I'm making a budget vacuum chamber, and I skimped on the bell jar by just buying a huge glass jar from walmart. The bottom lip is pretty warped due to how cheap it is which is keeping it from sealing properly with my gasket. My plan is to sand it down using silica carbide sandpaper. Will this work? How long would it take? Can you guys think of a better idea that would be faster?
>>17052014>silica carbidetry some pieces of high grit sandpaper first. try 2000 grit on a large flat surface, especially a stone kitchen countertop or granite surface block if you have one. diamond grit sandpaper would be better, but you probably just want to just the finest grit possible to polish down the high spots enough to see them take on a cloudy patch and the grinding action stops.from there you can probably move to a coarser grit, but not much coarser than 2000 and move in small steps until you are satisfied. the larger grit material will probably cause the casting flash of the glass to crack and cause a defect to grow. if you have access to some UV dye, make sure to spread some on the vacuum seal at the end. if there are cracks in the material you should be able to see them better under UV light in the dark.I had to do some similar stuff a few years ago when I was dumb and thought a career in automation was a good idea. something you can try is fiber optic polishing paper, though that is expensive. there are lapidary supply houses out there with large format polishing pads specific to glass.
When I say uneven I mean like millimeters of difference, I'm only pulling a medium vacuum
>>17052076>millimeters of differencethen buy a patch of rubber sheet or something and just use a gasket. orange urethane rubber is cheap. you could probably use a sheet of 1/8" thick solid, not foam, to do it. if not that, buy a tube of silicone rtv sealant, specifically the orange kind for cylinder heads and such which cures non-sticky better than the typical clear shit in caulk tubes.black rtv is good too. either way, lay down a patch of cling wax paper or something nonstick with maybe some release spray onto the mating surface and trace the circle of the glass dome on it. run a bead of RTV on the ring of the glass, place it on the surface, and then run another bead on the outer ring for the actual vacuum seal.test this on other parts to make sure you didn't glue it all together.after it cures, the RTV should release from the glass after some effort, but make it run up on the lip to keep it on. the base should release from the main body of the apparatus too. if you are able to leave a thickness of 1/8" or so uncured rtv in the interface it should make for a good vacuum seal when starting up. you'll still have to put pressure down on the glass when starting to establish a vacuum, but making a seal in place like that with a tube of rtv is exactly what it is for. practice on some test pieces and have fun.also, pipe flange mating gaskets are cheap and you can probably find one to match the diameter. look for EPDM flange gasketshttps://www.mcmaster.com/products/flange-gaskets/
>>17052014>budget>>17052096>mcmasterhttps://www.mcmaster.com/products/flange-gaskets/shape~ring/material~rubber-1/water-and-steam-resistant-epdm-pipe-gaskets~~/https://www.mcmaster.com/1082N124/standard off the shelf part. check the standard size and probably shop around to find one for $5 or so. mcmaster is good, but their customer is generally companies who are willing to overpay for the same thing sold elsewhere, so try ebay/amazon/whatever.the way they are manufactured are such that whatever your actual diameter of the mating circle, you'll probably find one on an interval to match it with a leftover flap either inside or outside. shouldn't matter.
>>17052100I've made my own gaskets out of 1/8" viton. Will the silicone just pop off of the rim of the glass?
>>17052145>Will the silicone just pop off of the rim of the glass?orange/red rtv probably will. try a test dab. another option is to use something like candle wax on the base where the glass needs to sit on the apparatus to prevent the rtv from gluing on. if there is a sort of flare or lip to the glass, you can try and make the rtv wrap around that.now that I think of it, you could probably use acetone/alcohol to clean the glass and then use something like plastidip or tooldip on the glass with a brush, let the first coat cure, then apply another coat on top of it to build up a gasket on the rim of the glass.you can get the RTV to stick to the glass, but you also want to focus on release for the apparatus side. applying something like candle wax prior to laying down the rtv, even a thin layer, should work. those sealants made for head gaskets are such that they do release at the bond interface from oil penetration, but they do not chemically degrade as fast.https://www.permatex.com/gasket-makers/double check the selection, but I think you could also do some sort of buildup with RTV. it will be messy if you don't plan a way to do it and make a fuckin mess. brushing on some tool dip around the rim would be a cheap thing to try first. maybe combine the two.
>>17052173>the selection>>17052145ultra red rtv is good as a gap filler, as they mention it being used on slip fit exhaust fittings and being high temperature and being able to take cyclic stresses. gray rtv more for rigid stuff, which I don't think would work for you. black rtv is good too, flexible and sticky, but it doesn't have the same tear strength and there might be a chance of it blowing in and failing the vacuum.try laying down a bead of ultra red onto a thin candle wax film on the apparatus and let it cure. stretch and tear it to see if it might work. there are better chemicals for cleaning glass than acetone/alcohol, but I think vinegar might be somehow compatible for those adhesives as a cleaning agent on glass.if you get the glass side to stick with running a bead on the glass and mating that to a bead on the wax film on the apparatus, you'll probably be good. ultra red also has the lowest offgassing of all three. probably important for your setup.
