Pressure Pots for casting questions

[judgedredd]

similar to how i always do it i used to do figure casting and i was shown to do rotation casting with a 2 piece mold with a silicone bung basically you use a low viscosity fast cure resin fill the mold to about 3 quarters then put the bung in give it a good few taps to dislodge traped bubbles and turn until it sets ! its hard work and time consuming but gives reasonable results as the turning stops bubbles from attaching to the surface and are forced into middle of the piece.
I would love to have a play with a vac or pressure chamber but dont want to spend money on something and find out i have the wrong parts plus i am in uK so its a bit more tricky

Being the poor cheap dude that i am i have in the past used a 5 gallon pail , a shop vac and a piece of plexiglass before with fair results. That pail method did remove alot but not all of the air bubbles. The other method i use alot is the claying half casts.

this way you pour your silicone over your half clayed subject and all the air bubbles rise to the top and away from your subject. When it dries flip it over, remove clay, apply mold release and pour the second half.

Sorry to get off topic:lol I do need a pressure pot myself and am watching this thread with great interest.

 

[SG Merc]

Being the poor cheap dude that i am i have in the past used a 5 gallon pail , a shop vac and a piece of plexiglass before with fair results. That pail method did remove alot but not all of the air bubbles. The other method i use alot is the claying half casts.

How long did you run your vacuum for with this method?

I only ask because it's my understanding that using a shop vac in this way will burn out the motor if you leave it on too long.

I found this on another F/X message board: http://www.donjarrs-place.com/07-how-to-vacpot

 

[moff man]

So far mine has held up but i did drill 3 holes around the top of the pail to give some relief to the motor. I run it till the bubbles die down no more then 5 minutes . Do this at your own risk, i will not replace your shop vac.:lol

 

[LordVdr]

Ok, so is there any tutorial or anything for converting the Harbor Freight pressure pot to a vacuum chamber, i.e. showing how to hook up the vacuum hose, changing out this and that, etc.?

And thanks for the all of the info so far....I've never even dreamed of using a pressure/vacuum chamber to do castings, and now I'm wondering how the hell I've gotten along without one.

Yes... As far as paint pressure pots... Personally I wouldn't use a pressure cooker pot as they are generally a MUCH weaker design, and I would NEVER use a pressure cooker pot as a pressure tank...



Yes, you can get the cheapy venturi one from Harbor Freight if you have a decent air compressor, or you can look around for an electric one... I have lucked out since they outlawed unlicensed servicing of many freons there are a bunch of AC unit vacuum pumps out on the market from handymen that used to do it, and no longer can... They can be found at garage sales and even Ebay pretty reasonable...



I was at a Smoothon distributor last week and saw that tank in person, it's real nice, and the additional size would be welcomed, but like you it's a little too rich for me and my needs...

 

[cheech9898]

Ok, so is there any tutorial or anything for converting the Harbor Freight pressure pot to a vacuum chamber, i.e. showing how to hook up the vacuum hose, changing out this and that, etc.?

And thanks for the all of the info so far....I've never even dreamed of using a pressure/vacuum chamber to do castings, and now I'm wondering how the hell I've gotten along without one.

It's been awhile since I've messed with one of those pressure pots and by just going by the HF Pressure pot manual ( http://www.harborfreight.com/manuals/93000-93999/93119.pdf ) if your wanting just a vacuum chamber.


1) There should be a paint pickup tube from the inside of the lid to go down into the inside of the pot, remove it.
2) I'd just pull the 90 degree setup off the lid for the fluid outlet adapter and use this hole to put the vacuum gauge in (using whatever brass adapters I needed to do this)
3) I'd leave the 'T' on the inlet side on.
a) pull the relief valve and replace it with a good ball valve (for a quick vacuum release)
b) pull the regulator side off the other side. put a 2nd ball valve on and then do whatever you want to hook the vacuum pump on. I'd probably put a quick connect female end on it then put a male quick connect on the pump hose.
If you only want to use 1 ball valve on that side you could just plug the other side of the T, or do a lid-ball valve-quickconnect (no T).

* note: probably wise to re-Teflon tape all threaded joints just to make sure there aren't leaks.

If your wanting to rig the pressure pot for both pressure and vacuum, you'd definitely want to replace the lid thumb screws with at least American made bolts/thumbscrews (for pressure casting) and I wouldn't trust the chinese pressure regulator, but you could plumb it with a T on the outlet side then do ball valves and your guages on each side to switch from pressure to vacuum guages, and then basically the same on the inlet side.... use another T w/ ball valves immediately and do 1 side w/ the regulator on it and then a quick connect for the compressor, then the other side just a ball valve and quick connect for the vacuum pump. More money in ball valves, but you can easily & quickly switch back and forth.

 

[exoray]

This is the only picture I have handy, this is the lid for one of my pots... Anyway everything was removed and all unused holes plugged... You will see a vacuum gauge on the top, and on the right you will see an on/off valve and a quick connect... And off to the side you will see my pressure dongle...

Basically when I want to pressure cast, I plug the pictured dongle into the tank and hook up the air compressor... The dongle has a pressure regulator on it and will hold the tank at whatever pressure it's set to as long as it's attached, even if it leaks it will compensate...

Also note that the quick connect on the tank lid also act as a valve, it's self shutting when nothing is plugged in, so I also use the pictured dongle as a pressure release dongle as well, basically just a way to hold the quick connect open... As long as the dongle is in place the valve to the tank is open it will return the tank to normal atmosphere for opening...

For vacuuming I simply plug my vacuum pump into the tank, and watch the vacuum gauge on the top... And to release the vacuum, like I said above I plug in the pressure dongle and open the tank valve... Originally I had a vacuum dongle just like the pressure dongle built from the cheap HF venturi pump, but that has been replaced with an electric vacuum pump...

The biggest thing to remember is to allow for a way to return the tank to normal atmosphere... Be it a secondary release valve or what not, care needs to be taken that it's at normal atmosphere prior to opening...

 

[MustangGTR1]

So let me get this straight...you can use a pressure pot as a vacuum chamber as well? I'm only asking as I am interested in getting a vacuum chamber for silicone casting, but don't have the $500+ for the one listed on Smoothon's site. Would I need a vacuum pump hooked up to it?

Thanks in advance for any info....

Yes you can. All you need is a 1/2 thick piece of Lexan, vac gauge and a value to cut off the suction and a rubber gasket for the top under the Lexan.
I have 3, 3 gallon, 1 10 gallon and a 45 gallon auto clave, none of which did I give over 99 bucks for.
With the gauge, get a liquid filled, they work the best.
It also dose not hurt to have a blow off value as well. This is just in case you forget and leave the air on. Some tanks will not take alot of airpressure.

My question is, if you have a pressure pot, why do you need to vac your rubber. I pressure all of mine, makes it go into the details better..Kev

 

[Kylash]

bumping this because the HF pots just came back in stock. Does anyone have a recommendation for what would be the best compressor for this pot at around 50psi? Im just casting small to medium size resin parts and figures.

 

[Kylash]

so i just got these today, upgrading some parts and hoping ive got it all worked out in the end before i plug anything in...

Is it best to be checking the psi on the pot or what its saying the output is on the compressor? both I suppose...

Ive got a quick connect on each side of the regulator, one will just be left alone to plug the out end, the other would connect by hose to the compressor. Ive then got a ball release valve on the extra out on the lid. I then used sealer tape to seal off the connections i was concerned about. Does this all look kosher? I havent swapped out the blow out seal yet. Does anyone know what the HF ones are set to?

 

[Rebelscum]

What's that open nipple in the last photo?

The pot has a maximim operating pressure of 60psi, though it is stated to be good for 80psi. I'd expect the safety valve is set for 80psi. I have one though I haven't tested it to that pressure.

 

[Kylash]

the one on the left is where the paint feed tube was that is now connected to the ball valve, and the one on the right is connected to the main feed with the regulator. I just put that extra pit oin the left hole because i dont think the top piece is in very far adn wanted some extra strength there since its now basically a backup release with the ball valve.

 

[Rebelscum]

Ah, I didn't recognize that was the inside of the lid. You should be good to go.

Just be sure and creep up to 60 psi when you are testing it. remember, tightening the regulator knob means more pressure.

 

[Kylash]

yeah im probably going to replace the blowout with a 60psi one just to be sure i never go over it. 80 is too close for comfort.

 

[Rebelscum]

I haven't adjusted mine, but I think that slotted ring concentric with the top of it is for adjusting the pressure.

 

[Kylash]

yup, it is, but im paranoid, so having a proper set blowout is something id like to have as well, just in case. I already had to return the original lid and regulator that came with it as the threads on the left and right basically unthreaded themselves from the main assembly when i attached my valves to it and tried undoing them.

 

[Kylash]

quick test with a random mold I had, not a pressure made mold so not ideal, but I think you can still see the difference...

 

[ThrowingChicken]

Nice results! I need to make one of these things.

 

[OldSkoolEffects]

i realize it's a but of a necropost, but in the interest of safety, I figured I'd say something. I recent;y emailed HF about a discrepancy between the pdf for this pot (60 psi) and the website (80 psi).

The reply I got was:

"Thank you for your recent inquiry.

The correct maximum air pressure is actually 40 PSI. We are aware of this problem and are currently working on getting it fixed in both places."

This means that even at the lower listed pressure of 60 psi, there's still a chance of explosive decompression.

 

[Luke0312]

I wonder if they are just referring to the stock PSV, since I believe it only goes to 40psi.

i realize it's a but of a necropost, but in the interest of safety, I figured I'd say something. I recent;y emailed HF about a discrepancy between the pdf for this pot (60 psi) and the website (80 psi).

The reply I got was:

"Thank you for your recent inquiry.

The correct maximum air pressure is actually 40 PSI. We are aware of this problem and are currently working on getting it fixed in both places."

This means that even at the lower listed pressure of 60 psi, there's still a chance of explosive decompression.

 

[robn1]

The pot has 80psi stamped into the lid. The 40 spec is based on the requirements for spray painting. But I still would not exceed 40-50 because of the poor clamp design.