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oekmont
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The problem with jars is the workshop environment. There are infinite many scenarios what could happen to make the jar turn into a flying shard cloud. Why should they be designed to withstand full vacuum? I doubt the food industry applys full vacuum before sealing. Usually they will take full vacuum, but you never know for sure. And usually the underpressured gas area is very small, as the jar is filled with liquid. Applying vacuum to the whole jar increases the potential explosion energy a lot, as liquids don't need much energy to change their pressure, but gases do. So filled jars are under low pressure, but contain very little energy, which could be released in case of failure (except for the enormous energy stored in their mass of course (e=mc^2))
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Lester Populaire
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I wouldn't recommend a jar as if it goes wrong it probably send glass flying everywhere. that being said - i have done it plenty of times without issue...
I think the better solution is to use a section of thick walled PE plumbing tube with a thick plywood lid. soak the lid in epoxy to get them airtight. i made a seal for those with a silicone rope which worked really well.
The MTI hose works really well tho and improves process reliability by quite a bit for complex parts.
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Hanaldo
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I wouldn't trust a jar to hold full vacuum. I've collapsed steel cylinders before, and only managed about half vacuum before they let go. They need to be pretty robust things to handle the vacuum well.
In all honesty, it probably wouldn't be that dangerous - but I'd still take cover. There's a chance that the thing would implode, the energy of which would send shards flying. It's much more likely that it develops a crack first that destroys the vacuum and nothing else happens, but flying glass isn't something I'd be taking chances with.
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quinn
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+xDon't use a jar. This is dangerous as hell. Do they shatter or something? Crossed my mind but they're meant to handle full vacuum, as well as high heat if hot resin is the concern, at least 100c anyway. What is the danger?
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oekmont
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Don't use a jar. This is dangerous as hell.
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Hanaldo
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If you dont want to buy a catch pot, have a look at MTI hose. Easier option than making something that is very likely to leak.
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quinn
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Ok, I'll do it how reto explains. Trimming the dry fabric flush to flange with a razor without fraying is the part im worried about, but ill give it a shot and try with spray glue if needed. I did order some web lock fabric which is supposed to really help with fraying and keeping pattern from distorting so that should help.
One thing I didn't buy yet is a resin catch pot. Is there a cheap option for this? I was thinking maybe a peice of pvc pipe capped at both ends with 2 lines on it. Use it once and throw away. Should that work ok?
After a quick search, it looks like a canning jar is an easy cheap option for a catch pot. Just drill the lid for 2 fittings and you're good
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Hanaldo
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Bang on ^
Quinn, that can be the case with larger setups or more complex geometry where you have an uneven spread of vacuum or the resin may start to gel before the dry areas can wet out. One should remember that the resin isn't being sucked through by the vacuum, it is being pushed through by the weight of the atmosphere and the pressure differential between the resin in the pot and the inside of the vacuum bag. So on a small part like this, you aren't going to overcome that differential by having the resin reach the outlet before the entire laminate is wet out.
Your 600cps resin is a bit thick. What is the pot-life on it? If it's got a decent pot life then the other option is to heat it up to about 45-50C prior to infusing. This will dramatically lower the viscosity and allow it to infuse, but will also dramatically shorten the pot life. I'd expect a part this size to fully infuse in about 5 minutes, so if your resin has a quoted pot-life of at least 40 minutes at 25C then this might be a good option.
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Lester Populaire
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+xGot all the materials coming to get going on this project. I have a pretty straight forward idea of how I'll get the plug and then molds done, but i still havent decided exactly how I'll do the lay up. I'm wondering if it might be more easy and controllable to do the 2 halves separately and after they have cured, trim them to fit eachother nicely down the middle. I can make a jig on my cnc that is a negative profile of the center line so the flange of each finished half will sit in this profile while I machine the joint line, basically just removing the flange of each half. The 2 halves will fit together perfectly. I can hold them together on the outside with packing tape while using a strip of fabric on the inside to join them. Should this work ok? I'm just worried that it would be difficult to do this whole shape in one shot with a decent seam line in the middle where fabric overlaps. Also I feel that bagging it effectively inside the cone shape with all the needed layers will be difficult. Doing each half separate becomes very simple, just depends how well my joining method works. If the machining of the joint doesn't come out perfect, I figure I can basically lap the 2 halves on a big peice of sand paper on a flat surface to get a nice tight joint between 2 halves. Keep in mind I'm a total newb at this so I'm ok with a process that takes more work but is more controllable. Also the mold will be designed in the standard way so I can try it both ways. All in one shot, or 2 separate halves. Not much material in each try so not very expensive. First try will be a single layer of 7.2oz fabric with reinforcment in strategic areas. It will be a pretty flexible flimsy part, but thats what's needed to get it light. Standard fiberglass canopies are usually 2 layers of 5.8oz. Goal is to get similar strength to regular fiberglass canopy but a bit less weight. Don't do it in two parts. Cut the fabric patches so they are a little too big and place them in the open mold halves with a little bit of spray tack. then use a very sharp razor blade to trim the fabric on one side of the mold flush to the parting line and use some scissors to cut it parallel to the parting line with a little overlap on the other mold half. bolt the two molds together, do your infusion setup, envelope bag the whole shabam and boom nice one piece part. it's not absolutely hassle free to cut the dry fabrics perfectly flush to the mold split line without fraying, but certainly possible. you can hit the fabric from the back with a little bit of spray tack and let it dry before cutting which helps to stabilize it. cheers, Reto
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quinn
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+xCheck the data sheet of your epoxy. If its mixed viscosity is above 500cps then I wouldn't use it. 500 is thick for infusion but will work for small parts. Under 300cps is ideal. Don't worry about the resin flow, on a small simple part like this it isn't going to be a concern. Flow issues tend to be associated with complex geometry and larger parts where your pot life may be on the edge. Realistically, you can just mix up a bit extra resin and allow some to flow into your catch pot until everything has wet out. Worst case, a brake zone will ensure you aren't wasting too much resin. Ah ok, for some reason I was thinking once resin reached the vacuum tube, it was game over and any spots left dry would remain dry but it sounds like you just let it keep going and it will continue to spread through the part as excess goes to pot. Sounds a bit less crucial now. My resin is 600cps so I guess I'll need some proper infusion resin.
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