Sculpting: Control Panel

I have been playing around for literally years trying to sculpt and cast miniatures / scenery bits.  I have been plagued by (amongst other things) silicone leaks, air bubbles and sheer clumsiness.  Today I have won a hard-fought victory against air bubbles!

When putting resin into a silicone mold, air bubbles get trapped in all the hard-to-reach places.  I tried a few things to get rid of them:

• Pouring a little resin in, then 'rolling' it around the mold by tipping it all different directions.  It spilt some resin, and took up some of its valuable pot-life.  Results: poor (although it might work for larger models).

• Adding flow-channels to model/mold.  This involved cutting away channels of the mold, or adding sprue-like protrusions to the model itself when making the mold.  It was very hit-and-miss, with some larger models coming out great some of the time.  Air would still end up getting trapped though, and the channels meant extra resin to remove after the cast. Results: okay, but lots of extra work.

• Injecting resin using a syringe/blunt needle.  This was lots of faff, cleaning the syringes/needles and fighting the resin's viscosity trying to get it into the syringe and out again.  In fact, I think the shear stress of going through the needle actually heated it up and accelerated the curing!  Results: okay, but very time-pressured and messy when it goes wrong.

With these mediocre payoffs for my extensive effort, I decided to buy a pressure pot and compressor.  Putting the mold and newly-poured resin into the pressure pot and raising to 50-60psi should crush the air bubbles down so small they'd be invisible.  Thus began another adventure in cheap-skatery!

I got a fairly cheap pressure pot from China via ebay.  I connected it up to a cheapy little tyre-inflator (via a 1/4" NPT to Schrader valve adapter) to get the pressure up. 

Before I tried it out, my wife and some friends started making worried noises about high-pressure equipment exploding and sending shards of metal into/through me.  When I stopped and thought about it, I realised they were right to be worried.  There's a reason nobody does high-pressure experiments in school science labs, and my equipment (including the safety pressure valve) was all cheap-ass Chinese crap...

So I bought a polycarbonate safety screen from Screwfix to put in front of the equipment when it was pressurised.  Nothing could possibly go wrong now.

First pressurisation attempt reached a paltry 20psi before the hissing started.  It turns out pretty much every joint was leaking, so I took it all apart and attacked it with plumbing-seal tape and adjustable wrenches.  After a fair wait I got it up to about 45psi, which would probably have been enough, as long as the resin didn't cure before it got there. :S

Then I was saved by my mother-in-law getting rid of her air-driven staple gun she'd used for upholstery.  This beautiful little 15-litre Bambi compressor would've set me back the best part of £300, so it was an amazingly generous gift.  After waiting for more connection adapters to arrive, I set it up today and got it up to 60psi no problem! 

That was the point at which the pressure-pot's safety valve let rip.  Thankfully it's a re-settable one, so no damage done, but it gave me a hell of a fright!  So I settled for ~50psi and got casting.

A cast of a self-sculpted control panel. ~14mm long

The picture above is the result of a small control panel I had sculpted a while back.  It's probably smaller than it looks on your screen (about 14mm long), so it doesn't look as impressive as I'd hoped.  I'm really please with it though.  It turns out the pressure is so good at squashing the resin-bubbles down that I'm going to have to use it to eliminate air bubbles in the mold as well!