a couple pressure cast resin questions.

qc · Post by qc » Sun Nov 04, 2007 9:56 pm

plan on purchasing a pressure pot soon...but have been wondering.

-most pots have a rounded bottom...how much of an issue does that cause...especially if casting an open face mold?

-i was considering making a couple open face rtv molds...then laying a piece of glass over top of them to to excrete the excess minicus (that the right term?) out of small vents out the side (upper face). would there be a problem with this concept? what of the excess resin spilling into the bottom of the pot...can i just line the bottom with paper for easy clean up or is there a recommended method.

-i'm looking at picking up a 2.5 gallon pot...and using an iwata sprint jet. i intend on using the smooth-on 300 products. i'm concerned it may take a while for my compressor to achieve the required pressure ...WHICH IS WHAT BY THE WAY....and the resin will set up before the pressure has time to do its wonders. i can get a slow resin.....but i may get some quicker setting resin to cast some thinner elements.

-lastly. what about casting several molds at one time. is it ok or not recommended to pressure cast at one time. if ok....can i just stack them...or do they need a little space. perhaps build little shelves within the pot..?

many thanks

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Mon Nov 05, 2007 12:36 am

I poured some resin into the bottom of one of my pots and let it self level and cure.

Oddessyslipway said he just cut an acrylic circle to place over the bottom of his pot.

Cast as many molds as you can squeeze into the pot before the resin kicks.
If you can make the shelf easy to drop in and lift out, you might make
a decent stack for open face molds. I don't do anything to my open face molds. I keep them clean and just to one side, so if I have extra resin, I can make a set of doors, or what ever is handy, or needed.

[edit]
I used to use 50 psi, but now keep the pot between 35-43 psi.
Most people I have talked to recommend + 1 atm. (is that right?)

BERT aka MODEL MAKER · Sun Nov 11, 2007 6:27 pm

Resin question, I know that SCI-FI METROPOLIS Was making their 2 foot Jupiter 2,s out of thermo-plastic and they said the hulls were so strong that they could stand on a hull half and not hurt it

HOWEVER, they told me that the Jupiter 2 is being retooled and will now be made out of RESIN

They say it will be a lot easier to work with PLUS, have a lip on each hull to mate them instead of the rings they had on the thermo-plastic Jupiter 2. My question is, what special problems will a RESIN version of the jupiter 2 be, if any ? They also e mailed me to let me know that a 4 foot Jupiter 2 resin of course, will be available soon. I am not sure i want a RESIN jupiter 2 if the material itself will be problematic.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Mon Nov 12, 2007 1:34 am

BERT aka MODEL MAKER wrote: ...

...

I am not sure i want a RESIN jupiter 2 if the material itself will be problematic.

It really depends on what formula of resin they use...
I have seen a solid resin cat, a clear solid resin cat, and a thin shell black poly resin cat all out of the same mold...

The thin shell was an interesting black shiney compound, but I keep forgetting to ask what it is...

BERT aka MODEL MAKER · Mon Nov 12, 2007 1:39 am

I am waiting for a reply to them on the hull thickness of both the 2 ft. and 4 ft. jupiter 2. The one they started with was ABS thermo-plastic, pretty strong stuff

vaderman · Post by **vaderman** » Thu Nov 15, 2007 1:27 pm

Bert,

Another question is is it going to be rotocast so it is able to be lit or will it be a squish mold, etc. Or is it going to be a slushed (my definition for essentially pouring and titlting the mold to get a surface layer all over), which I would not recommend due to potential thin spots.

Rotocast would be I deal, but a squish mold would work too. It's a big ship to cast in resin. Even if hollow, it will have some weight to it. You difintiley do not want it solid cast, then you are stuck with a big chunk of resin that will be very difficult to light and will be heavy.

Scott

BERT aka MODEL MAKER · Fri Nov 16, 2007 4:38 am

I have a 24 inch Lunar models vacuform kit i built but the LM hulls are not easy to line up at all

They are very strong though. SFM made the j2 from ABS at first and now switched to resin. They do not have any pictures of this new resin j2 on the website, nor, can i get info. on hull thickness. I know what they sold before and i would buy it. However, they are completly out of those and i don't want to buy until i see what i am getting.

qc · Post by qc » Fri Nov 16, 2007 7:41 am

bert,
thanx for hijacking this post.
next time....when you have a question totally unrelated to a topic, start a new post. thanx

BERT aka MODEL MAKER · Fri Nov 16, 2007 5:37 pm

It concerned resin and i had a resin question

qc · Post by qc » Fri Nov 16, 2007 8:25 pm

it (this post) was aimed at answering some concerns about CASTING resin in a PRESSURE POT.
had nothing to do about one particular model, how it was cast, etc.

message board etiquette suggests you stay (discussing) the topic at hand, but in addition you would likely get lots more responses to your own question if you posted it with your subject of interest, thus luring others who may be interested in your question. with your question hidden within this post, very few ppl may be able to help you with your question.

BERT aka MODEL MAKER · Sat Nov 17, 2007 2:56 am

I sincerely appologize, I am having a difficult & expensive decision to make regarding buying something that went from ABS to resin sight unseen. I know little of resin and thought you guys would know a lot more about its makeup in the way of strength and appearance

I truely did not mean to interupt the thread like i did

I am sorry i really am.
Bert

Sparky · Post by **Sparky** » Thu Jan 24, 2008 10:59 am

I hacked up an hold shoes rack from Target, to mount the pressure pots horizontal. Than got some scrap acrylic for a shelf. I got a paint scraper from wall-mart to scrap the resin overflow that happens when rolling a back down over an open face mold.

you can spray in some Mann mold release into the pot, I recommend spraying it on the lip of the pot and lid/rubber gasket. The stock rubber gasket is probably urethane, so a urethane resin (smooth-on 300s) will glue its self right well to that gasket. this will impede the pots ability to hold pressure. Once you can vacuum degass RTV, pour a new gasket in the lid too (pluck out the old one). That really helps it hold pressure, its also easier to clean.

Strictly speaking you shouldn't pressure cast if you are rolling a back down over an open face mold. Any air bubble that gets in there will compress under pressure and deform the parts, or change their shape/look significantly. if you're making general gribblies thats not a problem, but for kit parts its a pain, since the parts will exhibit dish or other issues that may render them a mis cast.

That said I pressure cast the open face gribbly molds anyways, as resin cures it tends to generate bubbles that can be suppressed under pressure.

qc · Post by qc » Thu Jan 24, 2008 2:17 pm

sparky,

what do you mean when you say "rolling a back down" on an open face mold?

(haven't done it yet) but was think'g the best way to do an open face (even in a pressure pot) is keep it open....provide a small overflow vent (outside of the mold) then place a small piece of thick glass over the top of the rubber (thus smooshing all excess resin out and not extra flash to be sanded)?

is THAT what you meant by "rolling a back down"?

Sparky · Post by **Sparky** » Thu Jan 24, 2008 2:41 pm

Yes the glass back is the rolling a back down. I've thought about how one should do it, with a reservoir/vent. This is something I might try. It would be useful for models where there are a lot of surface details that you leave off the main body, then provide detail panels in the kit. Think of how one would have resin cast the Fine molds MF, no pre attaching the detail bits either, cast it as they molded it.