Avoiding air pockets when casting?

[mikeoz]

I added a beard to a rotocast head. The beard very slightly overhangs the chin. When I tried casting the head, I got an air pocket at the end of the beard. Does anyone know of a way to prevent this?

[Blackkryptonite]

I usually fill the mold most of the way up with resin then cover the hole and rotate the mold all around while tapping it with something solid. that usually gets all the air bubbles out from those crazy under cuts. After that i just fill the mold the rest of the way up and let it cure.

[mikeoz]

^^^^
Thanks for the idea. I'll be trying it this weekend.

[Dave Mc]

A heated mold helps. I microwave the mold until it's nice and warm, then pour the resin. The heat helps. Also, when pouring into a mold that has a problem area like you mentioned, tip the mold on a 45 degree angle when pouring. In this case, chin down. That tapping method also helps alot. Combine all these and you'll have pretty good luck.

[mikeoz]

A heated mold helps. I microwave the mold until it's nice and warm, then pour the resin. The heat helps. Also, when pouring into a mold that has a problem area like you mentioned, tip the mold on a 45 degree angle when pouring. In this case, chin down. That tapping method also helps alot. Combine all these and you'll have pretty good luck.

Thanks, Dave. I'll give this a shot, too.

[JMC]

How long should you microwave a silicon mold?

[ctc]

Hmmmm....

For real problem areas, you can cut an air canal into the mold, to vent bubbles away. Then trim the extra bit once it hardens. (That's one reason some toys have them weird little notches and pegs on 'em.)

Don C.

[Dave Mc]

Depends on your microwave. I do 30 seconds. The mold should be warm on the inside but not super hot. I use smooth-on oomo products, so have never done this with any other brand and am not sure how other brands respond.

[AAAAA]

slow pour , shake and the above what is said.
I have Vibro-table that shakes the mold ,and the resin to get the air bubbles out.