Vacuum Potting in the "At Home" Shop

[Kazooman]

I have to say that the thickness of your cover that I see in the photo seems more than enough. You should be fine with or without the bracing. Just give the rig a good looking over from time to time to see if any cracks are developing.

I hope I didn't scare anyone away from trying their own vacuum potting. That was not my intent. I just wanted to make everyone aware of the potential hazards of vessels under vacuum. It is interesting that almost anyone would be wary of pressurizing a vessel, but they don't see the potential danger in a vacuum. You can certainly get to much higher pressure differentials with internal pressure, but the atmosphere is pretty impressive in its own right.

[kayakerca]

I have to say that the thickness of your cover that I see in the photo seems more than enough. You should be fine with or without the bracing. Just give the rig a good looking over from time to time to see if any cracks are developing.

I hope I didn't scare anyone away from trying their own vacuum potting. That was not my intent. I just wanted to make everyone aware of the potential hazards of vessels under vacuum. It is interesting that almost anyone would be wary of pressurizing a vessel, but they don't see the potential danger in a vacuum. You can certainly get to much higher pressure differentials with internal pressure, but the atmosphere is pretty impressive in its own right.

Hi Kazooman:

Don't apologize for concerns about safety. When I look at my potting video, I can definitely see the lid flex back when I release the pressure of the vacuum. I have had a glass thermos blow up on me in the past, so I understand the issue. Now, I had to go out this afternoon and buy a chunk of aluminum for the brace, a band saw to cut it and a milling machine to drill the 1 1/4" hole, but what are a few more toys for the shop. Ok, ok, so I already had all those things in the shop.

Your advice was sound and I took it.

[Lyrebird Steve]

Using Aquarium pum

Hi Guys,

was thinking of upgrading my setup to vacuum potting.

Saw this instructable on Converting an Aquarium pump with the demo version pulls 8" Hg ... would this be sufficiently strong enough for Vacuum potting (but not strong enough for imploding lids ??)

Steve

[David King]

Steve,
I have a carbon rotary fin vac pump that develops 25 "Hg on a good day and it isn't capable of degassing epoxy. i haven't tried it on wax which is a lot thinner but I don't think 8"Hg is going to do very much for you. Everything seems to happen between 27 and 29"Hg.

[RedHouse]

Just came across this link:

Making A Fridge Compressor Into A Vacuum Pump

[David King]

Those fridge compressors have a tendency to fog up your air with compressor oil if you don't have a way to capture it at the outlet (+ pressure side). I know this from experience... That said they can work really well.

[RedHouse]

Those fridge compressors have a tendency to fog up your air with compressor oil if you don't have a way to capture it at the outlet (+ pressure side). I know this from experience... That said they can work really well.

Yeah, the link was about turning one into a vacume source, but thanks for that, I'm sure someone can use that tidbit.

[jason lollar]

its funny that we both use such a similar set up, i use a rubberized cork gasket and have a grill in the bottom of the crock pot I made of plexi- the grill lets any contaminates sink to the bottom- like various pieces of grit or occasionally some small metal particles- dirt etc. Anyway when I first set mine up i used 1/4 inch lexan on top and it would last a couple months of daily use before it would fatigue and implode- amazing amount of force displayed. Anyway that happend three times and I switched over to 1/2 lexan about maybe 6 or 7 or 8 or 10 years ago and I still have the same top plate in service. One trick is to drill your air fitting hole towards the edge of the plate- dont put it in the center
Amazing amounts of air come out- thats not in the wax thats all air in the coil, the lead wires and believe it or not the forbon if you use forbon flatwork. Potting your flatwork eliminates dimensional changes due to humidity- tested that. I use one of those medical aspirator machines- you can find them on ebay occasionally for under $100. Gomco I think is the manufacturer- its quiet and so well made it stands up to daily use no problem

[David King]

Thanks Jason,

i saw a several of the Gomcos on ebay today and was wondering where they came out of. Dental offices don't generally need that kind of vacuum unless they are doing casting in-house. I'll keep an eye out for one on CL locally..

[kayakerca]

its funny that we both use such a similar set up, i use a rubberized cork gasket and have a grill in the bottom of the crock pot I made of plexi- the grill lets any contaminates sink to the bottom- like various pieces of grit or occasionally some small metal particles- dirt etc. Anyway when I first set mine up i used 1/4 inch lexan on top and it would last a couple months of daily use before it would fatigue and implode- amazing amount of force displayed. Anyway that happend three times and I switched over to 1/2 lexan about maybe 6 or 7 or 8 or 10 years ago and I still have the same top plate in service. One trick is to drill your air fitting hole towards the edge of the plate- dont put it in the center
Amazing amounts of air come out- thats not in the wax thats all air in the coil, the lead wires and believe it or not the forbon if you use forbon flatwork. Potting your flatwork eliminates dimensional changes due to humidity- tested that. I use one of those medical aspirator machines- you can find them on ebay occasionally for under $100. Gomco I think is the manufacturer- its quiet and so well made it stands up to daily use no problem

I am hoping that the 1 1/4" X 1/2" cross brace on the 1/4" acrylic lid will add enough extra strength to keep it from imploding. I had the aluminum in the shop, so it was an easy fix. If it doesn't hold, 1/2" will be the next step. Ya, I put the wire spacer on the bottom for all the same reasons as well as separating the p/u's from the more direct heat of the bottom of the crock pot. After watching a handful of potting videos on YouTube, I was amazed at the amount of air that was extracted from the p/u's. Was also wondering if air was actually extracted from the forbin and replaced with wax and it's affect.

Thanks for the observations Jason.

[RedHouse]

...Amazing amounts of air come out- thats not in the wax thats all air in the coil, the lead wires and believe it or not the forbon if you use forbon flatwork.

.... I use one of those medical aspirator machines- you can find them on ebay occasionally for under $100. Gomco I think is the manufacturer- its quiet and so well made it stands up to daily use no problem

Amazed me when I saw that video clip, I guess I'll need to invest in a better pump for coils that need no air.

Jason, is yours one of the "portable" unit's like these:



or a bigger one on a base/stand like this:

[jason lollar]

Be careful- when it implodes shards of the plexi will bounce off the bottom of the pot and fly back out all over your shop- potentially very dangerous. Also on all the crockpots I have owned they heat on the sides not the bottom but maybe they are not all like that.
i use the protable type- i have two one looks like the blue unit on the left and the other is much older and is just an exposed motor with the fluid container- that little jar with a valve is almost indispensible- keeps small bits of dried wax out of the intake. they use them in doctors offices for minor surgeries and taking beans out of little kids noses or ears- The air doesnt really start getting crazy until the vacuum reaches about 20 or 25 vac. you can pot for 5 or 10 seconds and just get the outer layers or go several minutes, its predictable and repeatable if you preheat your pickups

[RedHouse]

...i use the protable type- i have two one looks like the blue unit on the left and the other is much older and is just an exposed motor with the fluid container- that little jar with a valve is almost indispensible- keeps small bits of dried wax out of the intake. they use them in doctors offices for minor surgeries and taking beans out of little kids noses or ears- The air doesnt really start getting crazy until the vacuum reaches about 20 or 25 vac. you can pot for 5 or 10 seconds and just get the outer layers or go several minutes, its predictable and repeatable if you preheat your pickups

Ok, thanks for that.

[Joe Gwinn]

I am hoping that the 1 1/4" X 1/2" cross brace on the 1/4" acrylic lid will add enough extra strength to keep it from imploding. I had the aluminum in the shop, so it was an easy fix. If it doesn't hold, 1/2" will be the next step.

It's far better to use lexan (polycarbonate), which won't shatter. This is what many bulletproof windows are made of.

Plexiglass is famous for abrupt self-disassembly under stress. Nor will the aluminum prevent implosion.

Given Jason's experience that 0.500" lexan has survived years of heavy use in his shop, that's what I would use as well.

[Lyrebird Steve]

if you preheat your pickups

Jason, by this do you mean placing them in the wax to reach the same temp before applying vacuum ?