Pressure Casting Resin

This will be a down and dirty “how to” on pressure casting. I know it can be scary to even think about this, but it really isn’t that hard to do. I have already listed what materials you will need to do this, but I will re-list them for the benefit of those who didn’t get it earlier.
For those who aren’t familiar with pressure casting let me explain it. Pressure casting is the means of injecting air into a chamber in which a mold and resin have been placed. The pressure forces the resin into the nooks and crannies of the mold and ensures that the majority, if not all of them are filled with resin and not air. It is next to impossible to do this without pressure casting. Hand casting, non-use of a pressure chamber (Paint Pot), just doesn’t cut the mustard here. The example I am using for my castings is a 1/32 A-10 cockpit. I cast this for use in a scratch built Sci-fi project.
The process
The top picture shows the hand cast one. While the panels are visible, the switches and control knobs are little more than indentations or voids. The bottom picture shows the pressure cast one. Every little nook and cranny has been filled to include the small air pockets that were in the sidewalls of the mold. On the bottom right of the lower photo you can see what look like numerous pimples. These are those small air pockets in the mold. They will be sanded off and the part will be good to go! To avoid these “pimples” we need to de-gas our molds, but that is another story and I’ll touch on that later.

Okay, enough on that portion. What follows is what you will need to get things started. Once you have these, you can begin to get your casting chamber assembled. Feel free to use the pics of mine as a reference to assemble yours. Matt’s PP is pretty much the same as mine.
  • A compressor capable of at least 50 psi. with air hose
  • A sealable container for use as your pressure chamber, (2.5 gallon Paint Pot (PP) is what I use)
  • Fittings for connecting your air source to the PP. Mine are ¼” yours may vary in size depending on what you are using as your chamber.
  • A ball valve- starting/stopping airflow into the PP.
  • Pressure gauge
  • Pressure relief valve. ( I use a compressor drain fitting)
  • Teflon tape
  • Quick disconnect air fittings (Couplers like those used in connecting air tools)
The set up of the materials is pretty simple and straightforward. I have a quick disconnect coupler at my compressor and one on the other end of my air hose. There is a male air fitting at the PP, followed by the Ball Valve, and then a short length of ¼” pipe into the PP. The pressure gauge is mounted on top of the PP and shows me the amount of pressure in the PP. I didn’t know how much pressure to use when casting so I started rather high. NOT A GOOD MOVE. I found out later that 30-40 lbs psi is sufficient. I do know that you don’t want to put too much pressure into the PP as you can pretty much consider this thing a bomb if it gets too much pressure in it!! Always better to err on the low side. This is where that pressure relief valve comes into its own. I would suggest plugging a 50psi valve into the PP. If you exceed that pressure, it will automatically dump the excess pressure. It’s a nice safety measure.

The bottom of my PP was rounded. This would not have made a suitable platform to put the molds on. The inside diameter was 8 ½”, I cut a piece of ¾” wood and placed it inside to make a nice flat surface to set the mold(s) on. Other members who have built these have turned theirs on the side and inserted something as well to place the molds on. Whatever you decide to do, ensure that the mold is sitting flat and level when placed inside the PP. Now for the fun part.
applying pressure
Grab a mold! Mix up some resin or casting plastic. Try not to stir in any excess air. Every little thing helps and the less air the better. Pour it in the mold. Now quickly place the whole thing into the PP and seal it up. Hook the air hose up, open the ball valve and start adding some air. Keep an eye on the pressure gauge. Once it reaches the desired pressure, turn off the ball valve. Disconnect the air hose. Now set back and have a beer or twelve if that’s your drink of choice and wait for the resin to cure.

  • Pic_1_Voids
  • Pic_2_Clean
  • Pic_3_Compressor
  • Pic_4_PP
  • Pic_5_valve
  • Pic_6_guage
  • Pic_7_reliefvalve
  • Pic_8_quickconnect
  • Pic_9_PP_Bottom

About the Author

About Matthew Quiroz (Red4)

After a several year break from the hobby I have happily returned to it. Slowly, but surely getting my mojo back.