I've been bouncing ideas for a silicone RTV gasket off a few people over the past few weeks, and I will soon be testing if I can mold a gasket for the new v2.3 20 Bin Gridfinity BFS, using a PETG mold. The RTV I picked up is designed for BBQ grills, but it says it's food safe and high temp, neither of which will come in handy, but it has some good reviews and is a gasket material. My current plan is to use a 2 part PETG mold, which will be held together using some clips. The mold will be open top, so I can just squeegee the excess silicone to finish the casting. I'm planning to use some dish soap and alcohol as a mold release, which will hopefully retain the small details and also be super cheap.
I'm hopeful that a silicone gasket will help seal out moisture more effectively than the harder TPU gasket. Making a gasket from RTV is gonna be a messy and somewhat complicated way to do it, but I think for some applications, it may be worthwhile.
I'm hopeful that a silicone gasket will help seal out moisture more effectively than the harder TPU gasket. Making a gasket from RTV is gonna be a messy and somewhat complicated way to do it, but I think for some applications, it may be worthwhile.
Update 6/22/2024: I should be used to this by now but unfortunately an open top mold is very messy, and the idea of smoothing the base using (in my case) a plastic razor blade, did not result in a very nice finish. It may still work, but again, it's messy.
Something else I noted with my first attempt, and that is a good mold release is crucial. I am using PETG and thought it may be slippery enough on it's own, but still added some soap to it (Dawn Powerwash spray), but it still stuck like crazy. I'm gonna try something more substantial next time, like cooking oil spray or petroleum jelly
So plan B is to try a fully enclosed mold. I reworked the open top mold so it can fully enclose the part, and added several vent holes and a hole to "inject" the silicone RTV into. I'm sure that curing will take much longer with this approach, and I will have to clean up some sprues, but hopefully it will produce a cleaner result. I designed some clips to hold the parts of the mold together, however I also plan to use some binder clips.
Update 6/22/2024: I should be used to this by now but unfortunately an open top mold is very messy, and the idea of smoothing the base using (in my case) a plastic razor blade, did not result in a very nice finish. It may still work, but again, it's messy.
Something else I noted with my first attempt, and that is a good mold release is crucial. I am using PETG and thought it may be slippery enough on it's own, but still added some soap to it (Dawn Powerwash spray), but it still stuck like crazy. I'm gonna try something more substantial next time, like cooking oil spray or petroleum jelly
So plan B is to try a fully enclosed mold. I reworked the open top mold so it can fully enclose the part, and added several vent holes and a hole to "inject" the silicone RTV into. I'm sure that curing will take much longer with this approach, and I will have to clean up some sprues, but hopefully it will produce a cleaner result. I designed some clips to hold the parts of the mold together, however I also plan to use some binder clips.
Update 6/23/2024: 2nd attempt at making a silicone RTV gasket is underway. This time my recipe for disaster (or success) is:
The round holes in the mold are for the alignment pins, which I found are not really needed, since there are several other alignment features which do the job.
Plan C, if there are gaps, is to try and prefill the mold (overfill it) and increase the vent holes, then clamp it up, and inject some more RTV for good measure.
I asked the reddit hive mind to get their take on better ways of doing this, and may change Plan C (or D, E, or F), if there is a better idea or method for doing this (or a better material I should use, which is not too expensive).
- A fully enclosed mold
- Dawn commercial dishsoap mixed with water (highly concentrated but still flows like water and is a light blue color).
- Injected the soap mix into the mold just before injecting the RTV
- Every small clamp I own to hold the mold halves together
- Made sure the RTV oozed from the vent holes
The round holes in the mold are for the alignment pins, which I found are not really needed, since there are several other alignment features which do the job.
Plan C, if there are gaps, is to try and prefill the mold (overfill it) and increase the vent holes, then clamp it up, and inject some more RTV for good measure.
I asked the reddit hive mind to get their take on better ways of doing this, and may change Plan C (or D, E, or F), if there is a better idea or method for doing this (or a better material I should use, which is not too expensive).
Update 6/25/2024: The 2nd attempt failed. The mold did not fill completely and the RTV that did fill it, mostly stuck to the mold.
After doing more research, I considered thinning the RTV using mineral spirits and casting it that way, however I do not know if that affects the properties of the RTV, and it may take much longer to cure that way. The pourable silicones seem like they may work, however I have read there are issues with UV exposure and since they are not designed for use as a gasket, I question if they would be durable enough. So right now I don't see an option that will not take a good deal of trial and error - which I don't have time for. For the sake of simplicity, I decided to try some softer filament and try printing the gasket. I found some eSun TPE 83A filament, which looks like it may work. It's not cheap, though also not super expensive at $30/kg, so worth a try.
After doing more research, I considered thinning the RTV using mineral spirits and casting it that way, however I do not know if that affects the properties of the RTV, and it may take much longer to cure that way. The pourable silicones seem like they may work, however I have read there are issues with UV exposure and since they are not designed for use as a gasket, I question if they would be durable enough. So right now I don't see an option that will not take a good deal of trial and error - which I don't have time for. For the sake of simplicity, I decided to try some softer filament and try printing the gasket. I found some eSun TPE 83A filament, which looks like it may work. It's not cheap, though also not super expensive at $30/kg, so worth a try.
Update 6/30/2024: The 3D printed TPE gasket was a bit better than the TPU version, but still not water resistant enough. For now though, I'm setting the silicone gasket idea aside. There is too many variables with a molded silicone gasket, which would take a good deal of time and trial and error to figure out. Additionally, 3D printed parts are difficult to waterproof, without sealing, so that is something else that would need to be investigated. The cases I have tested have failed as much at the gaskets as they have in the porosity of the walls. This is a project for another time I think, I'm moving on to other stuff for now. Below are some pics of the eSun TPE 83A gaskets which were printed, they were not as easy as 95A TPU to print, but they are a bit softer.
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