To buy pressure equipment or not?

[Stranger83]

Hi everyone – stumbled across this site and I have found it really useful so far so thank you to everyone for all that.

I have a couple of questions. Up to now I have simply been doing my resin castings without a pressure pot or vacuum chamber, I’ve found the stuff is fine around 80% of the time which works fine for the amount of stuff I make as I can easily just do another if a cast fails – I’ve not had any major deadline to run to as it is largely personal use.

However I was wondering if I should look into getting a pressure chamber and vacuum chamber anyway or if the consensus was not to bother until the time issue becomes important? I would say over the last year I’ve probably wasted less in resin costs than the cost of either one of these pieces of equipment.

Other than improving the chances of a successful cast does a pressure pot/vacuum chamber have any other advantage? Does it cause less shrinkage or make for better quality resin?

I’ve read that a lot of people have made a pressure pot into a vacuum chamber too, how hard is this to do. Can anyone recommend a good pot for me to do this with (in the UK)

Also, I’ve been using a 2 part resin from sylmasta which I’ve found to be rather good, but does anyone have a better recommendation of a good quality one? I need something quite strong but also able to hold detail well – casting time again is not an issue to me, I’d rather have something solid that takes an hour to set than something ok that takes 10 minutes.

And I guess finally, does anyone in the UK have an old pot/chamber combo that they want to sell on?

[Fleafa]

A vacuum pump & chamber will help remove pockets of air.
A compressor & pressure pot should squash any bubbles so they are too small to see. Pressure also helps the resin pick up the detail better and could potentially result in a more dense cast.
Turn a pressure pot into a vacuum chamber by getting a lid with a vacuum gauge and a rubber seal. You can do this with your pressure lid but risk damaging the pressure gauge. Zac has avoided this by adding a valve to switch between purposes.
The Sylmasta resin looks fine. Probably the same resin as John Burn and a few others, judging by the names and properties. Similar to what I am currently using.
Where are you in the UK? I do have a pot I may get rid of.

[Stranger83]

Thanks for the reply

I had been thinking that pressure might help with the really fine detail so it's good to know I'm not wrong there, I think it's something I'll definately have to play around with.

Officially I'm in Yorkshire - but the day job takes me all over the coutry so I could go anywhere.

[mangozac]

Apparently pressure pots are quite expensive and/or hard to get a hold of in the UK, so if you can score one from Fleafa you'd be doing well!

Bubble removal is the primary advantage of pressure/vacuum casting. I guess it makes the resin stronger too (since it makes it more dense when the bubbles are removed), however I doubt that the small increase in strength is really going to be necessary 99% of the time.

I always suggest starting with pressure - vacuum is only necessary with certain techniques when you want to go from 90% to 99% perfect casts. If you're already getting good results at room pressure then I would expect just adding pressure would be all you need. If you decide later on that you'd like to add vacuum too then you can simply retrofit it onto the same pot at that stage.

Do you already have a compressor? Personally having to recast parts because of bubbles, even just for personal use, would irritate me big time. It's not just he cost of wasted resin - remember your time is valuable too! So if you can set up pressure casting without spending too much money I definitely think it's worth while.

There are a couple of downsides:
1. Your existing moulds will be no good for pressure casting. There are small bubbles inside the silicone which will deform under pressure. You therefore need to cure your moulds under pressure to prevent this.
2. Since the pressure forces the resin deeper into the mould, it also shortens the mould lifespan a little.

Hope that helps!

[Stranger83]

Yeah, the failed castings are an annoyance – which is actually why I started thinking I’d look into pressure casting – but hasn’t been enough of a pain to justify the cost to myself until now. You are right that getting hold of a pot in the UK is proving difficult. In fact it would be cheaper for me to order one from the US and pay for shipping via eBay than it was to get one from the UK direct.

As for compressor – I do have one for an air brush, but I imagine I will need something a little more powerful for this.

[mangozac]

Yeah you want a compressor with at least a 20L tank so that there's no problem filling the pressure pot nice and quickly. Here in Oz you can pick up something suitable from an auto store for around $100. It's crazy that they're cheaper than the pressure pot!