Problems casting small details - could use some pointers!

pandabarnes

Active Member
I'm after some casting pointers as usual!

The whole story is below, but basically I'm casting a tiny microwave oven (American Hustle), and my castings are always missing a bit of detail.

Oven is about 2.5cm long. details about 0.5cm.

I'm taking the molds with mold-star 15 slow, then casting with smooth-cast 310.

Do I need a harder Silicone for the mold, or a different resing to cast with?

Thanks in advance.


*** All the gory details follow ***

I'm trying to make my girlfriend a science oven pendant for christmas, inspired by that great scene in American Hustle, which she loves.

Don't put metal in the science oven!

Anyway, I've made this tiny science oven, it's about 2.5 cm long, with small trims of about 0.5mm glued to it.

I'm not great at modelling but I'm happy with how it's going, it's looking close enough to the reference for a pendant.

My plan was to make it, make a mold and take a cast, refine/clean up where needed then take a final mold and cast the finished piece.

I'm on mold number two, cast number three, I've tried pushing the resin into the details with a syringe, but there's always a tiny bit missing and at this size, it's going to be impossible for me to fill it and still have straight, square lines.

I'm taking the molds with mold-star 15 slow, then casting with smooth-cast 310.

Thanks.
 

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First thing i would check is the mold, was there any silicone infiltration under the detail part. That would leave a very thin "skin" under the infiltration and prevent the air from escaping.

Also use some talc in the mold, and if it's a 1 part mold uses something more like 1/16 brass to poke or pop the bubbles. If it's a 2 part mold try agitating the mold by shaking or banging it about a bit.
 
Thanks mslz22 - there were some tiny bits where the silicone had infiltrated under the plastic strips, but bizarelly this wasn't where I was seeing the casting problems - that was mostly on the outside/top corners of the detail strips.

It's a 1 part mold - I didn't use talc so I'll try that - I totally forgot that part! but I did vibrate the mold like crazy for a few minutes.

Thanks for the pointers man.
 
You may need a pressure pot or vacuum chamber. The first will shrink the bubbles to very tiny spots and the second draws the trapped air from the mold. There are plenty of post and threads concerning both item here on the forum, Just use the search function at the top left of the Home screen.
 
try after mixing your resin, grab an apropriate sized paintbrush and paint in a coat of resin. squarsh into the nooks and crannies and paint any bubbles out.
after a nice coating, pour the rest. works more often than not for me and i'm a cheap *******.

on another note, you don't really have to mold it twice if you get the master preprepped properly but i understand everybody has their own methods.
 
hey thanks for the pointers - I tried again today - dusted the mold with talc, then tried painting it into the finer details as modelcitizen suggested, should know in a few hours!

@19narvik40 - thanks, I hadn't even heard of those things! I'm doing some research now because I'll be making other stuff I want to cast too.

on another note, you don't really have to mold it twice if you get the master preprepped properly but i understand everybody has their own methods.

You know, I was struggling with the right way to approach this, even now I'm thinking of remaking the model and just taking one cast, but I thought I'd approached it the standard way! Are there better approaches? I couldn't work out how I'd get a nice 'solid' piece without the middle version, to make sure there's nothing getting under the details etc.

If you've got an tips on preprepping I'd be happy to hear them!

Thanks again everyone.
 
you were planning to clean up your first cast and mold again with said cleaned up cast. simply clean up your master in the same fashion and then mold/cast is what i meant. good luck!

btw in my past experience, pressure pot good for squishing bubbles. vacuum we used only to get the bubbles out of the liquids after mixing and before pouring. just another 2 cents (i'm using neither now as my shop is my kitchen table).
 
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Cool, thanks - I went back and reworked the original quite a bit, made it much cleaner and re-molded it.

Still having some minor problems bit I'm pretty much there now.

Thanks for all the help everyone!
 
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