FAQ - Cleaning optical windows, insulators and chamber interiors

[Richard Hull]

I have used one of these cheapo diamond table saws for tile to slab and shape U rock and other small mineral specimens as well as certain other ceramics.

It's wet and messy and you need to be in a swim suit to use it, but it works great outdoors.

Richard Hull

[Doug Coulter]

I've had OK luck with borosilicate going after it pretty hard, even using a belt sander with 60 grit.

Of course it's nicer with more refined tools, and if you can, use water as a lube/coolant, it really helps amazingly.

Yes, breathing powdered glass is how you get silicosis -- don't. It seems inert stuff is worse for your lungs than even cigarette smoke -- at least your body knows how to "eat" that latter, but stuff that just stays in there and irritates, like this or like asbestos is to be really avoided. I always use water to keep that dust out of the air and out of my lungs.

But of course, next time just get the right size -- I ran into that one too -- the SS pipe with weld bead tends to be about 5.9" inside.

[tligon]

I tried the belt sander with a fresh belt. Half an hour of work reduced the diameter about 0.005".

The already used diamond wheel took off 0.050" in about 5 minutes. I was amazed at the difference.

I used the belt sander to put a smoother finish on the result.

[Doug Coulter]

Yeah, I use it mainly on thinner stuff -- a good belt will eat 1/4" tubing almost as fast as you can push it in there, or a thin (like 1/16") window. The thick stuff....probably mostly just strips the abrasive off the belt.

I use diamond wheels and hole saws extensively here in glass and quartz working -- no question that's the way to go. I built what amounts to a lathe mountable dremel tool to hold the wheels for cutting tubing, and it's the cat's meow for that, I just use an eyedropper to drip water on it and keep the dust down. It wouldn't occur to me to try the table saw or angle grinder versions -- too fast and too brutal -- and I don't like having to wear a suit.

I use the hole saws in the milling machine to hole even thin wall quartz tubing, it works fine, and saves work making Tees and so on. You use modeling clay to make a little dam to hold some water, which also cuts down chipping around the hole, and just be patient -- it doesn't actually take all that long to get through and does a nice job. The reason to use the mill is it will go nice and slow (80 rpm), and has less wobble in the quill than any drill press I've had.

I use cerium oxide for polishing when I bother to do that (Caswell plating sells it online), make a slurry on a cloth wheel for example, chucked into a hand drill.

I did that to make some old CRT lead glass usable for a viewport cover to keep X rays down, the inside side wasn't smooth enough without that step. That was a decent stopgap until we found some real good lead glass from a radiology dept that really stops them cold and is clear (but must be almost all PbO, that is one heavy chunk of glass).

With that, and the lead dressing on the fusor, I can now stand right there and observe and take high rez pictures with the detectors sitting at background levels (except for neutrons). Really makes it easier to learn and make progress on these -- worth doing. The webcam approach just wasn't getting it done for us here, and it's hard to move a wobble stick from across the room anyway.

[tligon]

Some people like wet and messy.

I recall a bit of a learning curve. Stand to the side, wear old clothes, and only do it in the late evening when there is nobody to give you a hard time about being all covered in speckles.

And do your own laundry.

I got diamond wheels for the Moto-Tool to cut alumina tubing. What resulted was worn out diamond wheels. Dry-cutting alumina peels the diamonds right off the wheel. But the wetted tile-cutting diamond wheels cut right thru alumina with no apparent wear to the diamond coating in the time I used it. The cuts were beautiful.

The neat thing about a tile-cutting saw is my wife will think I bought it for her projects! She is thinking about some tile in the kitchen and has a gemstone project in which it would be handy.

[morgoth31]

ok in my vacume coating experiance we used mostly green scratch pads and iso propyl it takes elbow grease but let me tell you iso p evaps so easy you dont have outgassing problems.

for the glass protection

some systems used metallic mesh grids that are electrically connected to the chamber it makes it much cheaper. some used thin quartz glass as a sacraficial glass.

[Doug Coulter]

It seems most solvents work fine unless they combine with something in the tank, like Viton O rings not liking acetone (or, liking it all too well). The water in most alcohols is what's going to take the longest to finish outgassing, but even that usually isn't so bad. I've used NaOH/Water to clean off aluminum that got loose from the evap setup.

Though it will mess up my pix a little, I plan to try that screen deal soon. The reason is I just found it a good idea to replace the 3/8" thick sacrificial piece of pyrex in front of my viewport. Turning brown was one thing (probably electron bombardment) but it was developing a series of circular craze/cracks, kind of like a bullseye target, and no way would I like to see that fall apart in my turbo system (which is well screened and baffled, but...).

I do have to wonder if putting the grounded screen on there would simply attract electrons even more, most of which would get through vs a mostly floating piece of pyrex (which IS slightly conductive)...I suspect most of my browning isn't X rays, because pyrex doesn't really do much to cut them down, and the real window behind it is staying nicely clear. Tons of X rays come through both, so between them and me sits a very thick piece of PbO glass we scrounged from a hospital -- now that *really* stops them, where the two thick pieces of pyrex only cuts them about in half. That radiological room glass is very highly recommended -- you can then sit close and watch with both eyes, which beats a webcam all to pieces. My survey meter sits right at the normal background while running now -- the rest of the tank is covered in fairly thick lead so only the rare gamma from the fusion reaction itself gets through that. (there is a 1:10000 chance of a DD->He + y reaction that puts out one heck of a hot gamma ray) Not many of those happen, but the shielding you'd need would make your floor into a sinkhole if you wanted to stop those.

[morgoth31]

one of the big things is dont use your pharmacy grade isopropyl need to use the scientific grade this contains far less water. and remember to keep it closed at all times use it then close it. some high end vacume ppl i know have even gone as far as doing temprature contrled distilling to achive low water. but they were making very low torr systems (company i worked for was called UHV which is ultra high vacume) some of those guys were making 10-7 torr chambers space is only 10-3 lol.

you can also do bake out if you have real bad problems. a thermal blanket raises the temp while under vacume but this is only used for very high vac levels which these systems dont use.

alot of the dep your seeing might be from the ablation caused by the plasma itself this tends to be a brown funk that covers everything. the screen that i was talking about acts like the outside of the chamber and gives it something to accrue on instead of the glass. tho the glass normally isnt being a plating medium the atomic particles in that chamber will sometimes lay on even the insulators. (tho tends to be a small precentage compared areas that are conductive and in contact with the chamber) tho the glass can become electrostaticlly charged and can accrue at a higher rate.

i am not a SME (subject matter expert) but i have a working knowledge from working with gurus before. my knowledge is infamatesmal compared with thiers.

im sure if you look at your ball under a escope before and after you would see some ablation is happening. and charged particles from the reaction is prolly ablating your chamber while redeping the material to it.

[morgoth31]

one more thing the gaskets you should just use the vacume grease its high viscosity and will actually help your seal not alot tho just a bit to wet them.

you can also use the grease to help leaky areas from the outside by buttering some over the problem areas.

[Doug Coulter]

Baking out helps, period, and at ALL vacuum levels. Because what is stuck to all the surfaces isn't the stuff you want in there -- air and water. You don't need to go to real high temperatures to greatly speed the removal of this contamination, and as the Pfeiffer guy once told me - just about anything that puts in energy helps. Might as well blast all that junk off the tank walls (and it represents a lot -- calculate what a monolayer works out to if it were all released -- it's a good part of STP!). So baking in some form makes the pressure go up for awhile, which helps the pump take it all out of there quicker.

I know Richard has mentioned he will often run a glow discharge during pumpdown -- I've tried that and yep, it helps a *lot* to get to purity fastest -- I will even deliberately slow pumpdown by letting in some D during this process and that works better yet (for speed from STP to running conditions, not economy of D).

I use internal quartz heaters (basically big halogen lamps meant for this -- the normal ones will melt themselves in vacuum, or the connections to them) the the difference in gas evolution depending on whether I run them half power (not much UV) and full power (enough short UV to disassociate water molecules) is substantial, long before the tank walls themselves get warm -- you see a more or less instant response to this on gages and a mass spectrometer, with the former all the way "up" to vacuum (pressure?) merely factor 10 better than running conditions. (mass specs don't work well above e-5 mbar or so so at high pressure it's turned off) Which means if that's the best vacuum you can get, you have 10% *at least* contamination in your system, while experiments here show that even 0.1% of some things definately has a large effect. Look up "Penning mixture" for a bit more on that one. This is not the best link, but it gets to the basic idea:

http://en.wikipedia.org/wiki/Penning_mixture