Air bubbles in resin casting

[Hobbit 77]

I just made a couple of two part rubber molds and I'm getting some tiny air bubbles in the castings. Some times the resin castings turn out okay but others have a few air bubbles in them. Tried pouring the resin in very slowly and using the "burping" technique and have also made a crude centrifuge from a coffe can. You know, putting resin filled rubber molds into the coffee can and spinning it around a few times with a rope that I attached to it. Both have mixed results. Don't really have the money to purchase a pressure pot but does any body have any thoughts about getting bubble free castings?

Hobbit 77

[Schadenfreudian]

Do you have reasonably large 'reservoirs' attached to your castings? I don't know what the term really is, but I tend to make excessively large pour-channels and air-escape channels (what I referred to as reservoirs) when casting. When the resin is poured into the mould, I ensure that it fills it right up so that these 'reservoirs' are also filled with resin. When spinning the casting, in a similarly crude way to you, air bubbles are forced to float up into these reservoirs, displacing the resin in them. You should end up with a casting substantially bubble-free, but the reservoirs, which form sort of fat sprues, will be pitted and half-formed due to the bubbles displaced into them. In a sense, they form sacrificial extensions of the casting.

[jack wendt]

start by making your part in 2 pieces so you can have open face molds allowing the bubbles to rise AWAY from the surface. also the gentle vibration of your washing machine or dryer are enough to allow most bubbles to move away form the surface. use smoothon products.