New to vacuum pressure casting - check list

[Anvils Hammer]

Welcome to the "Made catastrophic errors whilst learning to cast" club. current membership- Every single person on this forum.

Dont get disheartened because it didnt work out first time

If the damage to the master is catastrophic, make another one! or leave it in a box for a week or two, then come back to it fresh and see what can be repaired/salvaged.

Pressure casting a mold is much easier with a short cure rubber, talk to your supplier, they might have a 2 Hour catalyst, or a 6 hour, 24 hour is the standard but its certainly not what I use!!

Does the rubber under vacuum expand massively and then collapse back down again? once its collapsed, even if itst still bubbling, its "de-aired" for our purposes..

Best of luck,

AH

[Arkangel]

[mangozac]

I'm quite sad to hear all of this, but especially that your wife is so negative towards your modelling hobby in general! It's such a great, positive hobby that hones manual skills and produces arguably artistic results. Would she rather you spend your free time watching sport on TV? Or continually down the pub drinking?

With regards to the softening styrene have you been using non polyurethane resin? I couldn't imagine the PU doing that!

If half the battle of producing decent resin casts is in refining a suitable technique then the other half is tracking down the best resin and silicone products to use. There's a few UK guys on here who can recommend the best products to be using. You want to get products with much shorter working and curing times - the silicone I use cures faster than my resin and can be demoulded from the master in 30 mins after pouring! That way the pressure pot only needs to hold pressure for 1 hour, not 24.

As both of the other guys said, we all wasted a lot of time, energy and materials on learning to cast. Don't despair!

[paulson games]

Yeah try not to give up, I had some major roadblocks early on. I pretty much ruined the first two batches of material I'd tried and just about quit. I'd tried Aluminite first and then Tap products and neither worked well for me.

Fortunately I am really stubborn and decided to give it one more go and managed to get thinge worked out using Mirco-Mark and later Smooth-On.

The point is it's not easy getting started and you make all sorts of mistakes early on. Once you get some sucesses it'll be a whole new world and feel so much more rewarding.

The big projects are really tough for first time stuff, I was doing small stuff but having done some bigger stuff since then I imagine that I would have been ready to tear my hair out had those been my first casting attempts. Maybe take a short break to recharge your energies and give it another go with something smaller just to get the feel down. It like riding a skate board, it's a total pain at first and even when you are good at it you fall down periodically.

(where with a bike you tend not to mess up on)

I still make lots of bone headed mistakes, tonight I just ruined a brand new mold because I forgot to add B side to the resin and dumped the raw A side in, which binds with the silicone if not taken off right away. oops.

With practice you tend to make less mistakes, but they still happen and you gotta stay posative.


As far as the pressure levels, none of my pots have ever held pressure for much longer than 1-2 hours. But that's ok as long as the pressure drop is fairly slow. Squeezing out the excess air bubbles is the main focus of pressurizing and that is actually completed within a few minutes. If the proper pressure level is reached if can slowly taper off and the molds shouldn't have any issues.

If you use the lego blocks for your walls and it returns to normal room pressure too quickly air can seep back into the mold along the lego faces. But this shouldn't occur if it's just a regular box made from solid plastic. (The legos trap air internally) I went and drilled exit holes along the outside of my legos that way the air exiting goes out that way rather than into the silicone should it depressurize suddenly.

Typically I only leave my molds under pressure for about an hour as my pot has leaked down to 2-5 PSI by then. I then set the mold on a level counter for several hours while it finishes curing. My compressor doesn't maintain pressure very consistantly and tends to blow the safetly valve if let unattended. Fortunately I just fill it initally and then let it slow leak and there's no issues.

Also if you are using the standard 2.5 gallon paint pots that most of us use it'll hold 60PSI no problem, you just have to buy a higher rated relief valve capable of 70-80PSI. I bought mine off ebay for about $7. I was really freaked out about taking it that high at first but it's held just fine.

I know that some materials witha sulfer content will mess with various plastics and styrene, haven't run into resin doing that but I've had a pack of clay make my legos all gooey and wreck styrene master. I've bought stuff labeled as sulfer free since then and not had a repeat of that.

There's times where learning how to cast feels like you are smashing your head against the wall, but it does get better.

[Fleafa]

What I really love about this forum, aside from the great wealth of information available, is how friendly and encouraging everyone is.
Like others have said, it is hard to start with but we've all managed to make big mistakes. The great thing about mistakes shared on here is that we all benefit from the experience.
Thankfully, my other half is incredibly supportive.

So, what products are you using and where did you get them from?

[Deadmeat30]

Smtk,

Keep trying methods out, and as Paulson says, try doing some smaller projects. Don't give up though, it's so much fun opening the mould and seeing a bubble free casting on your first pull! Stick with it, and if you need advice, then just ask, most here had to start somewhere, I've made so many mistakes with casting, spent loads solving them, but I've enjoyed every step. You have a great community of addicts here that will help you out as much as you can.

Stick in there mate.

[smtk]

Hi thanks for the support.

I think the best way of saving the model is to roughly patch it up then take non pressure moulds and see what comes out. I could then work on cleaning up the resin rather than the mushy styrene maybe make a new master.

As for why my wife hates the models I don't know. Probably a few factors we have our first baby, she's now off work and I work from home. I work for myself its stressful (large amounts on a commission bases) but there's a lot of idling time where I have to be at the house but have lots of time to kill. So I fill the time with games and recently modelling. I guess to her she sees me just sitting at my desk messing around with 'toys' all day but the reality is I'm dealing with work as it comes in then back to waiting for a response. Work is 24/7 for me meaning I take personal time wherever I can.

[Deadmeat30]

are you pressuring the silicone to make the moulds?

[smtk]

Originally I was attempting to vac degas the silicone and then the plan was to pressure cast the resin

However now the plan is to just pour and split mould at atmosphere same for the resin to try and get a workable resin piece to maybe pressure cast.

[Anvils Hammer]

working at atmosphere, its vital to get the rubber totally covering the surface, so grab some cheap toothbrushes and work the silicone into all the gaps/holes.details etc.

With the resin pour, you basically need to pour it while its really fluid and as you pour, hammer the table like you are trying to break it in two, this should cause most of the bubbles to dislodge from the sides atleast..

any remaining bubbles, and there will be a few, can be filled with milliput etc..

good luck!

AH

[mangozac]

[smtk]

Fair question I my share not as much as her but she gets way more support from me that anyone of the other mothers and my mother takes him for a few hours every day so we get some us time. I chauffeur her around to all her meetings as well as a share nappies, bath times, play time and night shifts. Compare that to some of her friends whose husbands are only there to help for 3 or 4hrs a day and weekends.

Those baby crazy hormones means she not exactly rational when it come to anything to do with the baby. Its probably convenient excuse for her to pick a fight to off load her frustrations. I remind her that we're on the same side and about just how much I do without fuss.

My friends wife had a similar thing about him playing on the PC. After one argument he spent the next 2 months drinking beers watching tv and she was as happy as a lamb about it.

Any way back to resin I was never planing to making a production run of this model just coping the mirrored parts (I was convinced to change scales to 1/60) This was a test to see how pressure casting worked (or didn't lol). Now I just want to see how it looks finished.

[mangozac]

[smtk]

Success !!

While I knew damage to the masters would pass on their flaws the moulds themselves worked great.

-The vac degassing worked (I could see no bubbles while cutting the rtv)
-I used split moulds for speed of set up and resin came out super.
-I did have to open up the pour holes and add vents so I could load the resin quicker. First try was very messy because of that but the 2nd run was bang tidy.
-The lack of bubbles in the resin was amazing! maybe 2 or 3 tiny ones. I still have to patch up the parts where the damage on the master was picked up other wise they be good enough to use right out of the box

One thing I did forget to mould of 2 parts so I'll have to do those tomorrow. I love split moulds too! Its my first time using them and I did it just out of laziness since I figured it would be a bust any way how wrong was I they worked better than my 2part moulds

Thanks all of the words of support I probably wouldn't of gone back otherwise

[mangozac]

Yay! This makes me very happy to hear and I'm so glad you stuck with it!

Split moulds are the indeed the way to go - I'll never go back unless a specific situation calls for it. It's pretty normal to have to widen your pour spouts, although try squeezing the mould in and out while you're pouring the resin in - that helps force the air out and suck the resin in.

And now we wanna see pictures!