Vaccuum only casting

[Chasper]

I've been casting PR without pressure or vaccuum for a couple years and I'm mostly happy with the results. I'd like to do a better job with "wrap around the tube" castings like snake skin, mother of pearl, etc. I also have a few bubble and equal dispersement problems when casting rice, coffee beans, chili pepper seeds, etc. I have absolutely no interesting in casting or stabilizing wood, worthless or otherwise.

I've read the tutorial in the library about setting up a pressure/vaccuum pot. While I'm more of a tool user than a tool builder, I can probably muddle my way through all of that, but do I really need both pressure and vaccuum for what I want to do? All I want to accompolish is to suck the air bubbles out of PR castings, wouldn't a few minutes of vaccuum get the job done?

 

[gketell]

If you only do one of the two, do pressure. Vacuum will get rid of the big bubbles but not the small ones. And if you leave it under pressure until set the little bubbles will be big. Pressure compresses the little bubbles into "nothingness" and the big bubbles to small bubbles.

If you are using PR then you can mix your resin then set it on something that vibrates (like a scroll saw table or shaky clothes-drier) and that will get rid of the big bubbles like the vacuum would. Then put the blank in your pot and put it under pressure and that will "get rid of" all the bubbles that were too little to shake loose.

GK

 

[nativewooder]

Getting rid of bubbles in casting can get to be an "art" by itself. I don't do casting any more but are you adding bubbles by mixing too vigorously? These are difficult to get rid of. Are you able to pour the mixture into the mold slowly to help float any air pockets to the surface? I worked on a project many years ago and wound up having to thin the epoxy with xylene to a point where I could get rid of enough of the bubbles that they would not be visible. It also took a little judicious use of heat from an alcohol lamp to speed the process along before the epoxy began to set. It may take a bit of experimentation if you don't want to do the vacuum.