Making Molds ~ INTERLUDE; The Pressure Pot

thanks---this is really great info!!!

 

THAT's what that thing is for!! I couldn't for the life of me figure it out, so I removed it, replaced it with a simple pressure gauge, and put ball-valves on the intake and output sides. I ended up destroying the emergence release valve when I tried to loosen that area, so I just keep a really close eye on the pressure when I use it. My system doesn't leak, unless the wingnuts holding the lid in place aren't tightened enough, but I also haven't gotten more than 35 psi in the tank at any point yet. (I'm using a cheap-o air-brush compressor, and it craps out above that point - I seriously need to upgrade, but can't afford it right now.. Will definitely reinstall the original nut & valve gauge and a new emergency release with the upgraded air compressor)

 

I was going to ask how in the world you tighten that thing by hand to withstand over 70 Psi.. Mystery solved. :p

Oh, and dad just bought himself a cute new 6 gallon air compressor... >:3 *grabby-hands!*

 

Thanks for posting all of this pressure pot info. It will be really helpful in the future. So, do you just need a pressure pot and an air compressor and you are ready to go, or are there any other tools one may need to get started?

 

Can you stack molds inside the pressure pot?

 

Thanks so much for the turtorial! I think this should be stickied!

 

Can you cast hollow casts without a spin caster?So that a doll can have glass eyes?
hugs

 

I'm very grateful to have found your post. Thanks so much for sharing your experience and knowledge.

 

We cast the outside of my doll's head, and the inside. So the outside was sculpted and the inside was sculpted, too. My brother (casting technician) is no longer working with me so I'm now learning casting and can't talk intelligently about it yet, but he made a mold of the back... the front... and a third one for the inside. Then he suspended the "inside" mold into the "outside" mold, and poured.

I can't find any writing about this technique for casting heads. Twigling, is this what you do?

 

Try looking up three part molds or core molds. More specific terminology helps with searching.

And another question for the thread- how big is your pressure pot? I've been looking at them online, but have no clue as to what size would be appropriate for an sd-sized doll (maybe cast it in two waves?)

Edited for a second question- are the pressure pots an "end-all" for air bubbles? Assuming low humidity can you easily (1-2 casts) get perfect or near perfect results?

 

Thanks ailieru.

 

it is easier to understand if you post pictures words are inaccurate sometimes

 

Pressure Pot Questions!! XD

I was thinking of making my own, it would be a lot cheaper but to tell the truth I have no Idea what I would be doing lol. Would it be safer to buy a store made one? *The best one I found thats actually a pressure pot is only $220, not too bad*

I saw you mention it gets really loud. I live in an apartment, so will there be anything too loud? Or can I just adjust it to not be so loud and just have to wait awhile for the air?

The pot Im thinking of getting looks exactly like yours *minus all the tweeking you did ^^* and I was wondering what you used for the air supply hose (does it have to be rigid nylone tubing?) and the NPT air inlet connector

 

I found this source for pressure pots with 80 psi capacity. They also have a selection of sizes that are larger than the 2.5 gallon:

http://www.finishsystems.com/resincastingpressurepots.html

Edited to note this site also carries an array of hoses and fittings.

 

How do you figure out which kind of hoses to buy? Tx...

 

I'm thinking about buying this compressor:

http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

It's 5.5 SCFM (does anyone know what the "S" stands for?) at 90 PSI, 26 gallon, and got great reviews on the automobile customizers' forum... figure those guys know their compressors!

Plus I'm pretty sure it's the one my brother (my erstwhile casting tech) used with good results...

Any thoughts?

 

Hi twigling;
great tutorial. Im just looking into making my molds. can you tell me how to post large pics on here. I posted in the work in progress a new thread. you can look at it. pics of my doll in progress. but the pics are small and you have to click on each one to view it. I ve looked all over the site for a loading pics tutorial here.

 

This may be a dumb question, but are pressure pots absolutely necessary for casting resin? Is there a cheaper alternative?

 

No, pressure pots are not necessary. But, you will have a hard time getting a bubble free cast without it. There are methods to help, and it does depend on the resin you are using a bit. I don't remember all the methods though. I know for molding, some people brush a thin layer of silicone over their model first then pour the rest before it completely cures, and I think I read some people do that for casting too. It seems difficult for a small mold though. It also helps to pour from high up so there is just a thin stream of resin going into the mold. Also, avoid over stirring and use something plastic instead of a something like a wooden paint stirrer. If you are just making dolls for yourself it shouldn't be a big deal. But a pressure pot will save you a lot of hassle if you plan on making a bunch.

 

Thank you, firefly! That's good to know!

 

Yeah firefly I was losing hope too, I'm looking for someone who can cast my Dolls in resin, but I'm not planing in a big quantity. So far I haven't find anyone so I was concerning about learning to cast myself, I'll see.

 

If you're planning on doing a small number by hand you can have the luxury of taking less time to cast so like firefly said - if you pre-coat your original parts by brushing the silicone on then pouring you will have a bubble free layer to pick-up all the finer details without worring about bubles interfering with your mould. As for pouring the resin in - the key to buble free resin without a pressure pot is having one with a longer pot-life (takes longer to cure) so you can tap/vibrate bubles out once its mixed and pour it in your moulds without rushing and churning bubbles back into it in the process... The only thing to watch for is small undercuts like in ears - but if your moulds are planned properly you can also avoid pockets of air by correctly placing vents and flash-flues to get bubble free casts without a pressure pot

Edited to add: Pinkysil is a great silicone for bubble free moulds - its not cheap but its the easiest silicone I have ever used to work with and its cure time is about 15 minutes for large pours and Its not a slow curing one like suggested by Twigling below but it is a very low viscosity kind of like hot treacle in consistensy and so far each of my unpressurized moulds have been perfect from it...

 

you guys sure do take the long way to do these dolls i dont need a pressure pot for my sil or rez lol

 

really? have you casted anything in resin? without a pressure pot
the amount of air bubbles you get when casting is not even cool

 

We succeed in doing mold without bubbles in the silicon or the resin cast... ONE TIME
No idea why this one work better than the others, anyway...

So we bought a pressure pot, I'm just trying it right now ^^ in molds that had some bubbles trouble, but just so as to see if the casts are better ^^

So yes, it is possible to get bubble-free molds and casts, but I think you'll need a lot of experiment to do them perfectly (and it depends of what kind of materials you're using... Some silicon/resin are doing a lot more bubbles than others...)

 

i had a lot of problems with my resin getting bubbles this past year. Most of it was caused by the humidity in the air. In Kansas I had central air, which dries out the air... then I moved to LA which is extremely dry naturally. Here in NorCal it's damp and there's no central air... so i was having a humidity of about 50% on average.

I found that if you cast at 30% humidity or less with fresh resin that hasn't absorbed moisture through the air you run a much lower chance of getting the tiny champagne bubble effect. You won't get perfect casts, but they aren't unusable. I went through about two gallons worth of imperfect resin casts before i was broken down enough that i was ready to get a pressure pot.

Poor Twigling had to listen to me and help me through the baby steps of getting an air compressor and pressure pot this past month. I'm still nervous but it's so nice not to be wasting so much time or resin!

 

How about a line-dryer for your air-compressor?
This is also known as a de-humidifier, and is used commonly with airbrush.
It would be connected to the line, between the air-compressor and the pressure pot.
So far, I have not seen anyone mention this gizmo for a pressure pot?

 

i haven't had any problems with the casts now that i'm using the pressure pot. The bubbly casts were from before i used one.
:3

 

I myself would love to get a pressure pot, but they're all so expensive! Since I'm not really planning on selling any dolls right now I don't think I'll get one, but it's still really nice to see these tutorials, since I may get one in the future.

 

Question about the compressor. Twigling you said yours is 15 cubic feet per minute and it is a bit overkill, if I remember.
So for exemple this http://www.spraydirect.co.uk/acatalog/abac_redline_230_24_portable_economy_compressor.html is
Capacity: 230 lt/min / 8Cfm
Pressure: 8 Bar / 116psi

116psi, if I understand how it works, is higher than the 80psi I need to use for the pressure pot for resin, so it is ok to get this one ? It won't be too weak or something ?

 

That is the less powerful one on the site I think, and it is already too powerful xD I am glad I don't have to move a nuclear plant kind of machine to my apartment thought, thanks for the clarification!

 

"Like that" you mean like yours or like my link ? Or should I get a more powerful one ? (incoming headache because have to make a decision ;_; )

 

Oh right, I wasn't sure. I think I'll stick to this website because I haven't found any other satisfying provider in the UK so far.
Next noobish question, I was planning to get the Binks 10 litres pressure pot but what is the difference between the stainless steel and zinc plated ones, besides the tremendous price difference ? Also would the no agitator ones fit for resin/silicon casting? Because it seems to be manufactured for paint spraying.
Love and thanks.

 

*looks at Twigling with demanding kitty eyes* Meow... ? XD

 

Some pots for paint spraying have a tube inside - my 10 gallon tank was a paint-pot straight off the shelf from a auto supply store - I used a hack-saw and cut off the tube and its perfect so either with or without doesn't really matter, as for an agitator - just check to see if its removable and if you would damage the integrity of the seal by removing it.

As for the difference between stainless steel and zinc plated - this wont affect your ability to cast in it. Stainless Steel Vs Zinc plated is only an issue from a painters perspective - some paints are more corrosive than others depending on their composition so are better suited to a stronger tank like stainless steel. So long as you have a tank rated above the maximum PSI you intend to cast too it wont matter what its manufactured from.

 

Thanks a bunch whitewings!

Humidity's a less b*tch => In the same area, I once thought oxygen/air was cool, like... to be able to breathe, then I started casting resin :p

 

No worries Its so bad here at the moment!! I ended up buying a line-dryer for my pressure pot because in Summer it averages 50% humidity most days and the wet season is definitely in full swing so I dont get a break from it LOL

 

http://www.abac-support.co.uk/individualmodels/cleanAir/30_7_S.htm about this compressor: for a 10ltr pressure pot filled at 80psi, isn't 3cfm not enough?
How do I know how long it will take to fill the pot depending on its size and the psi I require (once the compressor tank is filled and I open the tap)?
I can't find a mathematical formula to know and I feel so clueless.

Edit : I managed to get the information I needed. Cheers =)

 

I was wondering and I can't seam to find the answer . I have done some casting with out a vacuum and of course I get the air bubbles of doom . But resin cures pretty fast .So if its starting to cure as I'm putting the mold in to the pot will it still get rid of the bubbles ?

 

You can store resin in a mid-temp fridge (like a mini fridge not set to super cool -- NOT ONE YOU KEEP FOOD IN) if you're in a warmer climate to help give you a longer work time, had to do this at my last job as the building didn't have AC and trying to cast things in the summer could be quite the adventure.

There are also a variety of resins to choose from now, and you can get quite a few that give you more time to work with before they start to cure.

If you can't get a pressure pot just yet, have a palm sander or something of the like handy to help vibrate bubbles out of your casting. Just clamp it to a table and switch it on and shake the molds while the resin is in. We'd also do this when pouring the silicone for molds even after doing a degassing to get rid of extra bubbles.

 

Thanks so much for all the info. Sorry if this is considered necro-ing, but I couldn't find a more recent post.
Humidity in my country (Netherlands) is normally so high that I've reached the conclusion that it will probably be impossible for me to make completely bubble-free resin dolls without a pressure pot... At least not in colour. I tried several brands of both resin and colouring, and while I have found two resins that I can cast acceptable pieces with with without any machinery (Axson F18 and Alumilite casting resin), both start to get bubbles when pigment is added. I've got another resin lines up I want to try, but I'm not confident the same problem won't occur again.

(in case you wonder: I use the talc-powder trick, along with several things like slow stirring, pouring at an angle, vibrating the mould while curing etc)

One question though, since several of you guys have mentioned using compressors intended for the car-painting industry... Can ANY pressure pot be attached to ANY compressor (taking the max PSI in consideration of course)? I intend to give the doll that's causing me trouble two colours (she's a fox, so red tan skin and white)... And was thinking that if I can't manage to cast a dark, reddish tan skin myself, but clear resin versions (without any colour added) are turning out fine, it might be a solution to air-brush most of the parts. Makes more sense to paint red-brown onto something white than the other way around, after all, even if it might rub off the joints over time (I could perhaps leave those clear but I'm afraid it would look weird).
Can an airbrush be attached to the same kind of compressor as a pressure pot, or is there too big a difference in PSI or something?
I never worked with either, so sorry if I sound like a complete n00b. ^^'

 

I'm not too sure, but I do know that I would never be able to use the air compressor I used for my pressure pot to airbrush with or vice versa. I have an Iwata Smart Jet for airbrushing. It wouldn't be able to fill the pressure pot because it only goes to 35psi. My other compressor is a big one I stole from my dad (I think it is this.. http://www.beletti.com/ram/aircompressor.jpg). I am not sure how you'd limit it to 35PSI, but even if you could, it is super loud! But, I don't really know what I am talking about, I just know what works for me, so maybe it is possible. Sorry, that isn't very helpful. I don't think Twigling has been around here for a while but I'm sure she'd know.

 

Thanks, I'll see if I can message her if no other replies follow up soon.