I feel fairly confident about this vitrine à sandwich construction method. I’ve ordered some large format silicone ice cube trays, cup size about 5cm cubed, in the hope that I can make much larger vitrines. A 125ml vitrine possible in a mould that size might take a week to construct, one 8-10mm deep layer per day, but if you’re making 15 or more at a time that’s a very attractive proposition.
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I wouldn’t imagine bubbles would be a huge issue for an electronic use. Air should insulate about as well as resin. Unless there’s a chance that two isolated components within a bubble would connect over time. Is the concern over bubbles aesthetic?
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I’m going to assume it’s purely an aesthetic concern until convinced to the contrary. There are known techniques to remove bubbles so once I have the process working I can turn to that. I’m after the simplest possible recipe to reliably produce durable resin cases around electronics.
If anybody spots a way to simplify the process that I haven’t already mentioned, please feel free.
One of my principal concerns is that the recipe I’m working on will cease to be viable as the weather gets colder. I’ll work on fixing that when I need to.
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Vitrine test 4 episode 2: 17.5 hours in the toolshed
So it’s lunchtime and the ice cube tray has spent the night in the disused coal bunker which I shall from now on call the toolshed.
This is a crude handheld video without commentary, showing that the vitrines have set on the surface. The steel Swiss army knife blade I use as a probe produces clearly defined indentations in the surface, and there is no sign of oozing or of springing back into place. You can hear the satisfying clunking sound of the blade on the surface of the resin. The recommended curing time for this resin is 24 hours and I plan to try removing one of the vitrines from the tray this evening.
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Meanwhile my Amazon Prime order of giant silicone ice cube trays was delivered overnight. Here is a photo of the two trays. Each cup is 5x5x5cm, giving a maximum volume of 125ml. If I can perfect a process for vitrines of that gigantic size, I will probably consider that enough. I’ll have to stop before I end up vitrifying entire modules, or small animals or worse.
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Vitrine test 4 episode 3: 21 hours in the toolshed.
Test 4 is coming along very well. I removed the small vitrine (the one where I ran out of resin while pouring) and this gives a good view of how curing works at depth. The bottom of that vitrine I extracted in this video looks very much like the top layer of test 3 looked after three days or more.
The very bright daylight fooled my eyes and I said there were no bubbles visible to the naked eye. On the contrary, as soon as I got it in the shade the tiny bubbles appeared. When I start making mignons I’ll be able to test whether the bubbles have any important effects (mechanical or electrical) on the finished product.
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you mean the " potting shed " ? .
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“Potting shed”. I like it.
Incidentally the automatically generated English captions are pretty good. It has fun with my pronunciation of vitrines, sometimes translating it as betweens and sometimes latrines. And once even, to my astonishment, vitrines. All in all, I’m sure these captions will be useful to those who don’t understand my regional accent with its northern vowels, its mumbled consonants and its headlong gabble.
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Bubbles! On the whole it looks like a esthetic issue but there are a number of good electronic reasons to avoid them in any potted circuit or coil.
Chemistry and contamination.: adding a charge across or near a bubble has a chemical reaction. If heat is generated then you risk damage, corrosion or the production of new gasses. All of which can damage a potted circuit. Moulds and other Bio contamination can thrive in a bubble or component surface and ruin both the esthetic and function.
Signal issues: bubbles and the flow of electrons, whether near or in contact can generate some amazing signals and in themselves some bubbles can inhibit or even amplify a signal (yes really). Now the effect is small but if you have a single bubble on a guitar pickup coil you get a shit or dead pickup. A bubble on a potted amplifier can half the life of some components and affect gain and tone. DIY ham radio folks know a bubble can produce harmonic interference and micro signals (same thing really) . Bubbles on copper, bubble under or on a leg of an ic all cause issues.
@Maxhirez is right it’s not a huge issue for many circuits but without getting into both the physics and chemistry of it I’ll just say clean your circuit before potting and avoid bubbles if you can as a matter of good practice.
@devicex Potting shed! Classic.
Best to all
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Vitrine test 5: this one goes up to eleven.
No pictures yet but I’ve just mixed 50ml of resin and poured it in two roughly equal dollops into two adjacent cups of one of the 5cm ice cube trays. This is about 10mm deep, which is said to be the limit for this type of resin.
Changes in method: I measured the resin and the hardener in separate graduated cylinders (33.3 ml resin, 16.7 ml hardener), poured them together into the mixing vessel and gave the mixture a timed 5 minutes of thorough stirring. Then I poured the result by eye into the ice cube tray. I dumped each item of equipment into the bath of water when it was no longer needed, to reduce contamination.
0 hour recorded at 2000 BST.
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Time to run the numbers.
If I used both ice cube trays each with 8 cups, it would take a total of 16 x 25ml, 400ml per 1cm layer. A batch of two-layer, 50ml vitrines, measuring 5x5x2 cm, would need 800ml. That’s quite costly in resin. On the other hand, 16 50ml vitrines would be one hell of a lot of reusable, encapsulated electronics. Roughly £1 worth of resin per vitrine. And the process scales, so if I only have 100ml of resin I can make two vitrines at the same cost each. It’s just that this wouldn’t be the most efficient use of curing time because the trays would be mostly empty.
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Do a search on this entire site for “most efficient.”
We all work within our own time and financial budgets. You get one pristine vitrene and it’s worth it. Any more is gravy. Enjoy
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I’m designing an industrial process, albeit for a cottage industry and a customer base of one. Software engineers and production engineers might recognise what I’m trying to do. I want a painless way to make Arduinos and ESP32s and Raspberry Pis and Belas talk fluently to analogue modular equipment, and this process will provide a production line capable of giving me the tools. In the end I should be able to swap out an analogue module, insert a microchip and a few mignons, and the synth will still work exactly the same.
This is one of the reasons why I’m taking what may appear unusual steps. I’m mapping the territory, the design space. Does mixing matter? Turns out it matters very much. Do bubbles matter? Still to be determined. Does depth matter? Turns out the manufacturer was right, don’t try to cure a 20mm vitrine in a single layer.
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You have to document your process. This could be a very interesting read.
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My essential heuristic is to take a process and remove unnecessary elements until I have the simplest viable solution to the problem. This is why I’ve avoided solutions like adding heat (generates unnecessary risk as well as costs) or using release agents (need not yet demonstrated).
The other thread (called fast prototyping even though I’ve been at it for weeks and still don’t have a prototype) documents some of my other moves in the direction I’ve mapped out. Use of crafting materials in preference to wood, metal or plastics for front panels, using found objects such as book cases as my synth cases, experimenting with simpler patch cables that can be quickly made up on the spot with a wire stripper and a screwdriver, and so on. That last one is just my way of avoiding unnecessary soldering.
The resin is what really takes me far outside my comfort zone, and to a certain extent the experiments with point to point surface mount soldering which I am surprised to find so enjoyable. But in the end it’s all about making a modular synthesis environment that I would be comfortable working with. Software and hardware should work seamlessly together as first class citizens.
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Another possible potting compound I will investigate, with some caution, is polyester resin. It can cure much more quickly than epoxy but the raw uncured resin is smelly and somewhat toxic. It’s also less suited to lower ambient temperatures. This is an outdoor suit and respirator job, and the resin shouldn’t be stored indoors. There’s less room for improvisation here.
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Have you considered doughy-er materials, like Apoxie Sculpt? It wouldn’t be poured over the components but it should still be soft enough to let you embed the components without risking the connections. If transparency/translucence is important, it probably won’t do it for you, but it should cure more quickly and completely for you.
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I could use something like Milliput for potting but here I want visibility of the individual components so a glass-like finish is important (hence the name vitrine.) Both epoxy and polyester are capable of providing the necessary effect.
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Here’s a guy recommending an electric lunch warmer for quickly curing polyester resin on his balcony in the UK climate in November. I like the general idea but I think I could use a hot water system (such as hot water bottles) in an unpowered lunch box. At least I would be avoiding the 240VAC mains cable and associated risks.
I’m much less constrained for space than he must be, but unlike him I have to make sure whatever I use isn’t a health hazard to curious people who might just wander into the garden while I’m curing a batch of resin.
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You have a lot of kinds of epoxy resin.
Some cure as fast as 5min (there are probably even faster curing ones today ?).
I admit the 5min ones aren’t adapted to what you want to do because of their gooey consistency, but those curing in 1 to 2 hours are quite fluid and should do the job.
They won’t look as perfectly clear as thoses designed for jewelry/inclusion, they will stay slightly milky, and will probably have more bubbles (less time for them to get to the surface to escape, even if you get a vacuum pump).
They are also cheaper.
It really depends if the look is of importance to you, or if function prevails.
Isn’t an opaque mistery-minion something appealing ?
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