Vacuum vs Pressure pot

[piecemaker]

Someone gave me a vacuum pump awhile back and i finally got around to making a small test vacuum chamber/pot for it to degas the silicone molds and also hopefully use also for eliminating air bubbles in the cast resin.I tried it last night with a new mold.The results turned out worse than if i had not used it.The mold was full of very visible air pockets and when i cast a resin piece in that mold it came out with little pimples all over it.This pump was pulling about 16 Hg vacuum and i let the pump run for about 15 minutes and then shut the valves on chamber and let it sit under vacuum until cured.I'm assuming that wasn't enough vacuum?I have read on here that most people use a pressure pot and i am going to try that next,as soon as i get some more silicone,i'm fresh out.Will a pressure pot degas the mold? and eliminate the small air bubbles in the cast piece?The parts i'm doing now without anything are turning out good,just looking to improve them and maybe help with some real intricate pieces(like teeth)that i'am having problems with.Thanks,any advice is appreciated.

[nobody]

I don't pressure, but I tried to mold upside down..i.e. glued the head to the cup rather that suspend the head and ended up with air holes in the mold that left resin bubbles on the eyes and head. Wasted alot of Oomoo. I'm going back to suspending, at least that way I just had holes I could fill.

[BlackKnight]

A Pressure Pot, will illiminate all bubbles thru-out the resin piece.
Vacuum Chambers are better Designed for the Mold it's self right ?.


I dunno ****...
I just know when We Pour Concrete at Work ..., We gotta use a Vibrator, and Cure it so it doesn't crack .

[piecemaker]

A Pressure Pot, will illiminate all bubbles thru-out the resin piece.
Vacuum Chambers are better Designed for the Mold it's self right ?.


I dunno ****...
I just know when We Pour Concrete at Work ..., We gotta use a Vibrator, and Cure it so it doesn't crack .

Yeah,thats what i'm trying to find out(before wasting more silicone) if the pressure chamber will degas the mold or if i need to vacuum chamber the mold then put in pressure pot to cast.I read the mold has to be degassed before casting in the pressure pot otherwise you end up with a piece that has little pimples all over it.Exactly what i got when i attempted the vacuum chamber experiment.I'm thinking i need more vacuum to degas the mold,but if a pressure pot will do the same thing i will just go that route.

[piecemaker]

I don't pressure, but I tried to mold upside down..i.e. glued the head to the cup rather that suspend the head and ended up with air holes in the mold that left resin bubbles on the eyes and head. Wasted alot of Oomoo. I'm going back to suspending, at least that way I just had holes I could fill.

I done the molds both ways and one thing i do that helps eliminate air bubbles in the mold is slowy turn the mold while tapping on the sides of the cup with something.It doen't eliminate all air bubbles in the mold,but it usually gets all air bubbles away from the head,etc.

[nobody]

So you mean making the mold not the resin? I've notice sometimes the terminoligy gets crossed. I usually have good luck with resin but I was told to turn the mold when pouring resin also.

I done the molds both ways and one thing i do that helps eliminate air bubbles in the mold is slowy turn the mold while tapping on the sides of the cup with something.It doen't eliminate all air bubbles in the mold,but it usually gets all air bubbles away from the head,etc.

[piecemaker]

So you mean making the mold not the resin? I've notice sometimes the terminoligy gets crossed. I usually have good luck with resin but I was told to turn the mold when pouring resin also.

Yes,when making the silicone mold only.I tried tapping on the cup with resin in the mold once and it actually started the resin foaming up and out of the silicone mold.

[LonnieFisher]

Degas your silicone in a vacuum chamber before you pour it into the mold cup, box, or whatever. Then degas it again before it starts to cure. You can let it cure in the vacuum chamber. The longer the set time for your silicone, the more air that will escape. DO NOT make molds of original Mego heads this way!! In a vacuum chamber they get squished and you get a very warped casting!

[Confessional]

^^ Anti-Bubble 101: Super smooth & level mold form (clay) box, ample spray of release, pour your mold from the lowest/deepest point with a steady steady flow/stream, turning on the fill, and if you have vibration plate (or can rig up a similar action) they work great. Some materials can be temperature sensitive as well leading to slower releasing bubbles.

[LonnieFisher]

If you don't vacuum degas your silicone, you can't pressure cast your resin.

[Confessional]

I'm still learning too, but in most cases if you mix silicone properly and poured it carefully there shouldn't be any need for degassing... meaning what bubbles exist will naturally release. Lots of variables I know, but I was taught by someone who makes molds for things big and small, casts in a variety of materials and really has instilled quality control in my process.

That said, there's some good tips in this set-up that might be helpful: http://www.squidoo.com/how-to-build-...-for-degassing

[boss]

Lonnie's right. Degas before pouring your rubber on the part.

[piecemaker]

If you don't vacuum degas your silicone, you can't pressure cast your resin.

Thanks Lonnie,thats what i wanted to know.I'll give my vacuum chamber setup another try but will degas/vacuum the silicone before mixing,after mixing and then as it cures.Then pressure pot the resin in that mold.

[piecemaker]

I'm still learning too, but in most cases if you mix silicone properly and poured it carefully there shouldn't be any need for degassing... meaning what bubbles exist will naturally release. Lots of variables I know, but I was taught by someone who makes molds for things big and small, casts in a variety of materials and really has instilled quality control in my process.

That said, there's some good tips in this set-up that might be helpful: http://www.squidoo.com/how-to-build-...-for-degassing

Thanks for the link.It looks like i'm going to need a bigger vacuum pump.

[LonnieFisher]

I would:
1.measure and degas both parts A and B
2.mix and degas
3.pour and degas
That works best with the longer setting silicone. If it cures fast you don't have time for all the degassing. Silicone with a shore of 10 works best! The softer the better. I recommend dragon skin 10 from smooth-on.