in need of advice ( Vacuum chamber newbie)

[Nostok]

Also if this doesn't work I am going to pick up a slower setting resin.

[rattrap]

Just try getting a slower catalyst, or maybe try not adding as much of your existing catalyst to your resin to give it a chance to degas under vacuum.

[Nostok]

Okay so after degassing the separate parts of the resin until all bubbles had gone and they just started boiling I got the same results.

Next I did two things, firstly I stopped using the syringe as if seemed to add bubbles to the mix (and needed replacing anyway as the action was no longer smooth). Then I thought instead of just keeping the vacuum getting deeper and deeper I will lock it out as soon as I see bubbles start to form. This gave far better results, the items are not as hollow any more, there are bubbles inside but practically none on the surface of the model. I guess this is the stage at which pressure casters would turn on their compressor and squeeze the bubbles.

Okay so not perfect at the moment but better than it was as I now have usable parts with less surface bubbles than I had before vacuum. Tonight I will try the same but will release the vacuum gently so see if the bubbles disappear before setting.

I mentioned about the talcum powder earlier, this made no difference other than without it the casts were worse.

With regard to using less of the catalyst, which part would this be in smooth cast 300? Part B?

[Fleafa]

I pull a vacuum until I see foaming. At this point any trapped air and enough bubbles should have escaped. I shut it off and slowly let the pressure return to normal. I then apply pressure which squeezes the bubbles down so they aren't an aesthetic or structural concern.

Holding at 'full' vacuum, the resin won't ever stop bubbling as it is technically boiling. You should be able to reproduce the same effect with water if your pump is up to it.
Degassing the two components is largely pointless, as you'll reintroduce bubbles whilst mixing.
Do not adjust the ratios of Smooth Cast 300. If you want a slower cure, get Smooth Cast 305. This is what I use in Summer, 300 in Winter.
Could you post photos of your moulds as you would have them set up to cast? Without resin all over them, if possible

[Nostok]

We have friends over this evening and I was planning on trying out that method once they have gone. I'll post some picks of the mould as well.

[Nostok]

Sorry for not posting back sooner, life got in the way.

I tried what was suggested with resin and vacuum and have been getting consistent bubble free results.

I now degas larger volumes of resin parts A & B separately as one of them has a lot of bubbles after shaking the container as instructed by the product packaging. I found most of my spillage and cock-ups came from pouring from the larger containers so this sub stage removes that issue for me.

Because I am only doing one small mould at a time (I only have one mould made up) I then measure mix a small amount of that resin in little plastic pots. I pour this into the mould and then pull vacuum until it is bubbling, then I lock out the pump valve, turn off the pump and then open the release valve slightly and leave it to return to a room level pressure. I wait 10 minutes and de-mould my bubble free resin goodness.

Thanks everyone for your help and guidance.

[Fleafa]

[RageofAchilles]

I had another try following the instructions of Fleafa. Perfect cast! However holding the part up to the light it was apparent that a couple of small bubbles were inside. Still , gives me some hope . Thanks