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[jegner]

Well, last week was a mad one for me, so I did not post any tips. This week, I want to talk about 1-part silicone mold making.

I made a few molds of my Sterling L2A3 and here is how I did it. First, you need to examine the part you want to replicate. Are there any undercuts, or is there a flat or hidden side, that you can use as your sprue to pour your resin into? IF the answer is, no undercuts, and yes, I have a hidden side, then the easy way to make a 1-part silicone mold is to get some Lego's and make a box 1/2 to 3/4 inches larger on all sides than the part you are wanting to duplicate. You could even use a disposable cup if the part is small.

Set the part into the bottom of the box [or cup] with the hidden side facing down. You have to think of mold making in reverse. This hidden side is where you will be pouring your resin into. As an example, the endcap on the L2A3 has a hidden side, the part that slips into the barrel. Easy to just fill with resin at this point as this side is never seen.

Next you will want a good silicone. I prefer a 1:1 ratio, because I'm too cheap to buy a gram scale. Polytec Plasil 71-20 is a good general purpose silicone that meets my needs. It is platinum cured as opposed to tin cured, and costs a little more, but it can take higher heat. You can even pour low temp metals in this stuff. Heat kills silicone molds, so I don't recommend doing this much!

Mix the 1:1 silicone well, and try not to get the ratios off too much, and don't mix any more than you can use. Avoid whipping action or ytou will get a lot of air bubbles. Silicone has the ability to bond with itself, so if you run out, don't despair, just mix some more and keep pouring. Also the Plasil 71-20 only takes about 4 hours to cure. So, in an afternoon, you can be casting parts!

After it sets, you can start pouring resin. Remove the master pattern, and examine your mold. Make a test casting. if you have a lot of airbubbles, you might have to cut some burp lines.

Silicone does not need a mold release, but if you want to extend your mold's life then you will want some sort of mold release. You will loose some detail with mold release agents, though. I decided to just rebuild the molds when they get worn. You can grind the old silicone up, and use it as a filler when pouring new silicone.

[Stomper]

COOL!! I've been chomping at the bit to try and make a mold of my E-11's... AND the Hengstler Counter I just won off of Ebay! Wouldn't it be cool to be able to produce some rubber E-11's or even make them in that high-impact resin? I SWEAR I will get this done... I just have to make up my mind which way I want to go with suppliers.... choices, choices.

BTW... how'd your molds make out, did you make any castings?

DETAILS MAN, WE WANT DETAILS!!! LOL
_________________
Tony Krewson
FEAR... is not my god!!