DIY Viewport - Photos

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JakeJHecla
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DIY Viewport - Photos

Post by JakeJHecla »

Hello all-
In working on my fusor, I came across issues finding a suitable viewport. To get around risking my money on eBay or shelling out nearly $200 for a new one, I decided to try my hand at creating a DIY solution. I started with a cheap 2.75" CF blank purchased on eBay for $25. I then picked up two glass disks from McMaster Carr ( one measuring 1.75" x 3/16" and the other 1" x 3/16")
Link: http://www.mcmaster.com/#glass-discs/=jsln98
I then borrowed some time on my school's lathe to complete the project. I used a boring bar to make a 1.25" hole through the piece. Next, I made a 1.75" x .25" deep cut to seat the larger glass disk in. After cleaning up and sanding the area, I used JB weld to affix the window in the cutout. Once this had dried completely, I used a minute dab of clear RTV to hold the smaller disk in place as a sacrificial viewport protector. It seems to hold vacuum quite well, and I have yet to see evidence of significant outgassing from the JB weld, even when baking out with a heat gun at ~150C. While I can't comment on the use of this design for anything more advanced than a demo fusor, it seems to work quite well in that role.

Photos:
1) 2.75" CF flange on the lathe.
2) Finished VP on fusor, running about 10kV. Some fluorescence of either the glue or the borosillicate can be seen.
Attachments
LatheOne.JPG
Window.JPG
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Jim Kovalchick
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Re: DIY Viewport - Photos

Post by Jim Kovalchick »

Nice work. Is your glass borosilicate? It will hold up better to heat than regular glass. You should do fine with your JB Weld. When exposed to plasma, JB Weld seems to develop a hard coating and you will not have trouble with outgasing from it. If your window survives demo fusor conditions you will also be successful when you use D fuel. Good luck.
kcdodd
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Re: DIY Viewport - Photos

Post by kcdodd »

I think the way most large viewports are done is with o-rings. You just need something to hold the glass in place while at atm since vacuum will suck the window into the oring to make the seal, and a groove in the flange or something to keep the oring from collapsing. I am not sure if a small window will work as well since there wouldn't be as much pressure from the vacuum from the smaller surface area.
RobertTubbs
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Re: DIY Viewport - Photos

Post by RobertTubbs »

Most viewports use a glass to metal seal, I've never seen one with an o-ring.

Regardless, I'm a big proponent of JB-Weld, I've used it on numerous occasions with zero evidence of leaks. I'd dare to call it the new and improved parchment sealing wax of vacuum assemblies.

Kudos on the nice VP - I'm sure I'll be seeing more of these now.

-RT
kcdodd
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Re: DIY Viewport - Photos

Post by kcdodd »

well, most viewports are under a foot across.
Conrad Farnsworth
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Re: DIY Viewport - Photos

Post by Conrad Farnsworth »

Jake,

Very well done! I used a McMaster Carr O-Ring on my demo fusor and got away just fine! I few steps behind you! I will have to give this a shot if my viewport breaks! I wasn't so sure that your choice of sacrificial glass adhesive (RTV) was a good idea, but apparently it's not outgassing. Best of luck with neutrons Jake!

-Conrad
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Doug Coulter
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Re: DIY Viewport - Photos

Post by Doug Coulter »

In the spirit of TMTOWTDI (theres more than one way to do it), here's a viewport/door we made for BillF's cylinder fusor. We have an 8" flange intended to adapt to a smaller size, cut an O-ring grove where the original CF gasket seat was (nothing fancy here - just a square groove most of the depth of the O ring), used a viton ring, and our "magic sealing wax" which is ~80% pure beeswax (McMaster) and good grade oil (Diffoil-20) to grease it up a bit. The door is held on during times of no vacuum by those lift and twist pull-away little angle brackets, but can be easily removed when there's STP in the tank so you can build your ship in a bottle. There were no leaks due to this, or at least, none we could notice on a diff pump system. This system is what made our first neutrons, now in storage.
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ViewDoor.jpg
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Dan Tibbets
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Re: DIY Viewport - Photos

Post by Dan Tibbets »

O rings have worked well in my experience. There does seem to be a limit of ~ 1 to 1.25 inch diameter, below this and a good seal seems to be insufficient. Leakage and/or prolapse of the O ring is a problem. 1.5 inches or greater seems to work well- this would result in about 30 lbs of 'push' on the glass. Something like epoxy might work but I speculate that glass breakage may be more of a problem as the pressure and temperature changes. A small O ring would work if the glass is held down tightly with clamps/ bolts./ collars.

PS: Hot melt glue seems to work terribly. I don't know if it is out gassing or porosity, but it leaks vacuum quickly. I have had uncertain results with silicone glue. It might take a long time for the curing gasses to dissipate. It does seem to work fairly well as a sealer for threads, though I prefer epoxy, at least for metal to metal seals

Dan Tibbets
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Rich Feldman
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Re: DIY Viewport - Photos

Post by Rich Feldman »

Nice work, Jake!

Yours is not the first window fluorescence to be reported here.

While looking for windows to transmit shortwave UV (254 nm),
I found surprisingly affordable disks of fused quartz.
IIRC, some are specified to be low fluorescence.

Here's one from a dealer (not just on ebay) near me.
http://www.ebay.com/itm/Fused-quartz-gl ... 0966050438
All models are wrong; some models are useful. -- George Box
Peter Schmelcher
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Re: DIY Viewport - Photos

Post by Peter Schmelcher »

For what it’s worth another source of glass is a surplus optics outfit http://www.surplusshed.com/pages/item/l10449.html
The 41mm diameter 9.5mm thick window fits nicely onto a KF40 centering ring lip (41.2mm).
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Doug Coulter
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Re: DIY Viewport - Photos

Post by Doug Coulter »

Rich - when the fluorescence is white, and on pyrex, it's electron bombardment, and I proved it by waving a magnet around and having it move - it's not UV downshift, it's direct and damaging. I have to replace my sacrificial 3/8" piece of pyrex that guards my door glass every 100 hours or so or it shatters after turning brown and developing circular, bullseye cracks.

Here's a short vid showing the effect before I learned to put that sacrificial piece inside and screen it off.
Being far from the grid, it doesn't affect the fields much to have a grounded screen there, but it does help with the electrons and RF leakage.

http://www.youtube.com/watch?v=mTDrQg7U4Wg&feature=plcp

I got a nasty sunburn through a sapphire window once...Or it might have been a quartz one. Be careful, there's a *lot* more UV than visible light coming out of a fusor.
Why guess when you can know? Measure!
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Richard Hull
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Re: DIY Viewport - Photos

Post by Richard Hull »

All of the related UV, X-ray, complex removal and viewing issues are readily taken care of with a 3/4" - 1" diameter glass view port in a 2.75 conflat with a single board camera's focusable lens jammed against the glass and pointed away from any audience. You'll still have to clean the window over time, but it will be so much easier.

A large video monitor or giant flat screen can have you virtually inside the device. I guess I never saw the sense in having a viewport larger than 1" in diameter. I currently use a 3/4" diameter view port.

first image is the 3/4" glass port and camera Black cylinder that I fashioned. (X-rays blast into floor)

Next are two images of the star taken of video.

I have never looked into a fusor with my eye since fusor III in 1998.

Richard Hull
Attachments
best red star.JPG
neutron oven3.JPG
best green star.JPG
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