PaintPot to Pressure Pot, Lid conversion

October 22nd, 2005

I traded lids with Kevin, so I could docment the conversion

The inner face of the paintpot lid. Close up of the inner lip guide, its only tack welded inplace. The top face of the paintpot lid, as it comes out of the box.
The inner face of the paintpot lid. Close up of the inner lip guide, its only tack welded inplace. The top face of the paintpot lid, as it comes out of the box.
You could quickly cap the paintgun feed. Remove the crappy rightangle adapter, it leaks at the drop of resin flash. They use some sort of thread lock on the threads.
You could quickly cap the paintgun feed. Remove the crappy rightangle adapter, it leaks at the drop of resin flash. They use some sort of thread lock on the threads.
Remove the female adapter. Ya there's that crappy lock tight junk in here too. For this conversion I sealed the inner lip with alumilite's molding clay.
Remove the female adapter. Ya there's that crappy lock tight junk in here too. For this conversion I sealed the inner lip with Alumilite's Synthetic Modeling Clay.
   Kevin went down to HarborFreight Tools and got their 2 1/2 gallon paint pot.  He almost didn't get it, as he asked for a casting pot first.  The pot as it comes is not ready for casting, although you could do some casting with it in a pinch.  I gave him one of my lids for his new one, so I could docment how I do the conversion, and degas the rubber for the replacement gasket.

   Here I will document the process of how I converted the lid to a resin casting quality pressure pot lid.  Mainly we dump the right angle fitting used to attach the stock regulator.  This thing is really leaky.  Since it is designed to be hooked up to a compressor which works to maintain the pressure, it passes most end users requirements.  Also it is meant to attach to a paint gun.  We won't be doing this so we need to cap the paint gun feed.

    The paint pick-up tube won't be threaded in place, just keep the pipe it might come in handy for some studio scale ship's spine (that's what studio scale models use to allow the camera men something to mount to the tripod).

   I like to put a female pressure connector here, technically you could fill two or more pots up by daisy chaining them, I haven't done this and if the seal is good on the lid you don't need to keep the compressor hooked up (to maintain the 40 psi).

   Next I remove the right angle adapter from the other feed point.  There is a rectangle 'T' adapter on this feed point.  It allows the presence of a pressure relief valve.  Don't remove this, you want the pressure relief valve!  Every time you start to fill the tank, tug the ring that opens this valve to make sure it is free moving, and releases/passes pressure.  This will keep you protected should someone mess with the regulator and allow more pressure into the pot.  The pot's working pressure is 40 psi, more than enough to pressure cast with (max is 80 psi DO NOT run this hot!).

   Next I add what I call the red flag.  This is a cutoff valve.  Usually they have a red tool-rubber coating on the handle, this is where I get the 'red flag' naming.  I install the valve so that when I put the lid on (there are four lid clamps) the handle still moves from open to close, or at least I tried to.  When the handle is up, there is a red flag going off in my mind's eye, that pot is hot with pressure!  Opening the valve, i.e. lowering the flag (to relieve the pressure) makes it safe to fiddle with the lid clamps.

   The last thing to do is replace the hard rubber seal.  This material is actullay ok, I used it for the vacuum chamber set up.  It's a good piece of rubber, so don't toss it!  The thing is you have to clamp it down hard to keep 40 psi all night (resin really only needs pressure during its cure time though).  But as resin drips here-and-there, and it will, the hard rubber will not seat well enough to make a good seal.  Best to replace it and avoid wishing you had after a batch of casting comes out bubbly.  Now when mixing rubber to make a new seal it is best to degas the rubber.  My first lid used a poured oomoo 30 rubber gasket.  It has since worn out.  Looking at it I could see where it had torn in many places, thousands of micro-bubbles where present in the mixture and they allowed the rubber to tear just like perforated paper tears.  It might be possible to get a 'good' enough pour with lower viscousity rubbers like Moldmax 30, however we want the cured rubber to be, well, rubbery (alumilte rubber is much 'harder' post cure so its not a good choice).  So one could make a gasket without a degassing setup.

   Now we will need to seal the inner ring/lip of the lid.  Looking closely one can see that this piece is just a guide to wedge the hard rubber gasket in place.  It is welded in patches around its circumference so liquid rubber will run out in some places.  I used Mold Builder rubber from the local hobby store.  This rubber can only be applied in thin coats and is useless to the novice mold builder (maybe useless to everyone).  It is ammonia based and stinks to high heaven.  I could've used a thin bead of Kleen Clay all the way around.  Anything will do to seal the gap but be sure it won't react with the rubber.  I also sprayed a coating of mold release (Mann 800, Ease Release 800 from Smooth-on) into the lip, this way I could pull the gasket when/if it goes bad, or maybe pull the gasket and use it somewhere else (new vacuum chamber lid).

Replacing the rubber gasket Home Electronic Goodies
Replacing the rubber gasket on a lid, & examining the vacuum chamber lid Up Sealing the leaky vacuum lid