Duplicating custom parts with Silicone rubber and resin.

[Troy Henderson]

Over the last few weeks I have been working on a C-130H Hercules. Im using the Academy 1/72 (Italerai) kit, and as many will be aware, the engine nacelles are too short for the RAAF C-130H, So I set about modifying the ones that come in the kit, and then using it as a mould for casting new duplicate engines. I thought some of you might be interested in seeing how I duplicated the custom part


Here is a pic of a kit original, the flightpath after market piece that is too narrow to fit the kit properly (used as reference) and my modified nacelle, made by cutting the back and front off of two assembled kit nacelles and joinging them up so they become one longer nacelle closer to the correct dimensions.


I also added a lip to the lower intake.


First I made the master mould using a plastic cup, cut in half and sealed to the tile as a smooth base. Using bluetac, I stuck the nacelle buck on to the tile then mixed up equal parts by weight "PinkySil" silicone rubber from Barnes, which consists of two liquids that when mixed form a tough silicone rubber.


Once the rubber has set, about 20 mins, you pop out the buck and you're ready to pour the mixed two part "Easycast" polyurethane resin, again from Barnes Moulding, into the mould. It only has a two minute pot time, so you need to mix and pour pretty quickly.


As I said, it cures pretty quick and you can de-mould them in about 10 minutes, then just let them fully cure over the next 16 hours.


Not bad for two hours work. They aren't perfect, due to some imperfections I missed on the master, but nothing that can't easily be fixed with a bit of tamiya putty. I actually got the mix wrong on the two bottom ones, which makes them a little soft and translucent. but they cured just as hard as the others, just took a little longer. I've since taken the best four and made up another mould up, so I can now pour four engines at once.

[Justin Wooding]

Hi Troy,

You make that look easy! Those Herc engines came out nice. You could have a small local market for them

What does all the stuff cost? I had a look at Barnes, but couldn't see the gear listed.

[John Everett]

Hello Troy,

Casting your own is unbeatable when you need more than just two or three copies.

You can save a lot of rubber my using a more efficient mold box. 5-10mm of rubber around the edge of the master is more than adequate for smaller parts. Do a search about using Lego blocks to build mold boxes. They work a treat. If your kids don't want to share their Legos with dad, stiff cardboard (poster board) and hot glue also work well for building a box to hold the rubber while it sets up.

If you need to produce dozens of copies, look into getting your own pressure tank to "squash" the air bubbles trapped in the rubber during the process. The same pressure tank can be used the squash the bubbles trapped in the liquid resin during the pour phase.

Casting is a whole hobby unto itself.

[Troy Henderson]

Thanks guys.
Justin, for the 500 gram kits, it's around $38 for the Rubber and $28 for the resin.

Would you believe I just gave away all my Lego to a friends kid. I thought I had kept asides all my long straight pieces for this exact purpose, but I seem to have misplaced them somewhere in the garage. A good thick mould does give you a more solid and longer lasting mould too. Nothing worse than putting your finger through the bottom or side.

[Troy Henderson]

Justin, its really not that hard. Once you get your master they way you want it, you just have to figure out the best way to cast it. You want to avoid under cuts and deep hollows on the sides. The nacelles were easy as they have one flat side and all the hollows (the intakes) are mainly on the up.

So you mount the flat side to the flat smooth surface of the tile then build your mould box around it. I do prefer use lego as I can build it to size. Yes, keep around 10mm of rubber from the piece to the edge of the mould is good as it helps your rubber mould last longer. Pour the rubber off to the side of the piece in the mould box and let it flow up and into the details. If you pour directly onto the piece, especially if there is detail there, you can introduce an air pocket, which is not good, obviously.

http://www.barnes.com.au/addition-curin ... kysil-1591


http://www.barnes.com.au/polyurethane/easycast-1306