down between the
strands on the inside, so I'm guessing that there will be some sort of
feedthrough or connector beneath the white stuff. If it is indeed
causing the leak, then you'll have to remove it anyway, and see what's
underneath.

I agree; see my reply to Drew on this.

If you did indeed have to replace the goop with a sealant, your best
bet is probably a vacuum epoxy. Torr Seal
() and
Loctite Hysol 1C are two I've read about, although Torr Seal is bloody
expensive, and Hysol 1C seems impossible to find! Other option is one
of the softer Apiezon waxes -
. I
recently bought a load of the W wax sticks (the hardest) because I
wanted to see just what the stuff was like, not that I've got any time
to mess with vacuum stuff now, and it really is quite impressive
stuff. Very sticky, to metals and glass, easy to clean/dissolve in
solvent. A hot-air pencil is pretty invaluable for applying it.

You know, I used to have a handful of those wax sticks, I got them for
some repairs on my first SEM many years ago. They were in the toolbox that
was stolen when some scumbags broke into the house I was moving out of in
Florida, between truck trips #3 and #4. I bet the scumbags had no clue of
what they were so they probably hit the trash.

I couldn't talk you out of one or two of those sticks, could I? I can
only find places here that sell them in bundles of 20, for like $250. That
is, honestly, a lot of money to me these days.

Referring to my description of the ceramic insulator in my reply to Drew,
I'm thinking I could repair that crack using some Apiezon W. I will
disassemble it further soon to figure out what's going on in there.
It's a tough few days here so that may take me some time.

Hope you have some success, and do post how you get on with it!

Thanks, will do!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 4/4/22 10:49, Jacques Savard wrote:

THE STAT ARE VEERY LOOOOW
CAN I BE A MENBER OF LASER GROUPE AND LOOK AT ARCHIVE
JACK 47 71

Yes, the lasers mailing list is open to all, but as I mentioned earlier there has been very little traffic there lately. Feel free to change that. :-)

But please turn off your CAPS LOCK key. ;)

Note that it is a mailing list, not a "group" or a web forum.

Subscribe here:



-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 4/3/22 20:01, lrwweb wrote:

That whitish goop looks more like just a sort of strain relief or insulation for the cables than an actual seal. Even if it did seal to the outside of the cables, air could still leak down between the strands on the inside, so I'm guessing that there will be some sort of feedthrough or connector beneath the white stuff. If it is indeed causing the leak, then you'll have to remove it anyway, and see what's underneath.
If you did indeed have to replace the goop with a sealant, your best bet is probably a vacuum epoxy. Torr Seal () and Loctite Hysol 1C are two I've read about, although Torr Seal is bloody expensive, and Hysol 1C seems impossible to find! Other option is one of the softer Apiezon waxes - . I recently bought a load of the W wax sticks (the hardest) because I wanted to see just what the stuff was like, not that I've got any time to mess with vacuum stuff now, and it really is quite impressive stuff. Very sticky, to metals and glass, easy to clean/dissolve in solvent. A hot-air pencil is pretty invaluable for applying it.
Hope you have some success, and do post how you get on with it!

Hi folks, I'm getting back to this now after a little road trip.

I've disassembled the electron gun, and it was as you suggested, that the whitish goop isn't the seal. I really should've known that. Further, as I'd suspected earlier, the big ceramic insulator is cracked. I'm assuming that's the source of the leak. See attached photo. The gun assembly is able to be tilted by three external thumbscrews for rough beam alignment; this explains the oddly-shaped O-ring visible at the base of the insulator. That entire large plate rocks back and forth to align the gun, and that strange O-ring seals against the bulkhead at the top of the SEM's column.

With some effort I was able to get ahold of some Torr-Seal, which arrived today. My thought is to stuff it in where that ceramic insulator is cracked, and create a new seal between it and the smallest-diameter part of the metal cylindrical structure.

I have limited experience with this sort of repair, and I'm concerned about screwing something up. Can anyone offer any opinions on this, am I on the right track? It looks like a simple operation to me, but I've been around the block enough times to know that I should never trust that.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 4/21/22 14:05, Dave McGuire wrote:

? Hi folks, I'm getting back to this now after a little road trip.
? I've disassembled the electron gun, and it was as you suggested, that the whitish goop isn't the seal.? I really should've known that. Further, as I'd suspected earlier, the big ceramic insulator is cracked. ?I'm assuming that's the source of the leak.? See attached photo.? The gun assembly is able to be tilted by three external thumbscrews for rough beam alignment; this explains the oddly-shaped O-ring visible at the base of the insulator.? That entire large plate rocks back and forth to align the gun, and that strange O-ring seals against the bulkhead at the top of the SEM's column.
? With some effort I was able to get ahold of some Torr-Seal, which arrived today.? My thought is to stuff it in where that ceramic insulator is cracked, and create a new seal between it and the smallest-diameter part of the metal cylindrical structure.
? I have limited experience with this sort of repair, and I'm concerned about screwing something up.? Can anyone offer any opinions on this, am I on the right track?? It looks like a simple operation to me, but I've been around the block enough times to know that I should never trust that.

Ok, nobody waved me off, so I went ahead and did it. This Torr-Seal epoxy is pretty serious stuff; the MSDS is 26 pages long!

I've sealed up the ceramic insulator and reinstalled the electron gun assembly. With the vacuum system in manual mode, I set up the valve configuration to pump down the entire system with the roughing pump.

If the ancient TC gauges are to be believed, the system went down to about the 1mT level in less than 24 hours.

This is amazing to me, as this SEM has been down to air for many years, in a non-climate-controlled garage, less than a block from the ocean.

So, next I'm going to see about powering up the diffusion pump.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

Not really, no. The chip shortage has really tanked my revenue.

Besides, this is a bit of an antique instrument, and I'd really like to get it working in its original configuration. And further, I've never used a turbo pump before, so there's that "n00b factor" too...I don't even really know how to shop for one.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 4/23/22 18:32, Dave McGuire wrote:

? Besides, this is a bit of an antique instrument, and I'd really like to get it working in its original configuration.? And further, I've never used a turbo pump before, so there's that "n00b factor" too...I don't even really know how to shop for one.

Just following up on this (in bad form replying to my own message ;))...The attached photo tells the story!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

It's alive, nicely done!

Thanks! It's been tedious, but worthwhile. Now for a hundred little adjustments and optimizations.

-Dave

On May 20, 2022 3:22:38 PM "Dave" <dgrove@...> wrote:

It's alive, nicely done!

----- Original Message -----
From: "Dave McGuire" <mcguire@...>
To: [email protected]
Sent: Friday, May 20, 2022 10:02:08 AM
Subject: Re: [VacuumX] vacuum wax help?

On 4/23/22 18:32, Dave McGuire wrote:

Besides, this is a bit of an antique instrument, and I'd really like
to get it working in its original configuration. And further, I've
never used a turbo pump before, so there's that "n00b factor" too...I
don't even really know how to shop for one.

Just following up on this (in bad form replying to my own message
;))...The attached photo tells the story!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

--
Dave McGuire, AK4HZ
New Kensington, PA

I do have another one that I'd like to send on to a new home, but it probably needs more electronics work than you'd be up for, if I remember your aversion to "sparkies" correctly! ;)

-Dave

On May 20, 2022 3:43:56 PM "eosraptor1" <eosraptor@...> wrote:

very cool. Now I want one :_)))))

On Fri, May 20, 2022 at 1:02 PM Dave McGuire <mcguire@...> wrote:

On 4/23/22 18:32, Dave McGuire wrote:

Besides, this is a bit of an antique instrument, and I'd really like
to get it working in its original configuration. And further, I've
never used a turbo pump before, so there's that "n00b factor" too...I
don't even really know how to shop for one.

Just following up on this (in bad form replying to my own message
;))...The attached photo tells the story!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

--
Dave McGuire, AK4HZ
New Kensington, PA

On 5/22/22 11:38, eosraptor1 wrote:

if you get bored and want a commission, I will buy it off you once you get it working :_)))))

I run two companies and a public museum...I never get bored. Exhausted, pretty much all the time, but never bored. I took on the Amray 1200 restoration project because I was desperate for a change of pace.

The one I'd like to re-home is an ETEC Autoscan. It's a wonderful instrument, and I had it running years ago, but it's fairly large and my lab is full.

I really do not like electronics as they hate me.

Nah, electronics loves you! :-)

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

On 5/22/22 11:53, eosraptor1 wrote:

you work too much bud......

No argument there, but I have little choice.

I have proof the universal electronics gremlins?hate me..... right now I am seeing my warp drive thruster suck power out of a digital HV power supply that is turned off and powered down.? So either a turned off thruster is generating power while still somehow making thrust or there are a bunch of electrical gremlins?laughing their butts off at me from inside the chamber. ?Either way I got no explanation for what is going on.? I used to think making propellantless thrust was going to be the hardest thing to do.... turns out that turning the damn thing off is way more difficult.? I sooooooo hate electronics stuff.

Oh you could so master it if you felt like it.

Sounds like you're having serious fun, though!

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA